Paleomagnetism of Some Lake Superior Keweenawan Rocks By KENNETH G. BOOKS GEOLOGICAL SURVEY PROFESSIONAL PAPER 760 Remanent magnetization directions for lower and middle Keweenawan rocks fall into three groups that have their polarities alternately normal, reversed, and normal UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600117 For sale by the Superintendent of Documents, US. Government Printing Office Washington, D.C. 204-02 — Price 50 cents (paper cover) Stock Number 2401—2180 CONTENTS Abstract ____________________________________________ Introduction _________________________________________ Acknowledgments _______________________ , _____________ Field and laboratory techniques ________________________ Collection and measurement _______________________ Sources of error __________________________________ Magnetic cleaning ________________________________ General geology ______________________________________ Keweenaw Peninsula _________________________________ Geologic setting __________________________________ Description of results _____________________________ Portage Lake Lava Series _____________________ Rhyolite flows north of Lake Gogebic, Mich _____ Quartz porphyry north of Lake Gogebic, Mich--- Rhyolite intrusion in sec. 4, T. 56 N., R. 32 W- __ _ Rhyolite intrusion in secs. 24 and 25, T. 56 N., R. 34 W __________________________________ 'U a? (a mammmphwmwan-t 12 12 12 Ironwood-Mellen area ________________________________ Geologic setting __________________________________ Description of results_ _ _ _‘ _________________________ Lowermost Keweenawan lava flows ------------- Portage Lake Lava Series _____________________ North Shore of Lake Superior- ________________________ Geologic setting __________________________________ Description of results- - _ T _________________________ North Shore Volcanic Group ___________________ Isle Royale lava flows ________________________ Discussion of results- _ _ - _ _ _ - - _________________________ Lower Keweenawan ______________________________ Middle Keweenawan_ _ _ - _________________________ Portage Lake and North Shore sequences ------- Quartz porphyry north of Lake Gogebic, Mich-_- Upper Keweenawan ______________________________ Rhyolite intrusions-L _________________________ Summary and conclusions- _ _‘ -------------------------- References cited ____________ 1 __________________________ ILLUSTRATIONS FIGURE 1. Generalized geologic map of the Lake Superior region __________________________________________________ 2. Simplified columnar section for the Portage Lake Lava Series near Kearsarge, Mich ________________________ 3—15. Equal-area diagram showing directions of remanent magnetization for—— 3. Flows of the Portage Lake Lava Series below conglomerate No.14 near Kearsarge, Mich _____________ 4. Flows of the Portage Lake Lava Series between conglomerate No.14 and conglomerate No.15 near Kearsarge, Mich _________________________________________________________________________ . Flows of the Portage Lake Lava Series above conglomerate No.15 near Kearsarge, Mich ______________ . Middle Keweenawan rhyolite flows north of Lake Gogebic, Mich __________________________________ 5 6. Flows of the Portage Lake Lava Series northeast of those near Kearsarge, Mich ____________________ 7 8 . Quartz porphyry north of Lake Gogebic, Mich ________________________________________________ 9. Rhyolite intrusion in sec. 4, T. 56 N., R. 32 W ________________________________________________ 10. Rhyolite intrusion in secs. 24 and 25, T. 56 N., R. 34 W __________________________________________ 11. Basal quartzite and lowermost 400 feet of South Trap Range lava flows near Ironwood, Mich ________ 12. Middle Keweenawan flows from the Chippewa Hill quarry, Michigan"; __________________________ 13. Middle Keweenawan flows on the Black River near Algonquin Falls, Mich _________________________ 14. North Shore Volcanic Group, Minnesota 15. Middle Keweenawan lava flows on Isle Royale, Mich ________________ c __________________________ 16—18. Equal-area diagram showing— 16. Summary of mean directions of remanent magnetization for lower(?) Keweenawan rock units ________ 17. Directions of remanent magnetization for pre-Keweenawan units near Ironwood, Mich. and Grand Portage, Minn_ _ _ _ - - L ___________________________________________________________________ 18. Summary of mean directions of remanent magnetization for middle Keweenawan rock units __________ 19. Columnar sections showing comparison of chronological movements in inclination of the magnetic fields of the Portage Lake Lava Series and North Shore Volcanic Group ________________________________________ 20. Columnar sections showing comparison of chronological movements in declination of the magnetic fields of the Portage Lake Lava Series and North Shore Volcanic Group ________________________________________ Page 10 13 15 17 19 21 25 26 28 30 32 33 34 35 36 IV CONTENTS Page FIGURES 21—23. Equal—area diagram showing— 21. Comparison of mean directions of remanent magnetization for lava flows near Kearsarge and on Isle Royale _________________________________________________________________________________ 37 22. Alternative directions of remanent magnetization for the quartz porphyry north of Lake Gogebic, Mich- _ 38 23. Directions of remanent magnetization for rhyolite intrusions in T. 56 N., R. 32 W., and T. 56 N., R. 34 W., near Kearsarge, Mich _____________________________________________________________ 39 TABLES Page TABLE 1. Partial demagnetization data for four sites on the Portage Lake Lava Series ________________________________ 4 2. Paleomagnetic results for Portage Lake Lava Series near Kearsarge, Mich _________________________________ 11 3. Paleomagnetic results for miscellaneous flows of the Portage Lake Lava Series northeast of Kearsarge, Mich- _ _ _ 14 4. Comparison of declination and strike along the Ashbed Flow in the Portage Lake Lava Series ________________ 14 5—14,. Paleomagnetic results for— 5. Middle Keweenawan rhyolite flows north of Lake Gogebic, Mich ___________________________________ 16 6. Quartz porphyry north of Lake Gogebic, Mich ___________________________________________________ 18 7. Rhyolite intrusion in sec. 4, T. 56 N., R. 32 W., east of Kearsarge, Mich ____________________________ 20 8. Rhyolite intrusion in secs. 24 and 25, T. 56 N., R. 34 W., southwest of Kearsarge, Mich ______________ 22 9. Basal quartzite and lowermost 400 feet of South Trap Range flows near Ironwood, Mich ______________ 24 10. Portage Lake lava equivalents at the Chippewa Hill quarry, Michigan ______________________________ 27 11. Portage Lake lava equivalents on the Black River near Algonquin Falls, Mich _______________________ 27 12. North Shore Volcanic Group in Minnesota ______________________________________________________ 29 13. Middle Keweenawan lavas on Isle Royale, Mich _________________________________________________ 31 14. Pre—Keweenawan rocks near Ironwood, Mich., and Grand Portage, Minn ____________________________ 31 15. Summary of new paleomagnetic data for rock units in the Lake Superior region _____________________________ 31 16. Tentative correlation chart of Lake Superior Keweenawan units based on magnetic polarity sequences _________ 40 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS By KENNETH G. Booxs ABSTRACT The averaged directions of remanent magnetization for the Keweenawan rock units investigated fall into three general group- ings that have their polarities alternately normal, reversed, and normal. The older normal polarity and subsequent reversed polarity groups are found in lower Keweenawan rocks and have significantly different directions from the younger group with normal polarity which characterizes middle Keweenawan rocks. From all available paleomagnetic data for this area, it seems that magnetization directions among various rock units in the lower Keweenawan around Lake Superior are characteristically scat- tered, which may indicate long periods between volcanic events, a rapid rate of change in magnetic field directions, or changes due to metamorphism. Less scatter of magnetization directions among middle Keweenawan rock units may indicate a shorter time in- terval between volcanic events or a slower rate of change in mag- netic field direction. Upper Keweenawan magnetization directions, though not included in this study, are again more scattered among rock units. Beginning with known basal Keweenawan, the three magnetic polarity groups are represented in rocks on all sides of Lake Superior. The older normal polarization is found in the basal rocks near Ironwood, Mich., and in the lower part of the lower Kewee- nawan Sibley Series on Sibley Peninsula, Ontario. The reversely polarized group is a distinctive representation of a time interval that is present at many locations around the lake. Reverse polar- ization is found in some 6,700 feet of South Trap Range lava flows near Ironwood, Mich., lava flows near Grand Portage, Minn., gabbro in Cook County, Minn., sedimentary rocks of the Sibley Series in Ontario, and lava flows at Alona Bay on the eastern end of the lake. The younger normal polarization is also widespread and is represented in the great bulk of the extrusive and intrusive rocks around Lake Superior that are classified as middle Keweenawan in age. This group includes the Portage Lake Lava Series on the Keweenaw Peninsula and most of the North Shore Volcanic Group of Goldich and others (1961) in Minnesota. With the completion of this study, paleomagnetic field direc- tions are now available for all major geologic units of the Kewee- nawan Series in the Lake Superior region. INTRODUCTION The area of investigation lies in parts of the States of Michigan, Wisconsin, and Minnesota adjacent to Lake Superior (fig. 1) and is underlain mainly by igneous rocks of late Precambrian age. Because of its economic significance and structural complexities, the Precambrian of the Lake Superior region has been the object of geologic investigations for more than a century, and the section of lava flows of Keweenawan age near the lake is probably as well known as any such succession in North America. Nevertheless, the positioning of some nonfossiliferous rocks in the geologic column has been hard to assess, because of inherent difficulties in determining time relationships between extrusive rocks at some distance from each other, and even more difficulty in relating different intrusive rocks of the same age. Before radiometric dating methods were developed, most Precambrian rocks were correlated by comparison of facies and petrographic similarities, unconformities, and degree of metamorphism. Goldich and others (1961) built a time scale of radiometric dates for the Pre- cambrian of Minnesota, into which geologic units and events in the Lake Superior region can be fitted. Paleomagnetism can also be used to correlate rock units within the Precambrian. In recent years much progress has been made in measurement and inter- pretation of natural remanent magnetization of rocks. Paleomagnetic studies are based on the knowledge that rocks can acquire a stable magnetization in the direc- tion of the earth’s magnetic field during formation, and this direction can be measured by sensitive instru- ments in the laboratory. Therefore, by collecting many oriented samples from a particular rock unit, the direction of the earth’s magnetic field at the time the rock was formed can be determined, provided that the magnetization has been preserved. By collecting and averaging magnetization directions of samples from various rock units, it is possible to establish a sequence of paleomagnetic field directions to which data from rocks of all types may be compared. DuBois (1962) has attempted to show how paleomagnetism studies can aid and supplement geological interpretations in the Lake Superior region and has laid the groundwork for such studies in the area. The present investigation continues this type of study by detailed analysis of the paleomagnetic field directions in the Keweenawan lava flows and related rocks on both the southeast and northwest shores of Lake Superior. PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS .6 :v .muw 63$ gum “:3 .3 .mm £ng 833 .3 .3 .mmad £84 and 655 .55..— an 35602 485w.— uoiwasm 3—3 23 we 9:: Bwfioow gum—Eonvwlé Huh—Eh w 4 _ 8.2: 8 ow cm f:__:_: 0 ON v. 4A : 33m «:52. 1’ uEOfl m: (u maucmmsmo A H” Wu 025w. ZmFOO_l_IO_Z a 4VVA4AA._A._n <4 EBA mmeEm—z :o mic: m>n_ :mgmcuokox EBA. 9.5:»me co mic: «>2 :Qsmcwwimx “ENE. :3025225 :0 9:0: 95. coimcwwimx £325. 989 u_:uo_o> mmtwm 530 035 mm>£ xmm m:o_< m___m :mmnj «Dr/‘0 ,Nwm: W_Om DD (.540 .mwm: >MJWD7ZJ DZ< {Umm WZOCVUNJJOU m30_>mmn. szFomnjoo .rzmmmno m2 cuiwcmmzox «onwaOJ . 2331 2m. :0 :Esmcowiwx 22:2 , QJEO u_cmu_o> 0.9.5 552 . I mloz m>n_ cmimzowgox EUEE uwumm: new 93.. mmntOL . mxoo. 025.55 :mimcvmsox Boo: . .nfi .m: .ma 4: .mH NM .: .OH Hvaan wDij_ mkjw min 32% cmzcmwswx 530.— /_ 5.02 33:55 :ukucwokwvm 23:2 B AWV 3‘83 ESEE xmvuw ‘335 22 3:3 Know gwuusxek qu33u‘9:k 32 wofiiufis 39.: \rawfiwEwfivm E8393 CQBHEOQBwvm .5301— SSE‘SSEU :25: Swing fill 32: gigs?» :3».— unllmm {2: ES f2§sfim II I main—”833* San D acme—~00 33L Eggwfiwvw I :33 En QEEQE E»: 930.— Sim—Eta mxoou :aka=$kwm.e£ :«Ba:waoM 23:2 32: 5:3an I 1% A A A b ZO_F<10—8 emu/cm3 fOr lO-cm3 cores, and we have had good results down to 3X10“7 emu/cm3 in the US. Geological Survey laboratory. Over a period of 2 years of use, comparative measurements within the limits of the US. Geological Survey magnetometer for the same samples indicated a difference in results between the two magnetometers that is well within the claimed measurement error of 5° for direction and 10 percent for intensity for the high-sensitivity instru- ment. All data in this paper were reduced with computer programs and are presented in terms of declination (D), measured in degrees east of geographic north, and inclination (I), measured in degrees below the horizontal. All directions are corrected for present geologic dip of the rock unit unless otherwise noted. Radii for circles of confidence (0:95) have been de- termined by a Fisher (1953) statistical computer pro- gram at the 95 percent level; K is the precision param- eter. Unless otherwise noted, N refers to number of individual samples. In1 the summary table, N is the number of sites for which Fisher (1953) analyses have been computed. In the various figures, remanence results are plotted on the lower hemisphere of an equal- area net to permit direct comparison of directions on a single plane, regardless of polarity. Solid circles repre- sent polarization north-seeking down and open circles represent polarization south-seeking down. Due to local declination anomalies that were com- monly several degrees and occasionally near 10°, all magnetic compass readings at the collecting site had to be verified with a sun dial compass. Routine procedure included calibration of the sun dial compass with watch time for the particular lati- tude and in the particular area of site locations. Cali- bration stations were established at Kearsarge and Ironwood, Mich., at Mellen, Wis., and at Grand Marais, Minn. These stations were reoccupied whenever the sample collection period exceeded several weeks. A comparison of the magnetic compass reading of true north with that determined by the sun dial com- pass was made for each core. With the sun dial compass as base, the differential was applied as a correction to all magnetic compass readings for each core. The sun dial compass marks are placed at 5-minute intervals so that the instrument can be set up to within 2% minutes of time. This is equivalent to about 1° in azimuthal readings on the magnetic compass, and the precision of declination readings for each core sample is prob- ably near 1°. 1 SOURCES OF ERROR The total core collection and orientation errors in the field and in the laboratory are most probably less 4 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS than 3°. The prime source of error in computing paleo- magnetic field directions is probably due to uncertainty in the geologic dip component of the attitude for the lava flows, as their orientations are not easily measured in the field. Geologic dip measurements in the Kear- sarge, Mich., area where drill-hole data are plentiful are probably accurate to 10 (W. S. White, written commun., 1970), but dip values may be as much as 5° inaccurate in other places on the Keweenaw Peninsula. Dip values outside the peninsula are less certain. The North Shore Volcanic Group in Minnesota and the Isle Royale lavas dip less than 20°; consequently, the possibility of large errors in dip measurements is lessened, and geologic dip values are probably accurate to 5°. In the Ironwood, Mich., and Mellen, Wis., areas, the rocks commonly dip as much as 80°, and dip measurement errors are proportionately greater; dip values may be 5° to 10° inaccurate on individual flows and could be greater. MAGNETIC CLEANING Many groups of samples from igneous bodies col- lected for paleomagnetic research have scattered remanent magnetization directions, and the average direction may not represent the direction of the earth’s magnetic field at the time the rocks cooled. Such a scatter can often be attributed to secondary components of magnetization superimposed upon the original magnetization after cooling. One of the most common secondary components encountered is viscous magne- tization, which may be acquired over a long period of time. The intensity of this magnetization is propor- tional to the logarithm of time (Rimbert, 1959), and the direction is parallel to that of the magnetic field in which it is acquired. Other secondary components which arise from light- ning, chemical alteration, and stress effects may also be superimposed on the original magnetization. The components due to lightning effects tend to be scattered, as observed between samples from the same site. Both viscous magnetization and magnetization due to light- ning may be removed by alternating (ac) field de- magnetization. The components due to chemical altera- tion and stress effects may be stable and will be in the direction of the earth’s magnetic field at the time of the remagnetization. The partial demagnetization technique used in this investigation is that utilized by US. Geological Survey laboratories. In this method an alternating magnetic field (H) is slowly decreased as the sample orientation is changed by simultaneous rotation about three orthogonal axes. All samples reported in this paper were subjected to a-c partial demagnetization in order to eliminate any unstable secondary components. The optimum peak demagnetizing field selected was based on an empirical procedure utilized by others (Cox 1961; Irving and others, 1961). This procedure involves selecting afew samples from one collecting site and studying the dispersion of magnetic directions after each demagne- tization step. The a-c demagnetization that is found necessary to produce minimum dispersion is selected and applied to all samples from the site. Table 1 shows examples of partial demagnetization data in steps of 100, 200, and 300 Oe (Oersteds) for some of the sites in the Portage Lake Lava Series. Though small, the within-site scatter increases beyond the 100-Oe demagnetization level (as shown by c295 values), which indicates that 100 Oe is the optimum peak field for Portage Lake lavas, using this procedure. The 100-Oe demagnetization level for the Portage Lake lavas wasalso generally applicable for other igneous rock samples from the Lake Superior region, though some of the sites on the older and lithologically distinct flows required 150-Oe levels, and Beck and Lindsley (1969, table 1) found 75-Oe levels to be optimal for rocks of the Beaver Bay Complex of Grout and Schwartz (1939). TABLE 1.—Partial demagnetization data for four sites on the Portage Lake Lava Series, Keweenaw Peninsula, M ich. [N is number of within-site samples. H is peak alternating magnetic field (in Oersteds) used in magnetic cleaning. Other data for these samples are found in tables 2 and 3] Mean direction of magnetization at collecting site Precision Radius of Site No. parameter, confidence Decligation, Inclination, K circle, ass (degrees) (degrees) Natural remanent magnetimtion PL4 __________ 6 266.9 42.7 85.5 7.3 8 __________ 5 304.9 50.6 30.0 14.2 335 ________ 5 296.9 33.7 616.7 3.7 345 ________ 5 275.0 41.3 22.7 19.7 fi= 100 Oe PL4 __________ 6 261.0 43.2 204.6 4.7 8 __________ 5 297.7 44.2 423.2 3.7 335 ________ 5 296.1 33.7 762.4 3.3 345 ________ 5 281.2 38.3 104.7 7.5 1'1 = 200 Oe PL4 __________ 6 263.8 43.8 197.2 4.8 8 __________ 5 297.9 44.1 374.1 4.0 335 ________ 5 294.9 34.8 303.5 4.4 345 ________ 5 286.4 35.6 34.2 13.3 H=3oo Oe PL4 __________ 6 264.4 41.8 109.9 6.4 8 __________ 5 297.1 44.6 410.6 3.8 335 ________ 5 294.7 35.0 382.1 3.9 345 ________ 5 289.4 31.1 9.4 26.4 GENERAL GEOLOGY The Keweenawan Series of the Lake Superior region is characterized by great thicknesses of mafic volcanic rocks exposed around the margin of the lake (fig. 1). Structurally the series forms a large syncline with KEWEENAW PENINSULA 5 dips ranging from near zero to vertical. On the western end of the lake, the syncline trends northeast and has low-angle dips on the north limb and steep dips on the south limb. Gravity and magnetic highs and well data (Lyons, 1959; Thiel, 1956; Craddock and others, 1963) indicate that the Keweenawan igneous se- quence extends southwest across the midcontinent toward Kansas. The Keweenawan rocks have been separated into three subdivisions: 1. The term lower Keweenawan has long been applied to sedimentary rocks that overlie the Animikie Series (now called Marquette Range Supergroup)1 and are comformable with overlying Keweenawan lava flows. The maximum exposures of these rocks are on the Sibley Peninsula of northwest Ontario and consist principally of red, fine-grained sandstones and silt- stones. In Minnesota, lower Keweenawan rocks are represented by the Puckwunge Formation (Grout and others, 1951, p. 1051—1053) that consists of conglom- erate and sandstone; near Grand Portage the Puck- wunge overlies the Rove Slate of the Animikie Group with no visible discordance, and near Duluth it rests on the Thomson Formation as used by Schwartz (1942) with marked angular unconformity. Lower Keween- awan rocks also have been reported (Aldrich, 1929, p. 109—110) in northern Wisconsin overlying Animikie rocks. The Sioux Formation in Minnesota and Barron Quartzite of Winchell (1895) in Wisconsin are also possibly lower Keweenawan (Goldich and others, 1961, p. 149). It now seems desirable locally, if not regionally, to place the boundary between lower and middle Kewee- nawan rocks several thousand feet above the lava flows that immediately overlie these lower Keweenawan sedimentary rocks, thereby including a thick sequence of mafic lava flows within the lower Keweenawan (Hubbard, 1967; Books, 1968). Hubbard suggested that at least one unconformity separates the rocks of the so-called South Trap Range in the Ironwood- Mellen area (described in a later section) from the overlying Portage Lake Lava Series, which, in its type area, makes up the whole of the middle Keween- awan. 2. The middle Keweenawan is composed mainly of a thick sequence of basaltic andesite lava flows, with subordinate beds of sedimentary rock and rh‘yolite conglomerate. Rhyolite flows account for perhaps 10 1 The Animikie Group of Ontario and Minnesota is only partly equivalent to the Animikie Series as previously used in Michigan and Wisconsin (James 1958). In that area, the Animikie Series included the Chocolay, Menominee, Baraga, and Paint River Groups, and, according to the stratigraphic code, should have super- group rank. To avoid the confusion inherent in an Animikie Group and an Animikie Supergroup, Cannon and Gair (1970) abandoned the term Animikie Series and replaced it with the term Marquette Range Supergroup. In this paper, the term Animikie Series is used only when used by the author cited; otherwise the term Marquette Range Supergroup is used. The term Animikie Group remains in good usage in Minnesota and Ontario. 471-715 0 - 72 ~ 2 percent of the total thickness of flows on the north shore in Minnesota (Grout and others, 1951, p. 1054) but are less well represented on the south shore. These lavas are exposed around the periphery of Lake Superior in Michigan, Wisconsin, Minnesota, and in Ontario on the north and east shores. Michipi- coten Island and most of Isle Royale are also under- lain by middle Keweenawan lava flows. Grout, Sharp, and Schwartz (1959) gave a thickness of 25,000 feet for the lava flows exposed along the southern half of the Minnesota coast, and a greater thickness (White, 1966b) is suggested by the breadth of outcrop in the Keweenawan lavas in northwestern Wisconsin. White (1966b, p. 30) summarized by suggesting that parts of the section may be repeated in Minnesota and Wisconsin, and that thicknesses of 20,000 to 30,000 feet or more exist in parts of the Lake Superior basin. Middle Keweenawan intrusive rocks are abundant in the Lake Superior region, especially in Minnesota and along the northwest shore. Sills, dikes, and more irregular bodies of basaltic rocks intrude the gently dipping Keweenawan and older rocks. With the excep- tion of the Duluth Gabbro Complex and the Beaver Bay Complex of Grout and Schwartz (1939), these bodies are known generally as the Logan intrusions. Paleomagnetic pole directions (DuBois, 1962, p. 59) indicate that some of these intrusive rocks in the Nipigon, Ontario, and Baraga County, Mich., areas are probably lower Keweenawan. The Duluth Gabbro Complex is a large sill-like mass intruded below the middle Keweenawan lava flows and is, by far, the largest Keweenawan intrusion in the region. It extends northeast into Cook County, Minn., where it divides and extends approximately another 40 miles eastward as two separate sills (Grout and others, 1959, p. 40—41). Elsewhere around Lake Supe- rior, Keweenawan dikes occur locally in large numbers, and one other large sill-like mass akin to the Duluth Gabbro Complex intrudes Keweenawan lava flows near Mellen, Wis. 3. The upper Keweenawan sequence consists largely of fine-grained sandstones and shales. On the Kewee- nawan Peninsula and west into Wisconsin, these sedi- mentary rocks overlie a thick conglomerate (the Copper Harbor Conglomerate) interbedded with a few lava flows. Upper Keweenawan rocks are exposed mainly in northern Michigan and Wisconsin but are also found in Minnesota southwest of Duluth, and on Isle Royale. KEWEENAW PENINSULA GEOLOGIC SETTING On the Upper Peninsula of Michigan the Keweena- wan rocks form ’part of the southern limb of the Lake 6 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS Superior syncline so that at most localities they are inclined northwest toward the lake. Dips range from near horizontal to near vertical, and generally the lower beds dip more steeply than the upper beds. Strike of the rocks is generally northeast, but it turns from N. 33° E. near Kearsarge to S. 79° E. on Keweenaw Point. The Portage Lake Lava Series is more than 15,000 feet thick in the Delaware 7%-minute quadrangle, Michigan (Cornwall, 1954). This sequence is terminated at the base by the Keweenaw fault which has thrust the flows over the adjacent Jacobsville Sandstone to the south, cutting out an unknown thickness of lava flows. The Portage Lake lavas are composed of basalt and andesite flows with a few thin interbedded rhyolite conglomerates. Some of the flows are fine grained, but most flows increase in grain size from both top and bottom toward the center. Capping each flow is a layer of amygdaloidal lava generally 5 to 10 feet thick. Conglomerate and sandstone beds within the lava- series are mostly rhyolitic material. The bulk of the elastic particles are less than 6 inches in diameter, and boulders more than 1 foot in diameter are uncommon (White and others, 1953). The Copper Harbor Con- glomerate (Lane, 1911, p. 37—40) comformably overlies the Portage Lake Lava Series and consists mainly of pebble to boulder conglomerate and lesser amounts of sandstone. Lava flows interstratified with the con- glomerate are typically fine-grained andesite. Intrusive rhyolites are exposed at a number of loca- tions on the Keweenaw Peninsula and are typically pale reddish brown on fresh surfaces and lighter on weathered surfaces. Most of the rhyolites intrude mid- dle Keweenawan lava flows, but one intrudes rocks at least 10,000 feet above the Portage Lake Lava Series. These intrusions are believed to be of middle and upper Keweenawan age (White and others, 1953). DESCRIPTION OF RESULTS PORTAGE LAKE LAVA SERIES A total of 380 samples from 76 sites were collected from flows of the Portage Lake Lava Series for remanent magnetization measurements. Of these, 35 samples from seven sites were not utilized because of the large scatter of directions after partial demagnetization in a—c fields as great as 300 Oe. Of the remaining 69 sites, 17 are scattered along the peninsula northeast of Kearsarge, Mich., and 52 repre- sent a rather detailed sample collection across the lava flow sequence in the vicinity of Kearsarge in the Ahmeek 7%—minute quadrangle, Michigan (White and others, 1953). The bulk of the collections around Kearsarge represent the central parts of flows, which are probably least affected by later metamorphic events. Figure 2 is a stratigraphic column (simplified from White and others, 1953) indicating the horizons at which the samples were collected. Remanence data from the Kearsarge section are subdivided into three parts as follows: (1) all samples below conglomerate No. 14, (2) all samples between conglomerate Nos. 14 and 15, and (3) all samples above conglomerate No. 15. The separation into three parts is based on a significant difference in the direc- tion of magnetization for the samples between con- glomerate Nos. 14 and 15 and the directions for sam- ples both below conglomerate No. 14 and above con- glomerate No. 15. Results are shown in figures 3—5 and table 2. The paleomagnetic results for the 17 sites in the Portage Lake Lava Series northeast of Kearsarge are- shown in figure 6 and table 3. These flows haVe an average remanence direction that is not significantly different from directions of magnetization in the inter- vals below conglomerate No. 14 and above conglom- erate No. 15 near Kearsarge, Mich. In order to investigate the possibility of rotation of the lava flows around vertical axes during the anti- clinal bending in the northern part of the Keweenaw Peninsula, samples from the Ashbed Flow were collected at points where the strike ranged from N. 38° E. to N. 78° E. This component of structural movement (rotation about vertical axes) is not diminished by geologic-dip corrections, and, if present, it would re- main in the data and would be reflected as differences in the declination of the paleomagnetic field directions. In table 4, a comparison of the variations in strike with the variations in paleomagnetic declination indi- cates no systematic relationships, and hence there is no evidence for rotation about vertical axes in this region. RHYOLITE FLOWS NORTH OF LAKE GOGEBIC, MICHIGAN Thirteen samples from three separate sites represent rhyolite lava flows from the top of the lava series along the Bergland fire tower road north of Bergland, Mich. Paleomagnetic results are given in figure 7 and table 5. W. S. White (written commun., 1970) suggested that these flows belong to a group that locally overlies the Portage Lake Lava Series in this area. Whether this group underlies the Copper Harbor Conglomerate or grades laterally into it is not yet known. The proximity of the mean direction of magnetization for the rhyolite flows to those for the Portage Lake Lava Series and the Copper Harbor Conglomerate makes paleomagnetic measurements of little use in distinguishing this local group of flows from the formations above and below it. KEWEENAW PENINSULA l FEET I: 11000 _ FEET Green- l‘ PL33 FE_T ‘ FEET — PL44 stone FIow‘-PL34 Conglomerate No 15 _ PL35 -PL7 ~PL4 — PL324 - PLS - PL6 _ PL3 Kear- ‘ sarge Flow _ ngas —' L 4 Conglomerate No. 9 — PL1 Conglomerate No. 14 - PL55 1 1000 _‘ —- PL61 4000 _ — PL56 — PL150 — PL333 7000 — — PL49 10,000 - — PL326 Iroquois Flow _ PLSO Conglomerate Not 17 - PL329 Copper \Ashbed PL43 l City - PL343 Flow F'OW Conglomerate No. 13 Old Colony Sandstone — PL331 0 Conglom- L. P 344 erate No.6 L 3000— Conglomerate No. 16 6000 - PL27 Osceola 9000 — F'°w -PL51 - PL26 — PL25 — PL24 — PL330 — PL327 - PL22 — PL57 - PL52 — PL58 — PLZO Conglomerate No, 12 — PL19 Scales Creek Flow — PL59 _p|_14 '-PL323 2000‘ -— — PL60 — gtié — PLsa ... PL1). _ — PL325 -— PL10 500° - PL9 — PL8 8000 Green- stone Flow _ PL32 FIGURE 21—Simplified columnar section for the Portage Lake Lava Series near Kearsarge, lMich., showing stratigraphic posmon of samples studied. Section from White, Cornwall, and Swanson (1953). Labels next to points in this figure and succeeding figures refer to sampling sites. PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS 335 C 61 0 325 324 58 o 3‘“ 323 54 60 . 55 150 343 331 57..327 .56 .326 S EXPLANATION o + Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North-seeking polarization with circle of confidence. North-seeking polarization I Direction of axial dipole component of present geomagnetic field FIGURE 3.—Directions of remanent magnetization for flows of the Portage Lake Lava Series below conglomerate No. 14 (Houghton Conglomerate) near Kearsage, Mich. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 2 and figure 2 for sample locations. KEWEENAW PENINSULA Mean of site-mean directions Figure 5 + 7 Figure 3+ . S EXPLANATION 0 + Site-mean direction of magnetization. Mean of site-mean directions of‘ magnetization, North-seeking polarization with circle of confidence. North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE 4.—Directions of remanent magnetization for flows of the Portage Lake Lava Series between conglomerate No. 14 (Houghton) and conglomerate No. 15 (Allouez) near Kearsarge, Mich. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 2 and figure 2 for sample locations. 10 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS S EXPLANATlON 0 + Site-mean direction of magnetization. Mean of site—mean directions of magnetization, North-seeking polarization with circle of confidence. North-seeking polarization I Direction of axial dipole component of present geomagnetic field FIGURE 5.—Directions of remanent magnetization for flows of the Portage Lake Lava Series above conglomerate No. 15 (Allouez Conglomerate) near Kearsarge, Mich. Data corrected for geologic dip. Equal—area projection, lower hemisphere. See table 2 and figure 2 for sample locations. KEWEENAW PENINSULA 11 TABLE 2.—Paleomagnetic results for Portage Lake Lava Series near Kearsarge, M ich. [Paleomagnetic data are corrected for geologic dip. Stratigraphic locations of samples are shown in fig. 2] Mean direction of magnetization Number of at collecting site Remanent Site No. samples intensity Location and attitude of lava flow (N) Declination, D Inclination, I (emu/cmi‘XlO-G) ‘ (degrees) (degrees) Samples from below conglomerate No. 14 PL150 ____________ 4 284.4 33.0 4,110 700 ft northk, 1,100 ft west of SE. cor. sec. 31, T. 57 N., R. 32 Strike N. 37° E. dip 38. 5° NW. 50 _____________ 5 284.2 19 .9 900 Iroquois Flow. 2,050 ft south, 2, 700 ft west of SE. cor. sec. 6, T. 56 N, R. 32 W. Strike N. 35° E. dip6 40; NW. 331 ____________ 5 283 3 35.3 1,450 1, 950 ft south, 2, 350 ft west of NE. cor. sec. T.56 N. R. 32 W. Strike N. 38° E. dip 40° NW. 344 ____________ 3 294 7 38.2 450 350 ft south, 950 ft east of NW. cor. sec. 7, T. 57 N., R. 32 W. Strike N. 38° E. dip 40° NW. 51 _____________ 3 290.9 24. 8 480 Osceola Flow. 850 ft south, 100 ft west of NE. cor. sec. 6, T. 56 N. R. 32 W. Strike N. 40° E. dip 41° NW. 330 ____________ 5 286.8 21.0 431 725 ft north, 2, 500 ft west of SE. cor. sec. 6, T. 56N., R. 32 W. Strike N. 33° E., dip 40° NW. 52 _____________ 5 287 4 32. 9 1,580 1, 300 ft south, 1, 700 ft east of NW. cor. sec. 7, T. 56 N., R. 32 W. Strike ':N 32° E., dip 40° NW. 323 ____________ 4 289.6 30. 6 235 2, 150 ft south, 1, 850 ft east of NW. cor. sec. 7. T. 56N., R. 32 W. Strike N. 34° E., dip 40° NW. 53 _____________ 5 300.8 24.6 694 1,500 ft south, 2,100 ft east of NW. cor. sec. 7, T. 56N., R. 32 W. Strike N. 32° E., dip 40° NW. 324______-_____ 5 293.0 35.0 2,600 1,900 ftsouth, 2,150 ft west of NE. cor. sec. 7, T. 56N., R. 32 Strike N. 31° E, dip 40° NW. 335 ____________ 4 296 1 33. 7 249 Kearsarge Flow. 2,250 ft north, 1, 900 ft east of SW. cor. sec. 27, T. 57 N., R. 32 W. Strike N. 43° E. dip 38° NW. 54 _____________ 5 285.6 32.0 320 Kearsarge Flow. 1, 350 ft south, 1, 500 ft west of NE. cor. sec. 7, T. 56 N., R. 32 W. Strike N. 31° E, dip 41° NW. 55 _____________ 5 291.1 48. 8 148 1, 850 ft south, 1, 300 ft west of NE. cor. sec. ,.T 56 N. R. 32 W. Strike N. 31° E. ,dip 41. 5° NW. 56 _____________ 5 285.6 51 5 125 1, 800 ft south, 1,350 ft west of NE. cor. sec. 7, T. 56 N., R. 32 W. Strike N. 31° E. dip 41. 5° NW. 326 ____________ 5 279.8 50.0 197 2, 500 ft north, 200 ft east of SW. cor. sec. 8, T. 56 N. R. 32 W. Strike N. 27. 5° E. dip 40° NW. 327 ____________ 4 283 .8 41.5 132 2, 350 ft north, 600 ft east of SW. cor. sec. 8, T. 56 N. R. 35 ‘ W. Strike N. 27. 5° E., dip 40° NW. 57 _____________ 4 283 6 39. 6 720 2, 750 ft south, 800 ft east of NW. cor. sec. 8, T. 56 N., R. 32 . Strike N. 26° E. ,dip 45° NW. 58 _____________ 4 290.9 30. 2 3,200 2, 760 ft south, 800 ft east of NW. cor. sec. 8, T. 56 N. R. 32 W. Strike N. 26° E, dip 45° NW. 59 _____________ 4 290 3 32.5 1,280 Scales Creek Flow. 2, 600 ft south, 1, 200 ft east of NW. cor. sec. 8, T. 56 N., R. 32 W. Strike N. 27° E., dip 46° NW. 60 _____________ 4 288 5 40.0 353 2,750 ft south, 1,300 ft east of NW. cor. sec. 8, T. 56 N., R. 32 W. Strike N. 27° E., dip 46° NW. 325 ____________ 5 293 2 33.6 307 1,300 ft south, 100 ft west of NE. cor. sec. 7, T. 56 N., R. 32 W. Strike N. 25° E., dip 44° NW. 61 _____________ 4 294 2 31. 7 114 3,450 ft south, 2,350 ft east of NW. cor. sec. 8, T. 56 N., R. 32 W. Strike N. 22" E., dip 49° NW. 343 ____________ 5 285.7 37.1 2,030 Copper City Flow. 250 ft south, 2,350 ft east of NW. cor. sec. 17, T. 56 N., R. 32 W. Strike N. 17.5° E., dip 52° NW. Samples from between conglomerate Nos. 14 and 15 PL35 _____________ 5 264 .9 45.6 554 2,150 ft north, 1,175 ft west of SE. cor. sec. 31, T. 57 N., R. 32 . W. Strike N. 38° E., dip 38° NW. 7 ______________ 4 294.6 45.2 747 1,350 ft north, 1,850 ft West of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37.5° E., dip 38° NW. 6 ______________ 4 274 .7 45.2 117 2,000 ft north, 1,150 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 38° E., dip 37.5° NW. 5 ______________ 5 280.8 49 .7 330 2,100 ft north, 1,200 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 38° E.L dip 37.5° NW. 4 ______________ 6 261.0 43.2 107 750 it north, 2,350 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E.L dip 38° NW. 3 ______________ 5 279.5 36.6 1,020 700 ft north, 2,200 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E., dip 38° NW. 1 ______________ 5 265.6 51.6 2,200 0ft north, 2,200 ft west1of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E., dip 38.5° NW. Samples from above conglomerate No. 15 ‘ PL44 _____________ 3 287.9 29 .6 1,800 Section line, 1,250 ft south of NW. cor. sec. 1, T. 56 N., R. 33 W. Strike N. 37° E., dip 34.5° NW. 333 ____________ 5 281.8 28.8 2,380 2,450 ft north, 900 ft west of SE. cor. sec. 36, T. 57 N., R. 33 W Strike N. 34° E., dip 33.5° NW. 12 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 2.—Paleomagnetic results for Portage Lake Lava Series near Kearsarge, M ich.——Continued Mean direction of magnetization Number of at collecting site Remanent Site No. samples intensity Location and attitude of lava flow (N) Declination, D Inclination, I (emu/cmSX 10-“) (degrees) (degrees) Samples from above conglomerate No. 15—Continued PL49 _____________ 5 290.1 27.5 1,720 3, 350 ft north, 2, 200 ft west of SE. cor. sec. 36, T. 56 N., R 33 W. Strike N. 35° E., dip 35° NW. 329 ____________ 3 286.1 24 .4 188 Ashbed Flow. 1, 400 ft north, 2, 250 ft west of SE. cor. sec 20, T. 57 N., R. 32 W. Strike N. 39° E. dip 27. 5° NW. 43 _____________ 4 293.7 38.1 1,410 Ashbed Flow. 2,050 ft north, 450 ft west of SE. cor. sec. 36, T. 57 N. R. 33 W. Strike N. 38° E., dip 36° NW. 27 _____________ 4 282.8 41.5 2,640 2, 750 ft north, 2, 950 ft west of SE. cor. sec 31, T. 57 N., R. 32 W. Strike N. 37° E. dip 35. 5° NW. 26 _____________ 5 285.9 33.6 1,450 2, 900 ft north, 3, 350 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E. dip 36° NW. 25 _____________ 5 279.3 49.7 298 2, 650 ft north, 3, 300 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E., dip 36. 5° NW. 24 _____________ 4 280.2 35.7 2,260 2, 550 ft north, 3, 250 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E. dip 36. 5° NW. 22 _____________ 6 291.4 43.6 802 2 200 ft north, 3, 200 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37. 5° E. ,dip 37° NW. 20 _____________ 5 295.3 40.2 880 2,150 ft north, 3, 000 ft west of SE. cor sec. 31, T. 57 N., R. 32 W. Strike N. 37. 5° E., dip 37° NW. 19 _____________ 3 299.0 31.7 1,150 1, 950 ft north, 2, 975 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37. 5° E. dip 37° NW. 14 _____________ 5 294.7 32.0 713 1, 275 ft north, 2, 950 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37° E., dip 37. 5° NW. 13 _____________ 5 296.9 28.2 634 1, 250 ft north, 2, 900 ft west of SE. cor. sec. 31, T. 57 N., R. _ 32 W. Strike N. 38° E, dip 37. 5° NW. 12 _____________ 5 297.8 33.6 1,300 1,125 ft north, 2, 875 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37. 5° E, dip 37. 5° NW. 11 _____________ 5 293.6 30.3 826 1,110 ft north, 2, 850 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 38° E., dip 38° NW. 10 _____________ 5 293.6 33.7 423 1,100 ft north, 2, 825 ft west of SE. cor. sec. 31, T. 57 N., R- 32 W. Strike N. 38° E., dip 38° NW. 9 ______________ 4 297.6 40.8 837 1, 200 ft north, 2, 800 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 37. 5° E., dip 38° NW. 8 ______________ 5 297.1 45.5 526 1,050 ft north, 2, 800 ft west of SE. cor. sec. 31, T. 57 N., R. 32 W. Strike N. 38° E., dip 38° NW. 32 _____________ 5 296 .4 32 .0 431 Greenstone Flow. 600 ft north, 3, 700 ft west of SE. cor. sec. 29, T. 57 N., R. 32 W. Strike N. 46° E, dip 35. 5° NW. 33 _____________ 5 291.0 37.2 3,330 500 ft north, 3, 650 ft west of SE. cor. sec. 29, T. 57 N., R. 32 W. Strike N. 46° E., dip 35. 5° NW. 34 _____________ 4 293.7 39.1 767 350 ft north, 3, 600 ft west of SE cor. sec. 29, T. 57 N., R. 32 W. Strike N. 46° E. dip 35. 5° NW. QUARTZ PORPHYRY NORTH OF LAKE GOGEBIC, MICHIGAN Thirteen samples from three sites represent the quartz porphyry outcrops along the Bergland-White Pine road about 4 miles north of Lake Gogebic, Mich. This geologic unit lies between typical middle Kewee- nawan lava flows and is intruded by a basalt dike in this area. Dip of the lower contact is approximately 35° NW. (Brooks and Garbutt, 1969), and data in figure 8 and table 6 have been corrected for this dip. RHYOLITE INTRUSION IN SEC. 4, T. 56 N., R. 32 W. Paleomagnetic data for eight samples are shown in figure 9 and table 7. The samples are from a poorly exposed rhyolite body that intrudes the Portage Lake Lava Series east of Kearsarge, Mich. RHYOLITE INTRUSION IN SECS. 24 AND 25, T. 56 N., R. 34 W. Paleomagnetic data for six samples from one site are shown in figure 10 and table 8. These samples are from a rhyolite body that intrudes the Freda Sandstone in sees. 24 and 25, T. 56 N., R. 34 W. southwest of Kearsarge, Mich. No other intrusions are known to cut rocks so high in the stratigraphic column. Dip of the Freda in this area is 22° NW., and figure 10 and table 8 show the direction of magnetization corrected for this dip. IRONWOOD-MELLEN AREA ‘ GEOLOGIC SETTING Formations of the Keweenaw Peninsula in Michigan can be traced southwest toward the Wisconsin border. IRONWOOD-MELLON AREA N 159 O ‘ 345 158 160 349 S EXPLANATION O Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North—seeking polarization with circle of confidence. North-seeking polarization ‘ I Site-mean direction of magnetization for _ . . _ i locations in the anomalous conglom- Direction 0f axual d|P0|e component erate Nos 14-15 interval. North seek- of present geomagnetic field ing polarization FIGURE 6.—Directions of remanent magnetization for miscellaneous flows of the Portage Lake Lava Series northeast of the Kear- sarge, Mich., area. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 3 for sample locations. 471-715 0 - 72 - 3 13 14 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 3.—Paleomagnetic results for miscellaneous flows of the Portage Lake Lava Series northeast of Kearsarge, Mich. [Paleomagnetic data are corrected for geologic dip] Mean direction of magnetization Number of at collecting site Remanent Site No. samples intensity Location and attitude of lava flow (N) Declination, D Inclination, I (emu/cm1X 10-11) (degrees) (degrees) PL340 ____________ 5 284 .8 27.9 197 Ashbed Flow. 650 ft north, 2, 700 ft west of SE. cor. sec. 8, T. 58 N, R 30 W. Strike N. 76° E., dip 26° NW. 338 ____________ 4 286.9 19.7 2,240 Ashbed Flow. 100 ft south, 2, 750 ft west of NE. cor. sec 30, T. 58 N., R. 31 W. Strike N. 61° E., dip 28° NW. 339 ____________ 4 294.6 29.8 1,810 Ashbed Flow. 1, 700 ft south, 950 ft east of NW. cor. sec. 21, T. 58 N., R. 31 W. StrikeN. 70° E. dip 27. 5° NW. 342 ____________ 5 284.5 36.8 2,370 Ashbed Flow. 600 ft south, 250 ft east of NW. cor. sec. 12, T. 58 N. R. 29 W. Strike N. 77. 5° E., dip 22° NW. 349 ____________ 4 274.6 49.1 154 Greenstone Flow. 1, 500 ft south, 100 ft west of NE. cor. sec. 30, T. 58 N., R. 31 W. Strike N. 77° E., dip 24° NW. 348___-_ _-______ 4 315.6 33 .6 2,980 Greenstone Flow. 600 ft south, 4,150 ft west of NE. cor. sec. 16, T. 58 N., R. 30 W. Strike N. 77° E. dip 24° NW. 347 ____________ 4 301.0 33 .4 752 Greenstone Flow. 600 ft south, 2, 500 ft west of NE. cor sec. 16, T. 58 N. R. 30 W. Strike N. 77° E. dip 24° NW. 346 ____________ 4 288 .7 30 .9 338 Greenstone Flow. 1, 000 ft south, 2 000 ft west of NE. cor. sec. 16, T. 58 N., R. 30 w. Strike ’N’. 77° E., dip 24° NW. 345 ____________ 5 281.2 38.3 308 Greenstone Flow. 2,100 ft south, 160 ft west of NE. cor. sec. 16, T. 58 N. R. 30 W. Strike N. 77° E., dip 24° NW. 158 1____-______ 5 283.0 38.9 639 2, 250 ft north, 550 ft west of SE. cor. sec. 16, T. 58 N. R. 30 W. Strike N. 79° E., dip 24° NW. 160 1 ___________ 4 283.0 44.3 293 2,150 ft north, 650 ft west of SE. cor. sec. 16, T. 58 N, R. 30 W. Strike N. 79° E., dip 25° NW. 159 1 ___________ 4 284.3 48.8 498 2, 000 ft north, 500 ft west of SE. cor. sec. 16, T. 58 N. R. 30 W. Strike N. 79° E. dip 25° NW. 157 1_-_______-_ 5 254.7 40.4 2,660 1, 350 ft north, 300 ft east of SW. cor. sec. 15, T. 58 N, R. 30 W. Strike N. 79° E. dip 25° NW. 341 ____________ 5 287 .9 34 .9 138 Scales Creek Flow. 1,100 ft south, 400 ft west of NE. cor. sec. 25, T. 58 N., R. 30 W. Strike N. 74. 5° E., dip 42° NW. 154 ____________ 5 274.2 33.1 256 2, 400 ft north, 2, 400 ft east of SW. cor. sec. 30,T .58 N. R. 29 W. Strike N. 70° E., dip 56° NW. 153 ____________ 6 286.2 41.0 115 800 ft north, 1, 950 ft east of SW. cor. sec. 30, T. 58 N. R. 29 W. Strike N. 71. 5° E. ,dip 59° NW. 42 _____________ 4 326.7 19.5 376 1, 000 ft south, 2,050 ft eastla3 of NW. cor. sec. 32, T. 58 N., R. 29 W. Strike N. 79°E .,dip 63° N. 1 Site is in the anomalous interval between conglomerate Nos. 14 and 15. basalts, but they are lithologically distinct (Hubbard, 1968, p. 35) from the middle Keweenawan basalts farther north. In the Marenisco, Mich., area the South Trap Range basalts lie unconformably upon the TABLE 4.—Comparison of declination and strike along the Ashbed Flow in the Portage Lake Lava Series at sites in the northern part of the Keweenaw Peninsula [Site locations are given in tables 2 and 3] Site N°- 5‘11"“ Defgggrtggg: D Animikie (Van Hise and Leith, 1911, p. 234; Fritts, 1965) and near Ironwood they dip 60° to 85° northward. fi' 33: E 3236i Near Lake Gogebic the flat-lying J acobsville Sandstone N: 61° E: 286 :9 overlaps the South Trap Range lavas onto the Animikie fi- gg: E 33213 (Van Hise and Leith, 1911 ; Fritts, 1965) and again N: 78° E: 284 :5 farther east the South Trap Range lavas are over- lapped and buried by the Jacobsville Sandstone. Westward from the Ironwood area the South Trap In the Ironwood, Mich., area they are joined by lavas of the so-called South Trap Range; these are Kewee- nawan volcanic rocks distinct from those of the main outcrop belt of the Portage Lake Lava Series that can be traced eastward past the south end of Lake Gogebic, Mich. Two isolated exposures, one at Silver Mountain in Michigan (fig. 1) and one 3 miles southeast at Sturgeon Falls, are 25 miles northeast of the most easterly exposure of the main belt of South Trap Range rocks. Lavas of the South Trap Range are mostly Range lavas dip steeply northward and appear to be conformable on (Marquette Range Supergroup) rocks of the Gogebic Iron Range. According to Aldrich (1929, p. 108—109) proof of the unconformity in this area rests entirely upon broad field relations; however, suggestions of an unconformable relationship have been observed (Van Hise and Leith, 1911, p. 234; Aldrich, 1929, p. 108—109) west of Mellen, Wis. At Mellen and westward a gabbro-granophyre com- plex has been intruded along zones of weakness in IRONWOOD-MELLON AREA N Mean of site-mean directions of magnetization for Cooper Harbor Conglomerate, Portage Lake lava flows of figure 5, and Portage Lake lava flows of figure 3 I + S EXPLANATION O Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North-seeking polarization with circle of confidence. North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE 7.—Directions of remanent magnetization for middle Keweenawan rhyolite flows north of Lake Gogebic, Mich. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 5 for site locations. Data for Copper Harbor Conglomerate from DuBois (1962). 15 16 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 5.—Paleomagnetic results for middle Keweenawan rhyolite flows north of Lake Gogebic, M ich. [Sites are in T. 49 N., R. 42 W. Data are corrected for geologic dip] Mean direction of magnetization Number of at collecting site Remanent Site No. samples intensity Location and attitude of lava. flow (N) Declination, D Inclination, I (emu/cm’X 10") (degrees) (degrees) ER66 ____________ 5 281.1 24.8 44.6 1,000 ft south, 1,050 ft west of NE. cor. sec. 5. Strike N. 64° E., dip 23° NW. 67 ____________ 4 290.3 32.7 15.8 1,100 ft south, 1,100 ft west of NE. cor. sec. 5. Strike N. 64° E., dip 23° NW. 68 ____________ 4 290.4 26.4 24.5 2,000 ft north-northeast of Bergland fire tower. 800 ft north, 0 ft west of SE. cor. sec. 32. Strike N. 65° E., dip 23° NW. middle Keweenawan lava flOWS. Leighton (1954, p. 406) has shown that layering in the gabbro dips about 20° less than that in the enclosing lavas. His interpretation of the relation suggests the flows were inclined before intrusion of the gabbro and that further tilting occurred after intrusion. Paleomagnetic evidence (Books and others, 1966, p. D123) supports this interpretation. DESCRIPTION OF RESULTS LOVVERMOST KEWEENAWAN LAVA FLOWS In the Ironwood area, the South Trap Range rocks crop out in two parallel east-west ridges that have a total width of about 1.6 miles; these ridges are sepa- rated from the main belt of the Portage Lake Lava Series to the north by an area of low relief 2 miles Wide in which the nature of the bedrock is not known. Northeast of Ironwood the lowest South Trap Range flows are underlain by quartzite in sec. 12, T. 47 N., R. 47 W. Samples were collected at various sites across the South Trap Range outcrop belt and represent about 8,000 feet of lava flows. Results representing the upper 6,700 feet of flows have already been reported (Books, 1968). Those data show south-seeking polarization similar to that found in the upper part of the lower Keweenawan Sibley Series of the Nipigon basin by DuBois (1962, p. 42—45). Results representing the lowermost 400 feet of lava flOWs in the Ironwood area as well as the basal quartzite northeast of Ironwood are presented in figure 11 and table 9. These data show a magnetization that is northseeking down. PORTAGE LAKE LAVA SERIES Portage Lake lavas north of Ironwood trend ap- proximately N. 80° E., across the Black River. Collec- tions were made from four sites in the quarry at Chippewa Hill, Mich., in sec. 32, T. 49 N., R. 46 W., and from five sites 1 mile north near Algonquin Falls on the Black River. Figures 12 and 13 and tables 10 and 11 show the results. NORTH SHORE OF LAKE SUPERIOR GEOLOGIC SETTING The Puckwunge Formation of sandstone, quartz conglomerate, and quartzite forms the base of the Keweenawan Series in Minnesota, whereas to the northeast, in the Thunder Bay district, Ontario, the lower Keweenawan sedimentary rocks are represented by the Sibley Series. In both areas the sedimentary rocks are overlain by thick sequences of volcanic rocks, known in Minnesota as the North Shore Volcanic Group (Goldich and others, 1961) and in the Thunder Bay district, as the Osler Series. On Isle Royale, Mich., the middle Keweenawan lavas are overlain by upper Keweenawan clastic sedimentary rocks. These Keweenawan rocks form the northwest flank of the Lake Superior syncline and dip toward the lake at shallow angles that rarely exceed 20°. In general, the traces of individual stratigraphic units form a broad are that is almost parallel to the shoreline, but near Duluth and Grand Portage, Minn., the units curve lakeward and intersect the shoreline at sharp angles. Grout, Sharp, and Schwartz (1959, p. 37—38) have made a detailed study of the volcanic succession be- tween Grand Portage and Tofte, Minn. A total of 94 flOWS were found in this interval—the lowest is at Grand Portage and the highest, at Tofte. Total esti- mated thickness along the shoreline (less interflow sedi- mentary rocks, numerous diabase intrusions, and the Duluth Gabbro at Hovland, Minn.) is 17,500 feet. Thickness of the complete section could be as much as 29,000 feet. DESCRIPTION OF RESULTS NORTH SHORE VOLCANIC GROUP Sample collections were made from 52 of the total of 94 flows (Grout and others, 1959, p. 37—38) found between Grand Portage and Tofte, Minn. The collection sites are on or close to the shoreline and extend from flow No. 2 to flow No. 94 of Grout, Sharp, and Schwartz (1959). Paleomagnetic results for 11 site locations on NORTH SHORE OF LAKE SUPERIOR N + QP73 ‘3‘352753333 ' O Vacate“ (figure 5) I S EXPLANATION O Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North-seeking polarization with circle of confidence. ‘ North-seeking polarization Direction of axial dipole component of present geomagnetic field \ FIGURE 8.—Directions of remanent magnetization for quartz porphyry north of Lake Gogebic, Mich. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 6 for site locations. 17 18 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 6.——Paleomagnetic results for quartz porphyry north of Lake Gogebic, Mich. [Sites are in sec. 17, T. 49 N. R. 42 W. Quartz pyorphyry strikes N. 68° E. and dips 35° NW. Data are corrected or geologic dip] Mean direction of Number magnetization at Remanent o collecting site intensity Site No. samples (emu/cms Location (N) Declina— Inclina- X 10*“) tion, D tion, I (degreeS) (degreeS) QP69 ________ 4 310.5 25.0 11.7 3,200 ft south, 600 ft east of NW. cor. 71 ________ 4 289.1 20.9 7.2 3, 700 ft south, 750 ft east of NW. cor. 73 ________ 5 305.8 44.8 13.7 Section line 1, 500 ft east of SW.co1'. the lowermost 20 flows (representing 4,550 feet of strata) include a reversal of the paleomagnetic field direction and have been described by Books (1968). Paleomagnetic data for the remaining overlying flows, less five site locations where the data were too scattered to utilize, are shown in figure 14 and table 12. ISLE ROYALE LAVA FLOWS Nine site locations, represented by 44 samples, are in the vicinity of Lane’s (1911, pl. 1) Greenstone Flow in the Washington Harbor area of Isle Royale. Resulting directions of magnetization fall into two distinct groups as shown in figure 15. Site locations are given in table 13. DISCUSSION OF RESULTS LOWER KEWEENAWAN The Sibley Series of Tanton (1927) is lower Kewee- nawan according to the generally accepted classification of Keweenawan rocks (Leith and others, 1935). DuBois (1962, p. 42—45) collected at several different locations on the Sibley Peninsula and on the Black Sturgeon River (fig. 1). He cited (DuBois, 1962, p. 44—45) two reliable groupings that have opposing magnetic field directions. The group with the north pole on the lower hemisphere (fig. 16, point JI) was collected not far above the Animikie rocks on the Sibley Peninsula. The group with the south pole on the lower hemisphere (fig. 16, point JII) was collected from the upper part of the Sibley Series (DuBois, 1962, p. 44). He also indi- cated that the Logan sills of Lawson (1893) (fig. 16, point F), the Alona Bay lavas (fig. 16, point G), and the Baraga County dikes (Graham, 1953) (fig. 16, point H) have the south pole on the lower hemisphere, and he included them in the lower Keweenawan along with the Sibley Series. Palmer (1970) collected at various sites on the north shore of Lake Superior. He reported that the Logan sills in Ontario, the section of volcanic rocks at Alona Bay, Ontario, and the Osler Series near Thunder Bay, Ontario, have a reversed polarity; the Michipicoten Island volcanics have a positive polarity; and the North Shore Volcanic Group of Minnesota, the lavas at Gargantua Point, Ontario, and the section at Mamainse Point, Ontario, have both normal and reversed polarity sequences. Books (1968) reported on 14 sites in the South Trap Range (fig. 16, point C) near Ironwood, Mich., and on 11 sites in the lowermost flows (fig. 16, point E) near Grand Portage, Minn. Beck and Lindsley (1969, p. 2011) reported on seven sites in the northern tongue of the Duluth Gabbro (fig. 16, point 11) extension into Cook County, Minn. All these sites have paleomagnetic field directions that are south-seeking below the hori- zontal. In addition, the author has collected samples from the lower 400 feet of lava flows near Ironwood, Mich., and from sedimentary units below the basal Keween- awan flows; these samples represent new data for which results are shown separately in figure 11. From a summary of the new paleomagnetic data and previously published data (fig. 16), it is apparent that the direc- tions of magnetization fall into two groups with oppos- ing directions of magnetization. The two north-seeking magnetization directions (fig. 16, group A) are repre- sentative of rocks that lie above and are apparently structurally conformable with units believed to be of Marquette Range Supergroup age. At Ironwood, this direction (fig. 16, point 10) includes the basal quartzite and overlying lower 400 feet of basal Keween- awan lava flows. On the Sibley Peninsula, Ontario, this direction includes DuBois’ (1962, fig. 20) Group I, replotted on an equal—area projection (fig. 16, point J I). The south-seeking magnetization directions (fig. 16, group B) are representative of rock units at many loca- tions around Lake Superior. At Ironwood, this direc- tion of magnetization (fig. 16, point C) appears in volcanic rocks that are stratigraphically above and are conformable with volcanic rocks (fig. 16, point 10) lower down in the same section that have the nearly opposite direction of magnetization. On the Sibley Peninsula and in the Nipigon basin, the south-seeking directions of magnetization include DuBois’ (1962, fig. 20) Group II, replotted on an equal-area projection (fig. 16, point JII). This direction probably represents rocks in a higher stratigraphic position than the Sibley ‘Series rocks represented at point JI because most samples for this data were collected from the red dolomite unit on the Black Sturgeon River (DuBois, 1962, table XII). Wilson (1910, p. 67—69) believed that these rocks represent the upper part of the Sibley in the Nipigon basin. Evidently, then, similarities exist between magnetic field directions and between magnetic field direction changes in the Ironwood, Mich., and Sibley Peninsula, DISCUSSION OF RESULTS S EXPLANATION o Direction of magnetization for individual samples Site-mean direction of magnetization, with circle (site R36). North-seeking polarization of confidence. North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE 9.—Directions of remanent magnetization for samples from the rhyolite intrusion in sec. 4, T. 56 N., R. 32 W., east of Kearsarge, Mich. Data uncorrected for geologic dip. Equal-area projection, lower hemisphere. See table 7 for sample locations. 19 20 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 7.—Paleomagnetic results for rhyolite intrusion in sec. 1,, T. 56 N., R. 32 W., east of Kearsarge, Mich. [Data are uncorrected for geologic dip] Direction of magnetization at Remanent collecting site intensity Location from southeast Sample No. (emu/cm3 corner of section Declina- Inclina- X 10-“) tion, D tion, I (degrees) (degrees) 241.8 60.0 3.51 870 ft north, 2,540 ft west. 278.3 70.3 4.20 870 ft north, 2,530 ft west. 251 . 5 32 .2 3 . 74 800 ft north, 2,450 ft west. 233 . l 54. 0 3 .29 880 ft north, 2,500 ft west. 276.5 11.2 4.21 850 ft north, 2,500 ft west. 285. 5 45.5 3.64 890 ft north, 2,570 ft west. 246.2 2 .2 4.33 860 ft north, 2,510 ft west. 239.9 36.0 3.62 860 ft north, 2,520 ft west. Ontario, areas. The paleomagnetic sequence of events during lower(?) Keweenawan time for these two areas as well as for other lower(?) Keweenawan locations throughout the Lake Superior region appears to be as follows: 1. First, the earth’s magnetic field had a north- seeking polarization during the time interval in which the sedimentary and igneous rock units represented in figure 16, group A, were formed. In the Ironwood, Mich., area the upper limit of this interval can be located rather closely because the polarity change occurs somewhere between 400 feet and 1,200 feet above the base of the Keweenawan flows. The lower limit of this interval falls somewhere below the lowest Keweenawan rocks of the region. Figure 17 and table 14 show paleomagnetic results for one site from a pre-Keweenawan (Animikie) Marquette Range Super- group sedimentary rock unit east of Ironwood, Mich., that not only appears to conformably underlie nearby basal Keweenawan rocks, but also has a similar direc- tion of magnetization. Thus, the time interval repre- sented by the direction of magnetization in the basal Keweenawan quartzite and lower 400 feet of flows in the Ironwood area may have its lower limit in rocks classified by Irving and Van Hise (1892), Van Hise and Leith (1911), Allen and Barrett (1915), and Atwater (1938) as of Animikie age. Such a possibility is sup- ported by similar directions of magnetization for one site from the Rove Slate of the Animikie Group in the Grand Portage area, Minnesota (fig. 17, table 14). An alternative explanation for the similar directions in the lowermost Keweenawan rocks and the Marquette Range Supergroup sedimentary rocks would require that the original magnetization directions were subse- quently changed to those presently found. This inter- pretation does not seem impossible for the Ironwood area, because the basal Keweenawan there has been sufficiently metamorphosed to produce actinolite. How- ever, this interpretation does not explain the near reversal in magnetic directions that begins some 1,200 feet above the basal Keweenawan flows in the Ironwood area (fig. 16, point C); the later, middle Keweenawan magnetic field directions, which are significantly differ- ent (fig. 17, Portage Lake Lava Series and North Shore Volcanic Group); and the similar direction found in the Rove Formation (fig. 17) near Grand Portage, Minn. As the reversed field directions for units above the basal flows—both near Ironwood and near Grand Portage—are believed to be original mag- netization (Books, 1968, p. 251—253), any change in original magnetic directions for the basal flows must have occurred before the overlying reversely magne- tized units were formed. In addition, if any phenomenon had effected such a magnetic direction change in the basal Keweenawan flows and Marquette Range Super- group rocks it must have been sufficiently widespread to include the Ironwood and Grand Portage areas. 2. Second, following a magnetic reversal, the earth’s magnetic field in the Lake Superior region had a south- seeking polarization during the time interval in which the sedimentary and igneous rock units represented in figure 16, group B, were formed. This time interval was of sufl‘icient length for some 6,700 feet of lava flows to be extruded in the Ironwood, Mich., area as well as for the formation of various other sedimentary and igneous rock units around the periphery of Lake Superior. The northern tongue of the Duluth Gabbro extension (fig. 16, point 11) in northern Cook County, Minn., is included in this time interval, indicating that this gabbro complex must have begun to form very early in the history of volcanism in the Lake Superior region. In addition, Palmer’s work (1970) on the north and east shores of Lake Superior indicates that the Osler Series near Thunder Bay, some of the lavas at Gar- gantua Point, and some of the lavas at Mamainse Point, Ontario, may also belong in this same general time interval, as these units, in part, have a south- seeking polarization. MIDDLE KEWEENAWAN The middle Keweenawan is represented by the Portage Lake Lava Series of the Upper Peninsula of Michigan, their equivalents to the southwest in Wis- consin, the major exposures of lava flows in Minnesota along the northwest shore of Lake Superior from Grand Portage to Tofte, and the lava flows on Isle Royale; also included are the major intrusions in the region, most of the Duluth Gabbro Complex, the Beaver Bay Complex, the Logan intrusions, and various rhyolitic and granitic rocks. Although the Copper Harbor Con- glomerate has been arbitrarily classed as the lower- most formation of the upper Keweenawan (White and others, 1953), it is included with the middle Keweena- wan formations because, as DuBois has pointed out (1962, p. 61—62), there is little change in the direction of magnetization between the Copper Harbor and the DISCUSSION OF RESULTS 21 S EXPLANATION O Direction of magnetization for individual samples Site—mean direction of magnetization. with circle (site R62). North-seeking polarization of confidence. North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE 10.——Directions of remanent magnetization for samples from the rhyolite intrusion in secs. 24 and 25, T. 56 N., R. 34 W., southwest of Kearsarge, Mich. Data are corrected for dip of the Freda Sandstone, which the rhyolite intrudes here. Equal-area projection, lower hemisphere. See table 8 for sample locations. 22 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 8.—Paleomagnetic results for rhyolite intrusion in secs. 24 and 25, T. 56 N ., R. 3!, WI, southwest of Kearsarge, Mich. [Data corrected for dip of Freda Sandstone, which the rhyolite intrudes in this area. Freda Sandstone strikes N. 25° E. and dips 22° NW] Direction of magnetization at Remanent collecting site intensity Location from SW. Sample No. (emu/cm3 cor. sec. 24 Declina- Inclina— X 10—“) tion, D tion, I (degrees) (degrees) 296.1 15.1 696 2,550 ft north, 8,350 ft east. 305.3 18.5 700 2,600 It north, 3,380 ft east. 297.8 27.9 608 2,600 ft north, 3,300 ft east. 301.6 18.0 455 2,650 It north, 3,260 ft east. 283 .9 33. 5 538 2,700 ft north, 3,200 ft east. 285.5 18.2 705 2,800 ft north, 3,100 ft east. underlying Portage Lake Lava Series, but there is a large change at the conglomerate’s boundary with the overlying Nonesuch Shale. The data presented herein complete determination of directions of magnetization for most of the larger middle Keweenawan geologic units in this region. Previous paleomagnetic data are from DuBois (1962, table XVIII) for the Portage Lake Lava Series, the Duluth Gabbro, and the Copper Harbor Conglomerate; from Beck and Lindsley (1969, table 1) for the Beaver Bay Complex; from Beck (1970, table 2) for the Duluth Gabbro Complex; from Palmer (1970, tables 3—6) for the North Shore Volcanic Group and lava flows on Gargantua Point, Michipicoten Island, and Mamainse Point; and from Books, White, and Beck (1966, p. D120) for the gabbro near Mellen, Wis. The new data include directions of magnetization for the Portage Lake Lava Series and equivalents north of Ironwood, Mich., the North Shore Volcanic Group, the lava flows on Isle Royale, and the quartz porphyry north of Lake Gogebic, Mich. The results are shown in figure 18. PORTAGE LAKE AND NORTH SHORE SEQUENCES As noted in a previous section, the data for the Portage Lake Lava Series were divided into three parts, mainly because the middle division, between conglomerate Nos. 14 and 15, had a direction of mag- netization significantly different from directions in the flows below and above. No further subdivisions in magnetic field direction data for Portage Lake lavas are shown because none are obvious. Similarly, no subdivisions in paleomagnetic data are shown for the North Shore Volcanic Group as no significant shift in the direction of the earth’s magnetic field is discernible in these rocks. Figures 19 and 20 represent an attempt to correlate changes in the paleomagnetic field between the Portage Lake Lava Series and the North Shore Volcanic Group by comparing chronological move- ments in inclination and declination of the magnetic field for the two areas. Although the scatter in direc- tions between sites may be attributed to secular varia- tions, no obvious paleomagnetic patterns or correla- tions between the two sequences are found. If the flows in the two areas are of equivalent ages, either (1) the sampling was not sufficiently detailed to document equivalent variations in the earth’s paleomagnetic field on both sides of the lake, or (2) an insufficient number of lava flows of equivalent extrusion times are present to provide similar paleomagnetic patterns in both areas. If the two groups of lavas do not both represent the same time interval but overlap in part, the best fit for the paleomagnetic data would make the Scales Creek Flow (figs. 2, 19, and 20) of the Portage Lake Lava Series similar in age to a flow near flow No. 65 (figs. 19 and 20) of the North Shore Volcanic Group. Where equivalent groups of lava flows are present at some distance from each other there is some indica- tion that magnetic field direction similarities can be found. Figure 4 ShOWS that the flows between con- glomerate Nos. 14 and 15 of the Portage Lake Lava Series near Kearsarge, Mich., had a direction of mag- netization significantly different from that which pre- vailed before (fig. 3) and after (fig. 5) their extrusion. The same departure in magnetization direction can be found in rocks representing the same stratigraphic interval in the Washington Harbor area of Isle Royale; this supports the generally accepted correlation first noted by Lane (1898). In figure 21, point 4B represents lava flows on Isle Royale that would be stratigraphically just below the probable position of the Greenstone Flow as recent mapping has shown that flow to be slightly south of where it is shown on Lane’s map (N. K. Huber, written commun., 1969). Point 4A (fig. 21) represents the next lower group of lava flows. The site-mean direc- tions of the comparable flows near Kearsarge, Mich., presented in figures 4 and 3, respectively, are plotted as points 6 and 7 in figure 21 for comparison. The flows above the aberrant interval near Kearsarge, Mich., represented by figure 5 and by point 5 in figure 21, are covered by water in the sampling area on Isle Royale. QUARTZ PORPHYRY NORTH OF LAKE GOGEBIC, MICHIGAN A large body of quartz porphyry Within the lava series north of Lake Gogebic, Mich. (fig. 1), has long been regarded as an intrusion, but Brooks and Garbutt (1969) have recently presented evidence that the body is extrusive and separated from overlying mafic lava flows by an unconformity. Figure 22 shows the mean direction for this quartz porphyry before (A) and after (A”) a 35° correction for dip of the underlying lava flows. The proximity of A” to the average direc- tion for the Portage Lake Lava Series and Copper DISCUSSION OF RESULTS N I 13301 0 W M3306 + E O O leaos IB75 O S EXPLANATION o Site~mean direction of magnetization. Mean of site-mean directions of magnetization, North-seeking polarization with circle of confidence. North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE 11.—Directions of remanent magnetization for the basal quartzite (site IB322) and lowermost 400 feet of South Trap Range lava flows near Ironwood, Mich. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 9 for site locations. 23 24 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS TABLE 9.——Paleomagnetlc results for the basal quartzite and lowermost 1,00 feet of the South Trap Range flows near Ironwood, M ioh. [All sites are in T. 47 N., R. 47 W. Data corrected for geologic dip] Mean direction of magnetization Location and attitude 600 ft north, 2,150 ft west of SE. cor. sec. 12. E., dip 69° NW. 650 ft north, 2,150 ft west of SE. cor. sec. 12. E., dip 69° NW. 750 ft north, 2,150 ft west of SE. cor. sec. 12. E., dip 69° NW. 1,800 ft south, 2,000 ft west of NE. cor. sec. 82° E., dip 65° NW. 1,850 ft south, 2,050 ft west of NE. cor. sec. 82° E., dip 65° NW 700 ft north, E., dip 69° NW. Number of at collecting site Remanent Site No. samples intensity (N) Declination, D Inclination, I (emu/cm3X 10*) (degrees) (degrees) IB74 _____________ 6 260.8 29.3 1,150 75 _____________ 4 257 .6 21.7 10,400 76 _____________ 6 258.1 44.4 5,640 301 ____________ 5 274.7 53.8 1,420 303 ____________ 6 258.2 52.6 6,460 306 ____________ 4 268.1 17.9 550 322 1 ___________ 5 261.3 38.1 904 590 ft north, 2,150 ft west of SE. cor. sec. 12. 2 200 ft west of SE. cor. sec. 12. Strike N. 78° Strike N. 78° Strike N. 78° 10. Strike N. 10. Strike N. Strike N. 78° Strike N. 78° E., dip 69° NW. 1 Site IB322 represents the basal quartzite. Harbor Conglomerate is consistent with the interpre- tation of Brooks and Garbutt (1969), but not incon- sistent with intrusion during Portage Lake or Copper Harbor time before much tilting had occurred. The paleomagnetic data are not, however, consistent with the Rb-Sr (rubidium-strontium) age of 978i40 {my obtained by Chaudhuri and Faure (1967, p. 1020); if the quartz porphyry were younger than the Nonesuch Shale (see following section), as this Rb-Sr age sug- gests, the direction of magnetization should be closer to that of the Freda Sandstone and Nonesuch Shale. (See fig. 22, point F—N.) UPPER KEWEENAWAN Immediately above the Copper Harbor Conglomerate are the fine-grained siltstones of the upper Kewee- nawan Nonesuch Shale, which in turn grade upward into the Freda Sandstone; 5,000 feet of the Freda is exposed on the Keweenaw Peninsula (Lane, 1911, p. 40, 604), and 12,000 feet of Freda is estimated in Wis- consin (Tyler and others, 1940, p. 1479). DuBois (1962, table XVIII) calculated a magnetic field direction for the Freda-Nonesuch units (see fig. 22, point F—N), as well as for some of the succeeding sedimentary rock formations. RHYOLITE INTRUSIONS The two rhyolite intrusions Whose magnetic field directions are shown in figure 23 are included in the upper Keweenawan more on the basis of geologic in- formation than on precise paleomagnetic data, which does not disagree with the geologic interpretation but adds little to it. The rhyolite intrusion in secs. 24 and 25, T. 56 N., R. 34 W., near Kearsarge, Mich., cuts the Freda Sand- stone, which is the youngest formation known to be intruded by igneous rocks in this part of the Lake Superior region. Dip of the Freda near the intrusion is estimated to be about 22° NW., and the paleomagnetic data have been corrected for this dip. The divergence of point a (fig. 23) from the upper Keweenawan mag- netic field represented by the Freda direction (point F—N) can be explained by secular variation because the samples collected (6) were of limited extent. Placement of the rhyolite intrusion in sec. 4, T. 56 N., R. 32 W., near Kearsarge, Mich., in the upper Keweenawan on the basis of paleomagnetic data is somewhat tenuous and requires a more detailed ex- planation. The rhyolite intrudes middle Keweenawan lava flows whose present dip is near 62° NW., so that in the strictest sense, the paleomagnetic data indicate only that the time of intrusion could have ranged from after structural movement was completed (no dip cor- rection at all—point b, fig. 23) to before structural deformation of the enclosing flows (dip correction of 62° NW.-point c, fig. 23). The geologic evidence, however, suggests that the rhyolite is upper Keween- awan. White (1968, p. 313) stated that “5° to 10° of the total present dip of the top of the Portage Lake Lava Series and about 20° of the dip of the bottom antedates the deposition of the Nonesuch Shale.” White believes (written commun., 1970) that the rocks which now enclose the rhyolite intrusion were dipping 15° to 20° during early Freda time. If these dips were subtracted from the present 62° dip of the enclosing flows, the paleomagnetic data would plot at points (1 and e and would indicate a possible range for the direc- tion of magnetization at the time of intrusion. Note in figure 23 that points d and e are not significantly different from the Freda-Nonesuch unit direction at point F~N. DISCUSSION OF RESULTS N MK217 + Portage Lake lava flows MK21 (figure 5) MK216 .MK219 S EXPLANATION o Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North—seeking polarization with circle of confidence. ‘ North-seeking polarization I l Direction of axial dipole component of present geomagnetic field FIGURE 12.—Directions of remanent magnetization for middle Keweenawan lava flows (Portage Lake equivalents) from the Chippewa Hill quarry, Michigan, in sec. 32, T. 49 N., R. 46 W. Data corrected for geologic dip. Equal—area projection, lower hemisphere. See table 10 for site locations. 25 26 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS N MK319. Portage Lake lava flows (figure 5) .MK316 I I MK318 , S EXPLANATION O Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North—seeking polarization with circle of confidence. North-seeking polarization I A Direction of axial dipole component Direction of magnetization for rhyolite of presentgeomagnetic field flows north of Lake Gogebic (figure 7) which may be stratigraphically similar FIGURE 13.—Directions of remanent magnetization for middle Keweenawan lava flows (Portage Lake equivalents) on the Black River near Algonquin Falls, Mich. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 11 for site locations. SUMMARY AND CONCLUSIONS 27 TABLE 10.—Paleomagnetlc results for Portage Lake lava equivalents at the Chippewa Hill quarry north of Ironwood, Mich. [All sites are in sec. 32, T. 49 N., R. 46 W. Flows strike N. 85° E. and dip 40° NW. at all sites. Data are corrected for geologic dip] Mean direction Number of magnetization at Remanent o collecting site intensity Location from Site No. samples (emu/cm8 northwest corner (N) Declina- Inclina- X 104) of section tion, D tion, 1 (degrees) (degrees) MK216 ______ 5 282.6 80.9 698 2, ,GfOO fttsouth, 1,300 217 ______ 5 288.0 28.1 825 2, ,620 it south, 1, 320 8L: 218 ______ 5 286.3 29.4 586 2, $240“ ft south, 1, 320 219 ______ 5 279.4 35.0 732 2,680 ft tsouth, 1,350 ft east. TABLE 11.—Paleomagnet1'x: results for Portage Lake lava equivalents on the Black River near Algonquin Falls, M ich [All sites are in sec. 29, T. 49 N., R. 46 W. Lava flows strike N. 80° E. and dip 80° NW at all sites. Data are corrected for geologic dip] Mean direction Number of magnetization at Remnant of collecting site intensity Location from Site No. samples (emu/c1113 northeast corner (N) Declina- Inclina- X 10*“) of section tion, D tion, I (degrees) (degrees) MK316 ______ 5 287.8 39.5 836 1, ,2f00w ft south, 1, 200 es.t 817 ______ 4 929.9 28.5 1.110 1, ,5t00west ft south, 900 318 ______ 4 282.0 32.6 1,130 1, 750 1: south, 850 ftw 319 ______ 4 275.0 29.1 305 2.2100 Wft south, 1,100 Itw est. 320 ______ 4 278.4 31.9 471 2,2100%?!“ south, 1,300 SUMMARY AND CONCLUSIONS The directions of magnetization in all the Keweena- wan units sampled by the author (table 15) and others fall into three significantly different groups. The groups have polarities that are alternately normal, reversed, and normal. In the oldest normal polarity group are sedimentary and igneous rocks in the Ironwood, Mich., area and some of the lower sedimentary rocks of the Sibley Series on Sibley Peninsula in Ontario. In the Ironwood area, this group includes the basal quartzite unit and approximately 400 feet of immediately overlying lava flows in the lowermost exposures of South Trap Range rocks. In the reversed polarity group are some 6,700 feet of lava flows near Ironwood, Mich., some 4,550 feet of lava flows near Grand Portage, Minn., the northern tongue of the Duluth Gabbro in Cook County, Minn., part of the Sibley Series, part of the lava flows at Gargantua Point and Mamainse Point, Ontario, the lavas at Alona Bay, Ontario, part of the Logan in- trusions, the Baraga County dikes, and the Keweena— wan Osler Series on the north shore of Lake Superior. In the youngest normal polarity group are intrusive and extrusive rocks usually considered middle Kewee- nawan in age including the Portage Lake Lava Series and equivalents to the southwest in Wisconsin, most of the North Shore Volcanic Group, part of the Logan intrusions, the major part of the Duluth and similar gabbros, and many lesser sills and dikes cutting middle Keweenawan and earlier rocks. Also included in this group according to DuBois’ (1962, p. 61) results is the upper Keweenawan Copper Harbor Conglomerate. The paleomagnetic data indicate that many different rock units in the Lake Superior region may have formed within the same magnetic epoch as did the sedimentary Sibley Series (Tanton, 1931) in the Thunder Bay district, Ontario. Tanton (1931, p. 56, 58) found evidence for pre-Osler Series lavas in the red volcanic debris that makes up the greater part of the Sibley Series and the red porphyry pebbles in the basal conglomerate of the Osler Series of Ontario. DuBois (1962) related the Logan sills in Ontario and the lavas at Alona Bay, Ontario, to the lower Kewee- nawan and suggested a period of intrusive and extrusive activity in the Lake Superior region in early Kewee- nawan time. Thus, major igneous activity probably began very early in Keweenawan history and volcanism and sedi- mentation probably were concurrent in the Lake Superior region. While the basal quartzite and succeed- ing lava flows were being formed in the Ironwood area, the early Sibley sediments were being deposited in the Sibley Peninsula area. While the Sibley continued to be deposited during the reversal of the earth’s magnetic field, volcanism was dominant elsewhere. This reverse- polarization interval probably marked the initial stages of formation of the Duluth Gabbro Complex as well as the Logan intrusions; intrusion took place in such widely separated areas as Baraga County, Mich., and Nipigon, Ontario. Widespread extrusion at this time is represented by some 6,700 feet of lava flows near Ironwood and by lesser amounts across Lake Superior near Grand Portage, Minn., Alona Bay, Ontario, and Gargantua Point and Mamainse Point, Ontario. By middle Keweenawan time when the earth’s magnetic field was again normal, the igneous activity had almost replaced sedimentation, resulting in the bulk of the flows and intrusions found in the Lake Superior region today. During this normal-polariza- tion interval some 20,000 to 30,000 feet of lava flows poured out, and the Duluth Gabbro Complex and major parts of the Logan intrusions were emplaced. Sedimentation again became dominant in Copper Harbor time; only minor igneous activity occurred thereafter. A tentative correlation chart based on magnetic polarity changes and including all available paleomag- PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS N O 376 3" ‘171 377. g 359 227 229 257 253 170 362 255.. 330 2560:86sz 25‘ 331 0 373 .259 365.371 72. 58 375 265 O. 261 370. .357 260. O 379 S EXPLANATION O Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North-seeking polarization with circle of confidence. North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE l4.—Directions of remanent magnetization for North Shore Volcanic Group from flow No. 33 to flow No. 94 of Grout, Sharp, and Schwartz (1959), between Grand Portage and Tofte, Minn. Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 12 for site locations. SUMMARY AND CONCLUSIONS . 29 TABLE 12.—Paleomagnetic results for North Shore Volcanic Group, between Grand Portage and Tofte, Minn. [Flow numbers are from Grout and others (1959). Data are corrected for geologic dip] Number of Mean direction of magnetization at collecting site Remanent Site No. samples intensity Flow No. Location and attitude of flow (N) Declination, D Inclination, I (emu/cm3X10-6) (degrees) (degrees) NS254 ____________ 3 291.1 46.4 103 94 2, 800 ft south, 850 ft east of NW. cor. sec. 28, T. 59 N., R. 4 W. Strike N. 43°E .,dip 14° SE. 255 ____________ 4 293.6 47.8 629 91? 500 ft south, 3,300 ft east of NW. cor. sec. 28, T. 9N R. 4 W. StrikeN. 41° E, dip 14° SE. 256 ____________ 5 286.6 32.4 800 89 1, 65590 ft south, 2, 850 ft east of NW cor. sec. 22, T. 59 N., R. 4 W. StrikeN. 55° E., dip 12° SE. 263 ____________ 4 298.3 52.1 2,810 85? 650 ft south, 50 ft west of NE. cor. sec. 14, T. 59 N, R. 4 W. Strike N. 69°, dip 17° SE. 381 ____________ 5 296.0 51.1 226 82? 750 ft south, 50 ft west of NE. cor. sec. 31, T. 59 N. R. 4 W. Strike N. 59° E. dip 12° SE. 370 ____________ 5 285.0 54.2 2,890 81? 2, 250 ft south, 1,350 ft west of NE. cor. sec. 12, T. 59 N, R. 4 W. Strike N. 59° E., dip 18° SE. 382 ____________ 3 287.8 37.4 401 80 1, 000 ft south, 100 ft west of NE. cor. sec. 31, T. 59 N. R 4 W. Strike N. 52° E., dip 12° SE. 372 ____________ 4 288.8 43 .3 236 80 1, 850 ft south, 1, 600 ft west of NE. cor. sec. 12, T. 59 N., R. 4 W Strike N. 59° E., dip 18° SE. 379 ____________ 3 279.2 51.9 381 79? 400 ft south, 700 ft west of NE. cor. sec. 31, T. 59, N., R. 4 W. Strike N. 52° E., dip 12° SE. 371 ____________ 4 285.2 41.6 1,600 79 2,100 ft south, 1,400 ft west of NE. cor. sec. 12. T. 59 N., R. 4 W. Strike N. 59° E., dip 18° SE. 380 ____________ 3 299.4 57.3 566 78? 10 ft south, 856 ft west of NE. cor. sec. 31, T. 59 N., R. 4 W. Strike N. 52° E., dip 12° SE. 262 ____________ 5 286.6 40.1 985 78 150 ft south, 1, 300 ft west of NE. cor. sec. 34, T. 60 N. R. 3 W. Strike N. 61° E., dip 15° SE. 261 ____________ 5 282 .4 43 .4 939 76 2, 000 ft south, 1,050 ft west of NE. cor. sec. 19, T. 60 N., R. 2 W Strike N. 76° E., dip 10° SE. 260 ____________ 5 279 .0 44 .8 649 74 4,650 ft south, 1,750 ft west of NE. cor. sec. 17, T. 60 N., R. 2 W. Strike N. 75° E., dip 10° SE. 259 ____________ 5 292.8 52.8 437 72 3, 700 ft south, 250 ft west of NE. cor. sec. 17, T. 60 N., R. 2 W. Strike N. 65° E, dip 10° SE. 258 ____________ 5 289 .1 45.7 10,300 71 2, 600 ft south, 1, 350 ft east of NW. cor. sec. 16, T. 60 N., R. 2 W. Strike N. 69° E, dip 10° SE. 264 ____________ 4 289.0 43.9 2,450 68 800 ft south, 2,250 ft east of NW. cor. sec. 11, T. 60 N., R. 1 W. Strike N. 63° E., dip 10° SE. 257 ____________ 5 292.4 43.6 985 67 1,600 ft south, 2,050 ft east of NW. cor. sec. 6, T. 60 N., R.1 W. Strike N. 70° E. ,dip 12° SE. 377 ____________ 5 291.8 32.1 3,230 64 4, 850 ft south, 1,050 ft east of NW. cor. sec. 32, T. 61 N., R. 1 W Strike S. 87° E. ,dip 13° SW. 171 ____________ 4 297.4 37.5 1,220 64 450 ft north, 1, 950 ft east of SW. c.or sec. 32, T. 61 N. R. 1 W. Strike S. 85° E. dip 12. 5° SW. 170 ____________ 5 291.1 34.1 1,420 63 450 ft north, 2, 000 ft east of SW. cor. sec. 32, T. 61 N., R. 1 W. Strike S. 85° E. dip 13° SW. 169 ____________ 4 301.3 34.7 2,480 63 500 ft no,rth 2, 000 ft east of SW. cor. sec. 32, T. 61, N, R. 1W. StrikeS. 85°E, dip 13° SW. 376 ____________ 5 296.9 36.4 3,480 62 4,150 ft south, 3,050 ft east of NW. cor. sec. 32, T. 61 N., R. 1 W Strike S. 80° E, dip 13° SW. 374______-_____ 5 294.3 35.2 772 60 3, 300 ft south, 2, 500 ft west of NE. cor. sec. 33, T. 61 N, R. 1 W Strike S. 88° E., dip 14° SW. 369-____-___-__ 5 294.0 38.5 558 60 3,150 ft south, 1,500 ft west of NE. cor. sec. 33, T. 61 N., R. 1 W Strike N. 87° E., dip 14° SE. 368 ____________ 4 291.7 34.9 627 59 2, 000 ft south, 900 ft east of NW. cor. sec. 34, T. 61 N., R.1 W. Strike N. 76° E. dip 15° SE. 265-----_--_._- 3 286.0 47.2 2,150 58 600 ft north, 2, 700 ft east of SW. cor. sec. 27, T. 61 N. R. 1 E. Strike S. 77° E. ,dip 11° SW. 367____________ 5 285.5 56.0 244 58? 3, 800 ft south, 100 ft east of NW. cor. sec. 26, T. 61 N. R. 1 W. Strike N. 76° E., dip 15° SE. 365 ____________ 4 285 .2 38.7 237 57? 3, 000 ft south, 1, 200 ft east of NW. cor sec 16. T. 61 N, R. 1 E. Strike N. 87° E., dip 14° SE. 362 ____________ 5 292 .9 43.5 2,620 54 2, 400 ft so,uth 2, 000 ft east of NW. cor. sec. 13, T. 61 N., R. 1 E. Strike S. 61° E, dip 11° SW. 226 ____________ 3 295.5 25.7 2,330 50 4, 250 ft south, 2, 850 ft west of NE. cor. sec. 9, T. 61 N., R. 2 E. Strike N. 86° E., dip 10° SE. 375 ............ 5 287.9 53.8 407 49 4, 800 ft south, 1,100 ft west of NE. cor. sec. 3, T. 61 N., R. 2 E. Strike N. 84° E., dip 10° SE. 229 ____________ 3 298.4 46.9 534 47 2, 36100 ft south, 1, 900 ft west of NE. cor. sec. 1, T. ,.R 2 E. Strike S. 71° E., dip 10° SW. 227 ____________ 5 296.1 43.6 3,660 45 1, 3010 ft south, 250 ft west of NE. cor. sec. 6, T. 61 N., R. 3 E. Strike S. 77° E., dip 11° SW. 378 ____________ 5 290.6 47 .9 356 42 4, 000 ft south, 2 ,450 ft west of NE. cor. sec. 32, T 62 N. R. 3 E. Strike N. 90° E., dip 10° S. 269 ____________ 3 264.5 38.2 257 33 1, 950 ft north, 50 ft west of SE. cor. sec. 28, T 62N., R. 3 E. StrikeS. 87°E., dip 20° SW. 30 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS N S EXPLANATION O Site-mean direction of magnetization. Mean of site-mean directions of magnetization, North-seeking polarization with circle of confidence North-seeking polarization Direction of axial dipole component of present geomagnetic field FIGURE 15.——Directions of remanent magnetization for middle Keweenawan lava flows on Isle Royale showing two significantly diflerent groupings (A and B) for adjacent series of flows (see fig. 20 for comparison with the same stratigraphic position in the Portage Lake Lava Series). Data corrected for geologic dip. Equal-area projection, lower hemisphere. See table 13 for site locations. SUMMARY AND CONCLUSIONS 31 TABLE 13.—Paleomagnelic results for middle Keweenawarl lavas on Isle Royale, M ich. [All sites are located in T. 63 N., R. 39 W. Flows strike N. 60° E. and dip 12.5" SE. at all sites. Paleomagnetic data are corrected for the geologic dip] Mean direction of magnetization Number of at collecting site Remanent Site No. samples ——~——————-—— intensity Location (N) Declination, D Inclination, I (emu/cmax 10“) (degrees!) (degreeS) MK243 ___________ 4 264 .4 47 .3 2,080 3,100 ft south, 2,600 ft west of NE cor. sec. 1. 244 ___________ 5 274 .1 46.4 7,320 3,100 ft south, 3,000 ft West of NE. cor. sec. 1. 245 ___________ 5 272 .9 49 .3 8,450 3,200 ft south, 3,350 ft west of NE. cor. sec. 1. 246 ___________ 4 290.4 67 .1 2,240 3,250 ft south, 3,800 ft west of NE. cor. sec. 1. 247 ___________ 5 263.7 56.7 4,520 3,300 ft south, 4,200 ft West of NE. cor. sec. 1. 248 ___________ 5 285.2 25.2 1,710 2,700 ft south, 150 ft west of NE. cor. sec. 1. 249 ___________ 5 281.9 24.7 3,970 2,400 ft south, 250 ft west of NE. cor. sec. 2. 250 ___________ 5 289 .2 14.1 863 1,200 ft south, 2,400 ft west of NE. cor. sec. 1. 251 ........... 6 292.9 29.5 3,240 Section line, 1,700 ft west of NE. cor. sec. 1. TABLE 14.—Paleo'magrtetic results for pre—Keweenawan rocks near Ironwood, M ich., and Grand Portage, M irm. [Data are corrected for geologic dip] Direction of magnetization at collecting site Remanent Sample No. ——————— intensity Location and attitude of bedding Declination, D Inclination, I (emu/cm3x 10") (degrees) (degrees) Marquette Range Supergroup rocks near Ironwood, Mich.: K3111 _______________________________ 264.0 46.5 14.5 In the Black River. SEV4sec. 12, T. 47 N., 2 _______________________________ 267 .1 48.1 2 .64 R. 46 W Strike N. 85° E. dip 55° NW. 4 _______________________________ 260 .2 57 .2 12.1 6 _______________________________ 266 .3 40 .7 1.28 Rove Slate near Grand Portage, M1nn.. K1661 _______________________________ 222 .9 60.1 52 .0 Roadcut on U. S. Highway 61. Center sec. 34, 2 _______________________________ 246.0 66.0 37.0 T. 641N., R. 6 E. Strike S. 66° W., dip 3 _______________________________ 187.4 54 .1 41.0 20° SE. 4 _______________________________ 264 .9 52 .0 47 .0 5 _______________________________ 266.2 40 .9 44 .0 TABLE 15.——Summary of new paleomagnetic data for rock units in the Lake Superior region [N is the number of sites for which Fisher (1953) analyses have been computed, unless otherwise noted. Magnetization directions are corrected for geologic dip, unless other- wise noted. 6,.. and 6,, are semiaxes of the confidence oval about a virtual pole and are respectively perpendicular and parallel to the virtual paleomeridian] Mean of site-mean Location of rock unit Number directions of magnetization Precision Radius of Pole position Rock unit ————————— o ————————— parameter confidence ———-——-— 5m 6;» North lat West long sites Declination, Inclination, (K) circle North lat West long (degrees) (degrees) (N) D I (an) (degrees) (degrees) (degrees) (degrees) 1 ______________ 47.2 88.6 16 295.0 22.2 58.1 8.9 25.4 189.3 9.4 5.0 2 ______________ 47.2 88.4 18 2275.1 223.2 8.8 19.8 12.3 173.8 21.1 11.2 d .............. 46.6 89.6 3 298.6 36.0 25.4 24.9 33.9 186.0 29.0 16.8 4 ______________ 46.7 90.1 5 287.7 26.2 51.5 10.8 22.1 183.2 11.7 6.3 5 ______________ 46.6 90.1 4 284.2 30.9 332.7 5.0 21.7 178.4 5.6 3.1 6 ______________ 46.7 89.6 3 287.2 28.0 164.3 9.7 22.5 181.5 10.6 5.8 7 .............. 47.3 88.4 22 291.0 34.9 105.5 3.1 28.2 180.0 3.6 2.1 8 ............... 47.3 88.4 7 274.5 45.8 72.9 7.1 22.6 162.1 9.1 5.8 9 ______________ 47.3 88.4 23 289.3 35.1 77.1 3.5 27.1 178.6 4.0 2.3 10 _____________ 47.4 88.1 17 288.4 36.4 27.2 7.0 27.1 177.1 8.1 4.7 11 _____________ 47.9 89.2 5 271.8 53.8 60.8 9.9 25.9 155.7 13.8 9.7 12 _____________ 47.9 89.2 4 287.3 23.4 106.7 8.9 20.6 183.7 9.5 5.1 13 _____________ 47.7 90.4 36 291.2 43.9 46.2 3.6 ‘ 32.6 176.9 4.4 2.8 14 _____________ 46.5 90.1; 7 262.5 37.0 28.8 11.4 9.8 160.4 13.5 7.8 15 _____________ 46.5 90.0 14 261.2 45.0 88.4 9.8 ‘ 13.3 155.3 12.4 7.9 16 _____________ 48.0 89.7 15 240.9 58.5 14.8 20.6 ‘ 12.6 133.6 32.2 20.6 1 Indicates number of samples rather than number of sites. ‘ 2 Data uncorrected for geologic dip. ‘ 1. Rhyolite intrusion in sec. 24, T. 56 N. R. 34 W., near Kearsarge, Mich. 11. Upper lavas on Isle Royale, Mich. 2. Rhyolite intrusion in sec. 4, T. 56 N. R. 32 W, near Kearsarge, Mich. 12. Lower lavas on Isle Royale, Mich. 3. Quartz porphyry north of Lake Gogebic, Mich. 13. North Shore lava flows (Nos. 83 to 94) between Grand Portage and Toite, 4. Portage Lake lavas near Algonquin Falls, Mich. Minn. 5. Portage Lake lava equivalents from the Chippewa Hill quarry, Mich. 14. Basal quartzite and lower 400 feet of South Trap Range lavas near Ironwood, 6. Rhyolite flows north of Lake Gogebic, Mich. Mich. 7. Portage Lake lavas above conglomerate N015 near Kearsarge, Mich. 15. Marquette Range SMupergroup sedimentary rocks' in sec. 12, T. 47 N., R. 46 W. 8. Portage Lake lavas between conglomerate Nos. 14 and 15 near Kearsarge, Mich. near Ironwood,M1.ch 9. Portage Lake lavas below conglomerate No. 14 near Kearsarge, Mich. 16. Rove Slate' 1n sec. 341, T. 64 N., R. 6 E. near Grand Portage, Minn. 10. Portage Lake lavas northeast of Kearsarge, Mich. 32 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS N .¢. Mean direction of magnetization, with circle of confidence. North-seeking polarization FIGURE 16.—Summary of mean directions of remanent mag- netization for lower(?) Keweenawan igneous rock units in the Lake Superior area, showing two groups (A and B) with opposing magnetization. The rock units are: 10, basal quartzite and lower South Trap Range lava flows near Ironwood, Mich.; 11, northern tongue of Duluth Gabbro extension in Cook County, Minn.; C, lower se- quence of Keweenawan lava flows at Ironwood, Mich. ; E, lower sequence of Keweenawan lava flows at Grand Portage, Minn.; F, Logan sills of Lawson (1893); G, lavas at Alona Bay, Ontario; H, mafic dikes in Baraga S EXPLANATION {I} Mean direction of magnetization, with circle of confidence. South‘seeking polarization County, Mich., circle of confidence not shown; and J (I and II), the Sibley Series of Tanton (1927). The data for point 10, the quartzite and succeeding flows, are new (from fig. 11); data for point 11 are from Beck and Lindsley (1969, table 3); data for points F, G, H, J1, and JII are from DuBois (1962, table 18); data for C and E are from Books (1968, fig. 3); and data for points 12, 13, and 14 are from Palmer (1970, tables 2, 4, and 6). Data are cor— rected for geologic dip. Equal-area projection, lower hemisphere. SUMMARY AND CONCLUSIONS Portage Lake Lava Series ®@Nonh Shore Volcanic Group Lower 400’ of lava flows at Ironwood Marquette Range Supergroup rocks at Ironwood O Rove Slate near Grand Portage s. 33 EXPLANATION o Site-mean direction of magnetization, with circle of confidence. North-seeking polarization FIGURE 17.—Directions of remanent magnetization for pre— Keweenawan units near Ironwood, Mich., and Grand Portage, Minn., compared to directions of magnetization in lower Keweenawan units. Rock units are: Rove Slate of the Animikie Group near Grand Portage, Minn.; Marquette Range Supergroup sedimentary unit near Ironwood, Mich.; and lower 400 feet of lava flows near Mean of site-mean directions of magnetization, with circle of confidence. North—seeking polarization Ironwood, Mich. Directions of remanent magnetization for the North Shore Volcanic Group and Portage Lake Lava Series are also shown. Data corrected for geologic dip. Equal-area projection, lower hemisphere. Site locations for Rove Slate and Marquette Range Supergroup unit are given in table 14. 34 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS S EXPLANATION Mean of site-mean directions of magnetization, with circle of confidence. FIGURE 18.—Summary of mean directions of remanent mag- netization for middle Keweenawan rock units in the Lake Superior region. The units are: 1, lava flow sequence near Algonquin Falls, Mich; 2, lava flow sequence in the Chippewa Hill quarry, Michigan; 3, rhyolite flows north of Lake Gogebic, Mich.; 4A and 4B, lava flow sequences on Isle Royale; 5, lava flow sequence above conglomerate North-seeking polarization No. 15 of Portage Lake Lava Series at Kearsarge, Mich.; 6, lava flows between conglomerate Nos. 14 and 15 at Kearsarge, Mich.; 7, lava flow sequence below conglomer- ate No. 14 at Kearsarge, Mich.; 8, North Shore Volcanic Group; and 9, quartz porphyry north of Lake Gogebic, Mich. Data corrected for geologic dip. Equal-area pro- jection, lower hemisphere. SUMMARY AND CONCLUSIONS I 35 INCLINATION, IN DEGREES I | l I | | | I I II I I 50 60 Underwater 10 . 20 30 40 50 60 C 13 20 '30 t40 FEET op er arbor Cong omera e FEET 94 11.000— — 11,000 ——" =— 83 L’_: 10.000— 2 10.000 —=_ —_ 70 : -—’/Sandstone and :— shale ——-—65 _. —: t 9000- 9000 _ _Sands one I: _ I— —_ I: 60 8000 E 8000 — _ Greenstone _ : _/Sandstone Flow / E = Conglomerate Z _ No. 15 I Conglomerat No. 14 —— 7000— ” 7000 6000— — 6000— _ 53 _. 5000— 2 5000__— Kearsarge~—‘I— 50 — Flow —: — 4000- _ 4000- _ \ 3000- 3000; ,_ Scales = _ Creek __ Flow\ : ——- 2000 -—’_ 2000 _ I— 41 _ 1000 J — 1000 :— I____ — 33 _ Copper City—— — Flow OH—I 0- Keweenaw fault 29 Diabase and gabbro ‘ PORTAGE LAKE LAVA SERIES NORTH SHORE VOLCANIC GROUP FIGURE 19.—Comparison of chronological movements in inclination of the paleomagnetic fields of the Portage Lake Lava Series and North Shore Volcanic Group. Bars indicate confidence circle radii for 9. Fisher analysis (Fisher, 1953) of no less than three samples from a single site. Data corrected for geologic dip. Numbers within column are lava flows of Grout, Sharp, and Schwartz (1959). 36 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS DECLINATION, IN DEGREES | I I I | I | | l I I I I 250 260 270 280 290 300 310 Underwater 260 270 280 290 300 310 Copper Harbor Conglomerate FEET —<‘94 — FEET 11,000 - — 11,000 ——— 83’ — 10,000 — : 10,000 - — = =70 /Sandstone and shale _ 1—65 9000 — 9000 — :Sandstone 8000 E 8000— _ Greenstone/ I —/Sandstone Flow ; : : Conglomerate : — No. 15 — Conglomerate *__ ’ N°‘ 17%00 — — 7000 ~— 6000 — _ 6000 — _ 53 _ 5000 r : 5000 - — Kearsarge_—_ 50 —— Flow -—: — 4000 — _ 4000 — 3000 - 3000 —- Scales E __ Creek FIOW\ _ 2000 -—: 2000 — i 1000 - — 1000 -- _ 33 Copper\. —‘ City — Flow 0 4— o — l— ,_ Keweenaw fault 29 Diabase and gabbro PORTAGE LAKE LAVA SERIES NORTH SHORE VOLCANIC GROUP FIGURE 20.—Comparison of chronological movements in declination of the paleomagnetic fields of the Portage Lake Lava Series and North Shore Volcanic Group. Bars indicate confidence circle radii for a Fisher analysis (Fisher, 1953) of no less than three samples from a single site. Data corrected for geologic dip. Numbers within column are lava flows of Grout, Sharp, and Schwartz (1959). SUMMARY AND CONCLUSIONS 37 S EXPLANATION Mean of site-mean directions of magnetization, with circle of confidence. North-seeking polarization FIGURE 21.—Comparison of mean directions of remanent magnetization for Keweenawan lava flow sequences near Kearsarge and on Isle Royale, Mich. Rock units are: 4A, lava flow sequence in the Washington Harbor-Grace Harbor area, Isle Royale; 4B, lava flow sequence above 4A and near Lane’s (1911, pl. 1) “Greenstone” horizon; 5, lava flow sequence above conglomerate No. 15 near Kearsarge; 6, lava flow sequence between conglomerate Nos. 14 and 15; and T, lava flow sequence below con- glomerate No. 14 near Kearsarge. Data corrected for geologic dip. Equal-area projection, lower hemisphere. 38 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS S EXPLANATION 0 Mean direction of magnetization, with circle Mean of site-mean directions of magnetization, of confidence. North-seeking polarization with circle of confidence, North-seeking polarization FIGURE 22.—A1ternative directions of remanent magnetization for the quartz porphyry north of Lake Gogebic, Mich., before (A) and after (A”) correction for 35° dip of underlying lavas. Other points represent data for: PL, Portage Lake Lava Series; CH, Copper Harbor Conglomerate; F—N, Freda Sandstone-Nonsuch Shale unit. The Copper Harbor and Freda-Nonesuch data are from DuBois (1962, table XVIII); the other data are new. Equal-area projection, lower hemisphere. SUMMARY AND CONCLUSIONS 39 S EXPLANATION Mean direction of magnetization, with circles of confidence. North-seeking polarization FIGURE 23.—-Directions of remanent magnetization for the rhyolite intrusions in T. 56 N., R. 32 W., and T. 56 N., R. 34 W., near Kearsarge, Mich. Directions shown are: a, rhyolite intrusion in secs. 24 and 25, T. 56 N., R. 34 W., after correction for dip of the enclosing Freda Sandstone; and b, c, d, and e, alternative directions based on dip cor— rections for the rhyolite intrusion in sec. 4, T. 56 N., R. 32 W. Dip corrections for the latter intrusion are: b, no dip correction; e, 42° dip correction; d, 47° dip correction; and c, 62° dip correction. The Freda Sandstone-Nonesuch Shale unit (F—N) direction is from DuBois (1962, table XVIII); the other data are new. Equal—area projection, lower hemisphere. 40 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN RO-‘CKS TABLE 16.—Tentative correlation chart of Lake Superior Keweenawan units based on magnetic polarity sequences [Based on data from this report and from DuBois (1962, table XIX), Books and others (1966, table 1), Books (1968, table 1), Palmer (1970, tables 2, 4, and 6), and Beck and Lindsley (1969, tables 2, 8)] Polarity Upper Peninsula Ironwood, Mich., Mellen, Northwest shore North shore Eastern shore sequences of Michigan Wis, and south shore (western Ontario) Chequamegon Sandstone Later Jacobsville Sandstone Orienta Sandstone Jacobsville Sandstone Keweenawan polarizations Eileen Sandstone Rhyolites Freda Sandstone and Nonesuch Shale Copper Harbor Conglomerate Bfiaer 33? Com- plex of Grout and Major Upper Schwartz part of Logan Logan normal Gabbro at (1939) Duluth intrus— intrus- polarizations Mellen Gabbro ions, in ions, in Portage Lake Quartz Com- part part Lava Series porphyry plex ————————— — — — — North Keweenaw fault Keweenaw shore fault (7) lavas, u per Gargantua and Mamainse ows Point lavas, in part North Osler Volcanic Gargantua and Mamainse shore eries Point lavas, in part lavas, lower North- 20 em flows tongue Logan Logan Reversed Upper 6,700 feet of o intrus- intrus- polarizations South Trap Range lavas Duluth ions, in ions, in Gabbro part part Com- plex Baraga County Upper Sibley Alona Bay lavas diabase dikes Series Lower 400 feet of Lower Sibley South Trap Range lavas Series (‘2) Lower normal polarizations Basal quartzite 4 Up er part of Marquette Rove State (Animikie nge Supergroup Group), in part \ netic data for Keweenawan rocks is presented in table 16. Placement of the geologic units within the several polarity divisions on the chart is somewhat arbitrary because deposition times for the intrusive and extrusive rocks may overlap. It is suggested (Books, 1968, p. D253, and Hubbard, 1968, p. 35) that the top of the reversed polarization sequence be taken as the top of the lower Keweenawan and following DuBois (1962, p. 62), that the base of the Nonesuch Shale be taken as the base of the upper Keweenawan. REFERENCES CITED Aldrich, H. R., 1929, The geology of the Gogebic iron range of Wisconsin: Wisconsin Geol. and Nat. History Survey Bull. 71, 279 p. ‘Allen, R. G., and Barrett, L. P., 1915, A revision of the sequence and structure of the pre-Keweenawan formations of the eastern Gogebic iron range of Michigan: Michigan Geol. Biol. Survey Pub. 18 (Geol. Ser. 15), p. 33—64. Atwater, G. I., 1938, Correlation of the Tyler and the Copps formations of the Gogebic iron district: Geol. Soc. America Bull., v. 49, p. 151—193. ,Beck, M. E., J r., 1970, Paleomagnetism of Keweenawan intrusive rocks, Minnesota: Jour. Geophys. Research, v. 75, no. 26, p. 4985—4997. 1Beck, M. E., J r., and Lindsley, N. C., 1969, Paleomagnetism of the Beaver Bay Complex, Minnesota: J our. Geophys. Research, v. 74, p. 2002—2013. Books, K. G., 1968, Magnetization of the lowermost Keweenawan 3 lava flows in the Lake Superior area: U.S. Geol. Survey Prof. Paper 600—D, p. D248—D254. REFERENCES CITED 41 Books, K. G., White, W. S., and Beck, M. E., Jr., 1966, Mag- netization of Keweenawan gabbro in northern Wisconsin and its relation to time of intrusion: U.S. Geol. Survey Prof. Paper 550—D, p. D117—D124. Brooks, E. R., and Garbutt, P. L., 1969, Age and genesis of quartz- porphyry near White Pine, Michigan: Econ. Geology, v. 64, no. 3, p. 342—346. Cannon, W. F., and Gair, J. E., 1970, A revision of stratigraphic nomenclature for middle Precambrian rocks in northern Mich- igan: Geol. Soc. America Bull., v. 81, p. 2843—2846. Chaudhuri, Sambhudas, and Faure, Gunter, 1967, Geochronology of the Keweenawan rocks, White Pine, Michigan: Econ. Geology, v. 62, p. 1011—1033. Cornwall, H. R., 1954, Bedrock geology of the Delaware quad- rangle, Michigan: U.S. Geol. Survey Geol. Quad. Map GQ—51, scale 1:24,000. Cox, Allan, 1961, Anomalous remanent magnetization of basalt: U.S. Geol. Survey Bull. 1083—E, p. 131—160. Craddock, Campbell, Thiel, E. C., and Gross, Barton, 1963, A gravity investigation of the Precambrian of southeastern Minnesota and western Wisconsin: J our. Geophys. Research, v. 68, no. 21, p. 6015-6032. Doell, R. R., and Cox, Allan, 1965, Measurement of the remanent magnetization of igneous rocks: U.S. Geol. Survey Bull. 1203—A, 32 p. DuBois, P. M., 1962, Paleomagnetism and correlation of Kewee- nawan rocks: Canada Geol. Survey Bull. 71, 75 p. Fisher, R. A., 1953, Dispersion on a sphere: Royal Soc. London Proc., set. A, v. 217, p. 295—305. Fritts, C. E., 1965, Stratigraphy, structure, and granitic rocks in the Marenisco-Watersmeet area, Michigan [abs.J, in Inst. Lake Superior Geology, 11th Ann., 1965: St. Paul, Minn., Univ. Minnesota, p. 15. Goldich, S. S., Nier, A. 0., Baadsgaard, Halfdan, Hoffman, J. H., and Krueger, H. W., 1961, The Precambrian geology and geochronology of Minnesota: Minnesota Geol. Survey Bull. 41, 193 p. Graham, J. W., 1953, Changes of ferromagnetic minerals and their hearing on magnetic properties of rocks: Jour. Geophys. Research, v. 58, p. 243—260. Grout, F. F., Gruner, J. W., Schwartz, G. M., and Thiel, G. A., 1951, Precambrian stratigraphy of Minnesota: Geol. Soc. America Bull., v. 62, p. 1017—1078. Grout, F. F., and Schwartz, G. M., 1939, The geology of the anorthosites of the Minnesota coast of Lake Superior: Min- nesota Geol. Survey Bull. 28, 119 p. Grout, F. R, Sharp, R. P., and Schwartz, G. M., 1959, Geology of Cook County, Minnesota: Minnesota Geol. Survey Bull. 39, 163 p. Halls, H. C., 1966, Review of the Keweenawan geology of the Lake Superior region: Am. Geophys. Union Geophys. Mon. Ser., v. 10, p. 3—27. Hubbard, H. A., 1967, Keweenawan volcanic rocks near Iron- wood, Michigan {abs.], in Inst. Lake Superior Geology, 13th Ann., 1967: East Lansing, Mich., Michigan State Univ., p. 20—31. 1968, Stratigraphic relationships of some Keweenawan rocks of Michigan and Wisconsin [abs.], in Inst. Lake Superior Geology, 14th Ann., 1968: Superior, Wis., Wisconsin State Univ., p. 35—36. Irving, Edward, Stott, P. M., and Ward, M. A., 1961, Demag— netization of igneous rocks by alternating magnetic fields: Philos. Mag., v. 6, p. 225—241. Irving, R. D., and Van Hise, C. R., 1892, The Penokee iron-bearing series of Michigan and Wisconsin: U.S. Geol. Survey Mon. 19, 534 p. James, H. L., 1958, Stratigraphy of pre-Keweenawan rocks in parts of northern Michigan: U.S. Geol. Survey Prof. Paper 314—0, p. 27-44. " Lane, A. C., 1898, Geological report on Isle Royale, Michigan: Michigan Geol. Survey, V. 6, pt. 1, 281 p. 1911, The Keweenawan series of Michigan: Michigan Geol. Biol. Survey Pub. 6 (Geol. Ser. 4), 2 v., 938 p. Lawson, A. C., 1893, The laccolithic sills of the northwest coast of Lake Superior: Minnesota Geol. and Nat. History Survey Bull. 8, p. 24—28. Leighton, M. W., 1954, Petrogenesis of a gabbro—granophyre complex in northern Wisconsin: Geol. Soc. America Bull., v. 65, p. 401—442. Leith, C. K., Lund, R. J ., and Leith, Andrew, 1935, Pre—Cambrian rocks of the Lake Superior region, a review of newly dis- covered geologic features, with a revised geologic map: U.S. Geol. Survey Prof. Paper 184, 34 p. Lyons, P. L., 1959, The Greenleaf anomaly, a significant gravity feature, in Symposium on geophysics in Kansas: Kansas Geol. Survey Bull. 137, p. 105—120. Palmer, H. C., 1970, Paleomagnetism and correlation of some middle Keweenawan rocks, Lake Superior: Canadian J our. Earth Sci., v. 7, no. 6, p. 1410—1436. Phillips, J. D., and Kuckes, A. F., 1967 , A spinner magnetometer: Jour. Geophys. Research, v. 72, p. 2209—2212. Rimbert, F., 1959, Contribution a l’étude de l’action de champs alternatifs sur les aimantations rémanentes des roches. Ap- plications géophysiques: Inst. Francais Pétrole Rev. et Annales Combustibles Liquides, v. 14, p. 17. Schwartz, G. M., 1942, Correlation and metamorphism of the Thomson Formation, Minnesota: Geol. Soc. America Bull., v. 53, p. 1001—1020. Tanton, T. L., 1927, Stratigraphy of the northern subprovince of the Lake Superior region [abs.]: Geol. Soc. America Bull., v. 38, p. 114—115. 1931, Fort William and Port Arthur and Thunder Cape map areas, Thunder Bay district, Ontario: Canada Geol. Survey Mem. 167, 222 p. Thiel, E. C., 1956, Correlation of gravity anomalies with the Keweenawan geology of Wisconsin and Minnesota: Geol. Soc. America Bull., v. 67, p. 1079—1100. Tyler, S. A., Marsden, R. W., Grout, F. F., and Thiel, G. A., 1940, Studies of the Lake Superior pre—Cambrian by accessory- mineral methods: Geol. Soc. America Bull., v. 51, no. 10, p. 1429—1538. Van Hise, C. R., and Leith, C. K., 1911, The geology of the Lake Superior region: U.S. Geol. Survey Mon. 52, 641 p. White, W. S., 1966a, Tectonics of the Keweenawan basin, western Lake Superior region: U.S. Geol. Survey Prof. Paper 524—E, 23 p. 1966b, Geologic evidence for crustal structure in the western Lake Superior basin, in The earth beneath the con- tinents—A volume of geophysical studies in honor of Merle A. Tuve: Am. Geophys. Union Geophys. Mon. 10 (Natl. Acad. Sci.—Natl. Research Council Pub. 1467), p. 28—41. 1968, The native-copper deposits of northern Michigan, in Volume 1 of Ore deposits of the United States, 1933—1967 (Graton-Sales Volume): New York, Am. Inst. Mining, Metall. and Petroleum Engineers, p. 303—325. 42 PALEOMAGNETISM OF SOME LAKE SUPERIOR KEWEENAWAN ROCKS White, W. S., Cornwall, H. R.,and Swanson, R. W., 1953, Bedrock Wilson, A. F. G., 1910, Geology of the Nipigon basin, Ontario: geology of the Ahmeek quadrangle, Michigan: US. Geol. Canada Geol. Survey Mem. 1, 152 p. Survey Geol. Quad. Map GO—27, scale 1:24,000. Winchell, N. H., 1895, A rational View of the Keweenawan: Am. Geologist, v. 16, p. 150—162. U. S. GOVERNMENT PRINTING OFFICE : 1972 O - 471-715 7DAY (ff-[X ~. “3 r K: Geochemical Anomalies and é Alteration in the ‘ Moenkopi Formation, Skull Crook, Moflat County, Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 761 , ”a": if'kl.‘}1f\ { ) ' 5;; ; 1973 $3017 Geochemical Anomalies and Alteration in the Moenkopi Formation, Skull Creek, Moflat County, Colorado By R. A. CADIGAN GEOLOGICAL SURVEY PROFESSIONAL PAPER 761 Geologic and geochemical reconnaissance of a formation and an area containing significantly higher background metal values than are commonly found elsewhere in the Colorado Plateau region UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600255 For sale by the Superintendent of Documents, US. Government Printing Oflice Washington, D.C. 20402 — Price 70 cents (paper cover) Stock Number 2401—00221 CONTENTS Page Abstract ______________________________________________________________________ 1 Introduction __________________________________________________________________ 1 Geology ______________________________________________________________________ 1 Stratigraphy ______________________________________________________________ 1 Structure _________________________________________________________ ‘ _______ 2 Mineral occurrences and mining activity ______________________________________ 3 Alteration in the Moenkopi Formation ___________________________________________ 6 Geochemical studies ___________________________________________________________ 7 Analytical methods ________________________________________________________ 7 Sampling methods _________________________________________________________ 9 Distribution of elements ___________________________________________________ 10 Factor analysis ___________________________________________________________ 15 Summary and recommendations ________________________________________________ 20 References cited.r__,__-ch- .___4,, ________________________________________________ 21 ILLUSTRATIONS ‘ Page FIGURE 1. Index map of the northern part of the Colorado Plateau region ________________________________________________ 1 2. Photograph of part of the interior of the Skull Creek anticline _________________________________________________ 3 3. Geologic sketch map of the Skull Creek anticline area ________________________________________________________ 4 4—6. Photographs of Moenkopi strata: 4. Altered strata, southern scarp _____________________________________________________________________ 6 5. Interbedded altered and unaltered strata, western scarp ______________________________________________ 7 6. Altered strata, northern and western scarps _________________________________________________________ 8 7. Photograph of the southeastern arc of the erosion scarp ______________________________________________________ 8 8. Map showing sampling traverses at localities A and B _______________________________________________________ 10 9. Map showing sampling traverse at locality E _______________________________________________________________ 11 10. Photograph of altered Moenkopi strata west of Miller Creek water gap ________________________________________ 11 11. Map showing sampling traverse at locality C, malachite showings at locality D, and sampled area at the Gartra prospect ___________________________________________________________________________________________ 14 12. Map showing sampling traverse at Lone Mountain __________________________________________________________ 15 13. Diagram showing comparison of metal content of altered rocks with Moenkopi average for the Colorado Plateau region _____________________________________________________________________________________________ 16 14. Diagram showing comparison of metal content of the Skull Creek cupriferous zone samples with Moenkopi average__ 17 TABLES Page TABLE 1. Stratigraphic units present in the Skull Creek anticline area ________________________ ‘_ __________________________ 2 2. Results of geochemical analyses of 20 samples collected from locality A _________________________________________ 12 3. Coefficients extracted from the matrix of correlation coefificients of values for elements sampled from the Skull Creek geochemical halo _____________________________________________________________________________________ 18 4. Proportion of positive covariance of each metallic element with each factor _____________________________________ 19 III GEOCHEMICAL ANOMALIES AND ALTERATION IN THE MOENKOPI FORMATION AT SKULL CREEK, MOFFAT COUNTY, COLORADO By ROBERT A. CADIGAN ABSTRACT The Moenkopi Formation of Triassic age exposed in the scarp encircling Skull Creek anticline in Moffat County, Colo., contains a thick altered layer of greenish—gray siltstone which is overlain by reddish-brown siltstone in most localities. Metal content of both the red and the altered rocks in the Skull Creek area is sig- nificantly higher than the geometric mean of metal content of Moenkopi strata in the Colorado Plateau region as a whole. A very thin zone of enrichment at the upper contact of the green altered rock with the overlying red rock contains anomalous amounts of copper (100—5,000 parts per million) and other metals. Samples from the enriched zone are at least four times higher than the Moenkopi averages in contents of vanadium, chromium, copper, nickel, cobalt, silver, lanthanum, and boron. Mercury is present in anomalously high amounts (geometric mean of all analyses, 2 ppm; maximum, >10 ppm) in the altered Moenkopi exposed in the southeastern erosion scarp area, the only area where the Moenkopi is completely altered. No enriched zone was found there.‘ Other anomalous occurrences of mineralization and alteration include a copper-uranium deposit in the base of the Jurassic Curtis Formation, conspicuous alteration in the Triassic Gartra Member of the Chinle, sulfide minerals containing anomalous amounts of arsenic, lead, and zinc in the top of the Pennsylvanian and Per- mian Weber Sandstone and in joints in the Triassic and Jurassic Glen Canyon Sandstone and the Chinle Formation, and anomal- ously high values of chromium, vanadium, gold, and silver at one locality in the Gartra Member. Factor analysis of measurements of metal content of the enrich- ment zone suggests two major events: (1) Invasion of the rocks by metal-bearing solutions and alteration of part of the Moenkopi, and (2) an interaction at the contact between the red rocks which represent an oxidized environment and the green rocks which represent an invading reducing environment. This interaction re- sults in a thin zone of enrichment of leached and redeposited metals—mercury, copper, silver, uranium, and gold—at the geo- chemical interface. The area is recommended for further geochemical exploration. INTRODUCTION During investigation of the distribution of metallic elements in the Moenkopi Formation in the Colorado Plateau region (Cadigan, 1971a), anomalous concen- trations of some metals, particularly copper and mercury, were found in samples from the Skull Creek anticline in the extreme northwestern part of Colorado. Field studies and further sampling in 1969—70 estab- lished the presence of geochemical anomalies in the area as a whole, of which the most conspicuous was a copper anomaly associated with bodies of pale-greenish- gray rocks within the normally red strata of the Moenkopi in the scarp surrounding the anticline. The metal anomalies and abnormal color relationships suggest epigenetic alteration of the formation in this area. Skull Creek anticline (fig. 1) is in the northern part of the Colorado Plateau region, north of the settlement of Skull Creek, Colo. The area is shown on the US. Geological Survey’s 7 %-minute quadrangle maps, Lazy Y Point and Skull Creek, Colo., and occupies all of T. 4 N., R. 101 W., and parts of adjacent town- ships. It is approximately 11 miles (18 kilometers) northeast of the Rangely oil field. Unimproved roads, passable only in dry weather, lead into the central part of the anticline from US. Highway 40. Four- wheel-drive vehicles are recommended for off-highway use in the area. GEOLOGY STRATIGRAPHY Rocks exposed in Skull Creek anticline range in age from Pennsylvanian to Cretaceous. Table 1 sum- marizes the stratigraphic column. Thickness and descriptive data are adapted from Thomas, McCann, and Raman (1945); those data for the Moenkopi Formation are somewhat modified on the basis of the WYOMING 109° __ 41° .T. UTAH TCOLORADO ary Colorado Plateau bound Vernal O Douglas Mountain I Blue X IMountain WOLF CREEK FAULT O 25 50 MILES SKUL CREEK NE |—_|___—J ANTICLI Q23 Rangely I l l I 1 oil field 40° FIGURE 1.—Index map of the northern part of the Colorado Plateau region. 2 GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO work by Schell and Yochelson (1966), who redefined the contact between the Moenkopi and Park City Formations, and by F. G. Poole (oral and written com- mun., 1969), who described and measured a section through the Moenkopi at Skull Creek. The uppermost unit of the Park City Formation is exposed in the base of the southern scarp face west of Miller Creek water gap where the upper contact crosses the section line between secs. 28 and 29, T. 4 N., R. 101 W. This unit is a limestone 4 inches (10 centimeters) thick which lies at the top of the tawny beds of Schell and: Yochelson (1966) and which is overlain by reddish- brown siltstone strata assigned to the Moenkopi Formation. Light-colored strata above this contact are related to color changes within the Moenkopi Forma- tion. The base of the Moenkopi is covered by alluvial wash in most of the anticline area, but the rest of the formation is well exposed. The upper contact of the Moenkopi with the Gartra Member of the Chinle Formation is marked by the conspicuous coarse- grained, resistant, ledge-forming sandstone strata of the Gartra. The Moenkopi contains some resistant, thin calcareous very fine grained sandstone beds, but poorly resistant, coarse-grained siltstone strata predominate, as suggested by the exposures shown in figure 2. STRUCTURE Skull Creek anticline is an asymmetrical structural feature—almost monoclinal—on the southeastern flank of the Uinta Mountains structural system (Ritzma, 1956). Its southern limb dips more steeply (20°—45°) than the northern limb (2°—5°). The anticlinal axis arcs from a west-east orientation to a northwest- southeast orientation in the area of the study with the concave side of the axis to the south. This arc produces a structural feature which has been called Skull Creek dome (Rocky Mountain Association of Petroleum Geologists, 1941). The Skull Creek anticline is an excellent example of a breached anticline. Throughout an area (fig. 3) 12 miles (19 km) long and 6 miles (10 km) wide, it has been eroded down to the Weber Sandstone which forms a broad slightly to moderately dissected domed sur- face. An erosional scarp which has a perimeter of approximately 30 miles (48 km) and which encircles the exposed Weber Sandstone is cut in the Park City, TABLE 1.—Stratigraphic units present in the Skull Creek anticline area Period and unit Thiggiess General description Cretaceous: Mancos Shale ,,,,,,,,,,,,,,,,,,,, 5,000 Gray to black carbonaceous marine siltstone with minor calcareous beds and len- ticular sandstone strata. Frontier Sandstone Member_-_ 300 Thick- and thin-bedded gray sandstone interbedded with gray to black carbo- naceous siltstone. Mowry Member ______________ 50 Hard dark-gray to black siliceous shale weathering to light ash—gray chips. Dakota Sandstone ________________ 50 Resistant thick-bedded brownish—gray-weathering sandstone; characteristically forms prominent massive beds. Burro Canyon(?) Formation_ A , , . , . 50 Green to varigated gray—green and purple siltstone upper unit and a thick—bedded light-gray conglomeratic sandstone lower unit. Jurassic: Morrison Formation. _. , _ _, , , , - . _. . 675 Variegated green-gray, and maroon siltstone upper part, and a thick crossbedded, fine-grained, white sandstone lower part. Curtis Formation___.., , H . , .. 115 Thin-bedded gray shale, platy glauconitic brownish-gray very fine grained sand- stone; abundant Belemnite fragments. Entrada Sandstone ............... 175 Massive thick-bedded light-gray very fine to fine-grained sandstone; forms high rounded cliffs: glauconite in upper part. Carmel(?) Formation______- _ _ - , , , ., 25 Pinches out in area; reddish-brown silty sandstone. Jurassic and Triassic: Glen Canyon Sandstone 1-”- , __ -_ _ .. 540 Spectacularly crossbedded massive thick-bedded fine-grained sandstone; forms high, bare dome—shaped buttes. Triassic: Chinle Formation _________________ 250 Red calcareous siltstone, very fine grained red sandstone and lime-pellet con- glomerate. Gartra Member ., , _ “ _____ , _. 20 Basal conglomerate of the Chinle, white conspicuous ledge, medium-grained conglomeratic sandstone; hematite-impregnated. Moenkopi Formation ______________ 525 Reddish-brown to grayish-green regularly bedded micaceous coarse siltstone and very fine grained sandstone; red color absent locally. Permian: Park City Formation _____________ 220 Grayish-orange and yellowish—brown siltstone (the tawny beds of Schell and Yochelson, 1966) underlain by gray very fine grained calcareous sandstone. Permian and Pennsylvanian: . Weber Sandstone _________________ 975 Massive crossbedded thick—bedded gray fine-grained sandstone; forms steep- walled canyons, rocky tree-covered slopes. l Called the Navajo Sandstone by Thomas, McCann, and Raman (1945); renamed by Poole and Stewart (1964) on the basis of regional stratigraphic relationships. GEOLOGY 3 FIGURE 2.—Interior valley of the Skull Creek breached anticline, viewed northwestward. qu, basal sandstone of Curtis Formation; Je, Entrada Sandstone; Jig, Glen Canyon Sandstone; Trc, Chinle Formation; Fm, Moenkopi Formation; Ppc, Park City Formation; PPw, Weber Sandstone. White strata in the left foreground and in the distant scarp are altered rocks in the Moenkopi, and Chinle Formations, and in the rim- forming Glen Canyon Sandstone. Succeeding concen- tric hogbacks which are present only on the southern steeply dipping limb are (1) the Entrada Sandstone rimmed by the resistant basal sandstone of the Curtis Formation, (2) the persistent ledge-forming Dakota Sandstone, and (3) the Frontier Sandstone Member of the Mancos Shale. The east-striking Wolf Creek fault (fig. 1), a steeply dipping thrust fault related to the Uinta Mountains structural complex, borders the northern limb of the anticline (W. R. Hansen, oral commun., 1970). Num- erous fault and joint systems striking generally from north to east may be observed within the anticline, but only minor displacement is evident. Displacement of hogback ridges south of Miller Creek water gap, apparent in aerial photographs, suggests the presence of an important fault occurring in conjunction with a sharp fold. Some fault traces in the western part of the anticline converge on a broad center near Red Wash water gap; this convergence suggests fracturing in response to localized stress. Major open faults, some of which are shown in figure 3, and major systems of parallel joints trending between northeast and east cut the Weber Sandstone in the core of the anticline. Erosion along the northeast-trending zones of weakness has produced fairly straight narrow deep box canyons in the Weber Sandstone and in the rocks forming the south slope of the southern limb of the anticline. All drainage from the anticline is to the south. Subsequent Moenkopi Formation. Skull Creek is in the center foreground in the arroyo which is cutin thick valleyalluvium. The Carmel(?) Formation, which occurs discontinuously between the Entrada and Glen Canyon Sandstones, was observed in lenses as much as 10 feet thick in two exposures in the south scarp. Neither ex- posure is visible in this photograph. interior drainage parallels the scarp surrounding the core, particularly on the southern and eastern edges where deposits of reddish-brown alluvial sediment and loess up to 30 feet in thickness are deeply incised. The alluvial fill extends southward through the three major water gaps in the southern scarp, Skull Creek, Miller Creek, and Red Wash, and into the flatlands south of the anticline. MINERAL OCCURRENCES AND MINING ACTIVITY The Skull Creek anticline area and the region to the north have been prospected extensively since the 1870’s and have been the source of some mineral production. The Douglas Mountain district that is approximately 20 miles north of the Skull Creek area has a record of some copper and silver ore production (200:1: tons) from 1873 to 1947 (Vanderwilt, 1947, p. 144). Records in the Moffat County Clerk’s office describe a con- siderable amount of prospecting and claim staking in the Blue Mountain area between Skull Creek and Douglas Mountain from 1870 until much of the Blue Mountain area was incorporated into the Dinosaur National Monument in 1938. During the early 1900’s, high-grade radium ore was mined from the base of the Curtis Formation in the south limb of the Skull Creek anticline (NV; sec. 35, T. 4 N., R. 101 W.; fig. 3). The deposit was mined for vanadium from 1917 to 1920 and finally, for uranium in the 1950’s. According to Isachsen (1955), the ore occurred in carbonized plant-bearing mudstone and GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO 108°50' R. 102 W. 47'30" R. 101 W. 45' l | ZO‘l—l 40° _ 20' j anficline 375‘ \ / d 69 7 5 . ma‘e J ‘35“ / / 1 ,//// XE “‘r“ 4 ““\ \\\.\.‘ w“\\\\\‘\\ v;“ ‘w‘ ‘ s‘ \ s‘ .\\\‘\\\\ , ‘.\ \ “ ' \f\\\‘~“‘\\\“ ““fl ‘ 1 ,~ . \~\ , ~.\ w ‘\“A\\.s\\\\\\“\\\\ Zb—I [PD 1 7’ 30” 9 A u. . . u’ 8‘ ° ! i ~‘ ~ i t u , < s W -//’}”h; N. 33.”. ' N 11‘ ""$‘.-’/ / ‘ 1? y ”M 40° I ll ll w / I 15’ R. 102 W, R. 101 W. 0 1 2 3 MILES l I I | 0 1 2 3 K|LOMETERS | | l J FIGURE 3.—Geologic sketch map of the Skull Creek anticline area showing outcrop of altered strata in the Moenkopi Formation. contained copper, uranium, and vanadium minerals. sec. 35, T. 4 N., R. 101 W., and SEM sec. 33, T. 4 N., Production is believed to have been less than 1,000 tons. R. 101 W.) in 1953 (McDougald, 1955). Drill cores According to Stanley (Bud) Biles of Dinosaur, Colo., were taken through the basal sandstone ledge of the during the uranium boom of the 1950’s, the ownership Curtis Formation, and holes were bottomed in the top and the name of the mine changed many times. of the Entrada Sandstone. According to McDougald, The AEC (Atomic Energy Commission) conducted the mine in the Curtis was known as The Blue Mountain an exploration drilling program for uranium in the hog— Group mine during 1953 operations. back area east and west of Miller Creek (Nl/z NE% A small surface prospect in the base of the Gartra GEOLOGY ‘ 5 42’30" , 40' R. 100 W. 108°37’30" l . T. 5 N. 40:. EXPLANATION — 20’ JURASSlC CRETA- CEOUS Dakota Sandstone I I Burro Canyon(?), Mor- rison, and Curtis For- mations & AND TRIASSIC AND JURASSIC CRETACEOUS Sandstone Chinle Formation ‘ Moenkopi Formation ‘Em, reddish-brown part 'fima, greenish-gray altered M ECT‘ PIPpw part _ 17' 3o” Plew PENNSYLVANIAN TRIASSIC Park City Formation and Weber Sandstone Entrada Sandstone, Carmel(?) Formation, and Glen Canyon AND PERMIAN I L\ Contact Dashed where approxi- mately located and covered by thick alluv- ium in stream gaps Major joint or fault trace Not all are shown E General locality referred to in text T . 25 __l_ Strike and dip of beds iZ/ Q/ ”in r i // i \ 40° R. 100 w. i 15’ The map was compiled by the author from field observations and aerial photographs on topographic base maps that are cited in the text. Member of the Chinle Formation in the northeast corner of the area (8% sec. 20, T. 4 N., R. 100 W.; fig. 3) was opened in the 1950’s, according to Mr. Biles. Small amounts of uranium-bearing clay were found around mineralized logs, and several sacks of this ore were mined and sold. No copper or vanadium minerals are visible in the prospect excavations. The sandstone bed below the mineralized wood layer con- tains 1-inch pyrite concretions, but no other visible evidence of mineralization is apparent. A small uranium deposit in the Weber Sandstone just north of Skull Creek anticline is reported (Isachsen, 1955) to have been discovered and mined in 1954. Except for the drilling program conducted by the AEC in 1953, no coordinated modern surface or subsurface exploration has been attempted in the area. 6 GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO ALTERATION IN THE MOENKOPI FORMATION The Moenkopi Formation is a red-bed formation typical of several formations in the Colorado Plateau region. Petrologic evidence (Cadigan, 1971b) suggests that the red color is diagenetic and' resulted from the oxidation of iron in detrital minerals composing the rock strata. The pigmentation is in the form of mega- scopic to microlitic crystals of hematite impregnating the clayey and calcareous fractions of the coarse red siltstone and very fine grained sandstone, the dominant lithology of the Moenkopi. In the Skull Creek anticline area and adjoining areas to the east and west, the Moenkopi Formation contains lens-shaped light-greenish-gray to greenish-yellow bodies of rock with, in most localities, reddish-brown strata both above and below. An almost continuous zone about 1 cm thick that contains 100—5,000 ppm (parts per million). of copper coincides with the upper boundary of the grayish-green strata. The color boundary and the cupriferous zone are at many localities parallel to the bedding planes, but in others they cross bedding planes (fig. 4). At most localities the color change is not abrupt, but observed in detail the red beds are separated from the green beds by a narrow transition interval of mottled strata, or by an interval of interstratified thin beds or laminae of green and red siltstone (fig. 5). Viewed from a distance the color change is conspicuous and un- mistakable, as shown in figure 6A, B. The thickness FIGURE 4.——Altered grayish-green Moenkopi strata overlain by unaltered red strata. Note that the color boundary rises in the section away from the camera and crosses sedimentary beds. Exposure at locality A (N%SE% sec. 27, T. 4 N., R. 101 W.), southern scarp. sza, green Moenkopi; ‘fim, red Moenkopi; TI cg, Gartra Member forming the base of the Chinle Formation. The view is toward the east. of the greenish strata ranges from a few inches to approximately 500 feet in different parts of the area. Along part of the eastern scarp (area C in fig. 3) the entire formation is greenish yellow and there are no red strata to be found (fig. 7) in the Moenkopi Forma- tion except possibly one or two thin beds just below the Moenkopi-Chinle contact. The cupriferous zone may be detected at the upper color boundary of the greenish strata where these strata are 50—200 feet thick. It could not be found in the eastern scarp where there is no typical green-red color change and the entire formation is light greenish yellow or gray. At some localities (fig. 3A, B, and D) 1-millimeter-thick lenses of malachite (Cu2C03(OH)2) are found along the color boundary. Some unoxidized pyrite nodules occurring below the color boundary in the southern scarp are high in copper (200 ppm) and mercury (9 ppm). Where red strata interlayed with green strata divide the main green zone into two or more green zones, rock samples from each of the red-over-green contacts may show anomalous copper content, but, in most instances, samples from the highest such contact in the section contain the largest concentration of copper. The light-green strata were originally thought to be related to conditions of deposition or to ordinary diagenesis. Several factors suggest that rock in the green zone was altered from red to green as the result of an extraneous postdepositional event unrelated to normal diagenesis as it is observed in the Moenkopi; these are the restriction of the green strata to the Skull Creek and adjacent areas, the observed extreme variation in thickness of the greenish strata from locality to locality, the crossing of sedimentary structures and textures by the color boundary, and the coincidence of the cupriferous zone with the green-red interface. This alteration evidently occurred before the breaching of the Triassic rocks that formerly covered the Skull Creek anticline and may have been penecontemporane- ous with the structural deformation that produced the anticline and adjacent structural features. The Gartra Member of the Chinle Formation is also highly altered in some outcrops along the southern scarp; the altered rock, a coarse-grained sandstone, is variegated white, red, and purple, and contains clinker- like concretions of purple hematite-cemented grains and areally restricted 10- to 20-cm-thick lenses of discolored chert or jasperoid. Metal values other than those of copper are anomal- ously high. Of particular interest are the mercury values found in Moenkopi strata in the eastern and southern scarps, some of which are greater than 10 ppm. The presence of the high content of mercury in the rock suggests the dispersion patterns of mercury that were GEOCHEMICAL STUDIES 7 FIGURE 5,—Interbedded altered green and unaltered red strata in the Moenkopi Formation. The cupriferous zone is present in the upper- most part of the green strata. The exposure is on the western scarp at the approximate center of sec. 22, T. 4 N., R. 102 W. Thick- ness of Moenkopi shown here is 200~250 feet. Tuna, green zone; 'fim, red Moenkopi; H, upper cupriferous zone. found related to hydrothermal mineralization by Saukov (1946), Williston (1964), and Erickson, Mar- ranzino, Oda, and Janes (1964). GEOCHEMICAL STUDIES ANALYTICAL METHODS The general metal content of the rocks was de- termined by six-step spectrographic analysis for 30 elements, supplemented by atomic-absorption analyses for mercury, gold, silver, and copper. Analyses for uranium by a colorimetric method were done on a few selected samples. All samples were checked for radioactivity with a scintillometer. All analyses were made by the Denver laboratories of the U.S. Geological Survey. Analysts were‘R. N. Babcock, K. J. Curry, 8 GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO FIGURE 6.——Conspicu0us altered greenish—gray strata in the Moen- kopi Formation seen exposed on A, the northern scarp near Lone Mountain (secs. 11, 14, T. 4 N., R. 101 W.), and B, the western scarp near locality E (NEM sec. 23, T. 4 N., R. 102 W.). In A, reddish—brown strata occur in the middle of the altered B strata; in B, they occur near the top of the altered strata. The major cupriferous zone is at the top of the upper part of the altered strata.J‘Fz g, Glen Canyon Sandstone; ic, Chinle Forma- tion; Tzcg, Gartra Member of the Chinle; Ttma, altered strata of Moenkopi; Tam, unaltered reddish-brown strata of Moenkopi. FIGURE 7 .—The southeastern arc of the erosion scarp encircling Skull Creek dome as viewed looking eastward from the highest point on the south rim between Skull Creek and Miller Creek water gaps (SW% sec. 26, T. 4 N., R. 101 W.). The Moenkopi Formation forming the lower half of the eastern scarp is altered from base to top. The group of houses in the right medium distance is the settlement of Skull Creek. The road was U.S. Highway 40 in 1970. The low grass—covered hogback is formed by the resistant Frontier Sandstone Member of the Mancos Shale (Kmf). Kd, Dakota Sandstone; qu, Curtis Formation (basal ledge); Je, Entrada Sandstone; Jfig, Glen Canyon Sandstone; Twc, Chinle Formation; Fog, Gartra Member of the Chinle Formation; ‘fima, greenish-gray and greenish- yellow (altered) Moenkopi Formation. GEOCHEMICAL STUDIES 9 J. V. Desmond, M. S. Erickson, C. L. Forn, J. G. Frisken, D. J. Grimes, J. R. Hassemer, R. T. Hopkins, H. D. King, R. W. Leinz, D. G. Murrey, D. F. Siems, J. G. Viets, L. A. Vinnola, K. C. Watts, Jr., and A. W. Wells. Assistance in the field studies was provided by Laurette N. Bates, Norma L. Noble, and A. J. Toevs. Mrs. Bates also organized the sample collec- tions and analytical data reports. Element symbols Cu(A), Ag(A), Hg(A), and Au(A) used in tabular presentations indicate results of analyses made by the atomic-absorption methods described by Huffman, Mensik, and Rader (1966), Huffman (1968), and Vaughn (1967). The regular element symbols Cu, Cr, V, and so forth in tables and figures indicate results of analyses made by the semiquantitative six- step spectrographic method, slightly modified from the three-step technique described by Myers, Havens, and Dunton (1961). Both spectrographic and atomic- absorption values for copper and silver are given in the report and treated statistically as separate variables. The lowest concentration at which an element is detected and reported for quantitative geochemical purposes is called the detection limit. It varies according to element and analytical method used. The highest concentration that can be estimated and reported» quantitatively is called the reporting limit, which also varies according to element and analytical method; for example, the reporting limit of most abundant elements is 10 percent or 100,000 ppm for the spectro- scopic method. The detection limit in parts per million for the elements reported in this study are as follows: Magnesium, Mg ______ 200 Uranium, U __________ 20 Iron, Fe _____________ 500 Nickel, Ni ___________ 5 Calcium, Ca __________ 500 Cobalt, Co ___________ 5 Titanium, Ti _________ 20 Beryllium, Be ________ 1 Barium, Ba __________ 20 Scandium, Sc-___ _ _ . _ - 5 Manganese, Mn ______ 10 Lanthanum, La _______ 20 Strontium, Sr ________ 100 Molybdenum, Mo _____ 5 Zirconium, Zr ________ 10 Niobium, Nb _________ 10 Vanadium, V--- - _ _ _ _ _ 10 Boron, B ____________ 10 Chromium, Cr- _ _ -____ 5 Copper(A), Cu(A) . _ _ _ 10 Copper, Cu __________ 5 Silver(A), Ag(A) ...... .2 Yttrium, Y __________ 10 Mercury(A), Hg(A)_-- .01 Lead, Pb ____________ 10 Gold(A), Au(A) ______ .02 Silver, Ag ____________ .5 Zinc, Zn, is also occasionally mentioned in the report, but it is not treated statistically; it has a detection limit of 200 ppm. If the analytical data are to be treated statistically, certain properties of the frequency distributions of the concentrations of each of the elements must be con- sidered (Miesch, 1967). One of the problems involves truncated or censored distributions— those which con- tain values below the limits of detection or above the reporting limits. It is a common practice to assign arbitrary values Where no values can be reported to avoid the use of zero which would also be an arbitrary 475-889 0 — 72 ~ 2 and probably incorrect value in most instances. In this study, values reported as less than the detection limit have been assigned a value equal to one-half of the detection limit. For example, gold concentrations that were reported as less than 0.02 ppm were assigned values of 0.01 ppm. The problem was discussed in greater detail in an earlier report (Cadigan, 1971a). Elements discussed in this report for which censored statistical distributions of concentrations constitute a serious problem are uranium, gold(A), beryllium, molybdenum, niobium, and scandium. Absolute values (such as, means) computed for these elements are not reliable, but graphic comparisons of relative abundances and computed correlations are adequate for the pur- poses for which they are used. SAMPLING METHODS Detection and definition of the cupriferous zone were accomplished by the collection and analysis of four separate sets of samples. The first set consisted of stratified samples, as defined by Cochran (1953), of Triassic sedimentary formations of the Colorado Plateau region. Analytical results of Moenkopi samples collected from the south scarp at the Skull Creek locality (Cadigan, 1971a) suggested that the area was one of higher than average metal content. The first sample collected from the cupriferous zone itself was one of a second set of samples collected during the subsequent and more intensive stratified sampling of the Moenkopi Formation at locality A (figs. 3, 8). The character of the zone was determined from analyses of a third set of rock and soil samples collected along the strike of the bed represented by the sample collected in the second set which contained the highest copper values. Some of the analyses of the third set of samples were obtained from a Geological Survey mobile laboratory which was brought into the area for a few days to provide “instant” analytical results. The extent of the cupriferous zone was determined by using a man-carried copper-test kit to confirm the presence of the zone along the 30 miles (48 km) of erosional scarp surrounding the core of the anticline. A fourth set of samples was collected as representative of this cupriferous zone. For purposes of comparison the sample analytical results are separated into three different groups: (1) Those for stratigraphic samples selected as representa- tive of altered and unaltered but noncupriferous rocks of the Moenkopi Formation and Gartra Member of the Chinle Formation, (2) those for samples selected as representative of the cupriferous zone, and (3) those for miscellaneous unique rock and mineral samples from the Moenkopi, Gartra, and other rock units in the area. 10 GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO R. 101 W. \ \) \1/ \\2 Q \\\\\\; \ \\\\\\\\\ \\\\\ \T\\\\n‘\\\\\\\ \\\\\\“‘-\. m\\\\\\\\\\ \\®W3\\\\\\ EXPLANATION Contact Dashed where approximately located and covered by thick alluvium in stream gaps Dirt road FIGURE 8. —Sampling traverses at localities A and B, secs. 27 and 28, T. 4 N, R. 101 W. The area is divided by Miller Creek water gap. Kch, Burro Canyon, Morrison, and Curtis Formations; J} eg, Entrada and Glen Canyon Sandstones; Tic, Chinle Formation; “Em, Moenkopi Formation; 'Ema, altered Moenkopi; PIPpw, Park City Formation and Weber Sandstone. DISTRIBUTION OF ELEMENTS The distribution—of-elements study of the Moenkopi Formation (Cadigan, 1971a) and the Navajo mercury study (Cadigan, 1969) suggested that the rocks of the Skull Creek anticline area are anomalously high in metal content. This suggestion is confirmed by spectro- graphic, and other instrumental analyses of samples collected during the present study. Table 2 shows the analytical results from 20 samples collected at locality A (figs. 3, 8), the second suite of samples collected in the area. The samples consist of 10 pairs of samples, a pair being replicates taken from the same 0.3-meter-square area. The last four columns of table 2 shown for purposes of comparison are (1) the geometric mean metal values for 10 reddish-brown and reddish-yellow samples, (2) geometric means for eight greenish-gray and grayish- yellow samples, (3) geometric means for 18 of the 20 samples collected in the vertical traverses (fig. 8) at locality A, and (4) geometric means for 323 samples collected from the Moenkopi Formation throughout the Colorado Plateau region. The two samples from the cupriferous zone at locality A were not used in the geometric mean calculations in (3) because of their anomalously high values (for example, copper, vana- dium, lead, and zinc). Comparison of the four columns indicates that red and green and gray samples are not significantly different in metal content and that the geometric-mean metal values of the 18 samples collected at locality A are significantly higher in metal content than the re- gional geometric-mean values. Comparison of a similar suite of 20 samples collected from the bottom to the top of the Moenkopi at locality E (figs. 3, 9) showed similar results although the geo- metric-mean metal values for the samples from E were generally lower than the geometric means for those collected at A. The suite of samples with the highest metal values was that collected from the cupriferous zone at approx- imately 75-foot (23-m) intervals on a 600-foot (183-m) east-to—west lateral traverse west of Miller Creek gap at locality B (figs. 1, 8, 10). A partial listing of analytical results in parts per million for nine samples is given below, tabulated in the order collected. GEOCHEMICAL STUDIES 1 II R. 102 W. / / I \ / ’ T Sampling, J 4' traverse/ N. 23 / Plew / N / I l I / E I / / / I / I / / / 0 V2 1 MILE | L I FIGURE 9.—-Sampling traverse at locality E, sec. 23, T. 4 N., R. 102 W. The cupriferous zone is present at the inter- section of the sample traverse with the top of the altered zone ( ma). J? g, Glen Canyon Sandstone; 'EC, Chinle Formation; Tz m, Moenkopi Formation; K ma, altered zone in Moenkopi; Plew, Park City Formation and Weber Sandstone. Sample Hg(A) Cu(A) V U Ag(A) CD 5539A______-_- 2.1 870 150 <20 1.5 5539B _________ 2.5 270 100 <20 1.7 5540 __________ 2 .4 5 , 400 5, 000 200 2 .3 LB 69—20 _________ 3.5 5,200 500 40 1.8 69—22 _________ 10 . 0 2, 600 1,000 40 2 .0 69~—23 _________ 1. 0 5,100 500 80 12 .0 69—24 _________ 3 .5 2,200 200 40 4 .0 69—25 _________ .35 880 50 <20 2 .4 69—26 _________ 10.0 4,400 500 <20 2.4 Malachite-bearing laminae were observed in the cupriferous zone almost continuously along this lateral traverse at locality B (fig. 8). A suite of 23 samples taken from bottom to top, normal to the strike of the altered strata in area B but excluding the cupriferous zone, yielded much lower metal values. A summary of values in parts per million follows: Hg(A) Cu(A) v U Ag(A) Maximum _________ >10 34 100 <20 1.8 Median ___________ 2 .4 14 50 <20 . 8 Minimum _________ .4 < 10 30 <20 .4 A comparison of the analytical results for the two sets of samples from locality B shows that although the high copper(A), vanadium, uranium, and silver(A) values are confined to the cupriferous zone, high mercury(A) values are dispersed vertically throughout the sampled strata. Samples collected from the cupriferous zone on the east side of Miller Creek water gap at locality A (figs. 1, 3, 8) at 100— to 150—m intervals along a l-km lateral traverse are lower in metal content than the samples from the cupriferous zone of locality B. A partial listing of values in parts per million is given below. Sample Hg(A) Cu V U Ag(A) CD 5527 __________ 2.0 86 200 <20 1.1 5529 __________ 1 .5 250 200 <20 1 .1 5530 __________ 1.8 17 200 <20 1.7 5531 __________ 1.5 300 200 <20 1.6 5533 __________ 2 .2 800 300 <20 2 .7 5535A _________ 2.1 250 100 <20 1 .2 5535B__-______ 1.8 380 100 <20 1.5 Eleven samples were collected from the cupriferous zone at irregular intervals along the north scarp (figs. 3, 6A, 11, 12) from locality D to Lone Mountain during field checking of the continuity of the cupriferous zone. These samples show values of mercury(A) lower by a factor of 100 and values of silver(A) generally FIGURE 10.——Altered Moenkopi strata (”F-ma) appear as light- colored beds forming the bottom third of the scarp at Miller Creek water gap (locality B). Surface in the foreground is alluvial fill. Beds forming low white hillocks at the far end of the alluvial plain at the base of the scarp are in the Park City Formation. Rising slope to the right is Weber Sandstone. Rock in the immediate foreground, the Gartra Member ('Ecg), also crops out on the scarp slope at locality B. J'Eg, Glen Canyon Sandstone; Tic, Chinle Formation; "Em, Moenkopi Formation. 12 TABLE 2.—-Results of chemical and spectrographic analyses, in parts per million, of 20 samples of GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO the M oenkozn’ Formation from locality A the Colorado [Numbers in parentheses beneath sample numbers in boxheads indicate distance above base in meters. _ _ _ _, indicates data not available. Notation (A) as in Ag(A) detected in only two samples, and is not treated statistically. R—Y, reddish yellow; Chemical and spectrographic analyses, from locality A, of samples CD— 4748A 47483 4749A 4749B 4738A 4738B 4739A 4739B 4740A 47403 4742A (3.1) (3.1) (25.9) (25.9) (51.8) (51.8) (74.7) (74.7) (93.0) (93.0) (93.9) ' R—Y R—Y G—Y G—Y GR—G GR—G GR—G GR—G GR—G GR—G GR Ca ______________ 100 , 000 100 , 000 30,000 50 , 000 70, 000 100 , 000 70 , 000 50 , 000 150,000 150 , 000 2 , 000 10,000 10,000 30,000 30,000 10,000 15,000 30,000 30,000 10,000 15,000 50,000 20 , 000 20 , 000 30 , 000 20,000 20 , 000 20 , 000 30 , 000 30,000 15 , 000 15 , 000 20 , 000 2,000 2,000 5,000 5,000 2,000 3,000 5,000 5,000 3,000 3,000 5,000 700 700 700 700 700 700 700 700 700 1 ,000 700 300 300 700 700 500 500 500 700 1 ,000 1 ,500 500 1, 000 700 200 300 500 500 300 150 1 , 000 1 , 000 200 100 150 500 200 100 100 150 150 200 200 100 50 50 100 100 50 50 70 100 100 100 700 70 70 100 100 50 50 150 100 30 30 100 18 19 24 25 15 13 22 19 40 58 1 , 700 20 20 30 :20 '15 15 20 20 30 70 1 , 500 15 10 30 20 15 20 20 20 20 20 20 20 15 20 15 15 15 15 20 20 30 300 10 15 50 30 15 15 20 20 10 15 50 < 5 < 5 1 5 1 0 5 5 7 7 5 7 1 5 < 1 < 1 <1 < 1 < 1 <1 1 < 1 < 1 < 1 1 1.0 1.0. .6 .5 1.2 1 1 .6 .7 1.6 1.2 3.4 .04 04 .04 <.01 .80 .60 .18 .04 .03 .07 .05 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <10 <10 10 10 <10 <10 10 10 <10 <10 10 20 20 50 50 20 20 30 50 20 20 70 20 20 30 30 20 20 30 30 20 20 30 5 5 15 10 5 5 10 10 5 5 20 Zn _____________________________________________________________________________________________________________________________________ 200 lower than the values shown by samples from the Hgm) Cum v U Ag,” cuprlferous zone in the south scarp at localities A and M _ 10 74 100 20 1 2 ~ ~ - ~ - ax1mum .......... > < . B. A statlstlcal summary of analytlcal results 15 glven Median ___________ 2 . 3 15 50 <20 . 8 below (values in parts per milllon). Minimum ......... .5 <10 30 <20 .6 Hg(A) Cu (A) v U Ag(A) Maximum _________ 0.04 1 ,800 700 20 1 .8 Median ___________ .02 320 150 <20 .8 Minimum _________ .01 100 50 <20 .6 Uranium was detected in only one sample (fig. 12) from the north scarp near Lone Mountain. It was detected in five of the six samples collected along the lateral sample traverse in area B (fig. 8), from exposures just west of the gap. Three halo samples from the cuprif- erous zone in the west rim contain values for mercury- (A), copper(A), vanadium, and silver(A) in the same order of magnitude as the samples from the north rim, but none contains detectable uranium. N0 cupriferous zone was found in the east scarp at locality C (figs. 3, 7, 11). Values for the five metals in the suite of 16 samples collected at irregular intervals from a 470-foot (143-m) vertical traverse of the grayish- yellow and greenish-gray altered Moenkopi Formation strata of the east scarp are summarized below (in parts per million). The geometric-mean values for 25 elements in four different sample suites of grayish and greenish rocks are compared graphically in figure 13 with the geometric means for 323 samples from the Moenkopi Formation as a whole in the Colorado Plateau region (Cadigan, 1971a). The geometric means for the 323 samples are referred to for the sake of brevity as Moenkopi Ma. The bottom scales of the bar graphs are multiples of the Moenkopi MG values shown in parts per million. Thus, the geometric mean for titanium in the 26 stratigraphic samples from the altered strata at locality A (fig. 3) is between four and five times the Moenkopi MG for titanium, or 2,900—3,700 ppm. For the Colorado Plateau region, usable analytical data are not available for the computation of Moenkopi MG values for scandium, lanthanum, molybdenum, niobium, and boron; scandium and lanthanum values were not sought; molybdenum, niobium, and boron values were sought but almost none of the values were high enough to be detected. These five elements, GE OCHEMICAL STUDIES 13 (figs. 3, 8) and comparisons between geometric means of selected analyses of samples of the Moenkopi Formation from both locality A and Plateau region indicates analysis by atomic absorption. Samples from cupriferous zone GR are not used in geometric mean comparisons. Zn has detection limit of 200 ppm, was G—Y, grayish yellow; GR—G, greenish gray; GR, green; R—B, reddish brown] Chemical and spectrographic analyses, from locality A, of samples CD—Continued Geometric means Locality A Colorado Plateau 474213 4741A 4741B 4743A 4743B 4744A 4744B 4745A 4745B R—B, R—Y GR—G, G—Y R—B, R—Y, (323 samples; (93.9) (94.5) (94.5) (97.5) (97.5) (120.4) (120.4) (132.6) (132.6) (10 samples) (8 samples) GR—G, G—Y Cadigan, 1971a) GR R—B R—B R—B R—B R—B R—B R—B ReB (18 sampla) 2,000 150, 000 150, 000 100,000 100, 000 100, 000 100,000 1 , 000 1 , 000 43,000 73,000 55, 000 22, 000 30,000 15,000 15,000 20,000 20,000 30,000 30,000 30,000 20,000 19,000 19,000 19,000 8,900 20,000 15,000 15,000 20, 000 15 , 000 30,000 30,000 10,000 7,000 17,000 22,000 19,000 5,100 5,000 3,000 3,000 5,000 3,000 5,000 5,000 5,000 5,000 3,600 3,700 3,600 740 700 1 , 000 1 , 000 700 700 1 , 500 1 , 000 700 1 , 000 870 730 810 410 500 1 ,000 1 , 000 700 700 1,000 1 , 000 500 500 510 710 670 190 200 500 300 300 300 200 150 1,000 1,000 440 400 440 100 150 200 200 200 300 500 300 300 300 230 180 210 76 700 50 50 100 100 100 100 100 100 76 80 77 31 100 30 30 50 70 100 100 70 70 71 66 1,600 <10 <10 38 <10 13 13 <10 <10 9.5 24 1,500 15 30 50 20 30 20 30 30 25 24 20 20 20 20 20 30 30 150 70 28 20 300 100 20 20 20 30 20 20 20 24 18 50 15 15 20 15 30 30 30 20 19 19 15 5 5 7 7 10 10 15 10 6.4 7.1 1 <1 <1 <1 <1 <1 1 2 2 .71 .55 3.4 1.1 2.4 1.2 1.2 1.2 1.2 .2 .2 1.3 .86 .05 .06 .05 .02 .13 .24 <.01 .04 .01 .035 .05 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 <.02 (.01) (.01) 10 <10 <10 10 <10 <10 <10 10 10 7.0 7.1 70 20 30 50 30 50 50 50 50 34 30 30 20 20 20 20 30 30 150 150 33 24 20 5 5 10 10 10 10 10 10 7.6 7.5 200 however, were found in detectable amounts in the Skull Creek samples. To provide some standard of compari- son, the numerical limits of detection are shown for scandium and lanthanum and the limits of detection times 0.5 are shown for molybdenum, niobium, and boron. The geometric means of the metal values for samples of altered strata from four different localities, A, B, C, and E, are significantly higher than the Moenkopi MG values. In terms of the factor by which the metal values at each locality exceed, on the average, the Moenkopi Me, the localities are ranked as follows: locality C, 2.5; locality B, 2.1; locality A, 1.9; and lo- cality E, 1.6. Locality C ranks first in metal content of its samples, as shown above, and it is also the area where the color of all Moenkopi Formation strata is completely altered to greenish-yellow. Localities C and B have the highest mean mercury(A) values (2.0 ppm). Localities A and E, on the other hand, have mean mercury(A) values of only 0.05 ppm. The geometric means of the analyses of 17 samples representative of the Gartra Member in outcrops between localities A and C are also compared graphic- ally (fig. 13) with those of the Moenkopi Ma. The Gartra as a whole contains neither significantly more nor significantly less of the metals than the Moenkopi MG with the exception of calcium content, which is significantly lower; iron, titanium, zirconium, vana- dium, and chromium are notably (two to four times) higher; these differences suggest less calcite cement and more detrital minerals in the Gartra in the Skull Creek area than the average for the Moenkopi Formation in the Colorado Plateau. Mean mercury(A) content is significantly lower in the Gartra. Compared with samples of altered Moenkopi from localities A, B, C, and E, the Gartra tends to contain significantly lower calcium, magnesium, manganese, nickel, cobalt, and silver(A) but contains approximately the same average amounts of the other metals. Boron and lanthanum averages are well above their detection limit in all groups of Skull Creek samples. The Gartra Memberl samples have maximum values of 20,000 ppm for ironl, 5,000 ppm for chromium, and 3,000 ppm for barium. Siliceous (jasperoid) con- cretions in the Gartra contain as much as 5,000 ppm barium and 1,000 ppm strontium. Geometric mean values for 24 out of the 25 metals in the 36 samples from the cupriferous zone (fig. 14) l4 GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO R. 101 W. R. 100 W. \ \\ Malachite showings ‘ area / . / Zh—I EXPLANATION Contact Dashed where approximately— located and covered by thick allum’um in stream gaps W l / / 0 $é 1 MILE l I I ZU1-l \ FIGURE 11.——Sampling traverse at locality C (see. 31, T. 4 N., R. 101 W.), malachite showings at locality D (sees. 18 and 19), and sampled area at the Gartra prospect (sec. 20). J‘fi g, Glen Canyon Sandstone; Tic, Chinle Forma- tion; 'Ema, altered Moenkopi Formation (greenish gray or yellow); “Fm, Moenkopi Formation (reddish brown); P lew, Park City Formation and Weber Sandstone. GEOCHEMICAL STUDIES ‘ 15 ZUI—I PIPpw Zb—l 20 ppm U O l 1 MILE | FIGURE 12.—-—Samp1ing traverse (sec. 10, T. 4 N., R. 101 W.) at Lone Mountain. J‘E g, Glen Canyon Sandstone; ‘Ec, Chinle Formation; T! m, Moenkopi Formation (reddish brown); ‘fima, altered Moenkopi Formation (greenish gray); PIP pw, Park City Formation and Weber Sandstone. (all samples collected in previously described horizontal traverses) are higher than those of the Moenkopi MC. The geometric means for the cupriferous zone samples are significantly (at least four times) higher for copper- (A), copper, vanadium, nickel, silver(A), cobalt, and chromium. The 25 Gartra prospect samples (fig. 14) are, on the average, notably higher than the Moenkopi MG in nickel, beryllium, vanadium, cobalt, silver(A), and gold(A). The most remarkable aspect of the Gartra prospect samples is the high chromium, the geometric mean of which—about 620 ppm—is more than 27 times the Moenkopi Ma. The maximum value for chromium is 10,000 ppm (1 percent); for vanadium, 2,000 ppm; for gold(A), 1.5 ppm; and for silver(A), 22 ppm. High chromium-bearing samples in the prospect area consist of green or fairly bright greenish-yellow soft clays. An exploratory cross-country traverse (not shown on fig. 3) was made from south to north starting at the mouth, of East Rock Wall Draw (NEM sec. 5, T. 3 N., R. 101 W.) and ending on the eroded surface of the Weber Sandstone nearest the southern scarp (NW% sec. 28, T. 4 N ., R. 101 W.).' Grab samples collected on the traverse contain evidence of general mineraliza- tion; for example, partly altered sulfide joint fillings in the Glen Canyon Sandstone in the creek bottom con- tain as much as 2,000 ppm arsenic, and black sandy concretions in the canyon walls contain as much as 5,000 ppm manganese. Calcareous veinlets in both red and altered green siltstone in the top of the Chinle Formation exposed in a small window in the bottom of the draw show anomalously high metal values—as much as 700 ppm lead, 200 ppm zinc, and 2,000 ppm manganese. Joint fillings of hematite 25 mm thick are abundant in the Glen Canyon Sandstone near where the East Rock Wall Draw joint (fault?) system inter- sects the scarp rim north of the draw. Samples of gouge, however, apparently from the same large fault in the Weber, north of the scarp rim, contain only background, or smaller, metal values. Sulfide concretions in the top of the Weber Sandstone in southeastern outcrops, in the locality C area, con- tain as much as 700 ppm arsenic, 10 ppm silver(A), 50 ppm molybdenum, and 300 ppm zinc. FACTOR ANALYSIS Many geologic factors or causes control the location and proportion of each metal, but it would be difficult to determine each geologic cause and its proportional effect on the mode of occurrence of each of 26 metals. If we can group the metals that have a relatively high correlation of occurrence, then we can begin to get some idea of the major geologic causes that control the oc- currence of identifiable proportions of the metals. Even if grouping the metals does not account for all the variance of occurrence for each metal, general geologic interpretations may still be made on the basis of the determined groupings but with full realization that the groupings account for most of the variance present. Factor analysis is a form of multivariate analysis that evaluates the covariance among a set of variables and groups the variables according to their mutual dependency and the strength of their relationship to common factors. Factor analysis was used in this study to divide the elements into related groups that, on the basis of geologic experience, could be interpreted as representing a series of geologic events. The reader who is interested in gaining more than a cursory understanding of factor analysis is referred to the authoritative text by Harman (1967) and especially to an excellent, but brief, detailed introduction to the subject by Imbrie (1963). Factor analysis (R-mode) was applied to the ana- lytical results for 26 elements in the 36 samples from the cupriferous zone. The first step was the arrange- ment of the values into a 26x36 data matrix. Loga- rithms of the element values were used in the data matrix to normalize the statistical distribution of values for each element. Next, correlation coefficients were computed for all possible pairs of elements to produce a 26 X26 correlation matrix (table 3). The variance in GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO 16 A $536 as 95 $2 33?on NE @3583“: 82:8 8Q magma E 83E, and $2 aw @538: Z .O can 4 85:83 :33an $3 €80 :35 2% E $2850 59¢ wwuoozoo companion 35:0 93 «0 $3832 «.530 we: Sod mmEEsw Ho 35m a now 83.? SN @8938“. EEoEQSM om: domwm: smwuflm 25580 mfi 5 20:3 a ma noswfipoh flex—~82 23 wcsammwafi meEwm mmm 5 £55vo 95% 23 .8 32 oncwozv 2de oEumEow 93 fig @3358 m was .0 .m .< 33:82 as £0558..an oncoog wfi E SE? @381“ 80¢ kuomzoo meEwm «o 833 E 358% 3:32: «0 £39: oEmEomUILmH HEDGE .BEENm mmm 05 .8352 nomodfiucm .vonawfi :oSQSmo—aémfigw NE uwfifiao E wSowuwc no: a3. Ema—cm uawfiwa £5: :oBowawv an «E: n 33?on mwm we: 5 “Emu—om ac: fiSESH £5: Gomuuwuwfl N «vac flushing». 33me $3 as «55,528 £0£E>m unwfiwnm g wm34(> w: EOv—ZMOS. ZO....:-2.~.mm.w.rm(l no wuapiai m N _ m6 mNd mmfio o v m — md mmd E w v N H md o~ w v N ~ m.o m N A m6 mwd A__ A _ A A_A. A _ A:::_A:AA_ A A:::_A:AA_ A A__ A A m 8;, II II 32 8,8. I I, GE 8.8. II «a 8:” IIA II um Eh: I I I1 I ILA/«rim 20.0 I mmdv '33: 2.0 I, I II A¢§< omd II II mm mm.o 5 M; _Z No I II 2L : II II > : I :0 OH I II .3150 My .5 NN II > Mm II uN on IA I II hm OOH I II :2 8H I I I II mm 0: AB own I II II ME 003 II II 0% 00mm \uE 59:505. 32 _Q0xcw02\ wE oncwofixl a: .Qoxcw22\ 0: _Q0x:w02\ mo‘oV I, «0 ooon onEwm : m2aEam wN onEmm ma meEmm MN meEmm 0N 3 wwEEwm LonEo—z E0 MAC—mo 395m U933 39.? “5.32 numbm U232 Bubm .9233 N mam t._005 MG Moenkopi 8900 Fe 5100 Mg 740 Ti 410 Ba 190 Mn 100 Sr 76 Zr 31 V >27 22 Cr .L 13 CMA)‘ 10 (‘u 11 Y 11 Pb 62 Ni 3.8 Co 0.53 Be 0.26 Ag(A)' 0.13 Hg(A 0.016 AuiA)' 2(5.0) Sc 2(10) La 3(2.5) M0 ”(5.0) Nb ‘(1.0) B 0.5 1 2 4 7 0.125 0.25 0.5 1 2 5 ‘ MULTIPLE OF PARTS—PER-MILLION MOENKOPl-MG VALUE 1 Element symbols followed by (A) indicate analytical data obtained by atomic- absorption method. ? Detection limit. Element not sought in the 323 Moenkopi Formation samples. 3 Half of detection limit. Element sought but not detected in the 323 samples. FIGURE 14.—Geometric-mean metal content of cupriferous zone samples and samples from a prospect in the Gartra Member of the Chinle Formation in the Skull Creek area compared with the geometric means (Moenkopi Me) of the same elements in 323 samples representing the Moenkopi Formation as a whole in the Colorado Plateau region. Numbers at left are values in parts per million represented by Moenkopi MG line at multiple 1. the correlation matrix formed the basis for the factor analysis which followed. Factors were taken from the computed reordered oblique factor matrix. Calculations were made by utilizing the US. Geological Survey’s IBM 360~65 computer and available STATPAC programs. Only the first six factors in order of importance were selected for this investigation. These six account for 73 percent of the total variance in the correlation ma- trix. The six factors were selected on the basis of two conventional criteria; only factors with eigenvalues (a measure derived from the factor loadings) of at least 1.0 would be used, and element groupings for the factors should include no single element “groups” in the reordered oblique projection matrix. In this in- vestigation the first eight factors have eigenvalues of at least 1.0, but the seventh and eighth factor groupings contain one or more factors, each consisting of a single element. Beyond factor eight, individual factors in- creasingly are represented by individual metals until, for 26 factors, each is represented by a single metal. The results of the factor analysis are the element groups listed in six columns below. The element at the top of each column coincides with the factor axis, and elements are listed in order of their degree of covariance with the axis element. The elements in brackets are minor elements of the group and occur as major ele- ments, without brackets, in other groups; for example, [Ag], a minor element in the factor 1 group, is a major element, Ag, in the factor 2 group. Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Factor 6 (Alteration (Enrichment (Cements) (Micas) (Sulfates) (Heavy effects) efl‘ects) minerals) Co Hg (A) Ca Be Sr Ti Cr Cu Mn Sc Ba Zr Nb Ag(A) Y [La] [Sc] [B] Fe U Mg [Mg] [Ag(A)l [Fe] N1 Ag [Zr] [Cu] [Mn] V Cu(A) IV] La Au(A) B Pb [Ag] [U] [Yl [Cu(A)l With considerable dependence on the comprehensive work of Rankama and Sahama (1950) and aided by the minor previous experience of the author (Cadigan, 1971a, 1972), each of the factors was interpreted as being related to a geologic cause or event, as indicated. Factor 1 is the most important geologic event, or cause, in terms of its effect on the covariance of the metals. The other factors represent other causes and are listed in order of the importance of their effects on the covariance of the metals. Their relative importance is suggested by the proportion of total variance in the correlation matrix accounted for by each factor and is shown following each interpretation. Interpretations are made on the basis of geochemical relations and mode of occurrence of the major elements in each factor group. Each of the six factors is assigned a title related to a geologic event. The factors are the result of objective mathematical analysis, but the titles are based on interpretations. Factor 1: Alteration efiects—A group of elements similar in constitution and cobalt-nickel ratio to those GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO 18 oooé 3%.. ”rm. 3%. mmo. moN.| omo. wow. 871 owm.l gm. ohm. 5mm. :o. wow. wow. «mm. wNo. mo“. wNv. now. 23. | o: . wow. 1. mmfi. oov. ...... D D oooé oak. own. mm~.| hou.l Moo.| and. NS. awH.l o3. wmo. ooo. oNN.| HE. mv~.| wmo. Hmo.| owm. ohm. owfi. ma”! omo. Hom.| va.| o3. 11A > ooog o8. "2.1 woof ooo. «3.13:. So.1 woof woof moo. woof $3129 «:1 SN. 23.1»on ...... hm hm oooA moo. moo. fiof59139129189138 «3.1%?128138 so. moo. o2. ooo. ...... am am ooog so. SH. $9134.. «3. mod SN. 391 m3. wow. «5.1 EN. 891 o3. own. ..... on .3 8o; oz. now. won. «.3. owo. 3m. 25.1 so. So. 5. owo. «.21 E: «.3. ...... E 2 So; owo. woo. woo. now. $81 Now. o2. oa. ooo. go. so. woof Nov. ..... n2 n2 ooog so. 31 mow. mom. «2.1 mom. So. moo, How. «on. «5.. mg. ..... 3 3 8o.” N813“. «.2. EH. 3%.. oow. 5H1 mom. 29123.1 moo. ..... so so oooA ooh. on. moo. mom. 291 So. So. now. to. woo. ..... .6 6 oooA o2. «a. 5m. oom. oom, woo. m3. out moo. ..... oo 8 So; 891E. «2.1 5.1 So. 2&1 EN. «2. ..... om am So; so. go. now. HS. NS. woof o2. ..... am am ooog mom. «3. mow. $5.1 mow. o2. ...... m ||m11ooo4 woof «:1 o:.1 :2. 5H. ..... u< u< oooA moo. HE. wow. so. ..... :2 la ooog moo. vow. o5. ...... a. E. oooA own. v3.1 ..... no no oooA own. ..... mg a: .oooA ..... oh oh 2g oeuwfiofiooo £85 33am 2: 28¢ 332$” mm. 2.» 3:2:3» 8:88: am 3.x. $33 Ho moxowomovoo $8.328”. .3 8.22:: 2: E23 @3358» wooSBEvoDlum mamfih GEOCHEMICAL STUDIES ‘ 19 found in metal-rich veins that occur in granite, peg- matite, or other silicic rocks was probably derived from a granitic source and transported by migrating solutions during an event, the final phase of which resulted in the widespread but stratigraphically c0n- fined alteration in the Moenkopi Formation in the Skull Creek and adjacent areas. Percentage of total variance accounted for by factor 1 is 25. Factor 2: Enrichment efiects.—A group of metals typical of copper-uranium deposits in the area of study and in the Colorado Plateau region was probably the result of interaction between reducing solutions in the green Moenkopi altered zone and metal-bearing solutions (sulfates, bisulfates, bicarbonates) in equi- librium with the oxidized rocks of the red Moenkopi. The factor 2 group represents the heavy metals most susceptible to leaching and transport as salts; thus, segregation or grouping occurred during the leaching phase, not during the reduction-reaction phase which produced the metal-enriched cupriferous zone. The enriched zone then is composed of metals that were oxidized and separated from the metals introduced by circulating (hydrothermal?) solutions and then in small part recaptured by the reducing environment at the reduction-oxidation interface in the Moenkopi. Per- centage of total variance accounted for by factor 2 is 18. Factor 3: Sedimentary carbonate cements.~A group of elements related to the occurrence of carbonate ce- ments in the samples. The [Zr] covariance is probably the indirect effect of positive correlation between carbonate content and the proportion of fine sediment which is in turn positively related to zircon content. Percentage of total variance accounted for by factor 3 is 11. Factor 1,: Sedimentary micas and clays.—A group of elements related to the presence of micas and their hydrolyzate alteration products in the samples. Per- centage of total variance accounted for by factor 4 is 8. Factor 5: Interstitial precipitated sulfates.—Elements which commonly occur in detrital sediments as sulfate precipitates from interstratal solution. The covariance with [Ag(A)], [Cu], and [V] suggests a similar method of deposition for fractions of these metals. Percentage of total variance accounted for by factor 5 is 6. Factor 6: Sedimentary heavy mineral deposition.— Sedimentary processes that control the occurrence of elements which are closely associated with heavy minerals. Percentage of total variance accounted for by factor 6 is 5. Each of the elements listed in the correlation matrix (table 3) has a positive, negative, or zero relationship to each of the factors. The relationship may be stated in terms of the proportion of variance accounted for by the six factors combined. For example, the six fac- tors account for 0.84 (84 percent) of the covariance of iron with other elements. This figure, 0.84, is called the communality. A list of communalities is given in table 4. If the 0.84 is assumed to be the total amount of positive association of iron among the six factors, and if we reduce it to proportions in percent in which 0.84 is 100 percent, then the proportion of positive association (covariance) of iron with each of the six factors is as. follows: factor 1, 81 percent; factor 2, negative; factor 3, negative; factor 4, zero; factor 5, 2 percent; and factor 6, 17 percent. Proportions of negative covariance could also be computed but would have limited geologic use beyond indicating only an antipathetic relationship between a particular element and a particular factor. This indication can be made by merely showing that a negative relationship exists. Continuing with the example for iron, 81 percent of its occurrence in the six factors is related to the al- teration event, 17 percent is related to proportion of detrital sedimentary heavy minerals, and 2 percent is related to the proportions of interstitial sulfate minerals. The covariance of the other metals is similarly explained in table 4. Note that only 0.50 of the co- variance of gold appears to be related to the six factors. Sixty-one percent of the positive covariance of gold is related to the enrichment effects (factor 2), 25 percent is related to carbonate cements (factor 3), and 14 percent to the detrital heavy minerals factor (factor 6). TABLE 4.—Proportion, in percent, of positive covariance of each metallic element with each factor [Communalities indicate proportion of total covariance of each element accounted for by all six factors. Axis elements are in boldface type. (——)indicates that the covariance is negative between element and factor] Factor 1 Factor 2 Factor 3 Factor 5 Factor 6 Element (Altera— (Enrich- (Ce- Factor 4 (Sul— (Heavy Commu- tion ment ments) (Micas) fates) min- nality effects) effects) erals) Fe__-___- 81 (—) (—) 0 2 17 0.84 Mg ______ 9 2 39 31 (—) 20 .73 Ca ______ (—) (—) 100 0 0 (—-) .89 Ti _______ (—) 0 0 (—) (—) 100 .84 Mn ______ 4 (—) 70 0 13 13 .75 Ag ...... 43 57 (—) (—) (—) (-) .71 B _______ 46 10 (—) (—) (—-) 44 .59 Ba ______ 12 1 (—) (—) 75 12 .73 Be ______ 0 (—) 0 100 (—) 0 .82 Co ______ 100 0 0 (—) (—) 0 .85 Cr _______ 91 (—) 4 0 2 3 .82 Cu ...... 3 84 (—) (—) 13 (—) .84 La ______ 41 (—) 29 30 (—) (—) .54 Nb ______ 89 (—) (—) (—) 11 (—) .58 Ni _______ 81 (—) (—) 11 (—) 8 .82 Pb ______ 41 31 (—) 6 13 9 .62 Sc _______ (—) (—) 9 50 35 6 .54 Sr _______ 0 0 (—) 0 100 (—) .71 V _______ 62 20 (—) (—) 17 .71 Y---.‘-__ 32 2 40 10 16 (—) .82 Zr _______ (—) (—) 41 (—) 2 57 .66 Au(A)_,_ (—) 61 25 (—) (—) 14 .50 Hg(A)__ — 100 0 (—-) (—) 0 .82 Cu(A)_,- 19 64 (-—) (—) 17 (—) .82 Ag(A)___ 4 74 . (—) (—) 22 (-—) .75 U ——————— 41 59 . (-) (~)‘ (-) (-) .74 20 GEOCHEMICAL ANOMALIES AND ALTERATION, MOENKOPI FORMATION, SKULL CREEK, COLORADO Comparison of the communality for gold with those of the other metals indicates that gold has the lowest degree of involvement of any of the metals. To support this statement, when seven factors are selected instead of six, gold becomes a separate factor and increases its communality to 78 percent. Each of the axis elements (p. 17), cobalt, mercury(A), calcium, beryllium, strontium, and titanium, by mathematical definition has positive covariance (100 percent) with only one factor. Relationships to other factors either are zero or are negative. The percentages of positive association in table 4 are of some interest. For example, 70 percent of the manga- nese is related to cements. Lanthanum with a com- munality of only 0.54 is split three ways~41 percent in alteration effects, 30 percent in micas, and 29 per- cent in cements. Boron is almost equally split between the extrinsic alteration-effects factor and the intrinsic heavy-minerals factor with a small proportion of asso- ciation with the enrichment-effects factor. SUMMARY AND RECOMMENDATIONS The geochemical evidence derived from the brief investigation of anomalous metal occurrences in the Skull Creek anticline suggests that the anomalies are the effects of a regional alteration event of possible hydrothermal origin. The recognized effects, in sum- mary, are: 1. The area-wide altered strata in the Moenkopi Formation with an accompanying persistent copper-enriched zone. Though the altered strata were studied only in the Skull Creek anticline, they were also observed in exposures immediately east and west of the anticline. 2. The significantly higher average metal content in altered and unaltered rocks of the Moenkopi in the vicinity of Skull Creek as compared with that of the Moenkopi Formation as a whole in the Colorado Plateau region. 3. The copper-uranium-vanadium ore deposit in the base of the Curtis Formation. 4. Anomalously high mercury values found in the Moenkopi Formation and Glen Canyon Sand- stone in the southern (10c. B) and eastern (loc. C) parts of the scarp adjoining Skull Creek and Miller Creek water gaps. The highest average mercury values occur at locality C where the Moenkopi is completely altered. Mercury geo- chemical dispersion patterns are characteristic of hydrothermal mineralizing activity. 5. Anomalous values of gold, chromium, silver, and vanadium in the Gartra Member prospect in the northeast corner of the anticline area. 6. Anomalous values of arsenic, lead, zinc, manganese, and silver in observable sulfide minerals in joints in the Glen Canyon Sandstone and Chinle For- mation, in concretions in the East Rock Wall Draw area, and in concretions in the Weber Sandstone in the southeast corner of the anticline area. 7. The two major factor groups in the Moenkopi cupriferous or metal-enriched zone—a cobalt- chromium-niobium-iron-nickel-vanadium-lantha- num-boron-lead covarying suite of metals, and a mercury-copper-silver-uranium-gold covarying suite. These groups suggest (1) an invasion of the Moenkopi by solution-borne metals and (2) interaction between solutions in the reducing (altering) environment characterized by green rocks and solutions in the oxidizing environment of unaltered red rocks above. This red-green contact, the loci of the enriched zone, could have been a mobile interface which moved upward in the section to occupy different levels at different times and to leave traces of previous positions as indicated by isolated weak cupriferous zones. Major questions left unanswered are: What was the source of the metal-bearing solutions? Did this activity produce only trace mineralization over a wide area, or do the anomalies reflect the presence of economically significant deposits at depth? The samples collected in this reconnaissance study establish the area as anomalous in terms of metal oc— currences, but they do not yield data adequate to define the regional dimensions of the anomalies. Trends are suggested but not defined. Mineralization occurred in both stratigraphically controlled and structurally controlled loci. The following questions provide a starting point for any additional work that may be done in the area. Are the altered strata of the Moenkopi Formation a sulfide zone at depth, particularly southeast or east of locality C? Does sulfide mineralization in joints or faults in East Rock Wall Draw persist, disappear, or increase at depth? What happens to the unusual mineralization in the Gartra prospect beyond the face? What is the nature of the Curtis-Entrada contact to the east and south at depth, and does it appear to have a potential for addi- tional ore deposits in one or both of these directions? Are there even more anomalous metal occurrences in similar horizons and structures exposed to the east and west of the reported anomalies? These questions can best be answered by a program of detailed mapping and intensive geochemical ex- ploration, perhaps coupled with drilling, in the Skull Creek anticline area as a whole and particularly in the areas along the scarp between localities B and D. REFERENCES CITED 21 REFERENCES CITED Cadigan, R. A., 1969, Distribution of mercury in the Navajo Sandstone, Colorado Plateau region, in Geological Survey research 1969: U.S. Geol. Survey Prof. Paper 650—B, p. B94-B100. 1971a, Geochemical distribution of some metals in the Moenkopi Formation and related strata, Colorado Plateau region: U.S. Geol. Survey Bull. 1344, 56 p. —— 1971b, Petrology of the Triassic Moenkopi Formation and related strata in the Colorado Plateau region with a section on Stratigraphy, by J. H. Stewart: U.S. Geol. Survey Prof. Paper 692, 70 p. Cadigan, R. A., and Stuart—Alexander, D. E., 1972, Geochemical factor analysis of intrusion breccia and reconstituted rocks of Mule Ear diatreme, San Juan County, Utah, in Geological Survey research 1972: U.S. Geol. Survey Prof. Paper 800—B, p. B125—B135. Cochran, W. G., 1953, Sampling techniques: New York, John Wiley and Sons, Inc., 330 p. Erickson, R. L., Marranzino, A. P., Oda, Uteana, and Janes, W.W., 1964, Geochemical exploration near the Getchell mine, Humboldt County, Nevada: U.S. Geol. Survey Bull. 1198—A, p. A1—A26. Harman, H. H., 1967, Modern factor analysis (2d ed. revised): Chicago Univ. Press, 474 p. Huffman, Claude, Jr., 1968, Copper, strontium, and zinc content of U.S. Geological Survey silicate rock standards, in Geo- logical Survey research 1968: U.S. Geol. Survey Prof. Paper 600—B, p. B110—B111. Huffman, Claude, Jr., Mensik, J. D., and Rader, L. F., 1966, Determination of silver in mineralized rocks by atomic- absorption spectrophotometry, in Geological Survey research 1966: U.S. Geol. Survey Prof. Paper 550-B, p. B189~B191. Imbrie, John, 1963, Factor and vector analysis programs for analyzing geologic data: Office of Naval Research Geography Branch Tech. Rept. 6, ONR Task No. 389—135, Contract Nonr 1228(26), 83 p. Isachsen, Y. W., 1955, Uranium deposits in the Skull Creek and Uranium Peak districts, northwest Colorado, in Intermtn. Assoc. Petroleum Geologists Guidebook 6th Ann. Field Conf., northwest Colorado, 1955: p. 124—125. McDougald, W. D., 1955, Wagon drilling in the Skull Creek area, Mofi'at County, Colorado: U.S. Atomic Energy Comm. Rept. RME~80 (pt. 1), Tech. Inf. Service, Oak Ridge, Tenn., 15 p. Miesch, A. T., 1967, Methods of computation for estimating geochemical abundance: U.S. Geol. Survey Prof. Paper 574—B, 15 p. Myers, A. T., Havens, R. G., and Dunton, P. J., 1961, A spectro- chemical method for the semiquantitative analysis of rocks, minerals, and ores: U.S. Geol. Survey Bull. 1084—1, p. 207—229. Poole, F. G., and Stewart, J. H., 1964, Chinle Formation and Glen Canyon Sandstone in northeastern Utah and northwestern Colorado, in Geological Survey research 1964: U.S. Geol. Survey Prof. Paper 501—D, p. D30—D39. Rankama, K. K., and Sahama, T. G., 1950, Geochemistry: Chicago Univ. Press, 912 p. Ritzma, H. R., 1956, Structural development of the eastern Uinta Mountains and vicinity, Colorado, Utah, and Wyoming, in Am. Assoc. Petroleum Geologists, Rocky Mtn. Sec., Geol. Rec., 1956: p. 119—128. Rocky Mountain Association of Petroleum Geologists, 1941, Possible future oil provinces in Rocky Mountain region: Am. Assoc. Petroleum Geologists Bull., v. 25, no. 8, p. 1469—1507. Saukov, A. A., 1946, Geokhimiya rtuti [The geochemistry of mer- cury]: Acad. Sci. USSR Inst. Geol. Sci. Trans. 78, Mineralog- Geochem. ser. 17, 129 p. 'Schell, E. M., and Yochelson, E. L., 1966, Permian-Triassic boundary in eastern Uintah County, Utah, and western Mofiat County, Colorado, in Geological Survey research 1966: U.S. Geol. Survey Prof. Paper 550—D, p. D64—D68. Thomas, C. R., McCann, F. T., and Raman, N. D., 1945, Meso- zoic and Paleozoic stratigraphy in northwestern Colorado and northeastern Utah: U.S. Geol. Survey Oil and Gas Inv. Prelim. Chart 16, 2 sheets. Vanderwilt, J. W., 1947, Metals, nonmetals, and fuels, pt. 1, in Vanderwilt, J. W., and others, Mineral resources of Colorado: Denver, 0010., Mineral Resources Board, p. 1—290. Vaughn, W. W., 1967, A simple mercury vapor detector for geochemical prospecting: U.S. Geol. Survey Circ. 540, 8 p. Williston, S. H., 1964, The mercury halo method of exploration: Eng. and Mining Jour., v. 165, no. 5, p. 98—101. U. S, GOVERNMENT PRINTING OFFICE : 1972 O - 475-889 4‘ a " / B {1-13 if Instrumentation Studies of 2: Earth Tremors Related to Geology and to Mining at the Somerset Coal Mine, Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 762 DOCW NTS DEF \p fiENT J -“ 2 l§T3 75H 1 1973 1,., "*3‘wxii Lb: “iii". if"; cvihrauflgu Law»: an I.S.S.E1 Instrumentation Studies of Earth Tremors Related to Geology and to Mining at the Somerset Coal Mine, Colorado By FRANK W. OSTERWALD, c. RICHARD DUNRUD, JOHN B. BENNETTI, JR., and JOHN C. MABERRY GEOLOGICAL SURVEY PROFESSIONAL PAPER 762 The relation of bedrock and surficlal geology, coal mining, anda nuclear explosion to tremors in part of the Grand Mesa coal field, Colorado UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog»card No. 72-600237 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402—Price 70 cents (paper cover) Stock Number 2401-00227 CONTENTS Page Page Abstract _____________________________________________________________________________________ 1 Seismic work in the Somerset district ................................. 9 Introduction ............................ 1 Seismic interpretation ............................................................. 13 Acknowledgments... .............. 2 Effects of nuclear explosions ................................................. 19 Geology ....................................................................................... 2 Conclusions ................................................................................ 23 Coal mining ............................................................................... 9 References cited ........................................................................ 27 ILLUSTRATIONS Page FIGURE 1. Index map of Colorado ................................................................................................................................................. 2—4. Geologic maps: 2. Part of western Colorado ................................................................................................................................ 3 3. Somerset mining district and vicinity .......................................................................................................... 4 4. Somerset mining district and generalized mine workings ........................................................................ 6 5. Photograph of moraine along Hubbard Creek .......................................................................................................... 8 6. Block diagram of field instrumentation system used in Somerset mining district. 10 7. Graph showing frequency response of preamplifiers ............................................................................................. 11 8. Photograph showing arrangement of field instrumentation .................................................................................. 11 9. Graph showing frequency response of FM magnetic tape recorder (storage system) and paper re- corder (real-time system) .................................................................................................................................... 11 10. Schematic diagram of photocell-activated chronograph circuit ........................................... 12 11. Graph showing total elapsed time of the monitoring period and actual recording time ............................... 12 12. Calibration seismogram of station D ........................................................................................................................ 13 13. Graph showing frequency response of the EV—17 seismometer .......................................................................... 14 14—20. Seismograms: 14. First type of tremor, recorded by mobile network ................................................................................. 15 15. Second type of tremor, recorded by mobile network ............................................................................ 16 16. Third type of tremor, recorded by mobile network ................................................................................. 16 17. First type of tremor, recorded by fixed station ______________________________________________________________________________________ 17 18. Second type of tremor, recorded by fixed station ................................................................................... 17 19. Sonic boom from jet aircraft, recorded by fixed station ........................................................................ 18 20. Tremor of long wave train with high-frequency compressional waves and low-frequency late - phases, recorded by fixed station ....................................................................................................... 18 21—23. Semilogarithmic plots: 21. Number of tremors per day recorded by mobile network and at fixed stations, and times when no mining work was being done ......................................................................................................... 19 22. Number of large tremors per day ______________________________________________________________________________________________________________ 19 23. Seismic activity summed for 3-hour periods ............................................................................................. 20 24. Oscillogram of the first motion from the RULISON explosion ........................................................................... 21 25. Oscillogram of calibration signal injected into preamplifier before RULISON explosion ............................ 21 26—30. Seismograms: 26. Shock waves from the RULISON explosion, near Grand Valley, recorded by mobile network. 22 27. Nuclear explosion in Nevada, recorded by mobile network ............................................................... 23 28. Nuclear explosion in Nevada, recorded by fixed station .................... 24 29. Two small earthquakes, recorded by mobile network _______________________________ 25 30. Two small earthquakes, recorded by fixed station ................................................................................. 26 III INSTRUMENTATION STUDIES OF EARTH TREMORS RELATED TO GEOLOGY AND TO MINING AT THE SOMERSET COAL MINE, COLORADO By FRANK W. OerRWALD, C. RICHARD DUNRUD, JOHN B. BENNET’I‘I, JR» ABSTRACT A temporary seismic recording network was operated for about 2 weeks in the fall of 1969 on the ground surface around the Somerset coal mine, in Delta and Gunnison Counties, Colo., to study seismic activity as related to coal mining and geology. Tremors, most of which were small manmade earth- quakes, were recorded both on chart paper and on magnetic tape with sufficient precision that we could locate most hypo- centers within 750 feet of their true position. Nearly all the tremors originated within 1 mile of the actively mined parts of the Somerset mine and between 1,000 feet and 6,000 feet below the mine. Some tremors occurred directly beneath the mine; others occurred along a line west of the mine beneath the intersection of a southeastward-trending zone of steep dip in coal and several northward—trending clastic dikes. The line of tremor hypocenters, which is parallel to and beneath the east wall of the canyon of Hubbard Creek, is probably a result of stresses which, differentially concentrated in the zone of steep dip and the dikes by mining, were released and redistributed as underground mining progressed. The rapid lateral change of overburden stress along the canyon may have induced failures as stresses were redistributed by min- ing. Although the distribution of hypocenters clearly was related spatially to actively mined areas, no direct correlation between the rate of tremor occurrences recorded by the net- work and mining work cycles was observed during the moni- toring period. A fixed station located above the Somerset mine, however, recorded many local tremors, and rates of tremor occurrence detected by it are related to mining work cycles. A nuclear explosion detonated 41 miles northwest of Som— erset during the monitoring period apparently influenced the occurrence pattern of large tremors recorded by the network but did not influence the occurrence pattern of all tremors and did not disrupt the mining. INTRODUCTION Coal has been mined near Somerset, in Delta and Gunnison Counties, 0010., for many years. Coal mine bumps, which are Violent, spontaneous, and destruc- tive bursts of coal and rock from mine ribs, faces, floors, and roofs, are a hazard in the Somerset coal mine (fig. 1). Other failures of mine workings, such as heaving floors, pots (sudden release of inverted cone-shaped masses of coal and rock from roofs), and JOHN O. MABERRY and cave-ins, some of which may be caused by mechanisms similar to those causing bumps, occur in the Somerset mine. The US. Geological Survey began a research program in 1968 to study these mining hazards at Somerset as part of a continuing investigation of geologic factors that influence bumps and other failures of mine workings (Oster- wald and Dunrud, 1966). Most research to date has been done at Sunnyside, Utah; short-term monitor- ing experiments also have been conducted elsewhere in Utah (Osterwald and others, 1971). To aid the program, a continuously recording seismograph, with one vertical component seismom- eter, was installed at Somerset in July 1969. During the first month the seismograph recorded 1,000 small tremors in and around the mine. Conse- quently, an experiment was planned to use a mobile, temporary seismic array to locate hypocenters of these tremors and to study the relation of the trem— ors to geologic features and mining. To obtain the maximum information from the recording experi- ment, we planned to record during a nuclear explosion (project RULISON) scheduled to be deto- nated beneath Battlement Mesa, near Grand Valley, about 41 miles northwest of Somerset (figs. 1, 2). The minimum recording period was to begin 1 week before and end 1 week after the explosion so that any resultant changes in seismic activity in or near the mine could be detected. The Somerset mining district as designated by Lee (1912, p. 67—68) is on the southeast flank of Grand Mesa, a large flat-topped mountain with a maximum elevation of 10,800 feet (fig. 2) that is capped by remnants of Pliocene basalt flows (Yeend, 1969, p. 8). Below the caps of basalt are thick beds of claystone, siltstone, shale, and sandstone of Tertiary age which are weak and are prone to large- scale mass movements; these Tertiary rocks make up much of the upland part of the Somerset district (fig. 3). 2 INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO The Somerset district is about 60 miles east- southeast of Grand Junction (fig. 1). The towns of Somerset and Bowie, both owned originally by coal mining companies, are the only organized set- tlements in the district. Paonia, 9 miles by road west of the Somerset mine, is the residential and business center for much of the area surrounding the district. A paved road, Colorado State Highway 133, con- nects the district with the towns of Hotchkiss and Delta; this highway is partly paved to the east, con- necting the district, by way of McClure Pass, with Redstone and Glenwood Springs. A branch of the Denver and Rio Grande Western Railroad from Grand Junction provides freight service, by way of Delta, to Hotchkiss, Paonia, Bowie, and Somerset, as well as to a few small coal mines. 41°___ _109° __ 107° 105° 103?— (<5 "2: 0 Grand, 0 Junction % Colorado 0° Scmerset oSprings Deltao Pao 1ia bl Gun ‘ A n I ”on R 76am)!” River 0 4O 80 MILES l I 37°—_ Jl_____L__—._|_ ____L__.—J— | 0 /"_‘\ [#‘// N 1 G] d 9 1E R ,,. _ enwoo . 9x9 wfz’ R‘fle ll Springs 0% e5” $0.,” (r11 \92 ~4~ 0?} /Grand Valley ”e \ / Q3’ 0 " Carbondale\° (3‘ (1‘ r/ (1" (f! ’ PROJ ECT X Wu 0 R U LI 80 N /~ 097$“ Y], _.,:,¢// ¢ _, Q‘ q, / ‘C 11b 5 0 ran 54 [A @ fna Redstone. ’0 / McClure Pass Grand Q I Junction //J K 9500 . ‘ \\ \0'14:a @ 39°“ GRAND MESA SOMERSET MINE 5a BOW‘e'V Somerset ./ / Paonia Hotchkiss / X “(36‘ w' Mt. Gunnison 9/ Delta \ 1 O 5 10 15 MILES ._J___l FIGURE 1.—Index map of Colorado. Coal beds in the district crop out along both sides of the North Fork of the Gunnison River, which flows westward at the town of Somerset, and along some of the tributary canyons (fig. 3). The river at Somerset is at an elevation of about 6,000 feet and is 3,800 feet below mountain summits 5 miles to the north. This report describes briefly the instruments in the mobile system, especially those that were modi- fied after similar monitoring experiments were done in Utah (Osterwald and others, 1971). The geology of the Somerset district also is described briefly, particularly as it pertains to coal mining and to seismic activity. Responsibility for aspects of the work was shared by the authors. Dunrud and Osterwald planned the monitoring experiment and set design limits for the instrumentation, and Dunrud located the instru- ment sites. Bennetti designed and modified some of the instrumentation for the particular conditions expected during the monitoring period. Bennetti also supervised the assembly and installation of the equipment, calibrated the entire system, and super- vised its operation. Dunrud determined tremor hypo— centers, calculated ground-motion parameters of the nuclear explosion, and supplied much of the geologic information. Maberry and Osterwald helped install and remove the network and assisted in its operation at times. ACKNOWLEDGMENTS We thank many individuals who directly or indi- rectly aided the investigation. R. M. Case, of the US. Forest Service, gave permission to use National Forest land and permitted us to use the Forest Ser- vice radio network for emergency communications. Russell W. Ramey allowed ready access to lands and facilities controlled by his company at Somerset. Owen Jacobs granted us permission to install signal wires and to locate the recording van and supporting camp on his property in Condemn It Park. Jerome Hernandez and Theron E. Miller worked many long hours under very difficult field conditions to make the study a success. Ray W. Osterwald voluntarily helped to install the system and to remove it quickly because of threatening weather. GEOLOGY Coal, most of which comes from a bed known locally as the Somerset or B bed, is mined at Somer- set from the lower part of the Mesaverde Formation (Upper Cretaceous), a complexly interfingering unit of transgressive and regressive littoral-marine to continental strata. This coal bed is one of five major coal beds contained in an interbedded and lenticular sandstone and shale sequence 250—300 GEOLOGY 3 iIELD ” G :Af F \ l J5 ,, uu . N1 K‘ \4 , -. .;,.<:9_.H 8mm efx’faym H’Cf 0 10 20 MILES | I 1 I l | | FIGURE 2.—Geologic map of part of western Colorado, showing sites of mobile seismic stations (solid triangles) and of RULISON explosion (solid dot). Modified from geologic map of Colorado (Burbank and others, 1935). Kd, Dakota(?) Sandstone, ch, Mancos Shale, and Kmv, Mesaverde Formation, of Cretaceous age; Tw, Wasatch Formation, Tgr, Green River Formation, Tei, intrusive rocks, and Tv, extrusive rocks, of Tertiary age; th, terrace gravels of Quater- nary age. feet thick. This unit, which was termed the lower Johnson (1948). The! Rollins overlies several thou- coal member of the Mesaverde Formation by John- sand feet of Mancos Shale. son (1948), overlies a conspicuous cliff-forming The so-called upperlcoal member of the Mesaverde white to light-yellow-brown sandstone, 150 feet to Formation overlies the lower coal member and re— more than 200 feet thick, that was called the Rollins sembles the lower me} ber lithologically except that Sandstone Member by both Lee (1912, p. 30—32) and the upper is more lenticular (Johnson, 1948). The INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO is 7: _O . ,Lfmanh / OSN Vanna, :0ij me up: 5 GEOLOGY .wmam .muwpcooonz: SE95 was mcofigm $380833 vex—m 33 339: MESS? 6 mung so :05 -nnfimxw ANS .wwaH wauwfiow min .32 .2225 5me 513552 55 .33 532502 3.5qu $me vmwcwucnsv oooJNJ mggm Eomwofiomw .m.D 59G $358; as 93.5mm MEEE ”622:0 o AS: 058 BM 05 «.85 I.. . .. w v . . w w . fl v ._ U m @552.” INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO .wwmm M503 :0 sowamzflnxw n52 .«wmfi .uwmgwfiom «EN .mme “35.5% ”was“: Swsguazc 25.va hwzsw kumwomowo .w.D 89G ammm .mexBB oEE gum—«55w cc.» ”3358sz .8895 .mzofigm gwawEoEmmwm «:83 «EN 238: MEBEm 325% MEEE awmgofiom mo 92: umwflowm 3&2ngme I .w 552nm _ _ _ _ _ _ ._.mm_n_ 000m 000% 000m OOON OOOH o ”mg % ., dd . wuafifiwwfi 3353mm :32 «em 36%.. Sum ooo.m .938 we =o$d>2¢ "m 2st 5 3.8 :32: m nofiwhefi mm L. 3 2 N“ o 3 Na 2 m S S S v m: S m m 3 m m N E w N. H 5:2: .02 5:2: .oZ mo LEO .5595. .«o L39 .8595. “9:4 switwgwm. § 39:39: 98:8: 3V~vfi§§§ ESELLBmv was usSEK .333 33%.»? mfigcmfizt E. .393 Swm 3:5: msbek. 98 89.33:? 9.3.3333: 933$. seat?“ . ‘\ 2§qu :~ .8385: was houswocga .8595. m 33.3% v ouswmm .. . 0 $8 .2; .Emm .qu 38 m. E @2682 GEOLOGY 83 .2; .Eww £3 1.8 m E M555 5 ”Ewan—@2956 wfiaom .«o «24 man 38 o E 3.8 0.3-852 733 r L can Foo m 5 «ohm 50-352 E N38 0 E. 2L: $333.63 38 m § 2:: 33m. 95: avmuwfiow E 933 9935de .39 muwsfiwm 3 Eamon 5.30 33m .w.D >3 mQaE EoC chzauoauw gum. wiawwfiwcw was omwflowu unaouwuwucb .3133 .ztoawfi .O A. and 633.830 .3 um 65.52“— .m .0 .3 hmfloow £8555 quchEmmom €me 5% Eu P m4 3:32 imfiéodfi. x m§§so3 2S»: fiSSB Essmxg :23— ELEGQ 9:2; 8... E8 o E an. 9%: «o 28a rlLlll[|[ wufifiioS $8.3: fiSSve 3.2.833 33%: @233 £35: Kc 83m fifiaauigw Sc 233888. .8... 38 o 9.58: $53; .2220 anbmoflwa cwzaénoficnwm 3.5.952 :55 fioi 3% 3330 111%.. 38a :Sosffiiefi :o 3.3 Lass ssm .mSfiSZoS 36.3: ELSSLQLSSLS ‘3 “39 :31: figs: Sage». 3933.339 :22: fiwwgefi wfiwssubfi 23:3 353.» .22? €8.33 S36§§P§as 32x3 fisfst $338.58 EELS fivfiofi .Lfiwsswkqfi SSS: 32*st 63.32 Ewawfimxoham .uogsoo v was mmwhsmmm Z O _ L. < Z 4. J n_ X m AHVLLHELL SDOHDVLHHO AHVNHELVHO T f \l 013w meocwfi Ex :oEwEhoh $32,6on mo .88.:on magmwndm wfizom i somaaqioh wmzwimwwg we «53‘ .895 was Com—«53h V380 oEO EOXP aoflafigoh gamma? 3h €29.55 3E2 _._. £32550 was $55.88 E636 E0 mummonow $26653 _O 5335a 885m m0 v J snoaommo .wddn was 319 auaoo maooa n 01 . 1d suaooyoH pm) moms-yak; 8 INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO upper is as much as 400 feet thick and includes four coal beds and a thick but lenticular uppermost sand- stone bed. Lee (1912, p. 32—43) called the lower coal member the Bowie Shale Member (marine and brackish-water origin) and the upper coal member the Paonia Shale Member (nonmarine origin) ; however, Johnson (1948) found marine rocks in Lee’s Paonia Shale Member and nonmarine rocks in Lee’s Bowie Shale Member, and consequently he did not use the names. About 1,200 feet of non-coal- bearing lenticular and interbedded sandstone and shale that Johnson (1948) termed the barren mem- ber of the Mesaverde Formation lies above the upper coal member. Many of the sandstones of the Mesaverde Forma- tion in the Somerset district locally contain numer- ous fossils, termed Halymem‘tes major by both Lee (1912) and Johnson (1948), that are actually trace fossils called Ophiomorpha, domicile burrows con- structed by decapod crustaceans in marine sediments of a shallow neritic zone during withdrawal of the Mancos Sea. Other trace fossils found in cursory examinations of the shallow marine Mesaverde rocks below the coal beds include Thalassinoides and Aster- osoma. Large horizontal burrows, thought to be those of Planolites montcmus, and rare gastropod trails of undetermined taxonomy were found in mudstone beds and siltstone beds above the coal zone. These trace fossils, which are similar to those de- scribed from the Mesaverde rocks at Sunnyside, Utah (Maberry, 1971, p. 10-—17, 26—80), probably indicate continental depositional environments. A unit comprising beds of lenticular sandstone, conglomerate, shale, and mudstone of Paleocene age, called the Ohio Creek Formation by Gaskill and God- win (1963), overlies the Mesaverde Formation. Because the Ohio Creek and Mesaverde are lithologi- cally similar, they make a distinctive topographic unit below the Wasatch Formation; consequently, they are shown together in figures 3 and 4. The Mesaverde and Ohio Creek are difficult to separate in the district, particularly Where sandstones are thin or absent at the base of the Ohio Creek Forma- tion. The basal sandstones, where present, are more friable, coarser grained, less calcareous, and lighter colored than the sandstones of the Mesaverde. The basal part of the Ohio Creek rarely contains con- glomerate, but rounded granules, pebbles, and vari— colored chert and quartzite cobbles occur locally in sandstones near the top. The Wasatch Formation, a thick unit of vari- colored claystone and siltstone beds that contain lenses of sandstone and conglomerate of Eocene age, overlies the Ohio Creek (figs. 3, 4). Claystone is the dominant rock type in the Wasatch. Volcanic and plutonic rock fragments, as well as fragments from the Ohio Creek Formation, are common near the base. The abundant volcanic debris in the Wa- satch, including gravels, cobbles, and tutfaceous materials, causes most unpaved roads to become rough, slick, and almost impassable, even for four- wheel-drive vehicles, during wet weather. Quaternary sediments of various types are abun- dant in the Somerset district. Alluvial sands, silts, and gravels fill the valley of the North Fork of the Gunnison River, and remnants of alluvial terraces at elevations up to several hundred feet above the river occur on the valley walls west of Somerset. Highland areas north of the North Fork, where some of the seismic instruments were installed, are covered with thick soil. Slopes are so heavily mantled with colluvium and landslide debris that only a few outcrops can be seen above 7,500 feet elevation. A mass of unsorted debris ranging in size from silt to subangular boulders near the confluence of Hubbard and Willow Creeks probably is part of a terminal or lateral moraine (figs. 3, 5). The base of the mass is at an elevation of about 7,400 feet and is about 120 feet above Hubbard Creek, which flows in a narrow V—shaped gulch entrenched into a broad valley at that point. Although we do not know that the mass is actually till, Pleistocene glaciers reached elevations as low as 5,400 feet on the north side of Grand Mesa (Yeend, 1969, p. 22), and hence they could have reached 7,400 feet on the south side. Thick surficial cover in the district made proper installation of seismometers on bedrock very difficult. Numerous sills, laccoliths, dikes, and other intru- sive masses were emplaced in the coal-bearing rocks after deposition of the Wasatch Formation (Eocene) (Lee, 1912, p. 52—53). The largest of these masses FIGURE 5.—Moraine along Hubbard Creek. Hat near center of picture below large boulder indicates scale. Many boul- ders are striated. SEISMIC WORK IN THE SOMERSET DISTRICT 9 makes up Mount Gunnison, a prominent peak about 7 miles southwest of Somerset. According to Lee (1912, p. 52—56) most of the igneous rocks are quartz monzonite porphyry. The largest mass of igneous rock in the Somerset district is an irregular mafic intrusion several hundred feet thick which is in the barren member of the Mesaverde Formation at Iron Point (fig. 3), high on the west side of the canyon of Hubbard Creek. Small irregular clastic dikes, called rock spars by miners, that were injected into fractures at low temperatures are common in the Somerset mine. A small mass of intrusive breccia was found in the canyon of Bear Creek 1 mile west of Somerset. Geologic structure in the Somerset district is simple. Coal beds at the Somerset mine dip north and northeast at about 500 feet per mile, although a gentle northeast—trending anticlinal nose extends into the north-central part of the district (Johnson, 1948). Neither Lee (1912) nor Johnson (1948) mapped faults; however, several steeply dipping faults occur north and east of the Somerset mine (fig. 3). These faults trend west-northwest to east- northeast and have stratigraphic separations of 5—20 feet. A few steeply dipping faults which trend west- northwest to east and have stratigraphic separations of a few feet offset the coal in the mine. Clastic dikes probably were injected into some irregular fractures of about the same age and trend as these faults. Other faults, which have various dips and trends, occur in the northern part of the mine, in both the B and C coal beds. These faults may be part of a deformation zone around a probable intrusive mass beneath the canyon of Bear Creek (figs. 3, 4). An irregular channel sandstone, called a want by min- ers, truncates the C coal bed along the north limit of the mine, and a zone of steep dip truncates the C bed along the south limit (figs. 3, 4). The zone of steep dip may have resulted from differential com- paction around a thick sandstone-filled channel below the C bed and south of the south limit of the mine. Areas of numerous slickensided fractures are com— mon in coal near the sandstones and locally create hazardous mine roofs. Stresses, probably resulting from differential compaction between the rigid sand- stones and the weak shales and claystones, may have induced movement to cause the slickensides. COAL MINING Underground coal mining began in the Somerset district in 1901, when the Utah Coal Mining Co. opened a mine on a 20-foot-thick seam of bituminous coal (Denman, 1903, p. 93). After the completion of the Denver and Rio Grande Railroad from Delta to Somerset in 1902 (Beebe and Clegg, 1962, p. 374), the mine was shipping about 1,000 tons of coal per day (Lee, 1912, p. 12, 106). All mining in the district has been done by room—and-pillar methods, in which openings (slopes) are driven down the dip of the coal beds. Multiple entries are driven nearly parallel to the strike of the coal beds at intervals of about 500 feet, so that the coal is divided into large blocks several thousand feet long and 500 feet wide (fig. 4). These large blocks then are divided into areas of small, nearly square pillars, most of which are 50 to 60 feet on a side, by driving rooms up the dip of the coal seams from the multiple entries, and by driving small crosscuts between rooms. The rooms are later used as working areas from which the pillars are extracted. During final or “retreat” phases of mining as much of each pillar as possible is removed and the roof is allowed to collapse completely. This col— lapse eliminates accumulation of abutment stress in nearby working areas; if the roof over large mined- out areas does not collapse, large amounts of stress will be concentrated in nearby areas (abutment zones). An attempt formerly was made to keep the pillar lines in the C bed, along which pillars were being removed, slightly ahead of pillar lines in the B bed below, so that roof-control problems in the B bed could be minimized. The need for such coordi- nated work no longer exists because mining ceased in the C bed as a result of large sandstone-filled channels in the coal and of hazards from weak roofs, bumps, and many pots. Most of the mining in the Somerset mine is now done by continuous-miner machines. Methods for- merly used in the district included undercutting the solid coal with hand picks or cutting machines, then blasting or wedging it down (Lee, 1912, p. 94—110). Coal in the Bowie (Juanita) mine which adjoins the Somerset mine to the west (figs. 3, 4), formerly was blocked out by using prominent vertical joints trending N. 70° E. as the face. During mining the coal then “snaps from the face with considerable force in some places,” according to Lee (1912, p. 104), probably because it was under natural stress and was failing by small bumps. SEISMIC WORK IN THE SOMERSET DISTRICT Seismic activity in the Somerset district was stud- ied from August 30 through September 16, 1969, although continuous recording extended only from September 3 through September 16. The instrumen- tation system used at Somerset (fig. 6) was similar to one used to study earth tremors in Utah coal mining areas (Osterwald and others, 1971). Most of the system will not be described again in this report, but modifications in instruments and proce- dures will be described where pertinent. 10 Enclosed in van Battery-powered preamplifier INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO l 6-channel l | paper recorder Amplifier Time-mark unit Electronic 1—7 miles . » /’—‘. —_ ‘ ’ W \ [\K-T" 7 ,;“'— EV—17 "7—~ Seismometer; buried on bedrock chronometer Radio receiver Padder Record 0 electronics 14—channel magnetic-tape recorder Playback electronics I _ Oscillograph Speaker FIGURE 6. — Block diagram of field instrumentation system used in Somerset mining district. The instrument van containing the recording equipment and the supporting camp were located in Condemn It Park (fig. 3). Seven vertical component seismometers, sealed in plastic sacks and buried, were arranged in a triangle having sides of about 4, 5, and 8 miles. We had considerable trouble placing the seismometers on bedrock because of the heavy surficial cover. The seismometer at station A, in Poison Park about 2 miles north-northwest of Con- demn It Park (fig. 3), was on a large landslide mass in the Wasatch Formation. Three EV—17 seismom- eters were located along a county road in Hubbard Creek canyon southwest of Condemn It Park, and three others were placed along a pack trail extending southeast from Condemn It Park to Thousand Acre Flats (fig. 3). A vertical component Willmore seis- mometer was installed at station E (fig. 3) on the north slope of Pilot Knob, about 21/; miles southeast of Condemn It Park. The size and configuration of the array was necessary to give sufficient length and breadth that seismic waves reflected or refracted from deep layers could be detected. The triangular array thus enclosed most of the Somerset mine area. Signals from all the seismometers were boosted by battery-powered transistorized preamplifiers sim— ilar to those used in Utah (Osterwald and others, 1971). Circuitry was added to some of the preampli- fiers so that the normal voltage gain of 7,500 could be lowered easily and rapidly to 0.5 at station B, to 2.5 at station C, and to 50 at station F (fig. 3) simply by moving the input plugs to different sockets. This was done so that the seismic waves from the nuclear explosion could be recorded properly by selected sta- tions in the network and so that the remaining stations could still retain the capability of recording small earth tremors before and after the explosion. The locations for variable-gain preamplifiers were selected so that the direct seismic energy entering the mine could be compared with that coming out. Frequency response of the preamplifiers is shown in SEISMIC WORK IN THE SOMERSET DISTRICT 11 1.0— \: ask _ 9 ’: z 3 o 0.6 _ ._ D Lu N I: < 0.4 — _ S K o E E 0.2— _ < w 0 | l l | vl I 0 1 2 200 300 400 500 600 FREQUENCY, IN CYCLES PER SECOND FIGURE 7. -— Frequency response of preamplifier. figure 7. Signals from the preamplifiers were trans- mitted to the recording van by military-surplus twisted-pair telephone wire (assault wire). The pre- ‘ amplifiers were powered by nickel-cadmium 15-volt battery packs. Oscillatory signals were emitted from the pream- plifiers during some very heavy rains (fig. 26, trace E). These oscillations probably resulted from elec— trical ground paths created by water leaking into seismometer cases (although they were sealed in plastic sacks and buried). Other ground paths re- sulted from water leaking into splices in the signal .wires and from spots along the wires where sheep had eaten the insulation. Signals were split inside the recording van, so that paper and magnetic-tape records were obtained si- multaneously (Osterwald and others, 1971) for six of the seismometers. Seismometer G (fig. 3) re- corded only on magnetic tape. The various compo- nents in the instrument van were arranged as shown in figure 8. The tape-recording system was changed, however, from our earlier system. Time signals from National Bureau of Standards radio station WWV were recorded with a direct-record system; all other channels were recorded on an FM-record system. Frequency responses of the storage (tape) and real-time (paper) recording systems are shown in figure 9. The storage system consists of the seismom- eters, preamplifiers, tape recorder, and light-beam oscillograph; the real-time system consists of the FIGURE 9.—-Frequency responses of the two recording sys- tems. Curves were derived by experimentation with the systems before they were used in the field monitoring. A, FM magnetic tape recorder (storage system). B, Paper recorder (real-time system). FIGURE 8.—Arrangement of field instrumentation in van. a, power supplies; b, 6-channel paper recorder; c, padders; d, time-mark unit; e, WWV radio receiver; f, FM and direct-record electronics; g, power supplies; h, playback electronics: 1', magnetic tape recorder; j, oscilloscope; k, oscillograph; l, audio amplifier for WWV. Electronic chro- nometer not shown. 1.5 cps A / B" o o OUTPUT (NORMALIZED T0 UNITY) O 300 O b-‘_._ O 50 100 FREQUENCY, lN CYCLES PER SECOND 12 Potter Brumfield KCP 11 —_'-+ 15 T_VDC 2N2219 To recorder Photocell Second hand of GE—44 battery-driven clock Lamp 115VAC 6.3m a E FIGURE 10. — Schematic diagram of photocell-activated chro- nograph circuit. seismometers, preamplifiers, pen-drive amplifiers, and electric—writing recorder. By using the storage system, tremors could be replayed on an extended (faster) time base; as a result, a high degree of resolution was obtained in determining arrival times of tremors. The real-time system served as a guide 'in recovering specific events from the storage sys— tem, because both systems were synchronized with National Bureau of Standards radio station WWV in Fort Collins. Time marks were placed on the paper records every minute by a chronograph consisting of <— Tape recorder off for system calibration INSTRUMENTATION STUDIES OF‘ EARTH TREMORS, SOMERSET COAL MINE, COLORADO a battery-powered clock regulated by tuning fork. A small vane on the second hand of the clock inter— rupted a light beam focused on a photocell control- ling a relay which, when energized, closed a circuit to mark the record (fig. 10). The recording equipment ran on 60-cycle 115-volt single-phase electric power, provided by a 15-kilo- volt-ampere gasoline—powered generator unit mounted on a trailer, which also supplied power for the supporting camp. Voltage was maintained auto- matically; frequency was manually adjusted to 60 cycles by the throttle and was maintained between 59 and 61 cycles by a governor control on the throttle. Occasional governor malfunctions caused us to man- ually readjust the automatic voltage controls. Recording equipment was operated 24 hours a day during most of the monitoring period, except for brief periods when the electric-power generator was shut down for servicing. The instrument van was occupied 24 hours a day, and the operation of the instruments, the output voltage, and the frequency of the generator unit were checked every 4 hours. Recording time was about 95 percent of the total elapsed time (fig. 11). We had considerable difficulty with the electronic equipment because of erratic elec- trical ground paths caused by excessive rainfall which intermittently grounded the generator trailer and instrument van, as well as the signal wires. Thousands of sheep were grazing in the district at the time; they caused innumerable breaks, shorts, and grounds in the signal wires; as a result, various seismometers were not recording part of the time. Each seismometer installation was calibrated with its corresponding recording channel by injecting a 10-cps (cycles per second) signal from an oscillator into the input of the battery-powered preamplifier. The amplitude of the input signal was suflicient to obtain a 5—volt peak-to-peak signal at the output of C 3 O E E s E a f”. a 3: t a .3 *5 g s o o 13 w s ,2 a s a 8 E ‘5 ° ‘5 E E 9 L“ 2 ‘5 e g g a g 3 a $ <5 <5 12 w I I | I I I I I I I I I I—l—ir'l—F-J—I 12M 12M 12M 12M M M M M M M M M M M M M M September 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1969 FIGURE 11. —Graph showing total elapsed time of the monitoring period and actual recording time. M, midnight. SEISMIC INTERPRETATION 13 the preamplifier, as measured with a battery—powered oscilloscope. After connecting each preamplifier to the signal wires and to the recorders, the amplitude of the calibration signal from each channel, as re— corded in the instrument van, was adjusted with variable attenuators to 20-mm (millimeters) peak— to-peak on paper records of the real-time system (fig. 12). The calibration signals also were recorded on magnetic tape in the storage system, and the output of the playback electronics units (figs. 6, 8) was adjusted to yield an amplitude of 25 mm on the light-beam oscillograph. Both systems were cali- brated similarly before the nuclear explosion. Dur- ing all calibrations the output and frequency response of each seismometer were assumed to corre- spond to manufacturer’s specifications (fig. 13). Frequency response of the storage system was deter- mined by the seismometers on the low—frequency end and by the tape recorder on the high-frequency end. The recording procedure was similar to that de— scribed previously (Osterwald and others, 1971). Arrival times of tremors were indexed on the paper records; individual tremors were located later on the magnetic tape by listening to the voice and Interna- tional Morse code time announcements from WWV. Tape records of the tremors then were played back at a fast-time base on the light-beam oscillograph (fig. 8), which used a direct-writing light-sensitive paper that required no liquid processing. Timing lines were placed photographically on the paper every 0.01 second and 0.1 second; millisecond timing thus could be interpolated when necessary. Ground velocity of recorded waves was obtained by compar- ing measured deflections on the records with the deflections from the calibration signals and with the manufacturer’s specifications for the seismometers (fig. 13). SEISMIC INTERPRETATION Hypocenters of tremors were located in the field by measuring on the oscillograms the times of arrival of the first seismic waves detected by each seismom- eter and of the next clearly defined wave groups. A graph then was constructed for each tremor in which first-arrival times at each seismometer were plotted on the horizontal axis and the difference in arrival times between the first waves and the next clearly FIGURE 12.—Calibration of station D in real-time (paper) recording system, obtained by injecting a 10-cps 5-volt peak-to-peak signal into the signal line at station D with a battery-powered oscillator. The variable attenuator in the instrumentation van was then adjusted to get a 20-mm signal on the real-time (paper) recorder, and the galva— nometer driver amplifiers were adjusted to give a 25-mm signal amplitude on the oscillograph. 476—247 0 - ’72 — 2 defined wave groups were plotted on the vertical axis. On the assumption that both wave groups were gen- erated simultaneously at a point source, a line was drawn connecting corresponding points plotted for different seismometers which, when extended to the 12:20 pm. M... .a.-....w~.-..,v. . .. m', ~,“ H 4 INSTRUMENTATION STUDIES OF H O U! l I .— l i Damping: 0.7 critical 9 m | l | l 1 10 100 FREQUENCY, IN CYCLES PER SECOND OUTPUT, IN VOLTS PER INCH PER SECOND .0 _. P ... FIGURE 13. —— Frequency response of the EV—17 seismometer, manufacturer’s specifications. horizontal axis, yielded an approximate origin time for each tremor. Traveltimes of the waves to each seismometer were determined by subtracting the arrival time of the first wave (compressional) at each seismometer from the graphically determined origin time. A protractor specially designed for geologic condi- tions in the Sunnyside district of Utah was used to determine the hypocenter (map position and focal depth) of each tremor source (Osterwald and others, 1971). Geologic conditions in the Somerset district are sufficiently similar to those at Sunnyside to per- mit use of the protractor in both places. Use of the protractor to determine hypocenters in the Somerset district was very successful, because intersections from six stations sometimes matched to within 0.01 second on the traveltime curves. Within the district, hypocenters of tremors large enough to be measured on the seismograms probably were located within 1,000 feet of their true positions. Focal depths of tremors, for which no refracted waves were recorded, may be in error by a few thousand feet. Magnitudes of recorded tremors were estimated by measuring the maximum amplitude of compres- sional waves on the oscillograms and the paper rec- ords. The amplitudes then were compared with the amplitudes of paper records from the fixed seismo- graph station at the Somerset mine; magnitudes from the fixed station were determined by compari- son with records of earthquakes of known magni- tude. Magnitudes were further checked by dividing the oscillogram-trace amplitude by 2 and comparing the result with distance-versus-magnitude curves drawn for tremors in the Sunnyside, Utah, district which are detected and recorded by similar equip- ment. Tremors recorded in the Somerset district EARTH TREMORS, SOMERSET COAL MINE, COLORADO varied up to 2.7 in estimated magnitude. Compres- sional-wave or body-wave magnitudes (m) such as we used are related to Richter magnitude (M) (Richter, 1958, p. 340—345, 348—349) according to the following equation (Davies, 1968, p. 25) : m:2.5—|—0.63M. Analyses of seismograms from tremors whose waves were refracted from deep stratigraphic levels suggest that an important high-velocity layer exists about 6,500 feet below the Somerset district. This layer is about 2,000 feet nearer the surface than an important high-velocity layer in the Sunnyside dis- trict (Tibbetts and others, 1966, p. D134) ; refracted waves from tremors Whose map position was deter- mined accurately arrived at seismometers about 0.1 second sooner than similar waves in the Sunnyside district. The high-velocity layer at Somerset is of unknown composition but may be an igneous sill because no limestones or other high-velocity rocks are known at that depth from drill records. Between September 3 and September 16, 1969, we operated the mobile recording equipment almost con- tinuously in the Somerset district (fig. 11). During this time 38 tremors were recorded by the mobile equipment; 13 of these occurred within the district and were detected by several instruments, and so hypocenters could be determined (fig. 4). During this same period the fixed station (ELK, figs. 3, 4) at the Somerset mine recorded 517 tremors. Most tremors recorded by the mobile equipment were of local origin, but two resulted from nuclear explo- sions, and three were from earthquakes that origi- nated outside the district. One of the nuclear explosions was near Grand Valley (project RULI- SON) (figs. 1, 2), and the other was in Nevada. At least two of the earthquakes probably occurred near the site of the Rulison explosion, because their wave trains were similar to those generated by the actual explosion. Several sonic booms from aircraft were also recorded. Three types of earth tremors that originated within the Somerset district were recorded by the mobile equipment. The first type consisted of short wave trains that had moderately high amplitudes (fig. 14); these tremors were similar to ones re- corded previously in the Hiawatha and Sunnyside districts, Utah (Osterwald and others, 1971), that we inferred to have originated near the recording sites and to have shallow foci. The second type of tremor consisted of wave trains that were longer and were of higher amplitude and lower frequency than the first type (figs. 14, 15). Several wave-group ar- rivals can be seen in the compressional part of the SEISMIC INTERPRETATION seismograms, and waves in the trains have repeated amplitude peaks, probably resulting from reflec— tions or refractions from deep rock layers. This type of tremor originated farther from the seismometers and perhaps from deeper sources than the first type, because the various wave groups, which travel at different velocities, are separated more than those of the first type. The third type of tremor resulted in seismograms showing wave trains of about the same duration and frequency as the second type but had high-amplitude waves that were preceded by low but increasingly large compressional waves (fig. 16, trace A) ; this type wave produced seismograms that roughly resembled those produced by sonic booms from jet aircraft as recorded by the fixed station (fig. 19). Records from the mobile system, however, which were observed to have been caused by sonic booms, have a much shorter wave train. The origin of the third type of tremor is not known. A fourth type of tremor generated wave trains of about the same duration and frequency as the second type, but late-arriving wave groups had rapidly de- creasing amplitudes. This type of tremor probably originated at deeper levels than the second type but also may have resulted from a different source mech— anism. During the recording period the fixed station at the Somerset mine recorded some of the same types of tremors as the mobile equipment. Seismograms from the fixed station, however, differ in appearance from those of the network because the recorder at the fixed station is operated at a faster speed. Trem- ors of the first and second types (p. 14), when re- corded at the fixed station (figs. 17, 18), showed the wave characteristics, envelope, and frequency much more clearly than when recorded by the mobile equipment. The fixed station also recorded many sonic booms from jet aircraft; these are easily recognized by their long wave train, low-amplitude first-arriving waves, a group of large-amplitude waves arriving next, and long, low-amplitude late waves (fig. 19). An additional type of tremor recorded by the fixed FIGURE 14. —— Seismogram of first type of tremor, recorded by real-time system in the mobile net- work at 10:40 pm. m.d.t. on September 10, 1969 (0440 G.m.t. Sept. 11). Tremor probably had a shallow focus within the Somerset dis- trict and consisted of a short wave train. Let- ters designate seismometers shown in figure 3. Seismometer A was out of service. Time pro- gresses from left to right; l-minute time inter— vals shown by chronograph ticks at top. Hypocenter is No. 4 in figures 3 and 4; magni- tude is 1.9. See also figure 17. 15 station but not by the mobile equipment, consisted of long low-amplitude wave trains that showed high- frequency compressional phases and low-frequency late phases (fig. 20); the origin of this type of / / 10:40 pm. m.d.t. Chronograph 16 INSTRUMENTATION STUDIES OF EARTH l u 7 o - Chronograph/ ' \ 12:56 p.m.m.d.t. 1pm. FIGURE 15. TREMORS, SOMERSET COAL MINE, COLORADO l I I . Chronograph 7:04 pm. m.d.t4 A “l"‘l B ,, . ., v ,C_ 4r FIGURE 16. SEISMIC INTERPRETATION FIGURE 15.— Seismogram of second type of tremor, recorded by the real-time system in the mobile network at 12:56 pm. m.d.t. (1856 G.m.t.) on September 16, 1969. High amplitude and long wave train with successive peaks prob— ably indicate deeper source than tremor in figure 14; waves refracted from successively deeper strata. Letters designate seismometers shown in figure 3. Time progresses from left to right; l-minute time intervals shown by chronograph ticks at top. Hypocenter is No. 11 of figures 3 and 4; magnitude is about 2.7. See also figure 18. FIGURE 16. — Seismogram of third type of tremor recorded by real-time system in the mobile net- work at 7:04 pm. m.d.t. (0104 G.m.t.) on Sep- tember 3, 1969. Letters designate seismometers shown in figure 3. Seismometers C and E were out of service. Time progresses from left to right; l-minute time intervals shown by chro- nograph ticks at top. .1 “.4 , w..-“— ._..’...«-»--- -W. ...._...~—... .1 affi—v‘.” ,.,_,- M .w V41. ,1. “Auk , f ‘ , WM... .,._..-.,.,.. M-._...._._..__ _, .1.” -.. -.. -mw ) 11mg“, _ , ‘. ,t’ ' _ 3'. 1 F,,,._..-,..,._,,.....,.._._ M....,...._,-.,_. M. “rm“.-w...’ ... __,, ...... a x, " ' ' -1 j, __,- .. wwwwmmww,mn No.4 \«1 M; .J/ W, __,,,,._.-,,,,-Mawfimw ~w..-...,...._..,_ .~ MV'W ”MAW!" /. U..._._.~_--_w-_»~-~.MMWM.w-_ 4.. W_.“ > r .. 13,”; fl J- .. km”... W”... ,, - . - : _,,\_ f ’MAM” «3.. Wm“ V www.— a, _ n.0,... . , i a, 5». .. ; 1 .-.w., 4-..».mw I...~.a.~__,...mw-wu _. MW...— .. _’» K ,‘ s. «WM—“Wrw «mewm WW i [I - J. ,I M i L ,w ,’ . g -, . ~__‘ / ~~~~~ s‘ .r‘ , , “‘11 ‘_ / fl/ig-~-- w; / _m..-,-~.wa_ . , .4 W... ., _ I. _ ‘ ; ”3}, ,2 ,._- ,-M,__A_.~.,W.,.M.m..m~wm - - \... N.»- M ; f , - , \ ,5...” .. A - _‘ ,m .. ”A. _. -__,.~,..q..,.sm WW W FIGURE 17. — Seismogram of first type of tremor, recorded by the fixed station at 4:47:40 am. m.d.t. (114740 G.m.t.) on September 3, 1969. Consists of high amplitude and short wave train. Time progresses from left to right. Chrono- graph break on line to left of tremor is 4:47 a.m.; break is of 3 seconds’ duration. Tremor was too small for hypo- center and magnitude to be determined. ’ (gem....vaWywqufl—"V.N.w~w ”V” 3 I .J/Aivvmmmw 5 M-~:\~w~...v,v , , l- V FIGURE 18. —— Seismogram of second type of tremor, recorded by the fixed station at about 12:55 am. m.d.t. (1855 G.m.t.) on September 16, 1969. Consists of high amplitude, long wave train, high-frequency compressional waves, and wave envelope with several peaks. Time pro- gresses from left to right; 1-minute intervals shown by successive chronograph breaks. Hy- pocenter is No. 11 of figures 3 and 4; magnitude about 2.5. 18 INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO FIGURE 19.—Seismogram of sonic boom from jet‘aircraft, recorded by the fixed station at 10:54 a.m. m.d.t. (1854 G.m.t.) on September 16, 1969. Low-amplitude compress sional waves precede a high-amplitude but short wave train. 1-minute intervals shown by successive chonographic breaks. tremor is not known, but the source was probably outside the Somerset district. Of the 13 tremors whose hypocenters could be determined, 12 were within 1 mile of active mining areas of the Somerset mine (figs. 3, 4). Map posi- tions of six tremors (2—4, 11—13) roughly formed a north-northeast-trending line less than half a mile east of Hubbard Creek, adjacent to part of the mine that was being developed actively. This line, perhaps coincidentally, parallels several faults east and west of the Somerset mine. Although no faults were en- countered during mining in this area, three clastic dikes were found on trend with this line of tremors (fig. 4). The foci of these tremors were between sea level and 5,000 feet above sea level, or between 1,000 and 6,000 feet below the mine. Two tremors in the line had the highest magnitudes (2.6 and 2.7) of any natural tremors recorded in the district with the mobile equipment. The line of tremors probably re- sulted from the release and unequal redistribution of stress concentrated near a zone of steep dip in the C coal bed and the clastic dikes, as a result of nearby mining. The zone, probably resulting from compac- tion around a large sandstone-filled channel, com- pacted less than adjacent sections of rock and coal. Thus, a discontinuity was formed in which stress concentrated as a result of removal of overburden support by mining. The zone of steep dip in the C bed (p. 9) also intersects some of the dikes and the line of tremor hypocenters (fig. 4). The line of tremor hypocenters apparently was beneath a zone FIGURE 20. — Seismogram, recorded by fixed station at about 10:18:30 p.m. m.d.t. on September 16, 1969 (041830 G.m.t. Sept. 17, 1969). Tremor has long wave train with high- frequency compressional waves and low-frequency late phases. Source probably was outside the Somerset district, hence hypocenter and magnitude could not be determined. Chronograph break at right is about 3 seconds’ duration. of high abutment stress in nearby active mining areas (fig. 3) that resulted from rapid removal of coal. The line of hypocenters may also have resulted in part from redistribution of stresses beneath the east wall of the canyon of Hubbard Creek, where stress from overburden changes rapidly within short distances. Most other tremors whose hypocenters could be located also occurred within the mining area (figs. ’ 3, 4) and probably resulted directly from stress redistribution caused by mining. Most of these trem- ors occurred near areas in the mine from which pillars were being removed. Such tremors apparently increased in abundance after the RULISON explo- sion, probably as a result of slight increments of energy added to the area by seismic waves from the explosion. Foci of these tremors were 1,000—4,000 feet below the mine workings (from 2,000 to 5,000 ft above sea level). The tremor which occurred about 6 miles north of the mine (hypocenter No. 5, fig. 3) probably was a natural earthquake. The number of tremors recorded each day by the mobile network in the Somerset district varied widely (fig. 21A). The causes of the variations are not known, but the occurrence pattern was somewhat similar to the pattern of tremors per day recorded during the same period in the Sunnyside district, Utah (fig. 213), where many tremors were thought to be related to mining (Barnes and others, 1969), EFFECTS OF NUCLEAR EXPLOSIONS l9 w 100 _— __ 0: : : O — _ 2 I Z ‘52 — _ LJ '— — 2 “- I: o 10 _— z —_ n: - : Lu 2 O _ m — g _ _ _‘ 1 z _ c: _ 1 I | I I I I I I | I J I I 100 _I:— C 10 I I I I I I I J I 12 3 4 5 6 7 8 910111213141516 SEPTEMBER 1969 FIGURE 21. — Semilogarithmic plots of number of tremors per day recorded by: A, mobile network in Somerset mining district. Average number of tremors daily: four during mining, three during idle day, standard deviation 4 each. B, Fixed station near Sunnyside (Bear Canyon), Utah. C, Fixed station at Somerset, Colo. Average number of tremors daily: 41 during mining, 29 during idle day, stan- dard deviations 12 and 5, respectively. D, Times when min- ing work was being done in Somerset mine (shown by black sections). although total numbers of tremors at Sunnyside were much greater (fig. 213). Some of these variations may have resulted because the signal wires connect- ing the seismometer stations closest to the Somerset mine, which were the longest wires in the network, were broken more frequently than the shorter wires. The pattern of tremor occurrence recorded by the mobile network (fig. 21A), therefore, is different from the pattern recorded by the fixed station, which operated continuously (fig. 210). Little relation is apparent between the occurrence pattern of all the tremors recorded by the mobile network and by the fixed station (fig. 210). The rates of occurrence of all the tremors recorded by the mobile network also bear little obvious relationship to times of mining activity in the Somerset mine (fig. 21D), although such relationships between mining and occurrence patterns of tremors were reported for the Sunnyside and Hiawatha districts in Utah during monitoring experiments similar to the one at Somerset (Oster- H O ..a 10 RULISON I I I I 1 2 3 4 5 6 7 8 9 10 11 12 13 SEPTEMBER 1969 A 14 15 16 NUMBER OF LARGE TREMORS PER DAY FIGURE 22. — Semilogarithmic plots of number of large trem— ors per day. A, Natural tremors that were large enough to determine hypocenters, mobile network. B, Times when no mining work was being done (shown by black sections). 0, Fixed station, showing number of tremors whose esti— mated magnitudes were greater than 1.0. Open circles indicate days of recording when no tremor occurred. Days marked at 12:00 noon. wald and others, 1971). The average daily rate of occurrence of all tremors recorded by the fixed sta- tion during the monitoring period, however, was greater on days when mining was done than on days when no mining was done (fig. 23114., C, D). No apparent correlation was found between times of active mining in the Somerset mine during the monitoring period and the occurrences of tremors that were large enough to be detected by three or more stations in the mobile network (fig. 22A, B). The occurrence pattern of such large tremors re- corded by the mobile network (fig. 22A) generally is not similar to the occurrence pattern of large tremors recorded by the fixed station at the Somerset mine (fig. 220), which also shows no relationship to times of mining activity (fig. 223). Small sections of the curves do show some similarities, as should be expected because the seismometers Were measur- ing adjoining areas, but the entire network received signals from a much larger area than did the Somer- set mine seismograph. EFFECTS OF NUCLEAR EXPLOSIONS A 40-kiloton-equivalent nuclear explosion was det- onated 41 miles northwest of the town of Somerset at 3 pm. m.d.t. (2100 G.m.t.) on September 10, 1969 (Gauss, 1969). Before this explosion, which probably was detonated in the lower coal member of the Mesa- verde Formation (US. Atomic Energy Comm., 1969, p. 13), considerable local apprehension had arisen that the shock waves would damage various coal mines in the Grand Mesa coal field (Saile, 1969; Denver Post, 1969). We hoped to measure the effects 20 INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO 10 o C 9 n: LL] 0. a: D O I' l i 1 fl 1 cc I l- o: B L“ - I D' | m 2 g 0 Lu 2 g E El 10 D’— i- n: A L O or L|J to E I) z 1 | l l 9 10 11 12 Noon 12 Midnight 12 Noon 12 Midnight 12 Noon 12 Midnight SEPTEMBER 1969 FIGURE 23. — Semilogarithmic plots of seismic activity summed for each 3-hour period from 12 noon, September 9, 1969, to 12 midnight, Sept. 11, 1969. A, Mobile network. B, Times when no mining was done (shown by black sec- tion). C, Fixed station. of this explosion around the Somerset mine and to determine whether any change in the seismic activity occurred after the explosion. The daily occurrence pattern of large tremors re- corded by the mobile network and by the fixed sta- tion changed after the nuclear explosion at Rulison (fig. 22). Maximum number of large tremors per day increased, and variations in this maximum were greater than before the explosion. No changes, how— ever, were detected in the numbers of tremors per day after the explosion either by the mobile network or by the fixed station (fig. 21). The total number of tremors recorded by the net- work and the number recorded by the fixed station were summed separately for each 3-hour period from 12 noon (m.d.t.) September 9 to 12 midnight Sep- tember 11, so that the activity could be analyzed for shorter periods of time (fig. 23). We detected no significant changes in occurrence pattern recorded by the mobile network before or after the nuclear explosion and found no change in pattern during the time that the Somerset mine was worked after the explosion (fig. 23). We could not analyze the occur- rence pattern of large tremors for the shorter peri- ods of .time, because of the small number of such tremors. We did observe much more variation in the 3-hour occurrence pattern recorded by the fixed sta- tion after the nuclear explosion, probably because the seismometer at the fixed station was closer to the mine than the seismometers in the mobile net- work (fig. 230) and because of the rapid stress changes around the actively mined areas. The first ground motion from the RULISON ex- plosion was recorded by station E of the mobile network at 21: 00: 10.6 G.m.t. on September 10 (fig. 26). The amplitude on the record was limited by the maximum electronic output of the preamplifier and is not a true indication of actual ground motion. Station F, which had a lower gain setting than station E, recorded the complete wave envelope (fig. 24) ; the first ground motion was detected by station F at 21 : 00: 11.4 G.m.t., and maximum ground veloc- ity was recorded 4.8 seconds later. Station F was on about 10 feet of surficial material and therefore was not coupled to bedrock. Consequently, ground motion may have been slightly amplified, and arrival times, slightly delayed. The peak record deflection produced by the EV—17 seismometer at station F and recorded by the tape system was 28 mm. Using the manufacturer’s output specifications of the EV—17 and the system-calibra- tion information, shown by the measured deflection 'of a 10—cps 5-volt peak-to-peak calibration signal (fig. 25), we calculated the peak ground velocity at station F, as follows: Given: Preamplifier gain:G,,:50, Record deflection constant:K2:5 mm/ volt (by calibration) , Seismometer output constanit:K1:1.18 volts/ cm/ sec (manufacturer’s specs), and Record deflection:D:28 mm:2.8 cm, let: Ground velocitsz, Line voltage into trucszT, and Seismometer output voltagezEp; then: EszxKl, so Klep/V:1.18 volts/cm/sec (manufac- turer’s specs), and: DngxET, so K2:D/ET:0.5 cm/volt (by calibration, fig. 25). Also: DzETxngKngprsznglxV><10'3cm, or 37.8 microns. Substituting known values in equation 3, we have: {Ap1221r(4 cycles/sec) (0.095 cm/sec) 22.39 cm/sec2 Referencing this to the acceleration of gravity, we have: Ag—fl— 2.39 cm/sec2 — g —972 cm/sec2 :2.46x10“3g The paper record of the RULISON explosion shows clearly the response of stations with various gains in the mobile network to the shock waves (fig. 26). The RULISON explosion was not recorded by the fixed station at the Somerset mine because the shock waves were of lesser intensity than we ex- pected and because we had set the preamplifier gain too low to obtain a recording. Stations D, which had a normal gain of 7,500, and E, which had an equiva- lent preamplifier gain of 30,000 coupled to a Will- more seismometer, produced the largest deflections. Many of the wave envelopes from stations D and E were limited by the maximum voltage output from FIGURE 24 (above).——Storage-system oscillogram of the first motion from the RULISON explosion, detected by station F of the mobile network, 50 gain. FIGURE 25 (left).— Storage-system oscillogram of a 10-cps 5-volt peak-to-peak calibration sig- nal injected into the preamplifier at station F before the RULISON explosion, 50 gain. the preamplifiers. Thus, maximum amplitude of the shock waves cannot be determined from the deflec- tions on these records. They can, however, be com- pared with the records of tremors from local sources (figs. 14, 15, 16) to indicate the relative maximum amplitude and length of wave trains from the explo— sion. This comparison gives a rough impression of the energy imparted to the Somerset district by the explosion. Our field observations at different locations within the network and reports of miners and local resi- dents show that the peak defiections measured from the oscillograms, such as shown on fig. 24, were higher than the average ground motion in the dis- trict. Ground motion apparently was more intense at higher elevations, where thick surficial cover on the Wasatch Formation (figs. 3, 4) caused some amplifi- cation of the ground motion. It was less intense at lower elevations in the valley of the North Fork of the Gunnison River and its tributary canyons. Con- siderable ground shaking was observed at station F (Jerome Hernandez, oral commun., 1969) and by Dunrud at station C, whereas people in the Somerset mine and in Somerset and Paonia reported very little shaking (Donald Chapman, oral commun., 1969). A nickel placed on edge on a haulage rail in the Somerset mine was not disturbed by the seismic wave (Paul Butler, oral commun., 1969). The greater shaking at higher elevations than at low elevations may also have resulted from the lack of transmission of surface waves, which produce most of the violent motion of earthquakes (D. J. Varnes, oral commun., 1970), into the steep canyons along the river. At many outcrops along the canyons, we observed that loose rocks, ranging in weight from a few hundred pounds to many tons, were not dis- turbed on steep slopes, even in places where shaking was very noticeable. The earth tremor generated by the explosion was estimated to be equivalent to an earthquake of 5.5 Richter (surface-wave) magnitude 22 INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO ?a,‘té°'~f 91'. '9 plasma ' “(@6149 3 WM». "J; , l I FIGURE 26.—-—Seismograms of the shock waves produced by RULISON nuclear explosion, near Grand Valley, recorded by the real—time system in the mobile network. Small early signals on traces A and B are static; signals on traces A and B at time of explosion are also static; A was out of service, and B was set at too low a gain to detect the blast. Preamplifier gains were: A, 7500; B, 0.5; C, 2.5; D, 7500; E, 30,000 with Willmore seismometer; and F, 50. All stations but E used EV—17 seismometers. Time progresses from left to right; 1-minute time intervals shown by chronograph ticks at top. (Gauss, 1969), or of about 5.0 body-wave magnitude (Rutledge J. Brazee, written c0mmun., 1969). A nuclear explosion in Nevada was recorded in the Somerset district at about 8: 32 a.m. m.d.t. on Sep- tember 16, 1969. As shown in figure 27, seismic waves from this explosion also were large enough to force many of the stations to the maximum output of the preamplifiers. Although the maximum shaking did not extend for as long a time as the waves from the RULISON explosion, the wave trains from the Nevada explosion were longer than those from the RULISON explosion. The same explosion in Nevada was recorded by the fixed station at the Somerset mine (fig. 28). Much of the wave train also reached maximum out- put of this preamplifier, which had a gain of 7,500. The explosion imparted more energy to the district than was released by each of the local tremors shown in figures 17 and 18, which have less amplitude, shorter wave trains, and lower frequencies. Several local tremors occurred in or near the Somerset mine within several hours after the explosion, as did sev— eral small earthquakes outside the district. Records of these local tremors and earthquakes are shown in the lower part of figure 28. We recorded two small earthquakes at 3: 06 a.m. m.d.t. (0906 G.m.t.) and at 9: 09 a.m. m.d.t. (1509 G.m.t.) on September 12 (fig. 29, trace A). The arrival times and wave envelopes of these tremors at the stations in the mobile network indicate that the sources were to the northwest, probably near the site of the RULISON explosion. The wave envelopes of these tremors, recorded by the fixed station, clearly indicate that the tremors occurred outside the district because of their long wave trains, low ampli- tudes, and low frequencies and because of the long separation between first-arriving compressional CONCLUSIONS waves and late-arriving waves (fig. 30). We re— corded none of the 16 earthquakes of magnitude less than 1 that were detected near the explosion site within the first 43 minutes after the blast (Hamilton and others, 1970, p. 1). Similarities between the wave envelopes of the two small earthquakes (fig. 29) and the seismogram of the RULISON explosion by station F (fig. 26), re- corded by the mobile network, also suggest that the sources were near the explosion site. CONCLUSIONS Earth tremors in the Somerset coal mining district are similar in occurrence pattern, depth of focus, and origin to many that occur in central Utah coal mining districts (Osterwald and others, 1971). We also recorded some types of tremors that were not found in Utah whose foci were outside the mining area. Foci of most of the larger tremors at Somerset were either beneath the actively worked part of the mine or beneath the intersection of several clastic dikes with the zone of steep dip in the southern part of the mine. Stress redistribution resulting from mining, as shown by distribution of tremor hypo- centers (figs. 3, 4) occurs within about 1 mile of the Somerset mine and as much as 6,000 feet below the mine. A nuclear explosion 41 miles northwest of Somer— set apparently resulted in larger peaks in the daily occurrence pattern of large tremors in the Somerset district and in an increased variation of such trem- ors. The explosion may also have resulted in a shift of tremors from a zone near the western part of the mine into an area from which pillars were being extracted. Surface effects of the explosion in the mine area were greatest at high topographic elevations and in surficial materials. The peak ground—motion parameters of shock waves from the explosion indicated that no undue forces were in- duced around the mine. Two small earthquakes, presumably centered near the site of the explosion, occurred 2 days later. A later explosion in Nevada also imparted much energy to the Somerset district. FIGURE 27. — Seismograms of a nuclear explosion in Nevada, recorded by the real-time system in the mobile network in the Somerset district at about 8:32 am. m.d.t. on September 16, 1969. Parts of wave train at each station reached maximum output of preamplifier. Time pro- gresses from left to right; 1—minute time intervals are shown by chronograph ticks at top. W, M- «w; u . HM; , , F ’ ,6“?ng M4,, ,. INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO 24 515mm. 2: 03350 3x58 A358 83m 983 20595 >055U2WBS oufiznfiwfiwfim .850 .Q ”m .mwa :m ma and NH .32 33:80sz 2:8 uwmgoiom .23: .8 E 933 .31: .Ed «cum and .Ed «0; pm @8895 25:5 .mouDEE N uaonn .8...” .3350 Esfimxwfi :88» 3 83$ :83 $538me @833 593 «>35 £3535 3228-2 33ch mos: uzoomgm :o 933 smgwocoaso $qu :Quawocopno wimmmooSm ho— :Bosm 25:35 BSEEA $895 namawofiwwwm co mcosfinwv -5 cwmazw-D PE mxos smahwocouxu ”EM? 3 $2 88% mummmawoa «EB. .33 .3 awn—:Bnmm no .33: dam Nmnw ”Eons as 9:8 uwmgwfiomgw :ofiwam 682% ha @3583 56552 E commoaxw .3335: .«o ESMoEmmww I .mm 559m CONCLUSIONS 25 I . . ‘ , , , . I t l I l I I I I I 3:00 a.m. 3:06a.m.mld.t. 9:09 a.m.m.d.t. Chronograph .AM, i w .A B A FIGURE 29.— Seismograms of two small earthquakes, recorded by the real-time system in the mobile network, presumably occurring near the site of the RULISON explosion: A, 3:06 a.m. m.d.t. (0906 G.m.t.) September 12, 1969; B, 9:09 a.m. m.d.t. (1509 G.m.t.) September 12, 1969. Letters indicate seismometer stations in figure 3; station A was out of service. Time progresses from left to right; 1-minute intervals shown by chronograph ticks at top. 26 INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO 1 \‘11.[‘:‘J\A.A~vq/vk1,~i . r”~"* ”V!" -11 w... .1111.” 1.1.1... 1...... ......... 1.. w «Mir-n...” r1__,1 4 x1. MMHWW “yam w. N t /, .5. ~W~M: ‘ » v1 51 LUMWJREWWW éMMM 1.1% WWW Iv‘ 1.1... w ._,. H... «MM ”awn M~ 11., N“;“-W~\r~ow~ - ‘ vw 1’41”me W1W1M - -1“ J r,-MMM..M1M \ "U I .11 1111 1,, 11-11,- 11.11 .W 1.1.1.1 111 z 111 -111... Av , 11.._11,.1_11 11.1111, ”1-,111WWM M115v .5 1 _,Mm ”~1_1«W1MM-N.~_M_1~—-.— , "‘1‘. 1 , , 11-1.-- 111.111.111.111. rm. M..- ““L /W Mwwm’vwv—m—A k— A 2 1“ 354 5/” 1 '\ #1 “ L196“ ; I’ N... er M 1 m.M .M .45». kW 1,. ,_,,,1, 1 ”1 ~31 1 minute ~ M!” 11”,“. ~...,1,.1,,1,11.“m,, f “ML m.. ~‘~«~~LM_.,_ .1 -1 ‘1‘ .1- 11 MM... 111111 “111.111.,1 34019.13? mat WM NM 2140G.m.t?/5M‘,1_Mr" FIGURE 30.— Seismograms of two small earthquakes, recorded by the fixed station at the Somerset mine, presumably occurring near the site of the RULISON explosion: A, 3:06 a.m. m.d.t. (0906 G.m.t.) September 12, 1969; B, 9:09 a.m. m.d.t. (1509 G.m.t.) September 12, 1969. Time progresses from left to right; 1-minute intervals shown by chronograph ticks. Time correction between 2140 G.m.t. on local chronograph and 2140 G.m.t. from National Bureau of Standards radio station WWV is shown at bottom. ' INSTRUMENTATION STUDIES OF EARTH TREMORS, SOMERSET COAL MINE, COLORADO 27 REFERENCES CITED Barnes, B. K., Dunrud, C. R., and Hernandez, Jerome, 1969, Seismic activity in the Sunnyside mining district, Utah, during 1967: U.S. Geol. Survey open—file report, 26 p. Beebe, L. M., and Clegg, C. M., 1962, Rio Grande; mainline of the Rockies: Berkeley, Calif., Howell-North Press, 380 p. Burbank, W. S., Lovering, T. S., Goddard, E. N., and Eckel, E. B., compilers, 1935, Geologic map of Colorado: U.S. Geol. Survey, scale 1 : 500,000. Davies, David, 1968, Seismic methods for monitoring under- ground explosions: Stockholm, Sweden, Almquist and Wiksell, Stockholm Internat. Peace Research Inst., Stockholm Papers No. 2, 99 p. Denman, Henry, 1903, Tenth biennial report of the inspector of coal mines of the State of Colorado, 1901—1902: Denver, Colo., Colorado Bur. Mines, 228 p. Denver Post, 1969, Miners protest Rulison plan, slate work halt: Denver, Colo., Denver Post, Aug. 21, 1969, p. 37. Gaskill, D. L., and Godwin, L. H., 1963, Redefinition and correlation of the Ohio Creek Formation (Paleocene) in west—central Colorado, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475—0, p. C35— C38. Gauss, G. G., 1969, Colorado N-quake registers at 5.5: Salt Lake City, Utah, Salt Lake Tribune, Sept. 11, 1969, p. 4A. Hamilton, R. M., Smith, B. E., and Healy, J. H., 1970, Seismic monitoring of the RULISON underground nuclear explosion near Rifle, Colorado, on 10 September 1969: U.S. Geol. Survey open-file report, 6 p. Johnson, V. H., 1948, Geology of the Paonia coal field, Delta and Gunnison Counties, Colorado: U.S. Geol. Survey Coal Inv. Map. Lee, W. T., 1912, Coal fields of Grand Mesa and the West Elk Mountains, Colorado: U.S. Geol. Survey Bull. 510, 237 p. Maberry, J. 0., 1971, Sedimentary features of the Blackhawk Formation (Cretaceous) in the Sunnyside district, Carbon County, Utah: U.S. Geol. Survey Prof. Paper 688, 44 p. Osterwald, F. W., Bennetti, J. B., Jr., Dunrud, C. R., and Maberry, J. 0., 1971, Field instrumentation studies of earth tremors and their geologic environments in central Utah coal mining areas: U.S. Geol. Survey Prof. Paper 693, 20 p. Osterwald, F. W., and Dunrud, C. R., 1966, Instrumentation study of coal mine bumps, Sunnyside district, Utah, in Central Utah coals—A guidebook prepared for the Geological Society of America and associated societies: Utah Geol. and Mineralog. Survey Bull. 80, p. 97—110. Richter, C. F.. 1958, Elementary seismology: San Francisco, Calif., W. H. Freeman and Co., 768 p. Saile, Bob, 1969, Underground A-blast peril to coal mines feared: Denver, Colo., Denver Post, April 18, 1969, p. 31. Tibbetts, B. L., Dunrud, C. R., and Osterwald, F. W., 1966, Seismic-refraction measurements at Sunnyside, Utah, in Geological Survey research 1966: U.S. Geol. Survey Prof. Paper 550—D, p. D132-D137. U.S. Atomic Energy Commission, 1969, Effects evaluation for Project Rulison: U.S. Atomic Energy Comm., 33 p.; available only from U.S. Dept. Commerce Natl. Tech. Inf. Service, Springfield, Va. 22151, as Rept. NVO—43. Yeend, W. E., 1969, Quaternary geology of the Grand and Battlement Mesas area, Colorado: U.S. Geol. Survey Prof. Paper 617, 50 p. U.S. GOVERNMENI PRINTING OFFICE : I972 0—476-247 Stratigraphy of the Inyan Kara Group 5:53 and Localization of Uranium Deposits, Southern Black Hills, South Dakota and Wyoming GEOLOGICAL SURVEY PROFESSIONAL PAPER 763 Prepared on behalf of the US. Atomic Energy Commission "BBEBEAENTS atmrrmmr APR 1 5 1975 LIBRARY VERSITV 0F CALIFORNLA UNI Stratigraphy of the Inyan Kara Group and Localization of Uranium Deposits, Southern Black Hills, South Dakota and Wyoming By GARLAND B. GOTT, DON E. WOLCOTT, and C. GILBERT BOWLES GEOLOGICAL SURVEY PROFESSIONAL PAPER 763 Prepared on behalf of the U.S. Atomic Energy Commission UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 73—600275 Forszile by the Superintendent of Documents, US. Government Printing Office \Vashington, D.(1. 20402 — Price $5.10 (paper cover) ‘ Stock No. 2401702500 CONTENTS Stratigraphy of the Inyan Kara Group Lakota Formation ............................... Minnewaste Limestone Member ............................. Fuson Member Fluvial unit 3 Variegated mudstone ....................................... Fluvial unit 4 .................................................... Fall River Formation ...................................................... Lower unit ........................... Middle unit (fluvial unit 5) ............. Upper unit (includes fluvial unit 6). Petrography .............................................................................. Composition ........... Grain size ........... Heavy minerals .................................................... Source of sand and the influence of tectonic activity upon deposition of Lower Cretaceous sedimentary materials. Structure ........... *U m are m mommqqmmmwwwr—t 23 27 27 29 29 Structure —— Continued Structural interpretation ................................................ Precambrian structure ............................................ Recurrent deformation... Deformational forces... Subsidence structures ....... Ground water ............................................................................ Source of ground water in the Inyan Kara Group... Composition ....................................................................... Flow (as indicated by tritium distribution) ............... Reducing environment ...................................... Hydrogen sulfide .................................... Oxidation-reduction (redox) potential.. Hydrogen-ion concentration (pH) ........................ Carbon dioxide... Uranium deposition Effect of reducing environment Effect of the “plumbing” system and the Inyan Kara stratigraphy on localization of uranium deposits .......................................................................... Mineralizing solutions ..................................................... Ore deposits as related to the “plumbing” system and the stratigraphy ................................................... Effect of the Tertiary and Quaternary drainage systems on localization of uranium deposits .......... Exploration guides ............................................................ References cited .......................................................... ILLUSTRATIONS " [Plates are in pocket] PLATE 1. Geologic and structure maps and restored cross section of part of the southern Black Hills. Page 29 29 30 31 31 33 33 35 36 40 40 41 41 43 44 44 45 46 48 51 51 55 2. Map of part of the southern Black Hills, showing Mesozoic and Cenozoic deformation along Precambrian struc- tures. 3. Hydrochemical diagrams and map showing postulated evolution of artesian calcium sulfate type ground water from the Minnelusa Formation as it migrates through the Inyan Kara Group. 4. Map showing major tectonic elements, minor fault and solution collapse structures, springs, paleostreams, and uranium deposits in the southern Black Hills. FIGURE 1. Index map showing 71/z-minute quadrangles mapped that contain rocks of the Inyan Kara Group in the southern Black Hills ..................................................................................................................................................... 2. Histograms showing average mineralogic composition of sandstone units in the Inyan Kara Group and the Unkpapa Sandstone ............................................................................................................................................... 3. Diagram showing variation in average mica content and ratio of potassium feldspar to plagioclase by flu- vial unit ........................................................................................................................................................................... 4. Diagram showing. variation in average percent feldspar and average mean grain size by fluvial unit ............ 5. Histograms showing d1st11but10ns of phi mean grain sizes of samples from each fluvial unit.......; ................... 6. Correlation graphs of phi mean grain size measures plotted over phi standard deviation measures and over skewness measures of grain-size distributions of samples of sandstone and coarse siltstone from the Inyan Kara Group and the Unkpapa Sandstone .............................................................................................. 7. Histograms showing average percentage composition of heavy mineral suites in samples from sandstone units in the Inyan Kara Group and the Unkpapa Sandstone ............................................................................. Page 2 12 16 16 18 20 24 IV FIGURE 8. TABLE 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. N) . Localities of samples listed in tables 3, 4, and 7 ............................................................................... . Mineralogic composition of samples from the Inyan Kara Group and the Unkpapa Sandstone as deter- CONTENTS Diagram showing proportion of angular grains in combined zircon and tourmaline varieties for each of 76 samples from six sandstone units in the Inyan Kara Group and Unkpapa Sandstone ........................... . Map showing probable minimum extent of Jurassic rocks in the Western Interior region at the end of the Jurassic Period ............................................................................................................................................................... Map showing average orientation of joint sets in the southern Black Hills ............................................................ Stratigraphic sections of the Minnelusa Formation, showing correlation of brecciated rocks in outcrop with anhydrite-bearing strata of the subsurface in Custer County, S. Dak .................................................... Photograph of breccia pipe in the upper part of the Minnelusa Formation in Gettys Canyon, SE14 sec. 16, T. 3 S., R. 1 E., Custer County, S. Dak .................................................................................................................... Graph showing variation in geothermal gradient with depth of well in the Inyan Kara Group .......................... Graph showing average composition of calcium sulfate, sodium sulfate, and sodium bicarbonate ground water from the Minnelusa, Lakota, and Fall River Formations .......................................................................... Isogram map showing tritium distribution in ground water of the Inyan Kara Group of the southern Black Hills, August 1967 ............................................................................................................................................. Isogram showing oxidation-reduction potential of ground water in the Inyan Kara Group of the southern Black Hills ....................................................................................................................................................................... Isogram showing hydrogen-ion concentration of ground water in the Inyan Kara Group of the southern Black Hills ....................................................................................................................................................................... Diagram showing spatial relation of the uranium deposits to leaching of evaporites, brecciation, and pos— tulated direction of ground-water movement ........................................................................................................... Isogram map showing uranium distribution in ground water of the Inyan Kara Group of the southern Black Hills ....................................................................................................................................................................... Graph showing uranium in samples of three types of ground water from the Inyan Kara Group and from the Minnelusa Formation ............................................................................................................................................. Block diagram showing relation of channel sandstones to uranium deposits, carbonate cement, and pos— tulated direction of movement of mineralizing solutions ...................................... Idealized diagram showing zonal relations of several metals in the Runge mine. Map of mine workings, faults, and radioactivity in the Kellog mine ........................................................................ TABLES \ Unit designations of the Inyan Kara Group ................................................................................................................... mined by point-count analyses of thin sections ....................................................................................................... . Statistical measures of the phi grain-size distribution of samples from the Inyan Kara Group and the Unkpapa Sandstone ....................................................................................................................................................... . Comparison of results of three different methods for determining the phi parameters of the grain-size distribution of samples from the Unkpapa Sandstone .......................................................................................... . Averages of selected properties of sandstone from the Inyan Kara Group and the Unkpapa Sandstone ....... . Percentage composition of the heavy-mineral suite in the 0.043- to 0.297-mm size fraction of samples from the Inyan Kara Group and the Unkpapa Sandstone as determined by mineral grain counts ........... . Average percentage of selected minerals in samples from the Inyan Kara Group and the Unkpapa Sandstone . Calcium, magnesium, bicarbonate, sulfate, and uranium in water from springs in the Minnelusa Formation 10. 11. Analyses of Water from wells or drill holes in the Inyan Kara Group ................................................................. Carbon dioxide content of water from the Minnelusa Formation ............................................................................... Page 24 26 30 32 32 35 36 40 42 43 45 47 48 49 49 52 P age 4 13 14 17 19 19 22 25 34 37 44 STRATIGRAPHY OF THE INYAN KARA GROUP AND LOCALIZATION OF URANIUM DEPOSITS, SOUTHERN BLACK HILLS, SOUTH DAKOTA AND WYOMING By GARLAND B. GOTT, DON E. VVOLCOTT, and C. GILBERT BOWLES ABSTRACT The Inyan Kara Group in the southern Black Hills consists of the Lakota and Fall River Formations of Early Cretaceous age. The Lakota Formation constitutes approximately the lower two-thirds of the Inyan Kara Group, and the Fall River Formation constitutes approximately the upper one-third. The rocks are of continental origin and were deposited under vari- able depositional environments, resulting in a sequence of many rock units, each composed of several facies. The Lakota Formation is composed of the Chilson, Minne- waste Limestone, and Fuson Members and ranges in thickness from 200 to 500 feet. The Chilson Member is composed largely of fluvial deposits that can be divided into two major units, which have been designated fluvial units 1 and 2. The Minnewaste Limestone Member locally overlies the Chilson Member in the southern Black Hills but is not known to exist elsewhere. From east to west the Fuson Member successively overlaps the Minnewaste Limestone Member and both units of the Chilson Member. At places this overlap brings the Fuson Member in contact with the Morrison Formation. The mem- ber is composed of red, green, and gray siltstone and mud- stone that locally interflngers with a sandstone designated as fluvial unit 3. After deposition of the fine-grained siltstone and mudstone, deep channels were eroded and then filled with a fluvial sandstone, designated fluvial unit 4. The Fall River Formation is composed of a heterogeneous group of rocks that ranges in thickness from 100 to 160 feet. Laminated carbonaceous siltstones and fine-grained sandstones are abundant in the lower part of the formation. These silt- stones and sandstones are truncated by a thick crossbedded fluvial sandstone, designated fluvial unit 5. Fluvial unit 5 grades laterally into a fine-grained facies composed of tabular beds of alternating sandstone, siltstone, and mudstone. The upper part of the Fall River Formation is composed of a variegated mudstone 20—25 feet thick overlain by a sandstone similar to that in fluvial unit 5. This sandstone also grades laterally into a fine—grained facies. Petrographic studies indicate that the Unkpapa Sandstone of Jurassic age and sandstones in the overlying Inyan Kara Group are orthoquartzites and feldspathic orthoquartzites derived mainly from preexisting sedimentary rocks. Sand- stones of each fluvial unit of the Inyan Kara are identifiable by a characteristic mineral assemblage. Mineral assemblages of fluvial units 1 and 2 of the Chilson Member of the Lakota Formation are derived primarily from older sedimentary rocks and contain relatively little angular detrital material from igneous and metamorphic rocks which cropped out east and southeast, whereas the mineral assemblage of fluvial unit 5 of the Fall River Formation contains a significantly larger proportion of this material. Mineral assemblages of fluvial units 3 and 4 of the Fuson Member represent transi— tional assemblages having a smaller proportion of rounded grains from sedimentary rocks than the Chilson Member but a larger proportion than the Fall River Formation. The shape and orientation of the fluvial units and the direction of dip of the crossbeds within the sandstones indicate that the sand- stones were deposited principally by streams flowing north- westward. It seems likely that most of the detritus that composes the Inyan Kara rocks was derived from areas south- east and southwest of the Black Hills. The Black Hills uplift of Laramide age is an elongate northwest-trending dome about 125 miles long and 60 miles wide. Precambrian igneous and metamorphic rocks are ex- posed in the central part of the uplift, and outward-dipping Paleozoic and Mesozoic rocks form cuestas and hogbacks around the central core. Folds constitute the major structural features, and faults, which generally have less than 100 feet of displacement, are secondary features. In Early Cretaceous time minor deformation along concealed northeast-trending structures of Precambrian age affected the courses of the northwest-flowing consequent streams and their tributaries, thereby influencing the location of the fluvial sandstone de— posits of the Inyan Kara Group. The recurrent deformation along the northeast-trending structures, both during and after the Early Cretaceous, also fractured the Paleozoic and Meso- zoic rocks and indirectly contributed to the formation of collapse structures and breccia pipes of Tertiary to Holocene age. The Laramide uplift of the Black Hills caused the dome to be breached by erosion, resulting in ground-water recharge of the Englewood, Pahasapa,'and Minnelusa Formations of Devonian to Permian age and ground-water movement down the flanks of the dome. Artesian water ascended along frac- tures in these aquifers and dissolved evaporites in the Min- nelusa Formation. Collapse of beds overlying the evaporite zone resulted in subsidence breccias and breccia pipes that extend upward to the Inyan Kara Group. This same process continues today at the margin of the Black Hills. The breccia pipes constitute part of a “plumbing” system through which artesian waters transported low concentrations of uranium into formations of the Inyan Kara where sandstone-uranium deposits were formed. 1 Uranium is introduced into the Inyan Kara with the ar- tesian recharge of calcium sulfate type water from the Minnelusa. As this water migrates downdip, it is modified by ion exchange and sulfate reduction to either a sodium sulfate or a sodium bicarbonate type water, causing an increase in 1 2 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS pH values and a decrease in Eh values. Reduction of sulfate ions in the ground water was a major factor in creating a favorable environment for the precipitation of uranium. Other factors that affect localization of the uranium de- posits pertain to the concentration of metals in the ground water and to the rate of ground-water flow. Oxidation of ura- nium deposits near the Inyan Kara outcrop may locally increase the concentration of uranium in the ground water and thereby increase the volume of uranium transported to the site of deposition. The distribution of the fluvial sand- stones directly affects the rate of ground-water flow and, therefore, the volume of transported uranium. INTRODUCTION In 1951 uranium was discovered in the southern Black Hills by Jerry G. Brennan of Rapid City, S. Dak. (Page and Redden, 1952). This discovery caused an influx of prospectors and mining compa— nies into the area, resulting in the rapid discovery of many small carnotite-type uranium deposits. Although the reconnaissance geology had been mapped by N. H. Darton and published in several reports during the first decade of this century, more detailed geology was needed as an aid in prospecting for the uranium deposits. For this reason a program of detailed geologic investigations was carried out from 1954 through 1958 by the US. Geological Sur— vey on behalf of the Division of Raw Materials of the US. Atomic Energy Commission. The principal objectives of the investigations were to determine the relation of the deposits to their geologic and geochemical environments and to determine criteria that would be useful in the exploration for concealed deposits. As a result of these investigations thirteen 71/2- minute quadrangles, as shown in figure 1, were mapped and described in detail by Wilmarth and Smith (1957a—d), Brobst (1961), Wolcott, Bowles, Brobst, and Post (1962), Brobst and Epstein (1963), Connor (1963), Gott and Schnabel (1963), Schnabel (1963), Braddock (1963), Cuppels (1963), Ryan (1964), Wolcott (1967), Post (1967), and Bell and Post (1971). This report summarizes information about the stratigraphy, petrography, and factors affecting lo- calization of ore deposits in the formations of the Inyan Kara Group discussed in detail in the reports listed in the preceding paragraph. In addition, un- published information about the stratigraphy of the Minnekahta quadrangle and unpublished maps of the Runge mine by V. R. Wilmarth, formerly with the US. Geological Survey, were utilized. The quadrangle geologic maps have been recom— piled at a reduced scale on plate 1, which represents an area extending from Hot Springs, S. Dak., north- westward around the periphery of the Black Hills 104°OO’ PENNINGTON COUNTY s — — - — Lu : E E f O ,, .0 el 3. .9 S C7 CUSTER COUNTY ‘73 I 3 I c} a 0‘” \/ 3% 53%? _ l 103°3o' 43°30' I __ _ _ _ _ < ‘0 v «V e E H C" If ‘35 {53‘ 5‘0 Z (J 0 0° 0* .5 go <9 4* D 2 M 8* <3 s s Q «a o H|< «7 90 § s {p 0 5“: ‘° V. a: W E 09 so, 50" «328. <: B D ‘3‘ x 9,9 #5 03$ 91 1O 9‘7 \/\+ (311‘? $304" m '02 e « (a N. O . ._. Z FALL RIVER COUNTY 1 1 SOUTH DAKOTA WYOMING Reference ....................... Brobst and Epstein (1963). Quadrangle Fanny Peak ..... Clifton. ..Cuppels (1963). Dewey ........... .,Br0bst (1961). Jewel Cave S ..Braddock (1963). Burdock ............ ..Schnabe1 (1963). Edgemont NE .............................................. Gott and Schnabel (1963). Minnekahta: West—central part ................................... Wilmarth and Smith (1957a). ..Wilmarth and Smith (1957b). ..Wi1marth and Smith (1957c). ..Wilmarth and Smith (1957(1). East-central part Southeast part ..... Southwest part... Minnekahta NE .......................................... Wolcott, Bowles, Brobst, and Post (1962). Hot Springs ................................................. Wolcott (1967). Edgemont ..Ryan (1964). Flint Hill ...... .. ell and Post (1971). ..Post (1967). .................................. Connor (1963) . Cascade Springs ...... Angostura Reservoir FIGURE 1.—Index map showing 71/2-minute quadran- gles mapped that contain rocks of the Inyan Kara Group in the southern Black Hills. nearly to Newcastle, Wyo. A restored cross section (pl. 1, north half), constructed from the detailed maps and from many measured sections in the 13 quadrangles, summarizes the stratigraphic relations published elsewhere. The Inyan Kara rocks of Early Cretaceous age are the ore-bearing formations. These rocks were STRATIGRAPHY ‘ 3 deposited in varying continental environments, re— sulting in a sequence of diverse rock units, each composed of several facies. The stratigraphic com— plexities are such that it was necessary to map the beds in considerable detail before the sedimentary history could be determined. Other detailed studies were required to evaluate the effects of the Inyan Kara stratigraphy and structure on the problems of ore localization. STRATIGRAPHY OF THE INYAN KARA GROUP The Inyan Kara Group of Early Cretaceous age is composed of the Lakota and Fall River Forma- tions. The Lakota Formation is 200~5OO feet thick and makes up about the lower two-thirds of the group. The formation is composed of a diverse se- quence of deposits laid’down in streams, flood plains, lakes, and swamps. The Fall River Formation is 100—160 feet thick and makes up the upper one-third of the group. It is largely composed of a heteroge- neous sequence of fluvial sandstones, siltstones, and mudstones. In the western part of the mapped area the Lakota Formation is underlain by the Morrison Formation of Jurassic age, but in the eastern part of the area it is underlain by the Unkpapa Sand— stone, a formation thought to be equivalent in age to the Morrison (Imlay, 1947). The Fall River For— mation is overlain by the Lower Cretaceous Skull Creek Shale. Darton (1901) established, in ascending order, the names Lakota Formation, Minnewaste Limestone, Fuson Shale, and Dakota Sandstone for the sequence of rocks here referred to as the Inyan Kara Group. Later, Russell (1928) discovered that Darton’s Da- kota Sandstone was older than the type Dakota, and he changed the name from Dakota Sandstone to Fall River Formation. Rubey (1931) later assigned the Lakota Formation, the Fuson Shale, and the Fall River Formation to the Inyan Kara Group. As a result of a recent study of the Inyan Kara stratig- raphy in the Black Hills, Waagé (1959) proposed that a twofold division of the Inyan Kara Group be established, with the lower part called the Lakota Formation and the upper part called the Fall River Formation. He further proposed that the boundary between the Fall River and the Lakota Formations be placed at a transgressive disconformity that can be recognized throughout the Black Hills region. He reduced the Fuson Shale and the Minnewaste Lime- stone to member status within the Lakota. Detailed mapping subsequent to Waagé’s (1959’) regional stratigraphic studies has indicated that the pre—Fuson Lakota rocks, or the pre-Minnewaste rocks two complex fluvial units, each predominantly com- posed of channel and flood—plain facies. These two units were called the Chilson Member by Post and Bell (1961). In some places in the Elk Mountains in the Clifton quadrangle, the Chilson Member is absent, and rocks of Fuson age apparently rest on the Morrison Formation (pl. 1, north half). Thus the Fuson Member rests on progressively older rocks from east to west, and its lower contact must locally represent a major hiatus. While mapping in the southern Black Hills, we found the following informal terminology for the major fluvial units within the Inyan Kara Group to be useful. This terminology includes fluvial units 1 and 2 in the Chilson Member, 3 and 4 in the Fuson Member, and 5 and 6 in the Fall River Formation. Because of the interest in the uranium deposits in the area, many of the maps were published in pre- liminary form soon after their completion. Later it was found that some of the numbered units on these maps were of no regional significance and that the implied age relations of others were incorrect. These discrepancies and the current designation of the various numbered units are shown in table 1. LAKOTA FORMATION The lower part of the Lakota Formation is com- posed largely of fluvial deposits. These can be divided into two major units, designated fluvial units 1 and 2 (pl. 1, north half), which together are equivalent to the Lakota Sandstone of Darton and Paige (1925) and which Post and Bell (1961) included within the redefined Lakota Formation as the Chilson Member. Unit 1, the oldest, is present throughout most of the area between lower Chilson Canyon and the Elk Mountains (pl. 1). Unit 2, which overlaps unit 1, is present in the area between Hot Springs and Craven Canyon and in the southern part of the mapped area. It is thickest in the vicinity of Cascade Springs. In the Vicinity of Hot Springs and Cascade Springs, the Minnewaste Limestone Member, of lacustrine origin, overlies the Chilson Member (pl. 1). Between the Cascade Springs area and the northern part of the Burdock quadrangle, the limestone is present as small isolated patches, but it has not been found farther to the northwest. Three units within the Fuson Member are shown on the geologic map (pl. 1). The most widespread unit is composed of red, green, and gray siltstone and mudstone, probably of lacustrine origin. Highly polished chert and quartzite pebbles, some of which contain Paleozoic fossils, are sparsely distributed where the Minnewaste is present, are composed of l throughout this unit. In the Pass Creek and Elk INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS TABLE 1. — Unit designations [Lithologies of units are described on map explanations of previously published unit designations does not necessarily imply correlation between JEWEL AREA FANNY PEAK CLIFTON DEWEY CAVE SW BURDOCK EDGEMONT NE EDGEMONT MINNEKAHTA ,7, QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE Source of data_ _ 1 2 3 4 5 6 7 8 9 10 11 sm Kfusm srn Kfusm Kfusm L c g: Kfums Kfums ms Kfums Kfums 86’s Kfus Kfuse .2 a 5 45 D E m6 Kfum m5 Kfum Kfum LE 0 Kfr Kfr Kfr 3 E .4: E g g Kfmss Kfmss $5 Kfms5 Kfms5 s5 Kfmss 5,56 Kfms5 Kfmss 55,5 _ Kf | Kfmsm Kfmsm sm Kfmsm sm Kfmsm Kfmsm Kf :«3 rn Kfmm Kfmm ss Kfmss r a H 55 Kflss 3 E Kflss Kflss st Kflst Kflst ss Kflss Kflss m 3 3 s Kfls _ m Klfm4 m Klfm4 a: E . s Klfs4 Klf54 54 K|f54 S4 Klf54 Klf54 $4 (D E m Klfm m Klfm Klfm l 8 a: c g 82 3 $3 Klfs s3 Klfs Klfs 55,5 3 t; 3 g g “5, L“ 2a Klfs3 C ._ E 54 ' l Klm | Klm Kfml Kfml 1 l: m .9 ‘5 E E g s K|052 KIC52 5,51 0 E t g m chmz m.sm.ss ‘5 c E 2 chm chm sm,m LE 0 s chs s .s 1 1 Not exposed 1 sm,m chsml Sm chsh sm SOURCE OF DATA 1. Brobst and Epstein (1963, pl. 25). 11. Wilmarth and Smith (1957a. b. c. d). 2. Cuppels (1963, pl. 23). 12. Bell and Post (1957a. b, c, d, e, f). 3. Brobst (1958a, b). 13. Bell and Post (1971. pl. 32) 4. Brobst (1961, pl. 5). 14. Wolcott, Bowles, Brobst, and Post (1962). 5. Braddock (1963. pl. 20). 15. Post and Cuppels (1959a, b); Post and Lane 6. Schnabel (1958); Schnabel and Charlesworth (19598.13): POSt (1959a, b). (1958 a. b,c.d). 16. Post (1967, pl. 29). 7. Schnabel (1963, pl. 17). 17. Connor (1963. pl. 11). 8. Gott and Schnabel (1956a, b, c, d, e, f). 18. Wolcott (1967, pl. 28). 9. Gott and Schnabel (1963, pl. 12). 19. Mapel and Gott (1959). 10. Ryan (1964. pl. 27). Mountains area a conglomeratic sandstone desig- nated as fluvial unit 3 interfingers with the basal Fuson mudstones, and is included within the Fuson Member. This sandstone rests successively on fluvial unit 1, on the Morrison Formation, and locally on the Redwater Shale Member of the Sundance For— mation. After the variegated mudstones of the Fuson were deposited, they were locally dissected by pre- Fall River erosion, and the channels were filled with a medium- to coarse-grained sandstone. This sand- stone has been included within the Fuson Member and designated as fluvial unit 4. In addition to the three units just mentioned, other sandstones occur locally. The scale of the geo- logic map is so small that these units cannot be shown; their presence is indicated only on the cross section (pl. 1). Several erosional unconformities extend through- out the southern Black Hills. (1) The sandstone facies of fluvial unit 1 seems to be unconformable with the underlying black fissile Lakota shale, mapped as part of fluvial unit 1, or with the under- lying Morrison Formation. (2) The contact between fluvial units 1 and 2 is almost everywhere within the STRATIGRAPHY 5 of the lug/an Kara Group U.S. Geo]. Survey reports and on plate 1 of the present report. Position of quadrangles. Crosshatch pattern indicates rock unit is absent] fine—grained poorly exposed flood-plain facies of the two units. The contact relations, therefore, can rarely be observed. The regional relations, however, suggest that unit 1 originally may have extended farther eastward than it now does. Black fissile carbonaceous shale similar to that which occurs below the sand- stone facies of fluvial unit 1 is present several miles east of the main body of sandstone in this unit. One such area is near the mouth of Fall River canyon (WI/g sec. 30, T. 7 S., R. 6 E.), Where the carbona— ceous shale underlies fluvial unit 2. We observed similar shale in the Angostura Reservoir quadrangle. Inasmuch as the carbonaceous shale is known to occur only as part of, or underneath, unit 1, these isolated patches of shale are probably erosional rem- nants of unit 1. If they are, an unconformity must exist between units 1 and 2. (3) The Fuson Mem- ber overlaps successively the Minnewaste Limestone Member and both units of the Chilson Member. At places this overlap brings the Fuson Member in con- FLINT HILL MINNEKAHTA CASCADE SPRINGS ANGOSTURA HOT SPRINGS SOUTHERN NE RESERVOIR QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE QUADRANGLE BLACK HILLS SOUTHERN BLACK H'LLS 12 13 14 17 18 19 Present report (pl. 1) Siltsto n e, s a nd- Sm KfUSt stone, mudstone, L and shale Fluvial w .t C 55 S5,.s Kfus s d t Kfus6 unit 6 a: '2 Kfsm Kfusm Rejnanzznrzy Kfusm 3 16 m m,st,sst Kfum Kfum mudstone Kfum E Kfl’ sm Kfmsm Kfl' “- Kfmm rn Kfmm , g 5 Kfmst Kf Kfmss Kf Fluvial .0 t 3 Se Kfmss middle and 55,5 Kfms5 Kfs5 Kfms5 55 ms unit 5 g g E lower Thin—bedded sand- E rn undivided m Kfmsm Kfmsm stoneand siltstone Kfmsm u- Kflss Carbonaceous shale, E t' st Kflst sst Kfss Kflss siltstone, rnudstone, Kflss g C KfISt or sandstone .1 3 st Klfm4 Klfm4 Fluvial ; 54,5 K|f54 $4 KlfS4 K|f54 $4 Klf54 ””‘t 4 E Variegated mud- m m Klfm Klf m Klf Klfm Klf stone, siltstone, Klfm E 3 w l. Klfs Klfs sandstone Kflss g 3 82 Klf g a a E Fl ' | “' g E 4’ uVIa : $2.531?) Klf53 unit 3 E 3 E Minnewaste | Klm Klm Klm Klm Klm Limestone Klm Member Kfml g m 53 '5 Siltstone. claystone, Fl _ l h E mudstone, some uvua a; $2 ““2 chsz 52 ch52 KICSZ chsz interbedded sand- ch52 unit 2 E “5- chm2 stone to a “”5 chsmz m.sm chsmz K'cmZ Interbedded mud- K'CUZ 2 ‘5 stone, siltstone, : fi sm,st and sandstone 8 —’ S r: 1 - .c 51 K'CSI Carbonaceous shale, chsl Hr??? Q chrn siltstone, mud- u: chst stone, or sand- K'CUI stone tact with the Morrison Formation and indicates an unconformity of regional magnitude. (4) Fluvial unit 4, at the top of the Fuson Member, fills deep erosional irregularities in the Fuson variegated mud- stones, particularly in the Cascade Springs, Flint Hill, Edgemont, and Edgemont NE quadrangles. CHILSON MEMBER FLUVIAL UNIT 1 Fluvial unit 1 is present in the region northwest of the eastern part of the Flint Hill quadrangle and is composed of sandstone, shale, siltstone, and mud- stone. Locally, black fissile shale has been mapped as the basal part of this unit. The unit consists of a complex of channel sandstone deposits and their fine-grained equivalents and apparently was depos- ited under predominantly fluvial conditions. The unit is an elongate body whose long axis is oriented northwestward (pl. 1). Generally, the central part of the unit is a series of light-brownish-gray fine to 6 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS very fine grained channel sandstones. The sandstones grade laterally into other fine-grained deposits com- posed of thin alternating fine-grained sandstones, siltstones, and mudstones. This unit is one of the four uranium-producing units in the Inyan Kara Group of the southern Black Hills. The channel-type sandstone facies of unit 1 has been described by Bell and Post (1971), Braddock (1963), Brobst (1961), Brobst and Epstein (1963), Cuppels (1963), Gott and Schnabel (1963), and Schnabel (1963). The sandstone is exposed through- out much of the area between the Cheyenne River canyon in the southern part of the Flint Hill quad— rangle and the south end of the Elk Mountains in the Dewey quadrangle. It is best exposed in Chey— enne, Chilson, and Craven Canyons, where it forms massive nearly vertical cliffs 75—100 feet high. It is composed of numerous discrete filled channels result- ing in a complex sequence of scour and fill structures. The sandstone is light brownish gray or yellowish gray and is fine to very fine grained, except for a few medium- to coarse-grained lenses. The sand grains are well sorted and consist mostly of quartz, but on an average include about 5 percent feldspar, a few percent each of detrital chert and white de- trital clay grains, and less than 1 percent heavy minerals. Carbonized plant remains are randomly distributed throughout the sandstone. As discussed more fully later, the sandstone is, in places, cemented tightly by carbonate. Along and marginal to an axial line, the sandstone is thickest and rests unconformably on the Morrison Formation; but in some places laterally from the axial line, the sandstone rests on black carbonaceous fissile shales of the Lakota. This black fissile shale is the oldest known Cretaceous rock in the southern Black Hills and appears to have been laid down as a blanket—type deposit and to have been subsequently dissected during early unit 1 time. The shale is ex- posed in only a few places throughout the area in which the basal Lakota rocks crop out. For this reason it has been mapped as part of unit 1. It is best exposed in several places along each side of Red Canyon in the vicinity of the Fay Ranch, along Pass Creek, and along the east side of the Elk Mountains, in sec. 16, T. 5 S., R. 1 E. In these areas it is 10—50 feet thick, but where it has been penetrated by drill holes in and adjacent to sec. 1, T. 8 S., R. 2 E., it is as much as 75 feet thick. The direction of dip of crossbeds indicates that the sand was deposited in streams flowing northwest— ward. The sandstone thins in the downstream direc- tion along the channel axes from a maximum of 300 feet in Chilson Canyon to 250 feet in Craven Canyon, and it further thins to 200 feet in the Vicinity of the south end of the Elk Mountains. The sandstone also thins rapidly and grades into fine-grained deposits to the northeast at right angles to the direction of streamflow. Little is known of its extent southwest of the main channel, but presumably it likewise grades into fine-grained deposits in that direction. The fine-grained flood-plain facies of unit 1 is composed of thin alternating beds of very fine grained sandstone, siltstone, and mudstone in vari- able proportions. Limestone beds as much as 1 foot thick occur locally. A few thin coal beds are present. Streaks, pods, and fragments of carbonaceous mate- rial are sparse to abundant. The thickness of the flood-plain facies of unit 1 is greatest, as much as 150 feet, northeast of the margin of the sandstone facies in the eastern part of the Edgemont NE quad- rangle, in the southern part of the Minnekahta quad- rangle, and in the north-central part of the Flint Hill quadrangle. A varied assemblage of fossils was found in mod- erate abundance during this investigation. In some places the siltstone and mudstone beds contain abun- dant ostracodes. Estella Leopold and Helen Penn of the US. Geological Survey have recognized spores related to the tropical fern genus Anemia. Numerous cycads also indicative of a tropical to subtropical climate have been collected from this unit. The abun- dant carbonaceous material, including coal beds, indicates a humid, warm climate that supported a luxurious growth of vegetation. FLUVIAL UNIT 3 Throughout a considerable part of the southeast- ern Black Hills, unit 1 is overlain unconformably by a sequence of younger rocks that has been designated as fluvial unit 2. This unit extends from the Inyan Kara hogback in the vicinity of Hot Springs and Cascade Springs westward to the central part of the Edgemont NE quadrangle. The thickness of the unit averages about 250 feet east of the central part of the Flint Hill quadrangle; it gradually thins to zero west of the central part of the Flint Hill quad- rangle. The unit, like fluvial unit 1, is a fluvial com- plex composed of stream and flood-plain deposits designated as sandstone and mudstone facies, and it locally includes rocks of possible lacustrine origin. The unit is lens shaped and elongate to the north- west. Structural depression of the Cascade Springs area caused the axial line of unit 2 to shift to that area, about 6 miles east of the axial line of unit 1 (pl. 1, north half, restored cross section). Sandstone, which predominates near the axial line, grades lat— erally into interbedded claystone, siltstone, and silty STRATIGRAPHY ‘ 7 very fine grained sandstone. The sandstone facies generally is light yellowish gray and is fine to very fine grained. It is composed predominantly of quartz but contains a small amount of feldspar and clay. In general, the sand is well sorted. Several subtle differences are useful in distin- guishing unit 1 fromvunit 2. Unit 2 is more oxidized, probably as a result of climatic changes after the deposition of unit 1, as shown by its lack of carbon and its greater abundance of red, brown, and yellow colors in contrast to the presence of carbon and the less Vivid colors in unit 1. The mudstones of unit 2 are shades of red, green, and gray; those in unit 1 are predominantly gray, although a few are green and red. Fissile shales are absent from unit 2 but are commonly present in the basal part of unit 1. Many of the sandstones in unit 2 contain abundant pink calcite cement, Whereas those in unit 1 contain less abundant and characteristically gray calcite cement. The contact relations between the two units are variable. Throughout most of the area northwest of Craven Canyon Where unit 2 is absent, unit 1 rocks are directly overlain by the Fuson Member. Unit 1 is absent eastward from the northeastern part of the Flint Hill quadrangle, and there, unit 2 lies directly on the Unkpapa Sandstone of Jurassic age. Where the two units are present in the same area, the fine- grained flood—plain deposits of each are generally in contact. This distribution of rock types occurs near the northeastern boundary of unit 1 in the south-cen- tral part of the Minnekahta quadrangle and through- out the east-central part of the Flint Hill quadrangle. Farther west, in the eastern part of the Edgemont NE quadrangle, the sandstone facies of unit 2 ap- parently rests on the fine-grained facies of unit 1, although unit 2 fine-grained facies may be present in some places in this area. Where the boundary between the two units is within nonresistant fine-grained rocks, it is rarely exposed, and the contact relations cannot be observed in detail. In the 81/; sec. 18, T. 9 S., R. 4 E., and at other places along the Cheyenne River, the sandstone facies of the two units are in contact. The magnitude of the hiatus cannot be determined from the expo- sures in this area, but suflicient time may have elapsed to allow the removal of 300—400 feet of rock before the deposition of unit 2. MINNEWASTE LIMESTONE MEMBER The Minnewaste Limestone Member is restricted to the southern part of the Black Hills. It is continu- ous east, northeast, and southeast of Cascade Springs and is discontinuous from Cascade Springs west to the northeastern part of the Burdock quadrangle (pl. 1). It has not been recognized in the western, the northern, and much of the eastern part of the Black Hills. The Minnewaste Member in its thickest part is almost pure limestone, but it grades outward to sandy limestone and, toward the margins, to cal- careous sandstone. It ranges in thickness from a few inches to 80 feet. East of Cascade Springs it has an average thickness of about 20 feet, but where it occurs in the Flint Hill, Edgemont NE, and Burdock quadrangles, it generally has a thickness of less than 10 feet. The limestone generally is structureless and weathers to a hackly surface. It strongly resists weathering and forms a vertical cliff where it is exposed in the canyons. In some places, notably in the eastern part of the Angostura Reservoir quad- rangle, the limestone contains thin lenses of carbona- ceous siltstone and structureless sandstone. Commonly the limestone is highly brecciated and recemented with calcite. Baker (1947) reported that in the Amerada Petroleum Corp., South Dakota Ag- ricultural College well 1, SWIASEl/i, sec. 27, T. 8 S., R. 7 E., just east of the mapped area, the Minnewaste includes 30 feet of anhydrite interbedded with lime- stone, dolomite, sandstone, and shale. Solution of the soluble calcium sulfate and subsequent collapse of the overlying beds, therefore, seem to be the most reasonable causes of brecciation. In the Flint Hill quadrangle and eastward, the limestone commonly rests on red sandstone at the top of fluvial unit 2. Locally, however, gray mudstone separates the red sandstone from the limestone, and in places where fluvial unit 2 is represented by fine- grained flood-plain facies, the limestone also rests on mudstones. Westward the Minnewaste overlaps fluvial unit 2 and occurs as isolated patches resting on sandstones and mudstones of fluvial unit 1 (pl. 1, south half). Fresh-water sponge spicules have been found in a few places within the limestone. These fossils, to- gether With the limited distribution of the limestone, suggest that the limestone is lacustrine in origin. FUSON MEMBER The Fuson Member was evidently deposited in most of the southern Black Hills as gray to varie- gated mudstone containing variable amounts of fine- grained sandstone. In the vicinity of Pass Creek and the Elk Mountains, however, the lower part of the mudstone interfingers with conglomeratic sandstone that has been designated as fluvial unit 3 (pl. 1). In numerous places between the Elk Mountains and Hot Springs, particularly in the Edgemont area, the top of the Fuson mudstone has been channeled during pre-Fall River erosion. The sandstone that fills these 8 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS erosional irregularities has been designated as fluvial unit 4 (pl. 1). The Fuson member, therefore, is com- posed of a variety of rock types including fluvial unit 3, the variegated mudstone, which locally con- tains fine—grained sandstones, and fluvial unit 4. After the nomenclature of the formations now in- cluded within the Inyan Kara Group was established by Darton (1901), difficulty was encountered in rec- ognizing the base of the Fuson beyond the limits of the Minnewaste Limestone Member. The reason for this difficulty apparently was the variation in facies in both the Fuson and Chilson Members. After these facies were mapped in the area between Hot Springs, S. Dak., and Newcastle, Wy'o., however, it became apparent that the Fuson could be traced by detailed mapping beyond the limits of the Minnewaste Lime- stone Member. For several miles west of Cascade Springs the Fuson Member rests on an easily identified reddish- brown sandstone in the sandstone and mudstone facies of fluvial unit 2 of the Chilson Member. In some places, however, particularly in the northern part of the Flint Hill quadrangle and the southern part of the Minnekahta quadrangle, variegated mud- stone of the Fuson locally rests on similar mudstones of fluvial unit 2. There the Fuson-Chilson contact has been arbitrarily mapped Within the mudstone se- quence. Beyond the western limits of fluvial unit 2, the Fuson Member rests on rocks of fluvial unit 1 (pl. 1, north half). The rocks of these two units are gener- ally easily distinguished because of the contrast be- tween carbonaceous sandy beds in the underlying Chilson Member and noncarbonaceous variegated mudstone or white massive sandstone in the Fuson Member. Along the east side of the Elk Mountains in the Dewey quadrangle, where the basal part of the Fuson Member is the conglomeratic sandstone of fluvial unit 3, all the rocks that contain carbonaceous material are placed in the Chilson Member, and all the conglomeratic sandstone is placed in the Fuson Member. FLUVIAI. l'NI’l‘ 3 Fluvial unit 3 is a conglomeratic crossbedded white to yellowish-brown noncarbonaceous sand- stone. It crops out in parts of the Jewel Cave SW, Dewey, Clifton, and Fanny Peak quadrangles. It con- sists of many intertonguing well-sorted lenses that vary in texture from fine grained to conglomeratic with pebbles locally greater than 3 inches in diam- eter. Quartz comprises 90 percent of the rock; and chert, feldspar, clay grains, magnetite, zircon, tour- maline, and rutile are minor constituents. Carnotite in uneconomic concentrations has been found in the lower part of the sandstone in the SE%SW%, sec. 21, T. 5 S., R. 1 E., Custer County, S. Dak. The conglomeratic sandstone was deposited on the dissected surface of fluvial unit 1 and, in places, on Jurassic rocks. At the boundary between the Clifton and Dewey quadrangles, the sandstone is in direct contact with either the lower part of the Morrison Formation or the upper part of the Redwater Shale Member of the Sundance Formation of Jurassic age (pl. 1). Crossbeds in the sandstone indicate that the streams that deposited it flowed in a northerly direc- tion. The sandstone interfingers with the variegated mudstone. Fluvial unit 3 is generally 20—30 feet thick where it is present in the Jewel Cave SW quadrangle. Along the west flank of the Black Hills through parts of the Dewey, Clifton, and Fanny Peak quadrangles the unit ranges in thickness from about 20 to 120 feet and perhaps has an average thickness of about 70 feet. VARIEGATEI) lVI UI)STONE The variegated mudstone of the Fuson Member was partly or completely removed in many places by widespread erosion prior to deposition of fluvial unit 4. Where it is present the mudstone is as much as 180 feet thick and averages about 100 feet thick. It is nonfissile and noncarbonaceous and is charac- terized by gray, maroon, and green claystone and siltstone enclosing thin beds of fine-grained sand- stone. Silicified logs have been found in the unit, notably in the northeastern part of the Hot Springs quadrangle and the northwestern part of the Edge- mont NE quadrangle. Green sandstone float is dis- tinctive, yet the source of this material is rarely exposed. The claystone and siltstone beds generally weather to steep grass—covered slopes. Highly pol- ished subspherical quartzite and chert pebbles and cobbles also characterize this unit and help distin- guish the Fuson Member from the Chilson Member. These pebbles and cobbles have been found embedded in the Fuson mudstone in many places, but most are seen littering the mudstone surface. Similar polished pebbles, probably from equivalents of the Fuson Member, around the periphery of the Black Hills have been described by Mapel, Chisholm, and Ber— genback (1964, p. C25—C26), Waagé (1959), and many other writers. Commonly structureless and poorly bedded highly argillaceous silty sandstone that is white or is mottled and streaked with red, pink, and yellow iron oxide stains and cement is characteristic of the unit. The sandstone is lenticular, fine to very fine grained, and noncarbonaceous, and it is as much as 100 feet thick. The most conspicuous exposures of STRATIGRAPHY 9 the white structureless sandstone are in the Coal, Craven, and Red Canyons areas, in the Edgemont NE quadrangle. This sandstone is not shown on the geologic map but is shown on the restored cross sec- tion. FLUVIAL UNIT 4 Fluvial unit 4, the youngest rock unit in the Fuson Member, was deposited in channels eroded by north- west-flowing streams during partial dissection of the underlying variegated mudstone. The streams in places incised as much as 150 feet below the surface and cut completely through the variegated mudstone and into units 2 and 1 of the Chilson Member. Sub- sequently, these valleys were filled with the channel sandstone complex that comprises fluvial unit 4. The sandstone is extensively cemented with calcium car— bonate. The complex is composed predominantly of sand- stone; but red or red and gray mudstone is locally present at the top of the unit, and in places along the margins gray mudstone lenses are present. The sand grains are rounded to subrounded and on an average are composed of about 90 percent quartz; chert, kaolinite, illite, feldspar, and sparse mica con- stitute most of the remaining part. Unit 4 contains almost no organic carbon. The sandstone is resistant to erosion and forms yellowish—gray to light-gray vertical cliffs along the canyons. The basal part lo- cally is conglomeratic, particularly on the crest of the Chilson anticline in the southern part of the Minnekahta quadrangle, but generally the sandstone is fine to medium grained and, except for local clay lenses, is only slightly argillaceous. The sandstone is intermittently exposed from the Cheyenne River in the southern part of the Flint Hill quadrangle to the southern part of the Clifton quad- rangle, a distance of about 35 miles (pl. 1). A tributary channel, in which sandstone was deposited, apparently extended across the western part of the Cascade Springs quadrangle and eastern part of the Hot Springs quadrangle. Mudstone of variable thickness is locally present in the upper part of fluvial unit 4 west of the Chilson anticline. The mudstone generally forms gentle grass—covered slopes, and little of it can be observed. Where it is exposed it is similar to the red and maroon mudstone in parts of the Fuson variegated mudstone and to varicolored mudstone in the upper part of the Fall River Formation. The maximum thickness of the mudstone, about 50 feet, occurs in the western part of the Edgemont NE quadrangle and the east- ern part of the Burdock quadrangle (pl. 1). The mudstone probably was locally derived from the Fuson clays and silts and was deposited on the flanks of the principal channels. In contrast to the sandstone of other fluvial units, the sandstone of fluvial unit 4 is characterized by many sets of foreset crossbeds, each set ranging in thickness from a few inches near the channel margin to about 4 feet in the central part of the channel. The sets are separated by thin topset beds, none more than 2 inches thick. The crossbeds strike normal to the channel boundaries and dip northwestward. On weathered surfaces many of the individual cross- strata are etched into bold relief, evidently as a re- sult of contrasting textures of adjacent cross-strata. In several places betWeen the southern part of the Flint Hill quadrangle and the southeastern part of the Edgemont NE quadrangle the foreset beds within individual sets are bent downstream in such a manner that a “V” is formed which points up- stream. The deformed strata are overlain and under- lain by undeformed strata. The deformation of the crossbeds apparently resulted from preconsolidation slumping. According to McKee (1957, p. 132), fore- set beds of the type just described result when the base level is raised rapidly, and a series of these sets represents a series of base level rises. The sandstones of fluvial unit 4 are more exten- sively cemented with calcite than are the sandstones of the other fluvial units (Gott, 1956; Gott and Schnabel, 1963). Unit 4 sandstones are particularly well cemented along the east side of the Burdock quadrangle, in the southwestern part of the Edge- mont NE quadrangle, in the subsurface in the north- eastern part of the Edgemont quadrangle, and in various parts of the Flint Hill quadrangle. Most of the calcite contains much manganese and iron, and these metals cause the rock to weather dark gray to black where highly oxidized. The calcite generally is concentrated in spherical nodules, but to a lesser extent it occurs in elongate masses in and marginal to fractures. The nodules are commonly about a half inch in diameter but are locally as much as 4 inches in diameter, and most of them exhibit regularly spaced concentric bands. The cementation apparently grew outward from a nucleus. Where cementation proceeded to completion, the nodules coalesce, and the sandstone in the interstices between the nodules is cemented by calcite; but in many places the inter- nodular sandstone is uncemented. FALL RIVER FORMATION The Fall River Formation is composed of sand- stone, siltstone, and mudstone. In the southern part of the Black Hills it is 100—160 feet thick. Three units recognized in mapping could be traced over 10 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS most of the area. ( 1) Laminated carbonaceous silt- stones interbedded with thin sandstones in the basal part of the formation are informally designated as the lower unit. (2) A thick crossbedded fluvial sand- stone, which locally truncates the lower unit but which grades laterally into a sequence of alternating thin tabular beds of sandstone, siltstone, and mud— stone, is designated as the middle unit. (3) A varie- gated mudstone 20—25 feet thick and a local overlying sandstone which is similar to the one in the middle unit and which grades laterally into a fine-grained thin-bedded facies are designated as the upper unit. The lithologic character of the Fall River and Lakota rocks at the formational boundary varies greatly. Because of this, several combinations of lithologic units in each formation are variously pres- ent at the formational boundary. Most commonly the lowest part of the Fall River Formation consists of laminated carbonaceous siltstone thinly interbedded with very fine grained sandstone. In most places this unit rests On the variegated mudstone or the white sugary massive sandstone of the Fuson Member. The upper few inches to few feet of the Fuson is bleached, resulting in a strong color contrast between the rocks at the contact. Brownish—red, orange, and yellow siderite spherules commonly occur in the Fuson within 5 feet of the formational contact. These spherules have been discussed by Waagé (1959, p. 55—57) and Gries (1954). In many places, how- ever, the formational contact is much less obvious. In such places the basal Fall River unit was removed by erosion and replaced by sand during middle Fall River time, and in many places this Fall River sand- stone, designated fluvial unit 5, rests on the sand- stone of fluvial unit 4. At other places the sandstone of fluvial unit 5 is present at the base of the Fall River, but fluvial unit 4 is absent; or fluvial units 4 and 5 are both present but are separated by a thin sequence of the lower unit of the Fall River Forma- tion (pl. 1, north half, restored cross section). The criteria for identifying the contact vary considerably according to which of these combinations is present. LOWER UNIT The lower unit of the Fall River Formation is present throughout the southern Black Hills except where it is locally truncated by the sandstone facies of fluvial unit 5. It ranges in thickness from 0 to 50 feet and is composed principally of laminated mica- ceous carbonaceous siltstone. Interlayered with the siltstone is light—gray very fine grained slightly mi- caceous sandstone. The sandstone beds are generally less than 1 foot thick and are rarely more than 10 feet thick. The rock generally contains small ellipsoidal con- cretionary layers of siltstone or very fine grained sandstone that superficially resemble augen struc— tures of some metamorphic rocks. The unweathered rock contains pyrite nodules a few inches in longest dimension. As a result of oxidation of these nodules and concretions, the weathered sandstone is com- monly stained brown or yellowish brown. In general, however, the relatively high carbon content of the siltstones has inhibited oxidation to the extent that they are light or medium gray, particularly on a freshly broken surface. Some of the thin sandstone beds are covered on the upper surface with ripple marks and a vermicu- lated pattern of raised ridges that have been inter- preted as “worm tracks” (Henry Bell III and E. V. Post, written _commun., 1957; Waagé, 1959). Many of the siltstone lenses contain faint low-angle cross— beds that are 1—2 inches in total length, suggesting that the sediment was transported by extremely gentle currents. Because of the striking contrast between these rocks and those of the underlying Fuson Member of the Lakota Formation, the formational contact where the lower unit is present is easily recognized. Many small uranium mines have been developed in the lower unit of the Fall River. MIDDLE UNIT (FLUVIAL UNIT 5) The middle unit of the Fall River, designated flu— vial unit 5, is the fifth of six major fluvial units in the Inyan Kara Group. It comprises a fluvial sand— stone and its associated marginal fine—grained depos- its. The fluvial sandstone crops out in an irregular band that trends generally northwest throughout most of the southern Black Hills (pl. 1). It is as much as 110 feet thick and is commonly cemented with calcite and silica. Erosion of part or all of the carbonaceous siltstone in the lower unit locally preceded deposition of fluvial unit 5. In places the lower unit was completely re- moved, but generally only the upper part was eroded. The fluvial sandstone was then deposited over much of the irregular surface, leaving a plain of low relief. The streams that deposited sand in the princi- pal channelways also deposited extensive overbank flood-plain deposits marginal to the sandstone-filled channels. The irregular lower contact and the rela- tion between the channel and flood—plain facies are shown on plate 1 (north half, restored cross section). The sandstone is light yellowish gray on freshly broken surfaces, and it weathers to shades of yellow and brown; generally, it is slightly darker than the Lakota sandstones. It forms prominent vertical cliffs along the canyons. The sandstone is composed of PETROGRAPHY ‘ 11 about 90 percent subrounded to rounded quartz, less than 5 percent feldspar, and a minor amount of chert. The heavy-mineral content is generally less than 1 percent, and mica is more abundant than in the older, Lakota sandstones. The sandstone is cross- bedded, fine to medium grained, and sparsely car— bonaceous. Iron sulfide and iron oxide nodules are common, and silicified tree trunks occur in a few places, particularly along the west side of Red Can- yon. Calcite cement is abundant in the sandstone near the axis of the Sheep Canyon monocline in the western part of the Flint Hill quadrangle, the east- ern part of the Edgemont quadrangle, and the south- eastern part of the Edgemont NE quadrangle. It is also abundant in the subsurface in some of the places where fluvial unit 5 is in contact with fluvial unit 4, such as in the southern part of the Edgemont NE quadrangle and the northern part of the Edgemont quadrangle. In other places the sandstone is tightly silicified, particularly on the crest of the Chilson anticline in the southern part of the Minnekahta quadrangle and the northern part of the Flint Hill quadrangle, on Horse Trap Mountain in the south- eastern part of the Minnekahta quadrangle, on the Barker dome in the southeastern part of the Jewel Cave SW quadrangle, and at the crest of Battle Mountain in the west-central part of the Hot Springs quadrangle. The fine-grained facies of the middle unit is com- posed of alternating thin tabular beds of gray sparsely carbonaceous claystone, light-brownish-gray micaceous very fine grained sandstone, and dark- gray carbonaceous siltstone. This facies is lithologi- cally similar to the underlying carbonaceous siltstone, and thus in places the two are difficult to distinguish. The facies interfingers with the fluvial sandstone and, except for a difference in color, is indistinguish— able from the overlying variegated mudstone. The fine-grained facies of the middle unit is 0—50 feet thick. UPPER UNIT (INCLUDES FLUVIAL UNIT 6) The upper unit of the Fall River is composed of variegated mudstone at the base overlain by fluvial unit 6, a sequence of fluvial sandstone and fine- grained equivalents of the fluvial sandstone (pl. 1, north half, restored cross section) that is designated the sixth and youngest of the major fluvial units. It crops out in the southeastern part of the southern Black Hills. The thickness of the upper unit ranges from about 40 to 120 feet and averages about 75 feet. The unit is highly argillaceous and is characteris- tically mottled red and gray, particularly in the mid- dle part. The top 1—2 feet is. normally light gray and locally contains abundant carbonized plant debris. The mudstone generally is 10—25 feet thick, except in the Angostura Reservoir area, where it includes erratically distributed bodies of sandstone and gray clay and is as much as 60 feet thick. Its lower bound- ary is gradational with either the fine-grained or the sandstone facies of unit 5. In some places the upper part of the mudstone seems to be gradational with the fine-grained facies of fluvial unit 6; but else- where, part or all of the variegated mudstone was removed by erosion prior to deposition of unit 6, and the contact is obviously unconformable. The mudstone has been recognized and mapped throughout much of the area between Pass Creek, which is in the southwestern part of the Jewel Cave SW quadrangle, and Hot Springs. There is little doubt that equivalents of the mudstone are present to the northwest in the Dewey, Clifton, and Fanny Peak quadrangles, although the unit has lost its eas- ily recognizable color in those areas. Except for patches of variegated mudstone in the Vicinity of the Wicker—Baldwin prospect near the north boundary of the Dewey quadrangle and in a few places in the Clifton and Fanny Peak quadrangles, probable equiv- alents of the variegated unit are various tones of gray ranging from nearly white to dark gray with- out any of the characteristic red and maroon colors. This makes correlation with the variegated mudstone to the southeast questionable, and for that reason no attempt has been made to map the unit separately in the Dewey, Clifton, and Fanny Peak quadrangles. Fluvial unit 6 ranges in thickness from about 30 feet in the northwestern part of the Fanny Peak quadrangle to about 100 feet in a few places in the Flint Hill quadrangle. The sandstone facies is most prominent east of the Edgemont NE quadrangle and generally consists of light-gray sandstone that is con- sistently 10—25 feet thick over large areas. It is gen- erally fine-grained where no more than about 20 feet thick but is crossbedded 'and medium to coarse grained where very much thicker. The sandstone grades laterally into a sequence composed of variable proportions of thin alternating tabular beds of fine-grained sandstone, siltstone, and claystone. In general the average grain size of the elastic material increases from predominantly clay in the Fanny Peak, Clifton, and Dewey quad- rangles to predominantly silt and sand in the Edge- mont NE quadrangle. This sequence, at least in part, appears to represent flood-plain deposits perhaps at the margin of a seaway, as concluded by Waagé (1959). PETROGRAPHY A petrographic study was made of sandstones and a few coarse siltstones from fluvial units 1—5 within 12 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS the Inyan Kara Group and from the underlying Unk- papa Sandstone (fig. 2). Samples from the Unkpapa Fall River Formation Unlt 5 cm _,4 N o .t' : XLD a: an; E JO EH C o E E OH 9: E D Unkpapa Sandstone EXPLANATION E Quartz, quartz overgrowths, chert, and silicified limestone WM Potassium feldspar ‘ - k Plagioclase Altered, ash, tuff, and felsite Clay Other grains FIGURE 2.——Average mineralogic composition, excluding ce- ment, in percent, of sandstone units in the Inyan Kara Group and the Unkpapa Sandstone. Sandstone were included because locally the source of some sediments of the Lakota is the Unkpapa. The study was undertaken to determine differences in mineralogy and grain-size distribution for sand- stones of each fluvial unit and to provide information for determining the source of sediments and tectonic changes in the source areas and in the Edgemont uranium district. Chip samples were collected from 84 localities (table 2) for study of the mineralogic composition and texture and for determination of the heavy-min- eral content. The thin-section modal analyses and the textural analyses were made by R. A. Cadigan of the US. Geological Survey following his reported proce- dures and classifications (Cadigan, 1959, p. 530, 533, 535). The heavy-mineral studies were done by Wol- cott. In the following sections on composition, grain size, and heavy minerals, the terms “percent by vol- ume,” “percent by weight,” and “percent of grains counted” are used. The composition was determined by point counts of thin sections which yield the vol~ ume of each constituent (Chayes, 1949, 1946). The grain-size—distribution frequencies arebased on the weight of each selected size fraction. The heavy- mineral percentages are based on the numbers of each detrital heavy mineral counted. COMPOSITION Thin sections of 51 samples were prepared and studied as outlined by Cadigan (1959, p. 533). P0- tassium feldspars and potassium-bearing clays were stained canary yellow to facilitate their identifica- tion. Petrographic modal composition of the rocks was estimated by point-count method using 500 points in each thin section. The composition, in per- cent by volume of each sample, is shown in table 3, and the average composition of each unit, excluding cement, is shown by histograms in figure 2. On the basis of the average composition, all units of the Inyan Kara Group that were sampled are ortho- quartzites (defined as containing more than 60 per- cent detrital siliceous grains and not more than 25 percent feldspar), and the Unkpapa Sandstone is a feldspathic lorthoquartzite. On the basis of mean grain size (table 4), three of the samples (L—3254 in unit 1 of the Lakota Formation and L—3246 and L—3253 of the Unkpapa Sandstone) are coarse silt- stones. All the units, as indicated by the presence of chert, quartzite, and silicified limestone grains, were derived in part from preexisting sedimentary rocks. Some differences in mineral composition among the Inyan Kara sandstones seem to be consistent. PETROGRAPHY 13 TABLE 2. —Localities of samples listed in tables 3, 4, and 7 Field . Field . _ . saggle Section, township, and range1 662161333121: sarflpk Section, township, and range1 dill/3131:6312 INYAN KARA GROUP INYAN KARA GROUP—Continued Fall River Formation Lakota Formation — Continued Fluvial unit 5 CHILSON MEMBER Fluvial unit 2 ...NE14NW1A sec. 33, T. 7 S. ., R. 6 E ......... Hot Springs. SW14SE1/4 sec. 29, T. 8 . .. .Cascade Springs. .SE1/1NW1A sec. 4, T .Flint Hill. .NW1/4SE1A sec. 32. T. 7 S. .Edgcmont NE. 3294 ................... NE%NE% sec. 5, T. 42 N. ....Clifton. 9,S 3379... ....SW14NE1/4 sec. 27, T. 8 ........... Flint Hill. 3380... .NW14NW1/1 sec. 12, T.9 D. 3381... NW%SE1A sec. 32, T. 8 3382... ...1/Wf SE14 sec 9. T. 42 N, 60 ....Clifton. 3383... ....SE1ANE14 sec. 22, T. 6 S. ., R. 1 E..... ....chcl Cave SW. 3384 SW1ANE1A sec. 24, T. 8 S, R. 4 E.. Cascade Springs. 3385... SE%NW% sec. 20, T. 8 S. ., R. 6 E.. .Angostura Reservoir. 3386... ...SW1/4NE1A sec. 8, T. 8 S .. R. 6 E... Do. 3387... ...NE1ASE14 sec. 16, T. 7 S., R. 6 E... ....Hot Springs. 3388 .SW148E14 sec. 16, T. 7 S., R. 6 E . Do. 3389 S1/ZSE1A sec. 166, T. 7 S... R. 6 E. . Do. 3390... ....SEMSEM, sec. ,T. 8 S., R. 4 E. ....Minnekahta. w ,s E SW W1Ascc.9,..TSS. 3266— 3270... 3271 Lakota Formation FUSON MEMBER Fluvial unit 4 NE 1/NW1/45ec.33.T.7S.,.R6E SW1//:S W14 sec 9, T. .SE1/(N W14 sec. 4, T. NE1/lNE1/i sec. 8, T. .NW1ASW14 sec 29, ....NW1A sec. 18, T. 5S. NWMSWM, sec 12, SE1/4NE14 scc.18. NE1/4NW1A sec. 20. ....NE1ASE14 sec. 21, Hot Springs. Flint Hill. . ....SW1ASW1/1 sec. 14, 6 S, ....Jewel Cavc SW. 3373.. SE1/48W1A sec. 4, T. 7 S. ., Burdock. 3374—3375. NW1/4NE1/4 sec. 27, T. 7 S, .2 E. .Edgemont NE. 3376—3377. SE1/ NE1/ sec. 21, T. 7 S. ., R. 2 E... Burdock. 3378 ....SW1ASE1/ a sec. 16. T. 7 S, R. 6 E. ..... Hot Springs. Fluvial unit 3 3262. ...NW14NE1/i sec. 33, T. 44 N. R. 60W ....... Fanny Peak. 3263 NW%NE1A sec. 7 T. S. ., R. 1 E ....... 3264 NE14NW1/4 sec. 10, T 42 N , R 60 W NEM} sec 28, T. 5 , ................ . . .1 ...SE1ASW1A sec. 29, T. 44N, R. 60W. ....SE1ASE1/. sec. 30, T. 4 S., R. 1 E ........ NW1/4NW1/4 sec. 10, T. 6 S., R. 1 E SE1ASW1A sec. 22, T. 43 N., R. 60 W. NW1ANW1A sec. 19, T. 6 S., R. 2 E ....SW148W1A sec. 14, T. 6 S., R. 1 E Jewel Ca\ 9 SW. D. Sl/,SW1/, sec. 2, T. 8 S. , R. 4 E. NNW1/4 E1/4sec. 5, T. 8S.,R.3. NE1/ NW1A sec. 3, T. 9 S. ., R. 5 E. Cascade Springs . W1ASW14 sec. 34, T. 8S.,R.5E . NW1/4NE1/1 sec. 30, T. 7 S. ., R. 6 E Hot Springs W14N W14 sec. 3, T. 8S.,R.3E Edgemont NE NW1/IS E14 sec. 2. T. 8 S., R. 3 E Minnekahta w1/,s E14 sec 18, T. 9 s, R. 4 Flint Hill. NE‘ASEM; sec. 21, T. 8 S, R. 4 E. Do. 3346-3349 S1/»N W14 sec. 35, T. 8 S. ., R. 5 E ...Angostura Reservoir. 3352—3353 NSE1A E14 sec. 1, T. 8 S. ., R. 3 E Minnekahta. 3354—3357 NE1ASW1/1 sec. 34, T. 7 S... R. 4 E Do. 3358-3359 ..SW1/QSE1/4 sec. 29. T. 8 S. ., R. 5 E.." ..Cascade Springs. 3360 ...................... SW1/4SE1A sec. 4. T. 7 S. 3361 ,.T 7 S. 3362—3365... . .. R- 4 3395—3398 5, T. 8 Fluvial unit 1 3254—3255... sec. 31, T. 8 S., R. 4 E ..... 3256— 3257 ..SW‘A SE14 NW14N W14 sec. 30, T. 7 S., R. 3 E.. NWM} sec. 12, T. NW1/4 sec. 10, T 25 ......... .SW14NE1/4 sec. 22, T. 7 S., R. 2 E. 3259-3260 ..NW1/4NW1A sec. 19, T. 6 S, R. 2 E.. 3261 ................... NE1/4NW1A sec. 32, T. 44 N. ., 3319— 3320 ......... NE14NE1A sec. 33, T. 7 S, R. 3321 . W1AI§E1A sec. 18, T. 9 S. R. 8 S. R. 42 ., . ewel Save SW. NWl/4N W1Asec. 23, T 6 NE%sec.14,T. 7S.R. 2E 3329. NE14 Edgemont NE. 3330.. NE1ASW1/, sec. 1, T. 8 S. , R. 3 E Minnekahta. 3335. NW1/ NW1A sec. 10, T. 6 S. ., R. 1 ewel Cave SW. 3336— 1,-_.NE1/l sec. 9, T. 6 S. ., R. 1 E o. 3394. NW W14 sec. 16, T. 8 S. ., R. 4 lint Hill UNKPAPA SANDSTONE 3245-3247... 3248 3249-3251 , . . . .. Angostura Reservoir. 3252-3253 T. 9 S. R 5 E ..Cascade Springs. 3313 ............. 2 T. 8 S. R 4 E ..... Flint Hill. 3314.. ..... NW1/, SE14 sec. 15, T. 8 S., R 4 E .. Do. 3315.. .. SE1/. NW14 sec. 12, T. 8 S., R. 5 E Angostura Reservoir. 3316.. ..NE1/1SW1A sec. 3 , T. 7 S., R. 4 E. Minnekahta. 3317—3318... ..... SW1/4 NE1/4 sec. 4, T. 9 S., R. 4 E ............ Flint Hill. 1North townships and west ranges are in Wyoming; south townships and east ranges are in South Dakota. These differences are (1) a decrease in the ratio of potassium feldspar to plagioclase from older to younger beds in the Lakota Formation (fig. 3, table 6), (2) locally abundant chert and silicified limestone grains in fluvial unit 3 of the Lakota For- mation (table 3), (3) the highest percentage of vol- canic materials in fluvial units 1 and 3 of the Lakota Formation (table 3), and (4) a significantly greater amount of mica in the Fall River compared with underlying units (table 3, fig. 3). The variation in clay content reported is not significant, because ma- trix material was lost in preparation of some of the thin sections. As would be expected, the feldspar con- tent in general decreases with increasing grain size (fig. 4). 537-784 0 - 74 - 2 GRAIN SIZE Particle-size analyses (table 4) were made of 51 samples to determine the properties of their grain- size distributions. The samples, which had also been used for thin-section analyses, were disaggregated and sieved, with sieve sizes graduated at 1/2-phi in- tervals from *3 to 0 phi and at 1AL-phi intervals from 0 to 4 phi; grains smaller than 4 phi were ana— lyzed by pipette methods using l-phi intervals to 10 phi. These data were then used in calculating the grain-size distribution by the method of moments as described by Krumbein and Pettijohn (1938). Pa- rameters derived in this manner are not directly comparable to those derived by the graphic methods of Inman (1952) or Folk (1957). As an example, 14 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS TABLE 3. —Mine7‘alogie composition (in percent by volume) of samples from the Inyan Kara [Sample localities Grains Fielc} Q t Chert and M‘caceous Altered Z - l 5:21.356 andlllaurartz Quartzite silicified Pfotizassmm Plagioclase and mafic ash, tuff, overgrowths1 limestone e spar rock and felsite INYAN KARA GROUP Fall River Formation Fluvial unit 5 3287 .......................................................... 91.0 0.0 0.2 0.0 3.4 0.0 0.2 3288... .. 89.8 .0 1.6 .6 6.8 .0 .0 3289... 62.8 .0 .2 1.0 10.6 .2 .4 3290 83.0 .0 .0 2.4 8.4 .0 .6 3291 .......................................................... 79.2 .6 .8 .4 1.6 .0 .0 3292... .. 87.4 .4 .8 1.6 2.6 .0 .2 3293... 81.2 .6 1.4 2.8 4.0 .6 .4 3294 96.0 .2 .4 1.0 1.6 .0 .4 Lakota Formation FUSON MEMBER Fluvial unit 4 3279 89.4 0.0 3.2 0.2 0.6 0.0 2.8 3280... 81.0 .8 1.4 .0 .2 .0 .2 3281... 81.4 .0 .2 .0 1.0 .0 .2 3282... 85.6 .0 .4 .0 2.8 .0 .4 3283... 96.4 .2 .4 .0 1.4 .0 .0 3284... 93.8 .2 .6 .0 1.2 .0 .6 3285... 95.0 .2 .8 .0 1.2 .0 .2 3286 94.8 .0 .0 1.0 1.4 .0 1.0 3295 79.2 .0 13.8 .0 2.0 .0 4.0 Fluvial unit 3 3262 15.2 0 0 77.2 0 0 0.2 0.0 6.6 3263 74.0 8 16.8 0 .8 .0 6.6 3264 89.2 2 2.4 8 1 6 .0 4.0 3265 54.4 0 5.0 4 2 .0 3.6 CHILSON MEMBER Fluvial unit 2 3266 81.8 0.0 1.8 2.8 1.4 0.0 1.6 3267... 86.0 .0 1.0 3.0 1.8 .0 2.0 3268 90.4 .0 1.0 2.0 1.2 .0 1.4 3269 86.8 .2 4.0 1.0 1.0 .0 2.2 3270 92.0 .0 4.4 1.0 .2 .0 .2 3271 89.4 .0 1.0 3.2 1.6 .0 1.8 3272... 89.2 .2 .6 1.8 .6 .0 .2 3273... 77.4 .0 .4 7.4 5.2 .0 .4 3274 87.4 .0 .0 7.2 2.2 .0 .2 3275 90.8 .0 2.0 2.6 1.6 .0 .6 3276... 89.2 .2 1.0 3.0 2.2 .0 1.2 3277... 63.4 .0 .0 .0 1.8 .0 .2 3278 83.6 .0 .4 2.4 1.2 .0 .4 Fluvial unit 1 3254 79.4 0.0 0.4 7.4 7.6 0.0 3.4 3255... 94.8 .0 .2 1.6 2.4 .0 .4 3256... 87.8 .0 1.6 .6 .6 .0 8.6 3257 95.2 .0 4 3.0 .6 .0 .8 3258 88.0 .6 .4 1.8 .4 .0 7.0 3259... 83.8 .0 .8 2.0 .8 .0 12.2 3260... 78.6 .2 .8 6.4 3.6 .2 3.2 3261 91.4 .2 .0 1.6 2.4 .2 .4 UNKPAPA SANDSTONE 3245 74.4 0.4 0.0 9.4 2.4 0.0 0.6 3246 61.6 .2 .0 10.6 5.2 .0 1.0 3247 76.8 .2 .0 8.4 3.0 .0 2.6 3248 85.4 .0 .0 .0 1.8 .0 . 1.2 3249 79.2 .2 .2 12.2 3.2 .0 1.4 3250 .......................................................... 85.2 .0 .0 9.6 2.4 .0 .0 3251... 82.4 .0 .0 11.8 3.0 .0 1.0 3252... 82.0 .0 .2 11.4 .6 .0 3.0 3253 .......................................................... 69.2 .0 .2 13.8 5.2 .0 1.8 ‘Quartz overgrowths could not be distinguished from quartz grains in most thin sections. filncludes heavy minerals and indeterminate grains. Group and the Unkpapa Sandstone as determined by point-count analyses of thin sections are given in table 2] PETROGRAPHY 15 Grains — Continued Matrix Cement Total . n . Kaolinitic Illite and Montmorillonite ' Carbonate Red iron . . 3 ggiiéis £31231; Miscellaneous- Mica clays mica clays andcfgl’zted and sulfate oxide 8‘1”“ matrix INYAN KARA GROUP — Continued Fall River Formation — Continued Fluvial unit 5 —- Continued 0.0 0.4 4.4 0.2 0.0 0.2 0.0 0.0 99.8 0.2 .0 .0 .6 .2 .0 .0 .4 .0 99.6 .4 ‘17.6 2.8 4.4 .0 .0 .0 .0 .0 100.0 .0 1.8 .8 2.6 .4 .0 .0 .0 .0 100.0 .0 .0 .0 3.4 4.0 .0 .0 10.0 .0 90.0 10.0 .0 .8 1.2 3.6 .0 .0 1.4 .0 98.6 1.4 .2 .6 .4 5.6 .0 .0 2.2 .0 97.8 2.2 .0 .0 .4 .0 .0 .0 .0 .0 100.0 .0 Lakota Formation — Continued FUSON MEMBER — Continued Fluvial unit 4 —- Continued 0.2 0.0 2.8 0.2 0.0 0.0 0.6 0.0 99.4 0.6 .0 .0 4.6 .0 .6 .0 4.8 6.4 88.8 11.2 .0 .2 8.2 .0 .4 .0 7.4 1.0 91.6 8.4 .4 .4 6.8 3.0 .2 .0 .0 .0 100.0 .0 .0 .0 1.6 .0 .0 .0 .0 .0 100.0 .0 .4 .4 .0 2.8 .0 .0 .0 .0 100.0 .0 .0 .0 1.6 .6 .0 .4 .0 .0 99.6 .4 .0 .0 .8 1.0 .0 .0 .0 .0 100.0 .0 .0 .0 .2 .0 .0 .0 .2 .6 99.2 .8 Fluvial unit 3 —- Continued 0.0 0.0 0.0 0.4 0.0 0.0 0.4 0.0 99.6 0.4 .0 .2 .0 .8 .0 .0 .0 .0 100.0 .0 .0 .0 .0 1.8 .0 .0 .0 .0 100.0 .0 .2 .0 .0 .0 .0 36.2 .0 .0 63.8 36.2 CHILSON MEMBER —— Continued Fluvial unit 2 — Continued 0.0 0.0 1.2 8.0 0.0 0.0 1.2 0.2 98.6 1.4 .2 .0 2.6 3.4 .0 .0 .0 .0 100.0 .0 .4 .0 .0 3.6 .0 .0 .0 .0 100.0 .0 .2 .0 .0 4.6 .0 .0 .0 .0 100.0 .0 .2 .0 1.8 .2 .0 .0 .0 .0 100.0 .0 .0 .0 2.4 .6 .0 .0 .0 .0 100.0 .0 .2 .2 .8 5.2 .0 .0 .8 .2 99.0 1.0 .2 .0 .8 7.8 .0 .0 .4 .0 99.6 .4 .0 .0 .4 1.8 .0 .0 .4 .4 99.2 .8 .0 .0 .2 2.2 .0 .0 .0 .0 100.0 .0 .0 .0 .6 2.6 .0 .0 .0 .0 100.0 .0 .2 .2 2.4 20.8 1.0 .0 10.0 .0 90.0 10.0 .0 .0 1.4 .0 .0 8.4 2.2 .0 89.4 10.6 Fluvial unit 1 —- Continued 0.4 0.0 0.6 0.8 0.0 0.0 0.0 0.0 100.0 0.0 .0 .0 .4 .2 .0 .0 .0 .0 100.0 .0 .0 .0 .0 .6 .0 .0 .2 .0 99.8 .2 .0 .0 .0 .0 .0 .0 .0 .0 100.0 .0 .4 .0 .4 1.0 .0 .0 .0 .0 100.0 .0 .0 .0 .4 .0 .0 .0 .0 .0 100.0 .0 .4 .2 .4 5.6 .2 .0 .0 .2 99.8 .2 .0 .2 .4 3.2 .0 .0 .0 .0 100.0 .0 UNKPAPA SANDSTONE — Continued 1.2 0.4 0.0 11.2 0.0 0.0 0.0 0.0 100.0 0.0 .4 .0 2.0 18.2 .0 .0 .8 .0 99.2 .8 .4 .0 2.2 6.2 .0 .0 .2 .0 99.8 .2 .0 .0 3.4 7.2 .0 .2 .8 .0 99.0 1.0 .0 .0 1.8 1.4 .0 .0 .4 .0 99.6 .4 .2 .0 2.4 .2 .0 .0 .0 .0 100.0 .0 .0 .0 1.0 .6 .0 .2 .0 .0 99.8 .2 .0 .2 .2 2.4 .0 .0 .0 .0 100.0 .0 .0 .2 5.0 1.8 .0 .0 2.8 .0 97.2 2.8 “As authigenic chert. ‘17.4 percent identified as chlorite. 16 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS MICA, IN PERCENT 0 OIS 1.0 .8 X8 Fall River Unit 5 Formation G r0 up Form ation FusonMember ] Unit4 K a r a Unit3 .13 | n y a n L a k 0 t a Chilson Member UnIt2 8. Unit 1 .9 Unkpapa Sandstone | l I O 1 2 3 4 RATIO OF POTASSIUM FELDSPAR TO PLAGIOCLASE FIGURE 3. — Variation in average mica content (X) and ratio of potassium feldspar to plagioclase (0) by fluvial unit. Number beside symbol indicates number of samples. table 5 compares mean, standard deviation, and skew- ness derived by the graphic methods of Inman and Folk with those derived by the method of moments for nine samples of the Unkpapa Sandstone. For all samples shown in table 5, the values of mean grain size are coarsest using Folk’s method, intermediate in size using Inman’s method, and finest using the method of moments. The standard deviation and skewness for all samples show that Inman’s method gives the lowest values, Folk’s method gives inter- mediate values, and the method of moments gives the highest values. In their study of Jurassic and Cretaceous sand- stones, Mapel, Chisholm, and Bergenback (1964) reported the results of grain-size analyses of about 275 samples from 30 localities in the Black Hills; eight of their localities are in the area of this report. They (Mapel and others, 1964, p. C8) used Inman’s (1952) method (table 5) for determining standard deviation and skewness and Folk’s (written commun., FELDSPAR, IN PERCENT 0 5 10 15 I I as ._ LO 5’8 t‘ x8 .8 _E c / as 3 / LLLE / / / / / / / / ‘ \ cm N \\ _H t 13\ ° :C: ('13 XL l 3 I (“E I _lq.) ‘ 5— I C I E I E I OH I 8| 8 4.; o 'E >\ 3 \ \ \ \ \ \ \ \\ a? \ m3 .9 \ mm X9 x'U =§ 3w l I 0.0 0.1 0.2 0.3 GRAIN SIZE, IN MILLIMETERS FIGURE 4.—Variation in average percent feldspar (X) and average mean grain size (a) by fluvial unit. Number beside symbol indicates number of samples. 1955) method (table 5) for determining mean grain size. The mean grain sizes of samples used in this re- port (table 4) range from very coarse sandstone to coarse siltstone; most of them are in the fine to very fine grained sandstone range. The variation in grain size by stratigraphic unit is shown in figure 5. Sam- ples from the Inyan Kara Group are coarser grained than samples from the Unkpapa Sandstone, which are typically very fine grained. Samples from the PETROGRAPHY 17 TABLE 4. — Statistical measures of the phi grain-size distribution of samples from the Inyan Kara Group and the Unkpapa Sandstone [Sample localities are given in table 2] . Grain size Standard . . . . . . . . . Field . . - . Skewness Kurtosxs Gram-Size distribution by percentiles, 1n ¢-notat10n sample (millimeters) devxatiion (phi (phi (1“) Mean Mode Median units) “mm “““3’ P2 P5 P1. P50 P84 P95 P... INYAN KARA GROUP Fall River Formation Fluvial unit 5 0.16 0.18 1.06 2.40 27.15 1.88 1.98 2.17 2.47 2.87 3.81 6.74 .24 .22 .90 2.03 28.59 1.43 1.57 1.77 2.17 2.64 3.20 4.47 .15 .16 1.15 1.80 17.37 1.77 1.92 2.18 2.68 3.25 4.55 6.83 .15 .13 1.29 1.46 10.45 2.18 2.27 2.49 2.92 3.87 5.72 8.07 .49 .46 1.77 1.29 7.90 .22 .55 .72 1.12 2.60 5.43 7.94 .24 .23 .82 2.17 36.36 1.45 1.58 1.79 2.12 2.56 3.40 4.32 .15 .16 .71 2.78 45.50 2.28 2.41 2.51 2.66 3.02 3.69 4.79 .24 .24 .80 1.80 23.82 1.35 1.50 1.71 2.04 2.52 3.15 4.21 Lakota Formation FUSON MEMBER Fluvial unit 4 ‘4 0.30 0.30 1.49 2.10 20.03 0.85 1.03 1.23 1.76 2.53 3.13 9.49 .60 .82 2.42 .52 2.82 —8.00 —7.13 —-2.63 .28 1.58 2.72 6.52 .30 .29 1.32 1.42 9.42 .15 .34 .96 1.79 2.76 3.39 6.51 .14 .15 1.42 1.20 9.17 1.07 1.23 1.62 2.78 3.66 4.65 7.75 .14 .17 1.18 1.64 16.27 1.45 1.67 1.98 2.54 3.23 4.30 6.49 .15 .16 1.27 2.14 19.75 2.12 2.21 2.35 2.68 3.15 4.87 8.57 .31 .30 .79 1.98 29.98 .93 1.07 1.36 1.74 2.21 2.66 3.86 .26 .22 1.19 1.64 16.57 1.05 1.34 1.68 2.17 2.87 3.90 6.04 .24 .18 1.78 1.39 9.00 1.10 1.33 1.72 2.48 3.55 5.90 10.26 Fluvial unit 3 0.23 0.25 1.49 —0.10 3.45 —1.85 ——0.57 0.84 1.99 2.67 3.58 4.66 .19 .22 1.32 1.00 10.04 —.04 .45 1.29 2.21 2.90 4.30 4.95 .24 .28 1.61 .31 6.71 —2.22 —1.64 .80 1.81 2.48 3 22 4.31 .17 .19 1.21 2.26 24.17 1.69 1.83 2.07 2.38 2.75 3 6 7.50 CHILSON MEMBER Fluvial unit 2 0.14 0.15 1.36 2.02 17.82 2.22 2.33 2.53 2.72 3.45 4.64 9.65 .14 .15 1.66 1.40 8.30 1.82 2.06 2.33 2.77 3.95 6.99 10.27 .17 .18 .70 3.25 57.53 1.76 1.92 2.16 2.45 2.82 3.62 4.29 .14 .16 1.33 2.47 24.82 1.97 2.11 2.31 2.62 2.94 3.59 10.08 .14 .14 1.29 1.33 11.37 1.49 1.75 2.19 2.86 3.94 4.77 7.45 .14 .15 1.26 1.84 17.00 1.98 2.19 2.40 2.74 3.78 4.70 7.92 .15 .15 1.10 2.00 21.99 1.80 2.06 2.42 2.76 3.46 4.21 6.55 .08 .09 1.05 2.07 22.80 2.69 2.83 3.03 3.45 3.92 4.74 7.20 .15 .15 1.04 2.06 24.48 1.95 2.08 2.37 2.78 3.54 4.18 5.52 .12 .11 1.06 1.54 17.50 1.87 2.09 2.58 3.20 3.88 4.52 5.50 .15 .15 1.34 1.81 15.66 1.82 2.13 2.46 2.78 3.51 4.67 8.93 .12 .10 1.97 1.11 4.46 2.55 2.67 2.74 3.28 4.74 10.04 10.79 .11 .10 1.59 1.34 8.04 2.33 2.53 2.67 3.27 4.28 7.19 10.20 Fluvial unit 1 0.03 0.06 1.29 1.12 8.62 2.61 2.73 3.02 4.04 4.74 5.80 8.77 .11 .10 .76 1.40 21.21 2.38 2.85 2.93 3.30 4.26 4.81 4.98 .14 .15 .84 2.42 35.47 2.02 2.17 2.43 2.76 3.16 3.64 4.43 .08 .09 .72 1.53 23.86 2.60 2.71 2.94 3.45 3.93 4.36 4.75 .16 .17 .97 2.26 29.80 1.72 1.82 2.15 2.54 3.17 3.80 4.80 .18 .20 1.43 1.58 16.74 .87 1.08 1.55 2.29 3.22 4.15 8.25 .05 .10 1.23 1.13 10.45 1.52 1.78 2.15 3.28 4.04 4.79 5.65 .21 .19 1.07 1.88 21.15 1.49 1.65 1.85 2.36 2.97 3.93 5.87 UNKPAPA SANDSTONE 0.13 0.12 1.79 1.50 8.16 2.33 2.47 2.60 3.07 3.84 8.63 10.55 .09 .08 1.95 1.13 4.22 2.82 2.97 3.22 3.72 4.97 10.27 10.75 .12 .11 2.23 1.18 4.58 2.54 2.66 2.81 3.22 4.86 10.66 10.95 .12 .12 2.08 1.68 5.85 2.47 2.67 2.74 3.05 3.66 10.55 10.88 .12 .12 1.83 1.52 8.70 2.40 2.59 2.79 3.10 3.73 10.17 10.84 .12 .13 1.96 1.43 7.46 1.93 2.12 2.39 2.99 3.65 10.25 10.81 .13 .13 2.00 1.36 6.56 2.53 2.60 2.68 2.98 3.62 10.30 10.82 .11 .13 1.37 1.97 17.57 2.21 2.49 2.59 2.93 3.44 4.35 10.03 .08 .08 1.79 1.45 7.42 2.78 2.92 3.15 3.56 4.24 10.15 10.75 Chilson Member of the Lakota Formation are gener- samples from the Chilson. In fact, pebbles and cob— ally very fine to fine-grained sandstones, and samples bles are commonly present in the Fuson sandstones from the Fuson Member are chiefly fine- to medium- but are practically nonexistent in the Chilson sand- grained sandstones. With one exception, all samples stones. This provides one criterion for distinguishing from the Fuson are at least as coarse grained as the between these members. Sandstone samples from the 18 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS Fall River Formation are typically fine grained and contain less silt and clay than samples from the La- kota or Unkpapa. The sorting of sandstones is expressed in terms of phi standard deviations of the grain-size distribu- tions; the higher the values, the poorer the sorting. Cadigan (1959, p. 531) has proposed a classification of sorting in phi units which is as follows: Less than 0.5, very well sorted; 0.5 to 1.0, well sorted; 1.0 to 2.0, moderately well sorted; 2.0 to 4.0, poorly sorted; greater than 4.0, unsorted. According to this scheme, as shown in figure 6 and table 4, all the samples from the Unkpapa Sandstone are moderately well to poorly sorted. Those from the Chilson Member of the La— kota Formation are moderately well to well sorted. Samples from fluvial unit 3 in the Fuson Member of the Lakota are moderately well sorted, and those from fluvial unit 4 are chiefly moderately well sorted. The average sorting in samples from the Lakota For- mation (table 6) is best in fluvial unit 1 and becomes progressively poorer in the younger fluvial units. In samples from fluvial unit 5 of the Fall River Forma- tion the average sorting is about equal to that in unit 1. Skewness is a measure of the asymmetry of the grain-size frequency distribution. It is positive where the particles in the finer half of the distribution are more poorly sorted than particles in the coarser half of the distribution, and it is negative where the coarser half of the grain-size distribution is more poorly sorted than the finer half. All the samples studied have positive skewness except one from flu- vial unit 3 of the Fuson Member of the Lakota For— mation (table 4), and it has only small negative skewness. The relation between skewness and mean grain size is shown in figure 6. Kurtosis is a measure of the peakedness of the grain-size distribution. Commonly, high kurtosis values occur in well-sorted distributions, whereas low values occur in the poorly sorted distributions. The grain-size distributions for samples from the Unkpapa Sandstone are only moderately peaked (av- eraging 7.84), whereas the better sorted grain-size distributions from fluvial units 1 and 2 of the Chil- son Member of the Lakota are, respectively, very highly to highly peaked (table 5). Grain—size distri- butions in the moderately well sorted samples from fluvial units 3 and 4 of the Fuson Member are less peaked than the distributions in samples from the Chilson. As expected, the average grain-size distri— bution for samples from fluvial unit 5 of the Fall River Formation is very highly peaked (even more highly peaked than the distributions in the Chilson Member). 40 I r l ' 5 g 30 L 8 samples A .2 g m is s 20 * s 3 LE 3 10 _ L 0 l l l 50 40 gsamples fl U- 50, E W _ m 40, 13 samples , _ H N o g 30 ~ ~ _ x a ,V m .1 g 10 . l L E 0 2 __ g 40 : 85amp|es l 5 .4 30— E 20 D 10 UP: 0 l l 60 , 501» 9 samples _ a, . 8 E , m 2 . D. 0') x 'o = s 3 U) 0 —2 —1 0 1 2 3 4 5 PHI MEAN GRAIN SIZE (M4)) FIGURE 5. — Distributions of phi mean grain sizes of samples from each fluvial unit. The vertical axes represent percent of samples. The relation of mean grain size to sorting (stan- dard deviation) for each stratigraphic unit reflects the total energy level or tectonic environment of the system and therefore indicates the amount of up- warp of the source area and the amount of subsi- dence in the area of deposition. This concept, as PETROGRAPHY 19 TABLE 5. — Comparison of results of three different methods for determining the phi parameters of the grain-size distribution of samples from the Unkpapa Sandstone [All measures are in phi units] Mean Standard deviation Skewness Present Present Present Folk2 report3 Inman1 Folk2 report3 Inman1 Folk2 reporta 3.17 3.53 0.62 1.24 1.79 0.24 0.52 1.50 3.97 4.35 .88 1.55 1.95 .43 .61 1.13 3.63 3.92 1.02 1.72 2.23 .61 .73 1.18 3.15 3.63 .46 1.42 2.08 .33 .61 1.68 3.21 3.55 .47 1.39 1.83 .34 .60 1.52 3.01 3.48 .63 1.55 1.96 .05 .41 1.43 3.09 3.55 .47 1.41 2.00 .36 .63 1.36 2.99 3.15 .42 .49 1.37 .21 .36 1.97 3.65 4.07 .54 1.37 1.79 .26 .53 1.45 1Inman (1952, p. 130) gave the following formulas for determining the phi parameters. The phi values are the grain sizes at the given percentiles: Meanz—d’l6 + $84 2 Standard deviation 2.1584—34316 _ $16 + (1)84 — 2¢50 Skewness_ 4,84 _ ¢16 2R. L. Folk (written commun., 1955) gave the following formulas for determining the phi parameters: 4316 + 4350 + 4384 Mean: 3 Standard deviationZ‘M + M 4 6.6 _¢16 + 4.84 — 2¢60 425 + «:95 ‘ 295° Skewness— 2(¢84 _ 4,16) + 201,95 — (1)5) aThe phi parameters used in the present report were determined by moment calculations (Krumbein and Pettijohn, 1938; Griffiths, 1967). TABLE 6. —Averages of selected properties of sandstones from the Inyan Kara Group and the Unkpapa Sandstone ROCK COMPOSITION AND TEXTURE1 Composition‘ Texture N b . Stratigraphic unit “gt“ er Feldspar ggfiissggyf‘ Siliceous Volcanic Mica £41.33: Sorting samples (percent) plagfifilase ($113.1) (:éilg‘nst) (percent) (221:) (no) Inyan Kara Group: Fall River Formation, fluvial unit 5 ...................... 8 6.1 0.2 86 0.3 0.68 0.19 1.06 Lakota Formation: Fuson Member, fluvial unit 4 ............................... 9 1.4 .1 93 1.0 .12 .29 1.43 fluvial unit 3... 4 1.0 .4 92 5.7 .05 .25 1.40 Chilson Member, fluvial unit 2... 13 4.6 1.7 88 1.0 .03 .11 1.29 fluvial unit 1... .. 8 5.3 1.3 88 4.0 .05 .12 1.04 Unkpapa Sandstone ........................................................ 9 12.7 3.2 78 1.4 .09 .08 1.89 HEAVY MINERALS2 . Angular Zircon . Anatase Number Zircon plus Other Stratigraphic unit of plus]. angular Garnet“ 1 plus grains3 samples tfgzgggglf tfgé-fcuetl‘iae ( percen (21:11:13 (percent) Inyan Kara Group: Fall River Formation, fluvial unit 5 .............................................. 12 32 11 1 58 2 Lakota Formation: Fuson Member, fluvial unit 4 ...................................................... 13 34 9 1 57 1 fluvial unit 3... 7 41 5 3 50 2 Chilson Member, fluvial unit 2... 27 51 3 2 42 2 fluvial unit 1... 13 47 8 2 41 5 Unkpapa Sandstone ................................................................................ 6 44 4 14 22 15 1Based on thin-section modal-composition data. “Dominantly black Opaques. ”Based on heavy-mineral grain counts. presented by Cadigan (1961), is the basis for inter- the tectonic concept recognizes that crustal upwarp pretations of tectonic activity during the Early Cre- provides a stream gradient (that is, energy) for the taceous which are given later in this report. Briefly, transport of sediment from the source area to the 20 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS Fall River Formation Unit 5 w I 0 | | O O o I Unit 4 G r o u p Fuson Member K a r a Unit3 Formation | n y a n PHI MEAN GRAIN SIZE (M4)) Lakota Unit2 w | .., ‘- | | l '8 . 1 Chilson Member Unit 1 3 _ c" - _ '. o _ Unkpapa Sandstone 5 J | I i 1 1 o 1 2 3 — 1 o 1 2 3 4 STANDARD DEVlATION SKEWNESS (SK¢) (aq>)—— SORTING FIGURE 6. — Phi mean grain size measures plotted over phi standard deviation (sorting) mea- sures and over skewness measures of grain—size distributions of samples of sandstone and coarse siltstone from the Inyan Kara Group and the Unkpapa Sandstone. PETROGRAPHY 21 site of deposition and provides energy for reworking and sorting of the sediment. The grain size of the sediment is limited by the level of available energy. Deposition from streams occurs as the stream gradi- ent (and energy of transport) decreases. Where sub- sidence is rapid along a stream profile, deposition may be both rapid and permanent, but where subsi- dence is slow, sedimentary deposits may be exposed to much reworking and sorting. Values of skewness, kurtosis, and standard devia- tion are indicators of the amount of reworking and sorting during deposition. According to Cadigan (1961, p. 137), high skewness and kurtosis values indicate that a large amount of reworking has taken place in and adjacent to the point of deposition of the sample. High kur- tosis values * * combined/with very fine grain size indicate low—energy-level reworking. High kurtosis values * * com- bined with fine to medium grain size indicate high-energy- level reworking. Either high- or low-energy-level reworking would be indicative 1‘ * * that the supply [of material] is below the transporting capacity of the geologic agent in the area of deposition, and that deposition (and subsidence) is taking place at a slow rate. Therefore, we conclude that sands of the Unkpapa originated from source areas having low tectonic up- lift and that rapid subsidence in the southern Black Hills caused a high rate of deposition and little re- working of the sediment. Low tectonic uplift oc- curred in source areas contributing sediment for fluvial units 1 and 2, and in the slowly subsiding area of the southern Black Hills a low rate of deposition enabled low-energy-level reworking of these sedi- ments before burial. The source areas of sediment for fluvial units 3 and 4 were moderately uplifted causing some high—energy-level reworking before rapid deposition and burial. Source areas for fluvial unit 5 remained relatively high, and much moderate- energy-level reworking and sorting of sediment oc— curred before final deposition. HEAVY MINERALS Heavy-mineral grain counts were made for 78 samples. Grains were separated from the 0.043- to 0.297—mm size fraction because we thought that this size range would yield the greatest variety of readily identifiable minerals. The heavy-mineral content of the samples studied was commonly a few tenths of 1 percent by weight but ranged from 0.02 to 1.32 percent. Grain mounts were made for each sample, and counts were made by traversing each mount along lines 1—2 mm apart and counting all grains that came under the crosshairs. For nearly all sam- ples a minimum of 100 nonopaque grains were counted and a minimum total of 300 opaque plus nonopaque grains. The percentage composition of the detrital-heavy-mineral suites for all samples is shown in table 7. For purposes of deciding whether authi- genic or epigenetic minerals were derived from detri- tal or secondary minerals, the following arbitrary assumptions were made. Anatase and leucoxene prob- ably formed from detrital titanium heavy minerals and were therefore counted. Many, if not most, hematite grains are pseudomorphous after pyrite and were therefore not counted as detrital compo- nents. Authigenic barite and pyrite were also ex- cluded, as they are clearly not detrital. Zircon, tourmaline, and anatase plus leucoxene form the bulk of detrital or detritally derived heavy minerals in the Inyan Kara Group and the Unkpapa Sandstone. Figure 7 shows the average percentages of the minerals by unit. The suites of heavy minerals from all units are very similar and constitute a chem- ically stable assemblage. In the units sampled, the proportions of zircon and tourmaline combined range from 16 to 73 percent of total heavy minerals, but most samples contain 30—50 percent (table 7). Zircon is generally more abundant than tourmaline. In the Inyan Kara Group propor- tions of anatase plus leucoxene range from 22 to 81 percent of the total heavy minerals, but most samples contain 40—60 percent. In contrast, the Unkpapa samples contain less than 30 percent anatase plus leucoxene and average about 22 percent. Garnet is present in amounts less than 5 percent in most Inyan Kara samples but is more abundant in the Unkpapa, where it averages 14 percent. Rutile and staurolite are minor constituents in samples of all units, but staurolite locally constitutes more than 10 percent in fluvial units 4 and 5. Black opaque minerals and mis- cellaneous grains compose as much as 5 percent of the heavy minerals in samples from the Inyan Kara but average about 15 percent for the Unkpapa. In their study, Mapel, Chisholm, and Bergenback (1964, p. 023, 030) recognized three fairly consis- tent nonopaque heavy-mineral zones in sandstones from Jurassic and Cretaceous formations of the Black Hills. The lower zone includes the Hulett Sand- stone and Redwater Shale Members of the Sundance Formation, the lower part of the Morrison Forma- tion, and locally the lower part of the Unkpapa Sandstone, all Late Jurassic age. This zone is char- acterized by having a garnet content averaging 30 percent of the nonopaque minerals. The middle zone consists of the upper part of the Morrison Forma- tion, most of the Unkpapa Sandstone, and, in the southern Black Hills, all the Lakota Formation. This zone is characterized by the dominance of rounded zircon and tourmaline and by a much lesser amount of garnet, which generally forms less than 5 percent 22 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS TABLE 7.—Percentage composition of the heavy-mineral suite in the 0.043- to 0.2.97-mm size fraction of samples from the Inyan Kara Gmup and the Unkpapa Sandstone as determined by mineral grain counts [0 indicates mineral not found; X indicates mineral present in amounts less than 1 percent. Sample localities are given in table 2] Field Zircon Tourmaline Zircon and tourmaline Anatase _ sample Angular Rounded Angular Rounded Angular Rounded Garnet Rutile S1:1ai‘tlem- and Other1 £62156: (L—) grains grains Total grains grains Total grains grains Total leucoxene INYAN KARA GROUP Fall River Formation Fluvial unit 5 3 10 13 7 8 15 10 18 28 X 2 1 68 X 364 3 6 9 7 10 17 10 16 26 0 2 5 66 X 371 0 9 9 9 0 9 9 9 18 2 0 4 68 7 244 3 15 18 8 6 14 11 21 32 0 2 X 63 2 2124 8 24 32 3 6 9 11 30 41 3 5 X 50 1 279 9 14 23 6 3 9 15 17 32 X 2 2 55 8 257 4 8 12 9 17 26 13 25 38 2 3 23 32 2 170 4 12 16 5 12 17 9 24 33 3 4 2 57 X 316 1 11 12 8 8 16 9 19 28 0 3 9 56 4 330 5 19 24 5 8 13 10 27 37 0 5 2 54 2 324 1 21 22 5 6 11 6 27 33 0 5 X 59 3 274 3 4 7 8 10 18 11 14 25 0 2 X 69 1 397 Average .................. 4 13 17 7 8 15 11 21 32 1 3 4 58 2 ...... Lakota Formation FUSON MEMBER Fluvial unit 4 1 9 10 5 5 10 6 14 20 0 X 2 77 0 461 4 15 19 6 11 17 10 26 36 0 4 X 59 1 301 2 25 27 6 14 20 8 39 47 0 2 9 40 2 251 5 14 19 12 11 23 17 25 42 0 3 3 50 2 252 2 16 18 3 8 11 5 24 29 0 2 10 56 3 241 X 4 4 5 16 21 5 20 25 0 2 31 38 4 299 4 32 36 1 27 28 5 59 64 X 1 X 33 X 302 5 23 28 4 4 8 9 27 36 2 4 X 56 X 237 4 7 11 6 6 12 10 13 23 3 0 5 67 1 265 4 11 15 6 15 21 10 26 36 3 l 1 58 1 306 4 16 20 6 5 11 10 21 31 6 1 2 58 2 341 4 7 11 9 9 18 13 16 29 0 4 X 66 X 334 1 9 10 5 7 12 6 16 22 0 X 2 73 2 478 Average .................. 3 15 18 6 10 16 9 25 34 1 2 5 57 1 ...... Fluvial unit 3 2 10 12 1 3 4 3 13 16 X X X 81 1 553 3 32 85 1 8 9 4 40 44 3 1 3 47 2 262 1 17 18 1 8 9 2 25 27 3 1 2 67 X 362 5 32 37 1 13 14 6 45 51 7 3 2 35 2 167 1 20 21 2 8 10 3 28 31 4 X 4 59 X 337 3 23 26 3 25 28 6 48 54 4 3 4 32 3 243 3 40 43 2 14 16 5 54 59 X 3 6 28 4 220 Average ................. 3 25 28 2 11 13 5 36 41 3 1 3 50 2 ...... CHILSON MEMBER Fluvial unit 2 3 34 37 0 23 23 3 57 60 2 1 1 34 2 348 3 16 19 0 12 12 3 28 31 1 2 2 61 3 310 6 41 47 2 11 13 8 52 60 10 3 X 26 l 263 2 30 32 1 18 19 3 48 51 3 2 l 41 2 302 1 22 23 1 27 28 2 49 51 2 X 1 45 1 284 1 26 27 4 24 28 5 50 55 2 3 X 39 X 230 0 15 15 2 19 21 2 34 36 3 l 2 58 X 281 1 22 23 2 22 24 3 44 47 2 3 1 45 2 330 3 19 22 2 35 37 5 54 59 4 2 X 33 1 321 2 17 19 2 21 23 4 38 42 2 2 2 48 4 344 2 18 20 1 31 32 3 49 52 2 2 1 41 2 293 4 26 30 0 21 21 4 47 51 X 3 3 42 l 302 2 26 28 0 23 23 2 49 51 X 1 4 38 6 229 1 20 21 1 17 18 2 37 39 X 4 X 54 3 282 3 24 27 0 19 19 3 43 46 5 1 l 45 2 304 2 26 28 1 23 24 3 49 52 4 2 4 34 4 231 4 31 35 X 19 19 4 50 54 3 4 0 34 5 354 2 41 43 1 18 19 3 59 62 0 2 1 23 12 177 3 20 23 1 29 30 4 49 53 2 2 X 42 1 294 X 28 28 0 24 24 X 52 52 1 2 X 41 4 268 3 29 32 0 31 31 3 60 63 0 2 X 32 2 299 4 41 45 1 16 17 5 57 62 0 3 0 31 4 310 2 31 33 2 20 22 4 51 55 4 2 X 37 2 374 2 37 39 3 24 27 5 61 66 0 3 0 31 0 3116 1 3 4 1 24 25 2 27 29 X 2 2 66 X 319 0 49 49 0 22 22 0 71 71 0 1 5 23 0 383 1 11 12 2 22 24 3 33 36 X 2 6 55 X 123 Average ................. 2 26 28 1 22 23 3 48 51 2 2 1 42 2 ...... PETROGRAPHY 23 TABLE 7.-—Percentage composition of the heavy-mineral suite in the 0.043- to 0.297-mm size fraction of samples from the Inyan Kara Group and the Unkpapa Sandstone as determined by mineral grain counts —— Continued Field Zircon Tourmaline Zircon and tourmaline Anatase _ sample Angular Rounded Angular Rounded Angular Rounded Garnet Rutile Stauro- and 5,3236% Othcrl (IF) grains grains Total grains grains Total grains grains Total leucoxene INYAN KARA GROUP — Continued Lakota Formation —- Continued CHILSON MEMBER — Continued Fluvial unit 1 2 8 10 5 7 12 7 15 22 0 4 X 68 5 366 6 15 21 6 12 18 12 27 39 8 2 1 27 23 200 5 16 21 1 14 15 6 30 36 X 5 X 54 4 316 2 13 15 0 37 37 2 50 52 4 X 3 40 1 212 5 30 35 X 16 16 5 46 51 X 8 0 36 5 295 5 36 41 1 13 14 6 49 55 5 3 X 31 6 333 4 29 33 2 20 22 6 49 55 4 3 1 35 2 284 2 7 9 4 14 18 6 21 27 0 3 0 65 5 319 7 25 32 4 18 22 11 43 54 6 3 4 30 3 310 10 20 30 8 4 12 18 24 42 0 4 0 45 4 277 3 24 27 6 23 29 9 47 56 0 4 1 36 3 194 4 56 60 2 11 13 6 67 73 X 3 X 22 2 284 1 19 20 4 22 26 5 41 46 2 3 X 46 2 357 Average .................. 4 23 27 4 16 20 8 39 47 2 4 1 41 5 ...... UNKPAPA SANDSTONE 15 18 2 12 14 5 27 32 6 1 3 23 35 216 18 21 1 29 30 4 47 51 10 2 1 29 7 259 22 23 1 30 31 2 52 54 8 1 6 28 3 296 35 41 1 9 10 7 44 51 13 5 0 28 3 341 16 18 0 10 10 2 26 28 18 1 1 9 43 309 21 21 0 25 25 X 46 46 33 X 3 16 X 312 Average .................. 3 21 24 1 19 20 4 40 44 14 2 3 22 15 ...... 1Black opaque minerals, biotite, monazite( 7), and spinel( 7). 2Less than 100 nonopaque grains counted because sample was predominantly iron oxide. 3Less than 100 nonopaque grains listed because authigenic barite (counted but not listed) more abundant than total of all other nonopaque minerals. of the nonopaque suite. The upper zone, in the south- ern Black Hills, consists of the Fall River Formation and the Newcastle Sandstone. It is characterized by predominantly angular grains of zircon and tourma— line. The results of the present study agree rather well with the conclusions of Mapel, Chisholm, and Bergenback (1964) , but the results of the two studies cannot be compared directly. In the present study, detrital opaque heavy minerals as well as nonopaque minerals were included, and the 0.043- to 0.297-mm size fraction was used. Mapel, Chisholm, and Bergen- back (1964) confined their study to nonopaque heavy minerals, mostly in the 0.062- to 0.125-mm size frac- tion. The first factor lowers the percentages of the nonopaque heavy minerals listed in the present re- port; the second factor, which includes larger grain sizes, probably accounts for the greater percentage of rounded grains of the zircon and tourmaline listed in this report. Mapel, Chisholm, and Bergenback (1964, fig. 12) showed that of the combined zircon and tourmaline grains in the 0.062- to 0.125-mm size fraction, a line drawn at 40 percent angular grains separates 92 percent of the Fall River samples from 91 percent of the Lakota samples, with the Fall River Formation containing the most angular grains. A somewhat similar division can be made in the pres- ent study. Figure 8 shows the percentage of angular grains of the zircon and tourmaline. A line drawn at 26 percent angular grains separates 92 percent of the Fall River samples from 82 percent of the Lakota samples. The difference between the 26-percent ver- sus 40-percent division is probably the result of greater rounding of coarser grains and differences in operator judgment. All the samples from the Unk- papa Sandstone contain less than 20 percent angular zircon and tourmaline grains. The samples from flu- vial unit 4 in the upper part of the Lakota contain a greater percentage of angular zircon and tourma- line grains than samples from older units in the Lakota and are more similar to the samples from the Fall River Formation. This is in agreement with the findings by Mapel, Chisholm, and Bergenback ( 1964, fig. 12). SOURCE or SAND AND THE INFLUENCE OF TECTONIC ACTIVITY UPON DEPOSITION or LOWER CRETACEOUS SEDIMENTARY MATERIALS The sandstones that have been sampled have a considerable variation in the composition of the non- siliceous fraction, the heavy-mineral fraction, and the mean grain size. In general these variations con- stitute detrital assemblages that characterize the Unkpapa Sandstone, units 1 and 2, units 3 and 4, and unit 5, but some assemblages overlap these stratigraphic units. The assemblages of characteristic minerals that have been determined by the petrographic study are 24 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS as 2;: “7 oz“ .2 _E c __ 3 N LLB L c o _ L (U .. o (\I r: x c N D _l L 0 .D E 0 2 C O 2 LE 0 ._. 3: C :> 33 «8 all) .113 CC (V Dm PERCENT 60 50 40 3O 20 10 0 6O 50 40 30 20 10 O 50 4O 30 20 10 0 50 4O 3O 20 10 0 50 40 30 20 10 0 so 40 30 20 10 O 12 samples 13 samples 7 samples 27 samples 13 samples 6 samples A + L FIGURE 7.—Average percentage composition of heavy—min- eral suites in samples from sandstone units in the Inyan Kara Group and the Unkpapa Sandstone. Z, zircon; T, tour- maline; G, garnet; R, rutile; S, staurolite; A + L, anatase plus leucoxene; 0, other minerals. shown in table 8. The data show that the Unkpapa Sandstone is characterized by a very fine grained sandstone and siltstone containing more garnet and feldspar, having a higher potassium-feldspar—plagio— clase ratio, and containing less anatase and leucox— ene and generally less angular tourmaline than the sandstones of the Inyan Kara Group. Units 1 and 2 contain more rounded and less angular tourmaline and zircon than does unit 5 in the Fall River Forma- tion. Fluvial unit 5 contains much more mica than do the older units, and fluvial unit 3 contains an abnor- mally high amount of chert and silicified limestone. In general, however, the mineral assemblages of units 3 and 4 of the Fuson Member are transitional in composition between the assemblages of the Chil- son Member of the Lakota and those of the Fall River. All these assemblages are generally similar to assemblages described by Mackenzie and Poole (1962, p. 62—71). From a study of the Dakota Sandstone in the Western Interior, which includes equivalents of the Inyan Kara Group, they found two suites of detrital minerals diagnostic of source areas. (1) The eastern suite, relative to the western suite, contains more feldspar, muscovite, chlorite, chloritoid, angu- lar tourmaline, and heavy minerals in general and contains less chert. They concluded that most of the sandstones were probably derived from the Canadian Shield. (2) The western suite of detrital minerals was derived primarily from pre—Cretaceous sedimen- tary rocks of the Cordilleran region to the west. Similar detrital mineral suites are present in the Lakota and Fall River sandstones in the southern Black Hills. By analogy it would appear that these sandstones also were derived from eastern and west- Fall River U . . Formation rm 5 Unit 4 Fuson Member Unit 3 Unit 2 Inyan Kara Group Lakota Formation Chllson Member ‘ Unit 1 Unkpapa Sandstone O 20 4O 60 PERCENT FIGURE 8. — Proportion of angular grains in combined zircon and tourmaline varieties for each of 76 samples (0.043- to 0.297-mm size fraction) from six sandstone units in the Inyan Kara Group and the Unkpapa Sandstone. Each dot represents one sample. PETROGRAPHY TABLE 8.——Auerage percentage of selected 25 minerals in samples from the Inyan Kara Group and the Unkpapa Sandstone [High, intermediate, and low percentages for each column were determined by equal interval grouping of log values for the range in each column] 2 S C c —* E t 5 <3 = c g 5 a: h '_ ‘— '5 O d) O h 0 .: E E _ 5‘1; 13% S 33E.§_§ f; v, E +3 is}; -2 : ‘” 4- > S 1: EE 3 ggmwsg N .5 = 3:» 5:1; 2*“ g E ‘E 3 w 3 E :15 = :oEfiB- E g g «:3 37:05 =§ :1 153 :1 S E 2 '- go 8 3‘52; 3 ‘5 no a 23;: Dan; E‘g :0 m 22 a ‘5 ~“—’ E E “ 0: n:+2'—+"' '- .2 no; :2 2+3 <~ < g g m g g E g 'a s 1% S 4. ... a E a: I :2 .2 a E % g s k ~ 5 s s > = .g 5 § Percentage of heavy minerals o " Percentage of heavy minerals (J a. L = 8 samples 12 samples 12 samples samples 2 e f g Fluvial unit 5 1 . 8 13 21 32 17 . 7 4 0.68 E 5 (0—3) (3—17) (4—24) (9—30) (18-41) (7-32) (32—69) (6‘15) (3'9) (0-8) (0-2.8) u. . . 13 ' a samples 9 samples 13 samples 9 samples 13 samples :samples: 3 _ Fluvial “'1" 4 1 1.4 1.3 0,1 10 15 25 34 18 1 2.3 ’ .57 9 s g _ g (0—6) (0.2-2.8) (0.2-2.8) (0-1) (4-27) (4-32) (13—59) (20-64) (4-36) (0'4) (0-133) 433-77) (5-17) {1-12) .5 3 <5 3 E E“ ‘= E 1:: E E w c: g 4 samples 7. 4 samples samples .3 3 l. ._ g . '7. g m ‘-' hi. : x N Fluvial unll 3 1 0.7 0.3 11 _ 25 28 5.7 22.4 50 0.05 l: E (0.2-2.4) (0.2-1.6) (0—013) (3»25) (10-110) (12-43} : (316~6.6) (2.44712) (28-81) (070.2) : _ , . a o >, 1... ...... = 27 samples 27 samples sanllgles _ m .. I; 5 Fluvial unit 2 2.9 22 26 42 ‘51 23 3 1 2 0.03 s ‘E (0-57.43 (ll—353 . (3-49} (2841) (29»71) (4-49) (0-8) (0—4) (0—6) (0-0.2) m cu ’, E . _l c 8 g ..;;. $13 samples 13 samples samples :5 ...... .1 5:3 .. , . ,, U . . Fluwal unlt l 3.1 :6 23 39 47 ' 27 4 (0.6“? ,4) (M37) (7-56) (1543'!) (22-73) [9-60)‘ 0.4- 122 g sam les 9 samples 6 samples 6 samples 'U fi . ": w 14 12.7 a .53.] 21 40 as 2e § (6-33) (1.849) (0.6452) (Gm-13.8) (9-30) 5) (2&52) (28—54} (18-41) 3 ' ', » = D EXPLAN B High percentage Intermediate percentage B Low percentage 3 ern source areas. The detailed mapping that has been done in the southern Black Hills, however, permits a more detailed account of the stratigraphic distribu- tion of the detrital mineral assemblages than could be given by Mackenzie and Poole. If we assume that the sandstones making up the Unkpapa Sandstone and the sandstones of the Lakota and Fall River Formations were derived from east- ern and western source areas and if we utilize the same criteria to identify the sandstones that were derived from each area, then the depositional history can be surmised. In Late Jurassic time an eastern source area was Average mineral percentage for stratigraphic unit ATION (9-30) X Indicates mineral present in amounts less than 1 percent Range of mineral percent- age for each stratigraphic umt subjected to minor tectonic uplift and erosion. Sands with an eastern suite of minerals eroded largely from sedimentary rocks exposed toward the east were re- deposited to form the Unkpapa Sandstone of the southeastern Black Hills while finer sedimentary material was being deposited to the west. This mate- rial was in part derived from the area east of the zero isopach shown in figure 9. At the begining of Cretaceous time mild regional uplift accompanied by volcanic activity apparently occurred west of the Black Hills area, possibly to the southwest in central Cblorado, and contributed tufi‘, ash, and felsite to sandstones of fluvial unit 1 of the l 26 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS “2.... . West edge of i Jurassic -., ”’7" rocks /-/' 2 r i i i \‘ UNITEDi STATES ‘_____________. ‘\__‘__J- ‘\ O MEXICO \ 300 MILES 300 KILOMETERS ..\ 0 FIGURE 9. —— Probable minimum extent of Jurassic rocks (pat- terned) in the Western Interior region at the end of the Jurassic Period (modified from McKee and others, 1956, pl. 1). Chilson Member. A contribution from the western source is suggested by the increased chert and de- creased mica content of the sandstones. Erosion proceeded simultaneously in eastern South Dakota. Subsidence and deposition by streams along the axis of the Black Hills syncline as described by Bolyard and McGregor (1966) was not as rapid during early Chilson time as during Late Jurassic time; thus, more low-energy reworking and sorting of sediments occurred before burial. While the sands of fluvial unit 2 were being de— posited during late Chilson time, volcanic and tec- tonic activity was relatively quiescent. This resulted in the deposition of less volcanic material and little change in the grain size of the sand — that is, little change in the energy level of the streams. The pro- portion of western-suite minerals, including rounded zircon and tourmaline, increased during Chilson time as subsidence shifted the Early Cretaceous syncline eastward and the eastern source areas either were eroded to low topographic relief or were slightly de- pressed. At the end of Chilson time renewed tectonic activ- ity caused minor uplift locally along northeast-trend- ing structures (discussed in the structure section). This minor local tectonic adjustment possibly was related to a renewal of uplift to the west, which is indicated by the composition of younger fluvial de- posits in the lower part of the Fuson Member. Sev- eral lakes were formed, apparently as a result of the tectonic activity, and evaporation of lake waters rich in calcium bicarbonate and calcium sulfate caused precipitation of the Minnewaste Limestone Member of the Lakota. The Fuson Member is composed mostly of lacus— trine mudstones and sandstones, but it also contains the crossbedded sandstones of fluvial units 3 and 4. These sandstones probably were deposited at energy levels generally greater than those at Which the other fluvial sandstones of the Inyan Kara were deposited, although the sandstone of fluvial unit 3 locally ex- hibits foreset bedding suggesting deltaic deposition (Cuppels, 1963). Similarly, the alternating tabular sets of horizontal and cross stratification found in the sandstone of unit 4 (Ryan, 1964) suggest that some of the sandstone was deposited as local deltaic or lacustrine deposits. The paradox of simultaneous high- and low-energy-level deposition probably re- sults indirectly from tectonic activity, which was strongest at the beginning and at the close of Fuson time. We postulate that, at the end of Minnewaste time, stream erosion or tectonic activity breached natural dams formed by uplift along northeast-trending structures and released large volumes of water stored in the lakes. This release of water, which in some places may have been catastrophic, probably was coupled with relatively high rates of flow. Stream gradients were steepened by local uplift, and channels locally were incised through the Morrison and into the Redwater Shale Member of the Sun- dance Formation. . The Fuson Member is characterized by mineral assemblages that are transitional in composition be- tween assemblages of the Chilson Member, which contain a large percentage of western-suite minerals, and the assemblage of fluvial unit 5 of the Fall River, which contains an abundance of eastern-suite min- erals. This transition is also evident within the Fuson, between the mineral assemblage of fluvial unit 3 in the lower part of the Fuson and the assem- blage of fluvial unit 4 in the upper part of the mem- ber. STRUCTURE , 27 Deposition in fluvial unit 3 is characterized by an abundance of western-suite minerals. Chert com- monly ranging in grain size from sand to pebble size is especially abundant. Chert grains may have been derived either from distant sources or from Paleo- zoic sediments, but the larger chert pebbles prob- ably were derived from local sources including chert lenses in the basal Fuson Member, the Minnewaste Limestone Member, and the Sundance Formation. Other silicified material, consisting of petrified wood and silica-cemented sand and silt from the Lakota, probably is included in the siliceous material of flu- vial unit 3. A high percentage of volcanic grains indicates that volcanic activity accompanied a re- newed uplift of the western source areas. The lim~ ited contribution of sediments of the eastern suite is marked by a low feldspar content and by a clay matrix that contains very little kaolinitic clay but much illitic and mica clay. Toward the end of Fuson time the eastern source area contributed much sediment to the sandstone of fluvial unit 4. Volcanic material, rounded zircon, and chert are less abundant in this sandstone than in the older fluvial unit 3, whereas the mica content and the proportion of kaolinite to total clay are greater. The uplift of the eastern source areas may have been related to local deformation which shifted the axis of the Black Hills syncline to the west and caused the stream channel of fluvial unit 4 to migrate slightly westward in some areas. This shift of the channel is reflected by the maximum scouring of the channel and the maximum thickness of the fluvial sandstone at the southwest side of the paleodrainage, and by a noticeable thinning of the sandstone at the northeast side of the drainage (Gott and Schnabel, 1963, pl. 13). By Middle Fall River time the eastern source areas supplied most of the sediment to the southern Black Hills area. Paleocurrent directions in sand- stone of fluvial unit 5 in the southeastern Black Hills suggest a streamflow from the east and southeast which deposited much plagioclase feldspar and abun- dant angular tourmaline and zircon. Corresponding decreases in the abundance of rounded tourmaline and zircon and in the percentage of volcanic grains confirm the decrease in sediment from western source areas. The continued low garnet content in the sediments indicates that significant amounts of garnet were not eroded from the outcrops of Pre- cambrian rocks in the eastern source area at this time. STRUCTURE The Black Hills uplift consists of an arcuate north- to northwest-trending dome-shaped anticline that is surrounded by the Missouri Plateau (Fenneman, 1931, p. 79). The mapped area included in the pres- ent report has about 6,000 feet of structural relief and lies across the south end of the uplift (pl. 1). The area may be divided into three parts — eastern, central, and western parts — each having a different structural character. (1) The eastern part of the mapped area is folded into three relatively large sinuous south-plunging anticlines and several smaller anticlines (pl. 2) which shape the south end of the uplift. The Black Hills gravity axis coincides with the Chilson anticline 5 miles east of Edgemont, S. Dak. Nearly all the anticlines are asymmetric, having a gentle southeast—dipping flank, a steep west- dipping flank, and a parallel syncline lying about 1 mile west of the crest (pl. 1). The west side of this folded area is bounded by the south-plunging Sheep Canyon monocline along the flank of the Chilson anticline. (2) The central part of the mapped area consists of the southwest-dipping flank of the Black Hills, which is modified by the broad Dewey terrace, by three northwest-trending anticlines, by the north- east-trending normal faults of the Dewey and Long Mountain structural zones (pl. 1, north half), and by smaller normal faults. (3) North of the Dewey terrace, within the western part of the mapped area, major north- and northwest-trending Fanny Peak and Black Hills monoclines form the margin of the Black Hills uplift and the adjoining Powder River basin to the west. These monoclines are transected by small northeast-trending normal faults and by a few northwest—trending faults. In addition, a smaller monocline and two small north-trending anticlines are present. Configuration of the folds in the area is shown on plate 1 by structure contours drawn on the base of the Fall River Formation or on the recon- structed base Where the Fall River has been removed by erosion. FOLDS The asymmetric, slightly arcuate Dudley anticline, 2 miles east of Hot Springs, S. Dak., can be traced southward for 9 miles along the outcrop of the Inyan Kara Group to the Cheyenne River, 11/2 miles north of the Angostura Reservoir. The south-plunging anticline has an amplitude of as much as 600 feet and has about 100 feet of closure (Wolcott, 1967). The Cascade anticline, 2 miles west of Hot Springs, is the largest fold of the southeastern Black Hills. The anticline has an amplitude of 1,300 feet and has as much as 650 feet of structural closure (Wolcott, 1967). The steep west flank of this asymmetric anti- cline attains a maximum dip of 70° SW., as con- trasted to an average dip of 5° SE. on the east flank. West of Hot Springs the anticline forms a ridge that 28 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS is held up by dip slopes of the resistant Minnekahta Limestone, and farther south it forms a ridge that is held up by resistant sandstones of the Inyan Kara Group. The south-plunging structure follows a sinu- ous 17-mile-long course across the area as it trends first to the southwest and then to the south and southeast. The anticlinal axis bifurcates south of Cascade Springs; the main axis continues an addi- tional 8 miles south of the area of this report. The south—plunging Chilson anticline, 5 miles east of Edgemont, is at least 30 miles long, but only the northern 10 miles of the structure lies within the area discussed here. The asymmetric fold has an amplitude of 800 feet, and its gentle flank dips only 20—3O SE. Resistant sandstones of the Inyan Kara form a topographic high along the axis of the struc- ture. The northernmost 3 miles of the gently dipping southwest-trending Cottonwood Creek anticline lies within the mapped area and has little, if any, topo- graphic expression. The fold has an amplitude of only 100 feet, and strata exposed at the surface con- sist predominantly of easily eroded shales of Creta— ceous age. The south-plunging nose of another asymmetric anticline enters the area 7 miles northwest of Hot Springs and continues southward 4 miles before it terminates. The steep flank dips 10° W. and the gentle flank dips 3° SE., forming a fold with 400 feet of amplitude. Rocks of the anticline exposed at the surface consist of the Minnekahta Limestone, Opeche Formation, and Minnelusa Formation, a stratigraphic sequence of alternating resistant and nonresistant strata that erosion has irregularly dis- sected to partially mask topographic expression of the fold. Three southeast-trending anticlines having ampli- tudes of 100—200 feet are present in the central part of the mapped area. These parallel structural fea- tures dip 6°—13° (Braddock, 1963). The longest ex- tends south of the Dewey fault zone for 7 miles and then terminates in a 11/2-mile-wide closed structural feature known as the Barker Dome. The two smaller anticlines north of the Dewey fault zone are only 2—3 miles long and less than 1 mile wide. Two other south—trending anticlines are at the west side of the mapped area, 3 miles northeast of the L A K Ranch and 5 miles south of the ranch. The first-mentioned anticline is at least 5 miles long and has an amplitude of 600 feet. It is bounded on the west side by the Fanny Peak monocline and on the east by an asymmetric syncline. The other anti- cline, 5 miles south of the L A K Ranch, has an am- plitude of 200 feet and is bounded on the west by the Fanny Peak monocline and on the east by a shallow syncline. A part of the common boundary of the Black Hills uplift and Powder River basin lies within the area and is formed by segments of the intersecting north- west-trending Black Hills monocline and north-north- east-trending Fanny Peak monocline. Northwest of the intersection of these monoclines at the LAK Ranch, 7 miles southeast of Newcastle, Wyo., the basin-uplift boundary is formed by the Black Hills monocline (pl. 1). Sandstones of the Inyan Kara Group crop out on a hogback along the axis of the monocline, and then within a mile they plunge 2,000 feet beneath the shales that underlie the plains. South-southeast of the intersection, the monocline diverges from the margin of the basin and has about 1,000 feet of relief, but within 12 miles the monocline gradually merges into the southwest-dipping flank of the uplift. The Fanny Peak monocline forms the basin-uplift margin south of the L A K Ranch (pl. 1, north half) and, within the mapped area, has about 2,300 feet of relief. North of the ranch the monocline, exposed lower in the stratigraphic section, is steeper but has only 1,200 feet of relief. A smaller, unnamed monocline with 800 feet of structural relief lies between the Black Hills and Fanny Peak monoclines north of the L A'K Ranch. This monocline trends southward 3 miles from the northern boundary of the area before swinging to the southeast. About 21/2 miles east of Edgemont the west-dip- ping south-plunging Sheep Canyon monocline at the west margin of the Livingston terrace has 400 feet of relief within a distance of half a mile. The slightly sinuous monocline trends almost due north for 12 miles. The southwest flank of the Black Hills is modified by the Dewey, Edgemont, and Livingston structural terraces, as well as by several small unnamed ter- races indicated by the structure contours on plate 1. The Dewey terrace, bounded by the Fanny Peak monocline on the west and bisected by the Dewey fault zone, covers more than 30 square miles in the Dewey quadrangle and extends south of the mapped area, where it is not as well defined. The Edgemont terrace, which covers about 10 square miles (Ryan, 1964), is present at Edgemont, north of the Cotton- wood Creek anticline, and is bounded on the east by the Sheep Canyon monocline. Much of the terrace is overlain by alluvium of Quaternary age, and there- fore, details of the structure are not known. The smaller, Livingston terrace, 4 miles northeast of Edgemont, is bounded on the west by the Sheep Can- STRUCTURE 29 yon monocline and on the east by the Chilson anti— cline. Rocks of the Inyan Kara Group crop out on the terrace, forming a gentle south-dipping surface. A small unnamed terrace covering 1—2 square miles is adjacent to the northwest side of the Long Moun— tain structural zone about 8 miles north of Edge- mont. FAULTS Steeply dipping to vertical northeast—trending nor- mal faults are common in the northwest and central parts of the area but are sparse in the folded eastern part. Generally, the north sides of the faults are up— raised, as occurs in the Dewey and Long Mountain structural zones (pl. 2), in the central part of the area. The Dewey structural zone consists of sinuous en echelon steeply dipping to vertical normal faults that uplift the north side of the zone a total of 500 feet by a combination of fault displacement and drag. The fault zone can be traced for 13 miles northeastward across the Dewey and Jewel Cave SW quadrangles, before the zone bifurcates east of the mapped area (pl. 2). One branch continues east for 6 miles, and the other branch trends an equal dis- tance to the northeast. Although no direct evidence for horizontal movement along the faults is reported, the sinuous en echelon trace of the faults suggests that a minor strike-slip component of movement may possibly exist within the fault zone. The less well defined Long Mountain structural zone, 7 miles north of Edgemont, consists of small northeast—trending normal faults exposed in rocks of the Inyan Kara Group and Sundance Formation within a zone measuring several miles across. Indi— vidual faults within this zone generally have been traced less than a mile, and continuity of the struc— tures is variable. For 2 miles southwest of Long Mountain, where the faults border a structural ter- race, the zone is more clearly defined, and the north- west sides of the faults are uplifted. To the north, strata are downdropped toward the center of a wide northeast—trending fault zone. The faults have a dis- placement of as much as 40 feet, but adjacent to the faults as much as 60 feet of additional structural relief results from folding of the sedimentary strata. In the Clifton and Dewey quadrangles sinuous and arcuate or ring faults and low-angle faults have been mapped in addition to the usual northeast—trending faults. The sinuous faults are randomly oriented and may be associated with the arcuate faults, such as those 11 miles north of Dewey. There, the faults are present in an area where anomalous gravity measure- ments indicate high relief on the buried surface of Precambrian rocks. The faults may have resulted 537-784 0 - 74 - 3 from compaction of sediments around the basement high, as was suggested by Cuppels (1963), but they may also have resulted from dissolution and removal of evaporites in the Minnelusa Formation. Two minor northwest-trending reverse(?) faults in sandstone of fluvial unit 5 of the Fall River For- mation 3 miles north of the Dewey fault dip at low angles to the southwest. Dips range from nearly horizontal to 40? SW. and average about 25° SW. Slickensides and breccia along one of the faults were traced about 3 miles. The topography on the exposed fluvial unit 5 sandstone suggests that the southwest side of the faults may have been uplifted as much as 30 feet by reverse movement; however, most of the displacement probably occurred along bedding planes within the sandstone and is not readily discernible. jOINTs Joints within the southern Black Hills area are nearly vertical and commonly strike northeast or northwest. The major set of joints within the north and central parts of the area strike northeast, whereas a northwest orientation is dominant in the folded eastern part of the area (fig. 10). The differ- ences in orientation of major joint sets probably re- flect divergent stresses that deformed two major basement blocks, as discussed later. STRUCTURAL INTERPRETATION Uplift of the Black Hills probably began in Late Cretaceous time and continued until early Eocene time (Bartram, 1940). Chamberlin (1945) sug— gested that compression in a northeast direction may have produced north and northwest shear zones that determined the outline of the Black Hills; however, Noble (1952) believed that the main structural fea- tures of the uplift resulted from vertical forces asso- ciated with igneous intrusion. Osterwald and Dean (1961, p. 345—346) noted that structures of Paleo- zoic and Mesozoic age at the south end of the Black Hills trend parallel to structures of Precambrian age; they suggested that “the original Precambrian structures guided later and recurrent deformation.” PRECAMBRIAN STRUCTURE The Precambrian structure of a nearby area in the central part of the Black Hills was interpreted by Redden (1968) to have evolved during three periods of deformation. (1) Major north-northwest-trend— ing, west-dipping, isoclinal folds and subparallel faults were formed, and the rocks were metamor- phosed. Redden (1968, pl. 34) inferred that displace- ment along many of the faults resulted in reverse throw. (2) In the metamorphosed rocks, shear defor- mation, localized along northeast trends, formed 30 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS 104°00’ EXPLANATION \ 43° Primary joint set 45’ 2 I /’ Secondary joint set —< l l \3 4 \ \\ 3 / a 3b \' 0‘“ \ 0 “Kl/p/ I c.‘ sx$>’/ 103°45 103°30' 30' #dfi' I <5“ I 5 6 70““ ‘3 8 9 / Q l 2.. ‘10)“) xx“ x ‘/ $9 I 9%“ (,s/ < \p “(1‘ <83“ E 4* 9V \ c: O / 21M V No data El: / / O /10 11 ’ 12 13 >‘ E B D Lv \/7 \ IO / k0 / I 43" 15’ Joint Sets Map Reference AF— No. Primary Secondary 1 Brobst and Epstein (1963) ................. N. 45° E N. 20°~45° W. 2 Cuppels (1963) ..................... N. 40°—50° E. N. 50°—60° W. 3a Brobst (1961).... N. 10°—45° E. N. 10°—40° W. 3b ...... do .................... N. 45°~60° E N. 10°—40° W. 4 Braddock (1963).... N. 80 E. N. 50° W. 5 Schnabel (1963) ............... N. 75 —85" E N. 35°—45° E. 6 Gott and Schnabel (1963) ................... N. 20 W. NE. 7 Wilmarth and Smith (1957a, b. c, d) N. 30 —40° W N. 50°—60° E. 8 Wolcott and others (1962) .................. No data No data. 9 D. E. Wolcott (unpub. data, 1969).. N 40" W 10 Ryan (1964) ........................................... N 60° E N., N. 40" W. 11 Bell and Post (1971). N. 30° W N. 75°—80° E. N. 20°—40° W. N. 40°—50° W. 12 Post (1967) ............................................. N. 70° E. 13 J. J. Connor (unpub. data, 1969) ..... FIGURE 10. — Average orientation of joint sets in the southern Black Hills. nearly vertical foliation. (3) Intrusion of granite and pegmatite masses domed the rocks. At this time pegmatite dikes were intruded along the northeast— trending shear foliation, as well as along bedding— plane foliation. RECURRENT DEFORMATION Sedimentary rocks in the southern Black Hills were repeatedly deformed along northeast trends during the Mesozoic Era and again during the Lara- mide orogeny. This deformation, which paralleled northeast-trending structures of Precambrian age, is most evident in the Dewey and Long Mountain structural zones, where mild structural adjustments affected deposition of the Inyan Kara Group prior to faulting that displaced the Inyan Kara. Mild structural deformation during the Early Cretaceous diverted the main northwest-flowing consequent streams and affected the courses of their tributaries. Thick fluvial sandstones were deposited where streamflow was restricted to areas of more rapid subsidence, along the axis of a gentle northwest- trending syncline (Bolyard and McGregor, 1966), whereas finer grained and interbedded sediments were deposited on the more stable interstream areas. Locally, sandstone was deposited in small northeast- trending channels where tributaries flowed parallel to the secondary structures. The Dewey structural zone underwent minor de- formation during Middle to Late Jurassic and Early Cretaceous time, prior to the Laramide faulting. Early uplift of the area immediately north of the Dewey fault is indicated by the nearly total absence of the Canyon Springs Sandstone Member in out- crops of the Sundance Formation of Late Jurassic age. At one small outcrop north of the Dewey fault the Canyon Springs rests upon an irregular erosion surface on the Spearfish Formation, but south of the fault the Canyon Springs Member is conformable with the Spearfish (Braddock, 1963). The area north of the fault, therefore, was uplifted or upwarped during Canyon Springs time while sandstones were deposited south of the fault. Later during Early Cre— taceous time, mild deformation at the Dewey struc— tural zone affected the course of consequent streams that deposited channel sandstones of the Inyan Kara Group (pl. 1, north half). During deposition of flu- vial unit 1 of the Chilson Member, the northwest- flowing stream changed course and flowed westward at the structural zone before resuming its northwest course. Similarly, the stream that deposited fluvial sandstone of unit 4 of the Fuson Member altered course slightly at the structural zone. Recurrent deformation during Early Cretaceous time also preceded Laramide faulting in the Long Mountain structural zone. Repeatedly, the northwest- flowing streams that deposited fluvial units 1, 2, 5, and 6 were diverted to the northeast at the struc- tural zone as the area north of the zone remained stable or was slightly elevated. Rapid subsidence at the structural zone apparently determined the course of a northeast-flowing tributary during much of Inyan Kara time. Although direct evidence of Early Cretaceous movement along northeast-trending structures of Precambrian age is lacking, many of these older structures are known. Layered pegmatite dikes of Precambrian age, mapped northwest of Pringle by Redden (1963), mark northeast-trending structures STRUCTURE 31 of Precambrian age that are alined with a northern branch of the Dewey structural zone (pl. 2). Simi- larly, geophysical data indicate a large concealed northeast—trending wrench fault northeast of the Long Mountain structural zone (pl. 2). Another con- cealed structure of Precambrian age is indicated by the sharp bend in an aeromagnetic anomaly north of Hot Springs (Meuschke and others, 1963). This structure apparently yielded to Laramide deforma- tional stresses and thereby influenced the folding of the asymmetrical anticlines in the eastern part of the area. The concealed structure is coincident with the north end of a lineament that is marked by northeasterly bends and northward terminations of the Dudley, Cascade, Chilson, and Cottonwood Creek anticlines of Laramide age (pl. 2). This lineament trends S. 60" W. for 25 miles to Edgemont, S. Dak. During the repeated deformation along the struc- tural zones, the Paleozoic rocks probably were badly fractured. Later, when artesian pressures caused ground waters to migrate vertically through the stratigraphic section, these structural zones were especially favorable for the development of solution collapse structures discussed later. DEFORMATIONAL FORCES A major vertical force, as proposed by Noble (1952), probably caused the Laramide uplift of the Black Hills, but many structures within the mapped area indicate secondary compressive stresses from a westerly direction. These lateral stresses acted in a northeast to easterly direction and, locally, in a southeasterly direction. Northeastward compression probably formed the three northwest—trending anticlines in the central part of the area and the low-angle reverse(?) faults north of Dewey. Higher on the flank of the Black Hills, toward the axis of the uplift, the stress was eastward, as indicated by a change of strike of faults in the Dewey structural zone. Similarly, the general northeast strike of major joint sets changes to a more easterly orientation in the Jewel Cave SW quadrangle (fig. 10). The change in stress orienta- tion possibly is related to a buttressing effect by the granitic intrusive at Harney Peak (pl. 2) and to a deflection of the compressive force toward the east. An eastward compression is also believed to have formed the anticlines in the eastern part of the area. The stress probably was transmitted through a basement block lying north of the lineament previ- ously discussed. The eastward compressive force exerted by the northern block would have imparted both eastward and southward force vectors upon the adjacent southern block, and it would have created a resultant stress acting in an east—southeast direction. This east-southeast force probably caused the east- ward deflection of the anticlinal folds along the linea— ment. The divergent orientation of forces acting upon the two blocks created a different orientation for the major joint sets on each side of the linea— ment. Although local variations in joint patterns exist, the major joint set on the northern block strikes northeasterly, whereas the major set on the south block strikes northwesterly (fig. 10). To a lesser degree the Dewey and Long Mountain struc— tural zones also appear to have affected the orienta- tion of joint sets. SUBSIDENCE STRUCTURES Many structural features consisting of breccia pipes, collapse structures, and, possibly, synclinal folds are solution features formed by dissolution of beds of anhydrite, gypsum, limestone, dolomite, and, perhaps, salt with accompanying collapse or slumping of overlying rocks. Numerous caverns and solution breccias and a few breccia pipes present in the Pahasapa Limestone of Mississippian age locally cause draping and faulting of the overlying lower part of the Minnelusa Formation. More extensive solution has occurred in the upper part of the Min- nelusa, where nearly 250 feet of anhydrite and gyp— sum has been removed, as shown by figure 11 (see also Bowles and Braddock, 1963, p. C93), and sub- sidence of the interbedded sandstone, siltstone, and dolomite has formed founder breccias (Braddock, 1963). Most breccia pipes bottom within the founder breccias of the Minnelusa; some pipes are exposed in vertical canyon walls for as much as 200 feet, and a few pipes stope upward as much as 1,300 feet to the Lakota Formation (Bowles and Braddock, 1963). Diameters of the pipes range from tens of feet to several hundred feet. These breccia pipes (fig. 12) consist of disoriented blocks, fragments, and detrital particles of sedimentary rocks which were displaced downward and which later were re- cemented by calcite deposited from artesian waters. The brecciation and disorientation of displaced blocks within a collapse structure are less intense toward the upper limit of stoping, high above the zone of solution. Where the structure terminates, only minor faulting, slight slumping, or draping may be present near the center of the collapse. Minor collapse at the surface may extend downward into a typical breccia pipe. Similarly, recent sinks within the outcrop of the Lakota Formation (Wolcott, 1967) probably pass downward into cemented or partially cemented breccias. 32 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS USGS 2 Pass Creek drill hole Hell Canyon section and USGS 1 drill hole Unit r ,_. Measured section . >5 .‘2 / 1‘}: a 8 ' ' E e :2 3: 1:! m: . . - — is ‘ ,1. l 55:: ,/' 2c I , 9ft D... 60m . Total depth ‘_'_" 682 ft 3 < EXPLANATION ’ EH Sandstone Limestone 4 < Siltstone Dolomite V M Shale Anhydrite 5 FEET METERS W ‘531ft 50 100 30 FIGURE 11. —- Stratigraphic sections of the Minnelusa Forma- tion, showing correlation of brecciated rocks in outcrop with anhydrite-bearing strata of the subsurface in Custer County, S. Dak. The locations of the stratigraphic sections are: Hell Canyon section, NWlA sec. 3 and NE% sec. 4, T. 5 S., R. 2 E.; USGS 1 Hell Canyon drill hole, sec. 3, T. 5 S., R. 2 E.; USGS 2 Pass Creek drill hole, sec. 1, T. 6 S., R. 1 E. (From Bowles and Braddock, 1963, fig. 83.2.) Some small synclinal folds in outcrops of Minne- kahta Limestone and Spearfish Formation may have been formed in part by solution. Braddock (1963) attributed undulations of the Minnekahta to the solu- tion and extensive removal of underlying anhydrite and gypsum from the Minnelusa, but he believed that the small synclinal folds were formed by gravity sliding during uplift of the Black Hills. Several small east-trending synclines at the center of the Jewel Cave SW quadrangle trend parallel or subparallel to the Dewey structural zone and to the major joint FIGURE 12. — Breccia pipe (p) in the upper part of the Min- nelusa Formation in Gettys Canyon, SE14 sec. 16, T. 3 S., R. 1 E., Custer County, S. Dak. Photograph by J. B. Ep- stein. (From Bowles and Braddock, 1963, fig. 83.4.) set north of the zone. These small synclines are pres— ent at steeply dipping parts of the southwest flank of an anticline where artesian movement of ground water toward the surface is likely. Possibly these and other small synclines were formed, in part, by solution of evapbrites along fracture zones in ad- vance of the general zone of solution and founder breccias. Since the Laramide uplift of the Black Hills, brec- cia pipes and collapses probably have formed under artesian conditions. A similar origin has been pro- posed for fissure caves and vertical shafts in eastern Missouri (Brod, 1964). It is postulated that the pre- Pennsylvanian karst surface on the Pahasapa Lime- stone provided high permeability and permitted rapid ground-water recharge at Limestone outcrops high on the flanks of the Black Hills. Limestone solu- tion in the Pahasapa formed collapses that frac- tured, folded, and faulted strata in the lower part of the Minnelusa, permitting artesian ground water to ascend from the Pahasapa and from sandstones in the lower part of the Minnelusa through the over- lying evaporites. These waters were unsaturated with respect to anhydrite and gypsum before en- countering the evaporites. This permitted calcium sulfate to be dissolved by ascending waters and caused breccia pipes to form as an initial stage of solution, in advance of the general front of solution activity. Solution collapse is controlled in part by tectonic structure, in part by sedimentary structure,- and in part by topography. All three factors may affect artesian movement of the large volumes of ground water required to dissolve enough rock to cause col- lapse. Continued solution, both of soluble strata peripheral to the collapse and of soluble breccia k GROUND WATER 33 fragments within the collapse, enables further stoping. Pipes form prior to the development of founder breccias and may be present several miles downdip in advance of the founder breccias. Initially, solution occurs both along bedding planes and along fractures. Breccia pipes are likely to develop at the intersection of fractures, particularly in zones of intense fracturing and (or) faulting, such as the Dewey and Long Mountain structural zones. In these zones breccia pipes are more common on the uplifted side of the faults, where artesian water has a shorter path to the surface and may encounter less resistance to flow en route to a discharge point. An example of this structural control of pipe formation is present in the Jewel Cave SW quadrangle, where two pipes in the Sundance Formation are on the upthrown fault block, only 290 and 400 feet from the Dewey fault (pl. 1). GROUND ‘VATER This ground-water study, which tests the theory that ground water introduced uranium into the In- yan Kara Group to form the uranium deposits, was begun after unpublished analyses of water samples from 32 wells marginal to the southern Black Hills were made available through the courtesy of William Chenoweth of the US. Atomic Energy Commission. If this theory of mineralization is valid, studies of ground water at the margin of the Black Hills may provide an opportunity to examine the processes of uranium transportation and deposition. Data pre- sented in the following discussion indicate that in the southern Black Hills, uranium apparently is being introduced into the Inyan Kara Group by ar— tesian water from the Minnelusa Formation. Where a strong reducing environment exists at the locality of artesian recharge, uranium is rapidly precipitated and may form economic deposits; elsewhere, ura- nium introduced by the ground water is disseminated over a wide area to increase the uranium “back- ground” level within the Inyan Kara Group. As ero- sion of the Inyan Kara progresses, the leaching of low-grade deposits and disseminated uranium may provide an enriched mineralizing solution and result in secondary-enrichment ore bodies similar to roll— type uranium deposits found in several of the Ter- tiary basins in Wyoming. SOURCE OF GROUND WATER IN THE INYAN KARA GROUP Darton (1896, 1909) believed that ground—water recharge occurred at the exposures of what he called the Dakota Sandstone on the flanks of the Black Hills and that the water then migrated through this aquifer eastward under the plains of North and South Dakota. His View was generally accepted until Swenson (1968a, b) presented evidence indicating that much of the ground water obtained from the Dakota Sandstone in eastern North and South Da- kota was derived from recharge of the Englewood Formation and the Pahasapa Limestone on the east- ern flank of the Black Hills. This ground water flows eastward through the limestone aquifers until up- ward leakage into the Dakota Sandstone is made possible by the pre-Dakota erosion of the intervening sedimentary formations in the central and eastern parts of North and South Dakota. We believe that ground-water movement and the recharge of the In- yan Kara Group of the southern Black Hills is best explained by the following modification of the basic Swenson theory. The Minnelusa Formation, as well as the Engle- wood and Pahasapa Formations, apparently receives a significant amount of ground—water recharge from precipitation and runoff in the Black Hills, whereas only minor surface recharge enters aquifers of the Inyan Kara Group. Streams gaged by Brown (1944) at the east side of the Black Hills lost water—as much as 54 cubic feet per second — to the three major aquifers of Paleozoic age. In contrast, no measurable stream loss was detected at the Inyan Kara outcrop. In a recent study, Gries and Crooks (1968) reported that water losses to the Pahasapa Limestone for eight streams in the eastern Black Hills are roughly proportional to streamflow and that the losses vary seasonally. The total loss that they observed during the study, which did not in- clude water losses to the Minnelusa, ranged from “2.8 cubic feet per second in December 1967 to 164.5 cubic feet per second in June 1967.” The high rate of recharge to the deeper aquifers is possible because solution caverns in the limestones of Mississippian age and extensive solution brecciation in the Minne- lusa permit rapid ground-water recharge and enable a swift basinward flow. Locally in the outcrop area, ground water from the Minnelusa probably re- charges the underlying cavernous Pahasapa Lime- stone. As a result of the rapid flow of ground water, productive Minnelusa wells are scarce where the for- mation crops out, and yet, as reported by Whitcomb, Morris, Gordon, and Robinove (1958), large yields occur from some Minnelusa wells farther downdip at the margin of the Black Hills. The apparently limited recharge of the Inyan Kara Group by surface water seems incompatible with the large flow of water from wells in the Inyan Kara at the southwest flank of the Black Hills, just as it is incompatible with the amount of water pro- duced from the Dakota Sandstone during the last 80 years, discussed by Swenson (1968a). Davis, 34 Dyer, and Powell (1961) concluded that the water “must have moved into the aquifer by some method other than direct recharge at the outcrop.” They suggested that deeper aquifers, having appreciable artesian pressure, provide a part of the recharge to the Inyan Kara, even though relatively impermeable confining material intervenes. They also suggested that, locally, the Inyan Kara may be recharged at a high rate by an artesian flow of ground water from deeper aquifers through uncased and caved or cra- tered wells. Probably of greater significance, a high rate of artesian recharge may occur through the previously described collapses and breccia pipes, which form natural conduits to the Inyan Kara Group. The recharge of aquifers of the Inyan Kara Group by waters derived from older formations is strongly indicated by the composition of present-day spring waters emanating from formations older than the Lakota and Fall River Formations. Partial analyses of seven such spring waters are given in table 9 (see also Gott and Schnabel, 1963, p. 135) and show that the waters contain a high concentration of sulfate, bicarbonate, calcium, and magnesium. The equiva- lents per million of calcium and magnesium nearly perfectly balance the equivalents per million of sul— fate and bicarbonate. This balance demonstrates that the material being leached is largely anhydrite but includes lesser amounts of dolomite. The only pos- sible source for the sulfate, bicarbonate, calcium, and magnesium in these proportions is the evaporite zone in the Minnelusa Formation. Numerous collapse structures that served in the past as conduits for artesian flow of water were INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS located during mapping in the southern Black Hills (pl. 1). Direct artesian recharge of the Inyan Kara was possible where these structures penetrated the Lakota Formation. Elsewhere, pipes penetrated no higher than the Sundance Formation, and ground water may have flowed through the Canyon Springs Sandstone Member or other intermediate aquifers before finally encountering fractures that permitted continued upward migration to the Inyan Kara. Just as the older structures once served as conduits for artesian movement of ground water, recent collapses, such as the “Lost Wells” in the Lakota Formation near Hot Springs, S. Dak. (Wolcott, 1967), probably transmit artesian water at present. Temperatures recorded in water wells in the vicin- ity of the Black Hills also suggest not only a rapid surface recharge of the more porous and (or) cav— ernous formations but also, farther downdip, an ar— tesian flow of some of this water into overlying strata. Where rapid recharge of the deeper aquifers by surface water occurs, heat flow from underlying rocks may be insufficient to warm the ground water to a temperature predicted for an average geother- mal gradient; conversely, where rapid artesian re- charge of the higher aquifers by heated artesian water occurs, the heat flow to the ground surface may be insufficient to permit cooling of the water to the predicted temperatures. Adolphson and LeRoux (1968) reported an average geothermal gradient of 09°C per 100 feet for 42 wells that tap aquifers of pre-Jurassic age in the Black Hills area. The geo- thermal gradients, averaged for each formation, range from 07°C per 100 feet for the Minnelusa and Opeche Formations to 13°C per 100 feet for the TABLE 9. — Calcium, magnesium, bicarbonate, sulfate, and uranium in water from springs in the Minnelusa Formation [epm, equivalents per million (milligram equivalents per kilogram) ; ppm, parts per million; ppb, parts per billion] Calcium + Bicarbonate L H F’eld . c l ' M ' s If t- B‘ b P U ‘ (r133 ...:.1.ma,g,;;;1,um .31.)... .2312? mam 13.12.: ”agar . {saw Weston County, Wyo. 2208 33.38 33.25 532 83 1,420 225 12 2209 29.96 29.95 472 78 1,260 227 11 2210 24.66 24.76 402 56 1,040 190 4.7 2211 85.60 80.47 1,310 246 3,680 235 17 Fall River County, S. Dak. 2247 16.76 17.10 252 51 639 232 7.5 2249 34.56 35.36 508 112 1,610 112 6.3 2250 35.91 35.91 508 92 1,540 235 5.7 lN01: shown on plate 4 (outside mapped area). LOCALITIES SAMPLED Field sample Locality description 2208 ................... SE14 sec. 31, T. 45 N. R. 60 W. ,SW1/4 sec. 17, T. 45 N. .NElA sec. 31, T. 45N., R. 60W. R.60W. .About 7 miles north of Newcastle, Wyo., T. 46 N., R. 61 W. .Evans Plunge, Hot Springs, NwlA sec. 13, T. 7 S. ., R. 5 E. .N.W%sec 35, T, 7S., R. 5E. 2250 .................... Cascade Springs, SW14 sec 20, T. 8 S. R. 5 E. GROUND WATER 35 Spearfish Formation. Adolphson and LeRoux sug— gested that relatively low gradients computed for the Black Hills area may be due, in part, to “rapid down- ward movement of recharging waters in very porous formations” (such as the Pahasapa Limestone or Minnelusa Formation). In addition, their data indi- cate a progressive increase in the temperature gra— dient from the permeable Minnelusa Formation upward through relatively impermeable strata to the Spearfish Formation. The increase in the gradient probably results from an artesian movement of water from the Minnelusa Formation. Temperatures of water from wells and drill holes along the southwest flank of the Black Hills indicate that the warmer artesian flow progresses upward into the Inyan Kara Group. Geothermal gradients calculated for wells in the southern Black Hills ranged from 0.8°C to 70C per 100 feet (fig. 13). The average geothermal gradient for 19 wells that are deeper than 200 feet is 1.500 per 100 feet, in con- trast to the average gradient of 0.9°C per 100 feet determined by Adolphson and LeRoux (1968) for pre—Cretaceous rocks in the Black Hills area. The higher gradients calculated for temperatures re- corded at the shallower wells (fig. 13) are due, in part, to an artesian flow within the Inyan Kara, but GEOTHERMAL GRADIENT, IN °C PER 100 FEET 0 O 100 200 300 400 500 600 700 800 DEPTH OF WELL, IN FEET FIGURE 13. —«Variation in geothermal gradient with depth of well in the Inyan Kara Group. Numbers indicate selected wells shown on maps and listed in table 10. Temperatures recorded i1 flow at the surface. Well depths are reported depths. the magnitude of the gradients in some wells indi- cates that water probably has been heated in deeper aquifers and then has ascended to the Inyan Kara Group at the margin of the Black Hills. This inter- pretation of artesian recharge is further supported by the distribution and concentration of tritium in waters of the Inyan Kara and will be discussed later. (IOMPOS lTION The present composition of the ground waters probably reflects variations in composition that have existed marginal to the Inyan Kara outcrop since the Black Hills were uplifted and artesian circulation was established in the Paleozoic and Mesozoic rocks. Distribution patterns for the variations in ground— water composition have shifted basinward as ero- sion has progressively stripped the sedimentary rocks from the uplift- and lowered the water table. Ground water in the Minnelusa, Lakota, and Fall River Formations is classified into three general water types—calcium sulfate, sodium sulfate, and sodium bicarbonate—according to the most abun— dant pairs of cations and anions in solution (fig. 14). This system of classification was modified slightly so that ground-water composition could be mapped (pl. 3A) in the detail made possible by a plot of water composition on a multiple-trilinear diagram (p1. BB) of the type proposed by Piper (1944). The water types indicated on the combined cation-anion diagram are separated at the 50th percentiles, and the waters are named for the most abundant pair of cations and anions present in water of average com- position for each type. Because some ions, such as calcium and magnesium, are grouped together in the plot, water samples plotted near the 50th percentiles may have other ions in greater abundance than the indentifying pair. However, the grouping of these ions does not obscure the important genetic relation- ships within the ground water; therefore, the con- venience of easy referral to three water types and the advantage of more detailed mapping of ground— water composition provided by this system of classi— fication far outweigh the disadvantage of imprecise identification of an individual water sample. As the ground water migrates upward to the Inyan Kara Group and then basinward within the Lakota and Fall River aquifers, the composition of the water changes from a predominantly calcium sulfate water to a sodium sulfate water and, locally, to a sodium bicarbonate water (pl. 30). The first detectable change in composition of the ground water occurs within ascending waters where a loss of carbon di- oxide causes precipitat'on of calcite which results in a decrease in the proportion of calcium to other 36 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS cations remaining in the water. A second significant change takes place within the Inyan Kara Group where a further decrease of calcium ions as well as magnesium ions is accompanied by a proportionate increase in sodium ions in the water (fig. 14). This change is interpreted as a natural base-exchange softening of the waters. A third change in composi- tion of the water, occurring locally within the Lakota and Fall River Formations, results in modification of calcium and sodium sulfate water to sodium bi- carbonate water (fig. 14). The change from sulfate water to bicarbonate water in the Inyan Kara is interpreted as the prod- uct of several chemical reactions that probably occur simultaneously. Separate grouping ,of sodium bicar— bonate waters plotted on the aniOn and combined cation-anion diagram of plate 33 suggests that these 35 MINNELUSA FORMATION 30 2/6 x 1 a E Z LAKOTA 3 0 FALL RIVER z _ _ 0 j 25 Q FoflAT'O” FORMATION I; 5 ”/3' LAKOTA LAKOTA n: a: /’///, FORMATION FORMATION ’2 Lu 20 t ”/9? FALL RIVER 53,313: .0 Lu ”L 33:33: 0 m V 3’40: 2 I— /¢§’s’gfi 8 E 15 T 3“}3 0‘5 m 4 /3333 :3: 0 § /33::3 < - 3333 “3.3: 0! 310 e ’0’.‘o’4 ” ”9’: m o 3333 333 > m /3333: < 9.0.0.0, .9... P”Q « ’0’. /3:33 3'3 5 . 332:9: 3:30.: 9:...” ' .3 3:33" 39’ 92919:. :333‘ o "' I L Ncho, I EXPLANATION 323 m Na+K Ca Cl 7 W W . t a 33.3 A Mg HCO;,+C03 SO4 FIGURE 14. — Average composition of calcium sulfate, sodium sulfate, and sodium bicarbonate ground water from the Minnelusa, Lakota, and Fall River Formations. Concentra- tions are expressed as equivalents per million (cpm), that is, the chemical equivalence of a weight concentration (ppm) of ions in solution. Arrows indicate modification of water types. Composition of Minnelusa water is average from water sampled at localities 1—4 (pl. 4). All samples of water from Inyan Kara Group were obtained from wells (pl. 3A). chemical changes take place rapidly to completely transform the water as it flows through a zone less than 11/; miles wide (the minimum spacing between the sampled wells). Chemical reactions yielding high sodium bicarbonate waters were discussed by Foster (1950), who concluded that “carbonaceous material may act as a source of carbon dioxide which, when absorbed by water, enables the water to dissolve more calcium carbonate. If base-exchange materials are also present to replace calcium with sodium, a still greater amount of bicarbonate can be held in solution and high sodium bicarbonate waters * * * result.” In the bicarbonate water of the Inyan Kara, a low sulfate content and a concentration of as much as 150 ppm hydrogen sulfide (table 10), together with the isotopic fractionation of the sulfur (T. A. Rafter, 1969, written commun.) , suggest that sulfate reduction contributes to the genesis of the high so- dium bicarbonate water. The process of base-exchange softening in the sul— fate water and the genesis of bicarbonate water re- sult in two distinct patterns of distribution for the ground-water types in the Inyan Kara Group (p1. 3A). The softening of the sulfate water results in a pattern of progressive change from calcium sul— fate water near the Inyan Kara outcrop to sodium sulfate water southwestward down the regional dip. Superimposed on this pattern in the vicinity of the Long Mountain structural zone is the distribution pattern for the high sodium bicarbonate water. The chemical composition of the ground water is influenced by structures that affect the rate and di- rection of ground-water movement. A higher propor— tion of calcium may be present in the water where structure favors a rapid flow of artesian water from the Minnelusa. For example, the composition of ground water changes across the Dewey fault, where water on the upthrown, or north, block contains pro- portionately more calcium and magnesium and less sodium than water on the downdropped, or south, block (p1. 3A). Variations in water composition also occur at the southwestward projection of the Long Mountain structural zone (pl. 3A). FLOW (AS INDICATED BY TRITIUM DISTRIBUTION) The distribution of tritium in ground water at the margin of the Black Hills supports the interpretation of artesian recharge of the Inyan Kara Group and provides a measure of the rate of ground—water flow. Tritium, a radioactive isotope of hydrogen, has a half life of 12.26 years (Stewart and Hoffman, 1966). It is derived naturally by cosmic radiation in the atmosphere, but the concentrations are low and have been masked by large quantities of synthetic tritium GROUND WATER 0002 JN .23... hm 0.0m 5: MR .............................. 003 .m. .30 ............. 0N0 . ......................... 003 .5 .33. ......... 2.1.0 ................................ 00$ .3 ..E< ...... {em ............................... m00— ._~ .33... .m...00 .............................. 003 .3 .w=<: , Emu m... ....................................... 8 ,,,,,,, . ....... x ..mm ................................ 0002 .—N .23. ............ mN .0..m ............................. 00m; .3 .E<: ................. NN 5mm ............................... .003 .C .60 ....................... 2N wwwm .......................... $3 .3 .::< ....................... ow ..t ; .......................... 2 mm... .8 ................................ w. 5% $3 .2 .60 ....................... S .m .3550 3:: =3— VNd v0; ...... $2 .2 do ....................... 2 ................................ 002 .2 9.2.: 30— .ON .2: ................................. m0o~ .bfi “0.55.0 5m v m N n . de ow. c~.0N Vb. ...... mm go; 23 o 80 a En: ................................ 32 .E .92 ....................... _ .035 33.500 5.533 d S d S .I. S a m m. an 2... w. H m m m m. m o o m m m w 2 .1... HP 39 P s o m. I. e W m .D... a N u a d m. n z m 03 m 0 u 1 m. m. o s n u m. ) c m m w .12: am a m w. m a o w m. w m. w n... m m ) D u m. m. D. ) ) S m. m w m m ) ( m m:2 :8 50:00:00 . o M M m 0m m/u m m in... D mu 9 ) ) e ) mu 0 EoEoEwmuE 2:53 o AWE—a )0 m d m d W. w. W ( ( mm m m ( W ( :0 .ED 00 Ban. : m u MW mm. H s 3 .( G w m m $55 00 0:» 3 3:5 0:: 6:23.59 32:03 .3 03w: 0:: 33:53 202.520 0:: :03 :8 $2302 ”1m .3 :o 555 Em muEEmm :03 :3 302504 253239“ 5: .5 :39? Ho: Emu 28:02 A ...... 0 9.0034 .:2=E :0: 8.5: 3:: ”CB: :0: 3:302: N6 m mESa 5:053 ABC—:03 East: 2:: E22: .:.—. 62035:: .>E 2:2: .6: 2:2 .933 51.5.5250 50:25 :0: 2:253:00 :50 52:1: 5a 2.3; .50: ”22.35520 00 :0: .231?” .003 321.55. 03.255” 0:0 >03 .w=< E32: :3 02358 2255 .25.:qu 22:28 fieumuiumv4bv— Cu Catch—u.— ECEECC “Etna .CU: we u:Ct«:._FEE¢T >LCFLCr—n— 1:... In «C 3:4...» 0:;me Eva Eat 0323200 “00 003 «o :3 6:... 5:25.; w:t:0 200 05 E chwEhuS—u EENSQEB “Em .IQ .12E30n— xouum #02 .w: .3 5:25“; “2929:” zo>5w .2000 .m.D .3 mag—max dean—0:4... ES; .3 02396 3 .02 50.: 29:3 00 2min: ..:2mm_EEoU Guam 2an< .m.D :8 Eran—2: .2320 350:3 .05 .255 920:2 3 m:2 8.3:. 00 womb—2:: «$836 8.30M Saw: 2: 5 33.: 2.20 .8 £203 Skix $003. xo $323st I .3 Quad. INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS 38 N w 5N SMmSmm ............... H H w H a an $32,332. N m «N figmimm; : H w M w mm “\Hfiflfim . : v v ‘ N N H H N m oNv \Hva\Hm_m, N N H 0 ...ON Xmmim—m N w NH >3m>mz. H N H o H XBmXBZ N m NH XmZng. H N H e 2 SmZSmm N m 3 H8 v\H 3 H N H e Sulfiam N m :m N\HZ 5:50. H N H w “Humvmvzfim N w ..w SmZSmZ. . H 0 :5m :5 H N {m Q m . N x w 5252. H H gig”? .H. . m . $335 N m ..N N\HZ H850: H N H XBmSBZ H W m ,N . 3% N w o fiamfimm. H. N :2 {RHme .uNaQ .m. 3.230 L235 N w so Smmfiaz. H N : $2533 ow Hv ‘ wN .Hou X .Z 6 N w o Xamfiiz. H N mum gumxmfi ow Hv N Xmmfiaz m N w in immfimz H N o SmZXMm 8 HH. :N X32§mm v N w .m fimZXMZ. H N a X39332 co Hv .. oH N\_Z 6:: .m H32 6 N w .v fimmfima H N ..m Sulfi3m. 8 He ., N\_z 6:: .m .82 N N w :v immfimm. H N ............................... a a8 .32 ................. NH 8 av “““ Hm XmZSBZ H .H .m .m ..N Sm 62 .m .m .m. .N 5%. 52 .k .2 .2 .N 3m 52 62.5200 1 .QNaQ .m. SHHNNSD $3M Ssh dst .m .ESSD $3M 33R 63: ‘$339 233%» mm—EAAAHUOA HAL—243m 502 RA HH 8. NH .................. Ema ......................... ,mooH.mN.E< ....................... mm Nm we. +ONH: omA 3.55:5 l in: .m .3559 Six HHSH 1. n 1 H d H d G 5 3 S H 3 d S 3 I S m m w )5 >m m H a. m m m m m w m m m m u. m I. Hm. D o s o o m: m a. w m. an n. u m w . n z 0 00 X W u. u. I 0. 0 S U n ) u m w my” am a M w w a o w m. m m a 9 m. ) D u m. w D. ) ) 9 w m w m n ) ( m 2:: Ho“ cocoozoo do 1 d n )s )u a s d 3 O m ) ) e w 3 z EoEoSmmmE oEEmm H a d ( d n u o ( l v e ( oEEmm ) a. d m M m.. n. n.. ( ( ) D X ( ) ( «o HED we QEQ a ( m P w o N w. H 20 ( m J. ( 9 (m. ) 3 ( ( ( D. m 0 9 A U ( onHHHEHHoO I “3.30 GNSN :33: 95 5 33: ENE .8 £ng §P£ $328 .3 wwwSafiV I .OH mamflb placed in the atmosphere by thermonuclear explo— sions. Tritium is dissipated from the atmosphere largely by precipitation, or rain—out, of tritiated water (HTO), which then becomes a part of the surface— and ground-water systems. Since 1952, large quantities of tritium have been added to the atmosphere and peak concentrations in the water were reported during the winter of 1958—59 and in 1963. In 19 3 the average concentration of tritium in rain wa er in the Black Hills (data reported by Stewart an Hoffman, 1966) was about 3,500 Tu (tritium u its)1 (G. L. Stewart and R. K. Farns— worth, wri ten commun., 1968), or perhaps three times the 1 58—59 level of rain-out. During 1964—67, GROUND WATER tritium con clined, and concentratic entration in precipitation steadily de- in 1967 the weighted average tritium n of precipitation in the southern Black Hills was about 500 Tu (G. L. Stewart and T. A. Wyerman, written commun., 1970). (The average concentratic 2—10 Tu.) We samp Inyan Kara the time in at the marg May 1968, J n of natural tritium in the water is ed ground water from 26 wells in the Group during August 1967 to determine transit and rate of movement of water in of the Black Hills. During January— D. Larson of the US. Geological Survey analyzed the waters by using an analytical method having a minimum detection limit of 100 Tu (table 10). High conc entrations of tritium, ranging from 110 to 313 Tu, were distributed in a lobate pattern, and the southwest, leading edge of the detected tritium concentratio the Inyan K. taining triti three areas - cinity of Be tural zone, 2 River, west S. Dak. Hig n was as much as 4 miles downdip from ira outcrop (fig. 15). Ground water con— um flowed most rapidly basinward in — one on the Dewey terrace, in the vi- aver Creek north of the Dewey struc- nd two in the vicinity of the Cheyenne 3f Edgemont and southwest of Burdock, h tritium concentrations roughly paral- leled the Cheyenne River, and low values (less than 100 Tu) were present southwest of the river. We did not determine whether tritium values decrease to natural background amounts within the area sam— pled ; but L. L. Thatcher (written commun., 1969), by using a more sensitive method than the one used by Larson, analyzed one sample and found a con- centration of 14:20 Tu (table 10), apparently slightly more than the natural background level. The highe st tritium values are much lower than peak concentrations in rain-out during the 1958—59 and 1963 periods, indicating a dilution of young, ‘Tu E 1 tritium atom/10" hydrogen atoms E 3.2 picocurivs per liter. 39 highly tritiated water by an older water containing only natural concentrations of tritium. The amount of dilution can be estimated if the highest measured tritium values are corrected for radioactive decay and the age of the water is assumed. If we assume that the highest tritium concentration was derived from rain—out during 1958—59, then the initial value of the detected tritium, corrected for radioactive decay, was approximately 520 Tu. Similarly, if the highest tritium concentration was derived from rain— out during 1963, then the initial value, corrected for radioactive decay, was about 400 Tu. Both corrected tritium values are much lower than the weighted- average tritium rain-out for either period. The most highly tritiated water sampled in the Inyan Kara must have been diluted by older ground water in the respective proportions of either 1:1, if the tritium is from 1958-59 recharge, or 1:9, if it is from 1963 recharge. The 1:9 dilution ratio best fits the ob- served data. If the 1:9 ratio of tritiated water to older artesian water is valid, then the tritium con- centration in pre-1963 waters is reduced by dilution below the detection level employed in this study, and no lesser tritium pulse is observable. Conversely, if the 1:1 ratio calculated for 1958—59 recharge were valid, then a pulse of approximately 1,500 Tu should be present near the Inyan Kara outcrop. N0 com- parable concentration has been detected. We concluded, therefore, that the tritiated water recharged the Inyan Kara Group at the outcrop and then was diluted by older artesian water downdip along the margin of the Black Hills. Dilution has apparently occurred in the Vicinity of several wells near the Inyan Kara outcrop in the west-central and southeastern parts of the Burdock quadrangle, where less than the detectable amount of tritium (<100 Tu) was present in the water (fig. 15). These older waters are of the calcium sulfate type characteristic of artesian water from the Minnelusa Formation. In the west—central part of the Burdock quadrangle this Minnelusa type water forms the center of a tongue of a rapid basinward flow that apparently mixed with highly tritiated water farther downdip where the tritium content of the water increased to 113 Tu at well 21 and to about 200 Tu at well 24 (fig. 15). Widely varied rates of ground-water flow in the Inyan Kara are indicated by the tritium distribution. In the west-central part of the Burdock quadrangle, near the confluence of Beaver Creek and the Chey— enne River, a flow of 15 feet per day is required to transmit tritium rain—out of the year 1963 from the recharge area at the Inyan Kara outcrop to the posi- tion of the larger tritium concentrations detected by sampling during 1967. To the north, between the 40 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS 104°07’30” 43°37’30” 104 00 h a ‘2 .‘ '2. : > << i 32:: DEWEY ‘ ‘TERRACE 30’ WYOMING SOUTH DAKOTA 43‘22’30" 103°52’30” EXPLANATION QKs Sedimentary rocks of Quater- nary to Early Cretaceous age Inyan Kara Group of Early Cretaceous age JPs Sedimentary rocks of Jurassic to Permian age Contact 1 O3°4 5’ Dashed where projected. Bar and ball on dowhthrowu side >100“ Isogram showing tritium con- tent of ground water Dashed where inferred. Ha- chures indicate closed low value Interval is 25 tritium um'ts (Tu) .5 Water well Referred to in table 10 10 MILES l 5 10 KILOMETERS FIGURE 15.—Tritium distribution in ground water of the Inyan Kara Group of the southern Black Hills, August 1967. Beaver Creek—Cheyenne River area and the Dewey fault, ground water in the Inyan Kara flows less rapidly, but the flow rate cannot be calculated from the available data. The exceedingly rapid flow rate in the Beaver Creek—Cheyenne River area possibly results from artesian discharge of the Inyan Kara water into gravels of the two streams; if so, a high rate of flow would not occur within the Inyan Kara at greater depths in the Powder River basin. REDUCING ENVIRONMENT Ground water in the Inyan Kara Group changes from an oxidizing solution near the outcrop to a re- ducing solution farther downdip. The transition (fig. 16) is very abrupt along the southwest projec- tion of the Long Mountain structural zone, where the water changes from the calcium sulfate type to a very strongly reducing hydrogen sulfide—bearing water of the sodium bicarbonate type. Elsewhere, the reducing environment generally is less intense, and the oxidation-reduction front may be present farther downdip, as along the Dewey structural zone. HYDROGEN SULFIDE Hydrogen sulfide in the ground water ranges in content from less than 0.05 ppm in the calcium sul- fate water of the Minnelusa Formation to 150 ppm in sodium bicarbonate water in the Inyan Kara Group (table 10). Generally, the sulfate water of the Inyan Kara Group contains a trace of hydrogen sul- fide (about 0.05—0.1 ppm H2S), although none was detected in some water samples. The presence of hydrogen sulfide in the artesian waters is attributed to bacterial reduction of sulfate within the Inyan Kara. Jensen (1958), Lisitsyn and Kuznetsova (1967), and others have stressed the role of micro-organisms in the reduction of sulfate and the formation of ore deposits. Sulfate may be reduced by several bacteria, including Desulfovibrio desulfum'ca 13, to form hydrogen sulfide and other sulfide complexes where sufficient carbonaceous ma— terial is available to support the bacteria. Adequate to large flc ws of calcium magnesium sulfate water transmitted through porous aquifers or collapse structures to highly carbonaceous host rocks support intensive sulfate reductiOn and the formation of a large quantity of hydrogen sulfide, but sparsely car- bonaceous rocks and a flow of ground water that is restricted by low permeability limit the reduction activity. If the supply of carbonaceous material be— comes deplteted, then reduction activity by the micro- organism 1S terminated. The red iction of sulfate is also limited by Eh and pH, as shown by a study of sulfate reduction in soils by Connel and Patrick (1968). They showed that GROUND WATER reduction occurs bet accumulat of sulfate in waterlogged soils generally ween pH 6.5 and 8.5, and the greatest on of sulfide occurs near pH 7. Reduction occurs at a high rate from pH 7 to 7.8 and then de- creases to almost zero at pH 8.5. Their experiments also showed that the reduction of sulfate to sulfide is intense (millivolts below a threshold Eh of about #150 mv ) but is very slight at higher Eh values. OXIDATION-REDUCTION (REDOX) POTENTIAL The oxidation-reduction (redox) potential of the waters in (table 10 the Inyan Kara Group was measured at the well sites during the summer and fall of 1968 using a portable pH meter with calomel and platin 1m electrodes. Water was siphoned through an enclosed measuring cell, thus preventing absorp- tion of oxygen from the atmosphere and providing a constant temperature during the measurements. Redox measurements were made 20 minutes after the water was first introduced into the cell, and the values were reported as the potential difference be— tween the the platin vide only platinum saturated calomel reference electrode and um electrode. The redox measurements pro- relative values because equilibration of the electrode was not fully achieved in the more redL cing waters. In these waters, redox values, after complete equilibration of the electrodes, may be as much as 50 mv lower than the recorded values. It should equilibrat be noted, however, that even with complete ion, redox (and pH) measurements re— 41 corded at the surface in flowing wells cannot exactly duplicate the values present within the aquifer at depth because hydrogen sulfide and carbon dioxide are released from solution as the waters rise to the surface. At the margin of the Black Hills, redox values (fig. 16) decrease from a high of +162 mv near the Inyan Kara outcrop to less than —200 mv in the sodium sulfate water farther basinward, and within the strongly reducing hydrogen sulfide-bearing sodium bicarbonate water, redox values of 7400 mv were recorded. Anomalous redox values are present along both the Dewey structural zone and the projection of the Long Mountain structural zone. A redox value of +78 mv was recorded in well water flowing from a depth of about 700 feet at the Dewey structural zone 3 miles downdip from the Inyan Kara outcrop. Large differences in redox potential probably exist within or marginal to this zone. Within the Long Mountain structural zone, extreme differences in redox potential were measured in waters from closely spaced wells. In part, these differences in oxidation-reduction potential may be related to a separation of waters flowing from different sand- stone aquifers; however, some interconnection of the aquifers and mixing of the waters are expected in this area. More likely, the extreme differences in redox potential are caused by the introduction of an artesian calcium sulfate water, having slightly posi- tive to neutral redox potential, into an area where intense reduction of sulfate rapidly lowers the elec- trode potential. HYDROGEN-ION CONCENTRATION (pH) During the summer and fall of 1968 the pH values of the ground water were measured (table 10) at well sites using a portable pH meter. The pH gen- erally increases in a basinward direction from about 7.1 pH in the calcium sulfate water to as much as 8.3 pH in the sodium sulfate water (fig. 17). Values in the hydrogen sulfide-bearing sodium bicarbonate water generally range from 7.5 to 8.0 pH. Release of carbon dioxide and hydrogen sulfide as the water rises to the surface probably causes these pH values to be somewhat higher than true values within the aquifer. However, the release of hydrogen sulfide and carbon dioxide that produces an increase in pH and related chemical reactions is only partially com- plete at the time the water reaches the surface, be- cause the laboratory determinations of pH average 0.1 pH higher than field determinations for 12 sam- ples of sodium sulfate water, 0.2 pH higher for cal- cium sulfate water, and 0.8 pH higher for sodium bicarbonate water. Values of pH, as well as Eh, are affected by differ- 42 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS 104°07’30” “”45,’ 104 00 EXPLANATION QKs Sedimentary rocks of Quater- nary to Early Cretaceous age Inyan Kara Group of Early Cretaceous age JPs Sedimentary rocks of Jurassic to Permian age Contact 103°52’30” ———|—' —___. Fault Dashed where projected. Bar and ball on downthrown side 37’30” . V 0-" ‘ ( V ;, Isogram showing oxidation— ‘ ' ' reduction potential of ground water Dashed where inferred. Ha- chures indicate closed low value. Interval is 50 milli- volts .5 Water well or dril].hole Referred to in table 10 fl _ 193°45’ 30' O 5 10 MILES l O 5 10 KlLOMETERS FIGURE 16. — Oxidation-reduction potential (Eh) of ground water in the Inyan Kara Group of the southern Black Hills. Redox potential referred to KCl-saturated calomel electrode. 104°07’30" 43°37’30” 30’ ”"240 / / .21/6 ‘22 :«Burdock ‘23 r. o \‘ 43°22’30” FIGURE 17 GROUND WATER ‘ , 43 103°52’30” EXPLANATION QKs Sedimentary rocks of Quater- nary to Early Cretaceous age H Inyan Kara Group of Early Cretaceous age JPs Sedimentary rocks of Jurassic to Permian age Dashed where projected, Bar and ball on downthrown side 8.u”/ Isogram showing pH of ground water Dashed where inferred. Ha- chures indicate closed low value. Interval is 0.25 pH unit .5 Water well or drill hole Referred to in table 10 o——o ences in ground-water composition; therefore tec— tonic, solution, and sedimentary structures that influence the movement of ground water of different compositio pH values. ther basin‘ tural zone, section an as also influence the distribution of the Relatively low pH values are present far- Nard in the vicinity of the Dewey struc- where artesian water rises through the l, at one locality, discharges as a spring. Similarly, along the southwest projection of the Long Mountain 5 in calcium tructural zone, low pH values are recorded sulfate water introduced at the margin of an area containing sodium carbonate water of high pH. 10 MlLES J 5 10 KILOMETERS —Hydrogen-ion concentration (pH) of ground water in the Inyan Kara Group of the southern Black Hills. CARBON DIOXIDE The carbon dioxide content of water from 28 wells in the Inyan Kara was calculated from the bicarbon- ate content and pH of the water (table 10). Field measurements of pH were used in the calculations, rather than laboratory pH determinations made at the same time as the bicarbonate analyses, because pH alters with release of carbon dioxide from the water as the dissolved gases adjust to equilibrium at atmospheric pressure. The pH values changed 0.8 pH in sodium bicarbonate water before the water was analyzed in the laboratory. The calculated carbon dioxide content of these waters is a minimum value, because neither loss of lcarbon dioxide from the water 44 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS before it reaches the surface nor precipitation of calcium carbonate prior to analysis is considered in the calculation. The carbon dioxide content of the ground water sampled from the Inyan Kara ranges from 2.2 to 54 ppm CO: (table 10). Highest carbon dioxide values are present in samples of calcium sulfate water, which average 32 ppm C02. Surpris- ingly, the carbon dioxide content decreases downdip in samples of sodium sulfate water, which average about 6 ppm 00;}. Samples of sodium bicarbonate water contain intermediate concentrations of carbon dioxide, which average 20 ppm 002.. The large concentrations of carbon dioxide in the calcium sulfate waters of the Inyan Kara Group probably are derived chiefly from carbon dioxide species that were present in the water within the Minnelusa Formation. The carbon dioxide content of the calcium sulfate water from the Minnelusa sam- pled at three springs and one well in the southern Black Hills ranges from 29 to 47 ppm C02 and aver— ages 38 ppm (table 11). As the waters rise to the Inyan Kara, some carbon dioxide is immediately re- leased, but more carbon dioxide apparently is re- leased somewhat later as the water migrates downdip within the Inyan Kara and is softened by ion ex- change to a sodium sulfate water. The samples of sodium bicarbonate water contain less carbon di- oxide than those of calcium sulfate water sampled updip but contain more than the sodium sulfate water. This distribution of carbon dioxide in the sodium bicarbonate water also suggest some loss of carbon dioxide from the artesian water introduced into the Inyan Kara as the water continues to mi- grate through the group; however, other chemical and biochemical processes probably produce addi- tional carbon dioxide, thereby moderating the effect of this loss of carbon dioxide from bicarbonate ground water. TABLE 11. —Carbon dioxide content (calculated) of water from the Minnelusa Formation [ppm, parts per million] Locality HC03 COZ (pl. 4) pH (ppm) (ppm) 7.0 225 36 7.0 238 38 6.9 235 47 7.1 232 29 ........................................................ 38 LOCALITIES SAMPLED No. Description 1 .................... Spring, SE14 sec. 31, T. 45 N, R. 60 W. Weston County, Wyo. 7 .................... Flowing well LAK Ranch, C(nter Wl/zNW‘A sec. 5, T. 44 N., R 60 W., Weston County, Wyo. 6 .................... Spring, Cascade Springs, SWIA sec. 20, T 8 S. R. 5 E., Fall River County, S Dak. 4 .................... Spring, Evans Plunge. Hot. Springs, NWM, sec. 13, T. 7 S, R. 5 E. Fall River County, S. Dak URANIUM DEPOSITION The conditions necessary for uranium deposition probably have persisted intermittently since the es- tablishment of the present pattern of ground—water recharge and artesian flow following Laramide up- lift of the Black Hills. The general requirements for the deposition of uranium consist of a source of uranium, a favorable environment for deposition, and a means of transporting an adequate quantity of uranium to this environment. When these three con- ditions are fulfilled for a suflicient length of time, an ore deposit can be formed. Changes in the geochemical environment in the Inyan Kara Group occur continuously along the mar- gin of the Black Hills as erosion progressively lowers the surrounding plains. During erosion, the water table declines, and the zone of artesian recharge, as well as the oxidation—reduction front within the In- yan Kara, migrates basinward. Various stages in the evolution of the geochemical environment in which ore deposits are formed can be observed in the ground water along a line running northeasterly updip to the Inyan Kara outcrop. EFFECT OF REDUCING ENVIRONMENT Uranium is precipitated from solution by the re- duction of the complex uranyl ion U‘“ to the uranous ion U". This reduction can be brought about by several reducing agents, including those derived from organic material and hydrogen sulfide. Consid— erable evidence indicates that a reducing environ- ment resulting in the formation of uranium deposits in the southern Black Hills was brought about by the presence of hydrogen sulfide. The ore deposits are restricted to four strati- graphic units, of which only one is highly carbona- ceous. These units are (1) the highly carbonaceous sandstones and siltstones of the lower unit of the Fall River Formation, (2) noncarbonaceous fluvial unit 5, also in the Fall River Formation, (3) noncar— bonaceous fluvial unit 4, in the Fuson Member of the Lakota Formation, and (4) moderately carbonaceous fluvial unit 1 in the Chilson Member of the Lakota Formation (pl. 1, north half). The lack of a close spatial association between some uranium deposits and the organic carbonaceous material indicates that in these deposits the organic carbon did not directly cause precipitation of the uranium. As discussed previously, many of the water wells that were drilled into the Inyan Kara rocks along the southwest side of the Black Hills produce water highly charged with hydrogen sulfide. Where the water in the Inyan Kara changes from a predomi— nantly calcium sulfate water to a sodium bicarbonate water (pl. 3), hydrogen sulfide is abundant. Most likely, the hydrogen sulfide resulted from sulfate re- duction by bacteria that depend upon carbonaceous material within the Inyan Kara rocks for their life processes. This reduction resulted in the establish- ment of a geochemical environment favorable for the formation of uranium deposits. EFFECT OF THE “PLUMBING” SYSTEM AND THE INYAN KARA STRATIGRAPHY ON LOCALIZATION OF URANIUM DEPOSITS The route of migration and volume of flow of the ground water are major factors that influence the size and location of the uranium deposits. Extensive channel s indstones permit lateral migration of large volumes of aqueous solutions, and the stacking of channels (pl. 1, north half, restored cross section) URANIUM DEPOSITION 45 permits vertical migration within the Inyan Kara Group. As previously discussed, numerous breccia pipes as well as faults and fractures extend from the Lakota Formation downward to sandstone aquifers and solution breccias in the Minnelusa Formation to complete a complex plumbing system that permits vertical migration of solutions between the Minne- lusa and favorable host rocks in the Inyan Kara Group (fig. 18). Channelways provided by the superposition of flu— vial sandstones permit circulation of ground water from the base of the Lakota Formation into unit 5 sandstone in the Fall River Formation, and appar- ently they significantly influenced the location of the ore deposits by directing the mineralizing solutions into favorable host rocks. This is especially true of Spring Spring discharge/ / S e} F o°%e +0 0* (0 EXPLANATION v A A /‘°§ A, A. I V Brecciated rocks 0,155 Breccia pipe V569 \ Postulated direction Fracture/ 01' ground-water movement a] / Fracture ’X‘ T \/ Uranium deposit $474)]? 1 \/ A 8/ ‘ $66339 O FIGURE 18 —Spatial relation of the uranium deposits to leaching of evaporites, brecciation, and postulated direction of 537-784 D - 74 - 4 ground-water movement. Diagram not to scale. 46 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS fluvial unit 4, which fills irregularities on an ero- sional surface that partly dissected or completely truncated the Fuson mudstone, an impermeable unit that apparently was laid down as a bed of relatively uniform thickness across units 1 and 2 of the Chil- son Member. The Fuson mudstone, therefore, re— tards or prohibits ground-water circulation between the sandstones of the Chilson Member of the Lakota Formation and the sandstones of the overlying Fall River Formation except where the Fuson mudstone is cut by the channel sandstone of unit 4. The lower sandstone and siltstone unit in the Fall River similarly retards circulation of ground water from the Lakota Formation into stratigraphically higher units except in those places where the unit is faulted or is cut by the channel sandstone of unit 5. The “plumbing” system and the Inyan Kara stra- tigraphy, which control the volume of metals that are transported into favorable host rocks, are in- fluenced indirectly by tectonic deformation. As pre— viously discussed, pipe structures that transmit artesian water to the Inyan Kara are more numerous in the structural zones, where evaporites were frac- tured by recurrent deformation and thus were more susceptible to dissolution and collapse. In addition to the development of the breccia pipes, the stacking of the channel-fill sandstones of the main streams and their tributaries was influenced by recurrent structural deformation not only along the axis of the regional northwest—trending syncline, but also along secondary northeast—trending basement structures. Therefore, the location of the uranium deposits is indirectly influenced by tectonic structure, which was a factor in the development of the “plumbing” sys- tem and also in the location of superposed, or stacked, channel-fill sandstones of the Inyan Kara Group. MINERALIZING SOLUTIONS The relations between the reducing environment, the “plumbing” system, and the distribution of the deposits are interpreted to mean that uranium was introduced into the Inyan Kara Group with the cal- cium sulfate water that flowed from the Minnelusa Formation to recharge the sandstone aquifers of the Lakota. The uranium concentration in water from the Minnelusa sampled at seven springs (table 9) ranges from 4.7 to 17 ppb. Uranium in the water probably was derived from multiple sources, includ- ing sedimentary rocks of Paleozoic and Mesozoic age and the exposed granites of Precambrian age in the central part of the Black Hills. During Tertiary time volcanic ash of the White River Group of Oligocene age may have also contributed uranium. The uranium concentration in ground water of the Inyan Kara Group decreases in a basinward direc- tion (fig. 19) as the calcium sulfate water is modified to a sodium sulfate water (fig. 20) and simulta- neously is subjected to minor sulfate reduction. Where intensive reduction of sulfate occurs within the more carbonaceous rocks, and the water is modified to the sodium bicarbonate type, the uranium content de- creases very rapidly until less than 0.1 ppb uranium remains in solution. The decrease in uranium concentration in the basinward-flowing waters is interpreted to be the re- sult of the precipitation of uranium, although pos- sibly absorption and (or) adsorption of uranium by organic matter and by clay minerals may remove some of it from solution. The decrease in uranium concentration does not result from dilution by older, less uraniferous water, because such dilution should everywhere result in the simultaneous dilution of the tritium concentrations in the ground water. Simul- taneous dilution of uranium and tritium concentra- tions does not occur; instead, these concentrations decrease independently. Values of redox potential and pH recorded in the water flowing from wells (table 10) also indicate the probable precipitation of uranium from the ground water rather than a dilution of the uranium concen- tration by less uraniferous waters. High uranium values are present in calcium sulfate waters having higher redox and pH values, representing oxidizing conditions. Conversely, low uranium concentrations (less than 0.5 ppb U) are present in sodium sulfate or sodium bicarbonate waters in which low redox and pH values indicate the presence of reducing con- ditions that could precipitate uraninite. The primary mineralizing solution appears to be a calcium sulfate type ground water. Where the sul- fate water, carrying weak concentrations of ura- nium, is introduced into highly carbonaceous units of the Inyan Kara, relatively rapid reduction of sul- fate and uranium occurs. Rapid precipitation of ura- nium at the site of modification of the water to the hydrogen sulfide-bearing sodium bicarbonate type follows. Where calcium sulfate water is introduced into sparsely carbonaceous or noncarbonaceous rocks, uranium precipitation may proceed more slowly and occur across a broad zone as the water is modified to the sodium sulfate type; after this modification of water type, most of the uranium has been precipi- tated. Where ground-water movement is rapid, a low rate of uranium precipitation results in the dissemi- nation of uranium throughout the sandstone of the Inyan Kara, but rapid precipitation results in the formation of higher grade deposits. Some enrichment-type uranium deposits may have 43.934592? ) 104900,. ‘1 \<. S L QKs \ Q \3' 64x DEWEY ‘ x E fERRA‘eE' O a :77“ 30’ 43°22’30” 103“52’30” URANIUM DEPOSITION , 3 47 EXPLANATION Sedimentary rocks of Quater- nary bo Early Cretaceous age Inyan Kara Group of Early Cretaceous age Sedimentary rocks of Jurassic to Permian age Contact Dashed where projected. Bar and ball on downthrown side raw—m- Isogram showing uranium con- tent of ground water Dashed where inferred. Inter- val is 0.25, 0.5, or 1 ppb .5 Water well or drill hole Referred to in table 10 been derived from disseminated uranium and from older deposits in the Inyan Kara at higher elevations. These enrichment- or lateral accretion-type deposits are likely to be along well-defined oxidation-reduction fronts near the Inyan Kara outcrop and may occur as roll-type uranium deposits (Shawe and Granger, 1965). Lateral accretion of uranium can be most rapid where the uranium concentration in the host rocks is highest; therefore, roll-type deposits may lie downdip from areas that, in the past, have had much higher rates of ground-water flow and a sig- nificant contribution of uranium derived from arte- sian recharge. Ground water that forms roll-type deposits probably flows much more slowly than the 10 MILES I I 5 10 KILOMETERS FIGURE 19. -— Uranium distribution in ground water of the Inyan Kara Group of the southern Black Hills. rate of 15 feet per day calculated for the most rapid flow at the margin of the southern Black Hills; therefore, roll-type deposits are less likely to be pres- ent in areas having a high rate of ground-water movement. A low rate of flow, favorable for roll-type deposits, may be indicated by the presence near the Inyan Kara outcrop of sodium sulfate water, softened by ion exchange, as well as by the absence farther downdip of very young water containing high tri- tium values. The mineralizing solutions for the enrichment-type deposits may contain higher concen- trations of uranium than the primary mineralizing solution, thereby permitting uraninite precipitation in a somewhat less reducing environment (a slightly 48 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS Reported values are estimates Probable error of reported probable error :100 percent values :10 percent 50 L | I l l I l l I l I I I I II | l | l l I l l I l | | I I | l | E CaSO.-type water(16ana|yses) : — I no 4 :0 Number of samples — 25 ~ > mg / _ _ ‘“ m \ 3 _ ~ 2/_\.2 I: w ° _ : I _1__ \ 1 1 1 ' I I I | I I I l I | I I I I I I I I I I I I I I I I I I I I I I I I T 0 0) Lu a’ 2 100 I I I I I I I I I | I I I I I I I I I I I I I I I I I s i I _ LL _ NaZSOI—type water (19 analyses) : O ' g0 ‘ “J 50 f 10 — g , 5 5 “I i . . ._I E - fl\§ \ 2 L 1 - LIJ O 7 I l I I I I I I I I I I I I I I I .I I | \L I I I ,._. I I I I I I I I _ O II III a. 100 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I : NaHCO;I-type water (11 analyses) : _ I I _ 50 _— 4 g1 —_ 7 /. A _ 1 2/ 1 f3 2 1 _ , z‘ ’0‘ d O I I'I‘I\ . IX/I I I I I I I “Q‘L I II I I I I IJ’I I\T"I~L_L J_I "" I I I I I I I I 0.005 0.01 0.02 3.05 0.1 0.2 .5 2 5 10 20 50 100 RANGE OF URANIUM CONCENTRATION URANIUM, IN PARTS PER BILLION FIGURE 20. — Uranium in samples of three types of ground water from the Inyan Kara Group (light lines) and from the Minnelusa Formation (heavy lines). Points indicate percentage of samples reported for each range of uranium concentration. higher redox and pH environment) than the envi- ronment of primary mineralization. This influence of uranium concentration upon precipitation is indi- cated by the phase-equilibrium diagrams of Hostetler and Garrels (1962). ORE DEPOSITS AS RELATED TO THE “PLUMBING” SYSTEM AND THE STRATIGRAPHY One important factor in the formation of the ore deposits —a “plumbing” system adequate to trans— mit large volumes of solutions—has already been described. A brief description of representative ore deposits as they are spatially related to this system follows. In the vicinity of the Runge mine (El/g sec. 1, T. 8 S., R. 2 E.), in the southern part of the Edge- mont NE quadrangle, the major sandstones in flu- vial units 4 and 5 are in erosional contact (fig. 21). Fluvial unit 5 sandstone cuts through the highly car- bonaceous and pyritiferous basal Fall River siltstone and sandstone, thus permitting ground water in flu- vial unit 5 access to reducing agents derived from the carbonaceous unit. Ore minerals are extensively disseminated through the two sandstones near the contact. As shown by figure 22, several metals appear to have a systematic zoning pattern within the Runge mine (V. R. Wilmarth, unpub. data). The zones are identifiable by their mineralogy, color, and grade. They consist of (1) a basal zone which is tightly cemented by calcium carbonate and which contains pods, lenses, nodules, and concretions of unoxidized uranium, vanadium, and iron sulfide-bearing miner- als; (2) an unoxidized iron-rich discontinuous zone that overlies zone 1; (3) an oxidized vanadium—rich zone of reddish sandstone, in which iron oxide is con- centrated, that overlies both zones 1 and 2; and (4) a discontinuous zone at the top in which arsenic and molybdenum are concentrated. Possibly the m0- lybdenum has been recently redistributed. This zoning pattern suggests that, of all the elements, uranium moved the least distance and arsenic the greatest distance, from the point where waters from the two sandstones intermingled. Iron was present in all zones. The numerous ore deposits that occur in the basal part of the Fall River Formation in secs. 25 and 26, T. 7 S., R 2 13., could have formed under geochemical conditions similar to the Runge deposit. The deposits URANIUM DEPOSITION 49 \§+++*¢~*++++++++++ AreaofRungemIne +++++++++ v + - - + + , shown In figure 22 +++++++++++++++T++ ‘.+ + Subsidencefault +++++++++++++++++++++++++++§++ EXPLANATION .L V, > 4 At — < Z i L AA, > | Interbedded sandstone and Sandstone Mineralized sandstone E E noncarbonaceous mudstone Fluvial unit 5 Rock contains less than economic concentrations of g 33 Unit ls lateral facies of the uranium and vanadium __ E sandstone in fluvial unit 5 '— 54 N O In {1.4 5? _ . _: General position of uranium mines _ . ‘ r Interbedded carbonaceous sandstone Postulated direction of movement and Slltstone of mineralizing solutions + + + 4 :6 g + + + H ‘5 + + + + o ‘5 + + + if, E 5-4 ’4 é: Carbonate-cemented sandstone Fluvial unit 4 FIGURE 21. — Relation of channel sandstones to uranium deposits, carbonate cement, and postulated direction of movement of mineralizing solutions. Diagram not to scale. U 1.6 V .7 Fe 3.1 Ca 1.2 Mg .005 Filled fracture M0 .005 As .04 U 003 V/U .44 (V .08 Fe 1.3 U 0.0 Ca .09 zone4 V .6 Zone4 Mg .03 Fe 5.4 M0 .09 Ca 2.4 As .06 Zone 3 V/U2.66 FIGURE 22.—- Idealized diagram showing zonal relations of several metals in the Runge mine, Fall River County, S. Dak. Average concentrations of metals in percent. Diagram not to scale. 50 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS are partly oxidized and are in a sequence of alternat- ing thin beds of fine—grained sandstone and laminated carbonaceous siltstone. Corvusite, rauvite, carnotite, and tyuyamunite constitute the ore-forming miner- als. The deposits occur in the vicinity of several small faults that may be partly of subsidence origin and are also marginal to the western channel bound- ary of unit 5 sandstone (fig. 21). It seems likely that uranium-bearing solutions migrated upward from unit 4 sandstone into the carbonaceous silt- stone-sandstone unit either through the fault zone or by way of unit 5 channel sandstone. Entry of the solutions into the reducing environment of the car- bonaceous siltstones and sandstones apparently re- sulted in precipitation of the uranium and vanadium minerals. Evidence of vertical migration of mineralizing so- lutions through collapse structures is seen in the Kellog mine, which is near the center of the Flint Hill quadrangle (pl. 1), and near the northeast mar- gin of fluvial unit 1. The ore minerals occur in a 6- to 8-foot-thick fine-grained sandstone, the basal part of which contains numerous carbonaceous shale and siltstone layers that average about 1 inch in thick- ness. The sandstone is overlain by a black carbona- ceous shale and is underlain by a thin bed of greenish-gray plastic clay that locally contains cal- cite spherulites. The mine is traversed by numerous small intersecting faults that have displacements of as much as 2.3 feet (fig. 23). In order of decreasing age, they strike north, east, northeast, and north- west. The intersecting faults define numerous rela— tively small sandstone blocks bounded by the black carbonaceous shale at the top and the greenish-gray plastic clay at the base. Uranium ore occurs in inti- mate association with carbonaceous material in the lower 2—5 feet of the complexly faulted sandstone, and it also occurs stratigraphically higher along the fault planes. The uranium minerals have not been identified but are assumed to be either uraninite or coffinite or both. The fault pattern is typical of that formed by sub- sidence, a pattern similar to that found locally throughout the mining district. The relatively high concentrations of the ore-forming minerals along and marginal to the fault planes indicates that the faults served as pathways of vertical migration for the mineralizing solutions. Many small oxidized uranium deposits occur along or near the outcrop of the major sandstone in fluvial unit 1. In many of these deposits the uranium min- erals are selectively concentrated around carbonized wood fragments and macerated plant remains. In the many other deposits, in which this relation does not exist, the uranium minerals seem to have been pre- cipitated by an ephemeral agent. As discussed previ- ously, there is reason to suspect that biogenically derived hydrogen sulfide has become enriched in the ground water in some areas, and this enrichment probably accounts for those deposits not directly associated with organic material. It is interesting to speculate about the low vana- dium content in these small carnotite deposits. The vanadium-uranium ratio ranges from 0.25 to 0.68 and averages about 0.4 (Gott and Schnabel, 1963, p. 175). This amount of vanadium is barely enough to form the mineral carnotite, and inasmuch as some vanadium is known to be present in the clays, prob- ably all the available vanadium was used in the for- mation of carnotite. Under such a circumstance uranium may have been lost during oxidation. After all the vanadium had been utilized in the formation of carnotite, excess uranium, if any existed, would have been carried away by ground and surface water. The uranium carried downdip by ground water would have been reprecipitated below the zone of oxidation. The location of the deposits in fluvial unit 1 may have been influenced by pre-Fall River folding. With few exceptions these deposits as well as those in stratigraphically higher units are restricted to favor- able host rocks within a gentle syncline, the center of which trends through the northwestern part of the Flint Hill quadrangle, through the northeastern part of the Edgemont quadrangle, and diagonally northwestward across the Edgemont NE quadrangle (pl. 1; see also Gott and Schnabel, 1963, pl. 14). The syncline apparently was formed by mild structural deformation during Lakota time. The effect of the syncline apparently was to control the position of streams which deposited the thick channel sandstones that constitute the major distributors of migrating solutions. Calcium carbonate cement seems to be an indicator of the extent and ramifications of the “plumbing” system. The cement impregnating the ore-bearing sandstones is so extensive that it seems evident that the cementing material was imported from an exter— nal source, for there is no evidence that an adequate source ever existed within the Inyan Kara rocks. For example, one 10—mi1e segment of fluvial unit 4 in the southwestern part of the Edgemont NE quadrangle and adjacent areas is estimated to contain more than 1 billion cubic feet of calcite. An extensive segment of the sandstone of fluvial unit 5 is similarly ce- mented along the axis of the Sheep Canyon mono- cline along the western part of the Flint Hill, the eastern part of the Edgemont, and the southeastern part of th these and nificant vc cemented evaporite Inyan Kai the calcite e Edgemont NE quadrangles. Elsewhere, other sandstones are cemented with sig— lumes of calcite cement. Numerous calcite- breccia pipes extend upward from the zone in the Minnelusa Formation to the a sandstones, indicating that the source of was the Minnelusa evaporites. The breccia pipes evidently were the “pipelines” through which large volu kota Forrr mes of solutions were supplied to the La- ation, and the calcite-cemented sandstones were the distributors of these solutions through the accessible Inyan Kara rocks. Polished-section studies show that some of the uraninite although uraninite raneity in part from gests that bonate we tion of evz to permit nelusa Fc therefore, sulted in t EFFECT OF SYSTEM! The La topograph posed Mes of aquifer ment of a away fro ground w confined t impermea was sufiic puncture tures, ana collapse s1 lay deeply to the sur localities g rocks was Relocati posed the taceous ag resistance in modific of Tertiar remnant t ders, and . Broad grz s contemporaneous with the calcite cement in general the calcite is earlier than the (Gott and Schnabel, 1963). This contempo— dicates that the two minerals resulted in the same mineralizing process and sug— uranium, vanadium, calcium, and bicar— re transported in a common solution. Solu- Lporites and the formation of breccia pipes circulation of ground water from the Min— rmation to the Inyan Kara Group are, among the combination of factors that re— he localization of the ore deposits. THE TERTIARY AND QUATERNARY DRAINAGE . ON LOCALIZATION OF URANIUM DEPOSITS ramide uplift provided the structural and ic relief necessary for the erosion that ex- ozoic and Paleozoic rocks for the recharge s by surface waters and for the establish- pattern of surface- and ground-water flow the central part of the Black Hills. Where ter at the lower flank of the uplift was 0 an aquifer by overlying and underlying ble strata, artesian pressure developed that iently strong to force water up through points or conduits formed by faults, frac- stomosing sandstone channels, and solution ructures. In places where conduits under- incised valleys, ground water was forced face to be discharged by springs. At these {round-water flow through the Inyan Kara relatively rapid. on of drainages occurred as erosion ex- formations underlying shales of Late Cre- re. Structural deformation and the varied to erosion of the older formations resulted ition of the drainage pattern. The position y and Quaternary streams, as indicated by errace gravels, wind gaps, incised mean- shallow upland valleys, is shown on plate 4. Ivel terraces along the dip slopes of the EXPLORATION GUIDES 51 Inyan Kara hogback on the southwest flank of the Black Hills indicate a downdip migration of major southeast-flowing streams as erosion progressed. One of the major ancestral drainage courses in the Craven Canyon area is an excellent example of stream relocation. The stream that formed Craven Canyon originally crossed the Chilson anticline and continued southeast through the lower part of Chil- son Canyon until it was diverted by stream capture, first into Sheep Canyon and later into the lower part of the present Red Canyon. The occurrence of uranium deposits near drain- ages of the Tertiary and Quaternary streams, as well as in the areas of . northeast-trending structures (pl. 4), reflects the influence of both vertical and horizontal movement of ground water during forma- tion of the ore deposits. Where artesian water flowed at the maximum rate through the Inyan Kara, proportionately larger amounts of uranium were transported to sites of reduction and precipitation. Continued erosion within the Black Hills and on the adjacent plains, periods of stream aggradation dur- ing Tertiary and Quaternary time, and minor struc- tural deformation all contributed to the shifting of the streams, influenced the rate and direction of ground-water movement within the Inyan Kara aquifers, and caused a shifting of the sites of ura- nium deposition. For example, the upper part of Chilson Canyon, which was deeply eroded prior to the capture of the drainage from Craven and Red Canyons, contains uranium deposits, whereas the lower part of Chilson Canyon, which was eroded by a much smaller discharge of water and which prob- ably has had relatively little effect on ground-water movement, contains no known uranium deposits. EXPLORATION GUIDES Exploration for uranium in the Inyan Kara Group of the southern Black Hills can be facilitated by the combined use of stratigraphic, lithologic, structural, and hydrologic guides. Solution of evaporites in the Minnelusa Formation resulted in subsidence and (brecciation of many of the overlying rocks. Of particular significance was the formation of breccia pipes that extend upward from the Minnelusa Formation and permit large vol- umes of artesian water carrying relatively low con- centrations of uranium to ascend into the Lakota and Fall River Formations. Factors within these forma- tions affecting the localization of the uranium de- posits pertain mainly to the “plumbing” system, which transmits the mineralizing solutions, and to the geochemical environment in the host rocks. Ex- ploration for concealed uranium deposits, therefore, 52 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS EXPLANATION ’60 1.5 Fault, showing dip Boldface number indicates displacement, in feet, and is shown on upthrown side of fault Mine workings 0. I — — 0.5 — — Isoradioactivity lines Dashed where approximately located. Number indi- cates milllroentgens per hour 1A cor. secs. 19 and 24 bears N. 47°00’ E. from poi'tal 1460.2 feet Geology and radioactivity measurements by G. B. Gott and D. E. Wolcott, 1959 FIGURE 23. -— Mine workings, faults, and radioactivity EXPLORATION GUIDES 53 3O METERS in the Kellogg mine, Fall River County, S. Dak. 54 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS should be based on the coincidence of favorable host rocks and vertical conduits caused by the subsidence of rocks overlying the evaporites, particularly in zones of fracturing and faulting. Many billions of cubic feet of calcium carbonate cement are in the sandstones of the Inyan Kara Group. The cement is continuous from that part of the Minnelusa Formation that has been leached of calcium sulfate, upward through many breccia pipes, and into the Lakota and Fall River Formations. This continuity indicates that the source of the calcite cement is the leached evaporite zone and other car- bonate rocks, which were accessible to the ascending solutions, and that the abundance of the cement in the Inyan Kara is evidence that ground water from the Minnelusa has ascended at least as high as these calcite—cemented sandstones. The presence of so much cement would mean that there may have been an adequate volume of solutions to import enough ura- nium to form an ore deposit, but it would not neces— sarily mean that a geochemical environment favor- able for its precipitation also existed. Ore deposits are restricted to fluvial units 1, 4, and 5 and to the sandstones and siltstones of the basal Fall River Formation, indicating that sandstones in these units have offered an environment favorable for uranium deposition and therefore favorable for exploration. Conversely, the sandstones of fluvial unit 2 are unfavorable for exploration. Unit 2 is mostly well oxidized and therefore forms an environ- ment in which uranium would tend to be soluble and would not precipitate from solutions migrating through the unit. One of the requirements for the formation of ore deposits by precipitation of uranium from the ground water is a circulation system within which the cir- culation is rapid, thereby permitting the influx of a large volume of mineralizing solution. Under ideal conditions, including the flushing of tremendous vol— umes of ground water through the system, signifi— cant amounts of uranium can be derived from minute concentrations of uranium in the ground water. Both the Lakota and the Fall River Formations normally contain fine-grained, poorly permeable rocks that retard ground-water movement. Examples of these fine-grained rocks are the fissile shales at the base of the Lakota, the Fuson mudstones, and the tabular siltstones interbedded with fine-grained sandstones at the base of the Fall River Formation. Where these fine-grained rocks have been removed by, intraformational erosion, the'ground water can migrate freely through sandstones of fluvial units 1, 4, and 5, in which the geochemical environment is favorable for precipitation of uranium. The stacking and interconnection of these fluvial sandstones should be considered when planning an exploration pro- gram. Structural deformation has influenced the deposi- tion of the fluvial sandstones, thereby affecting the later flow of ground water through the Inyan Kara Group. The pre-Fall River structural trough shown by Gott and Schnabel (1963, fig. 26) appears to have been a particularly favorable area for the transmis- sion of large volumes of solutions and for the forma- tion of ore deposits. Most uranium deposits within the Edgemont district are in fluvial unit 1, which was deposited along the axis of the structural trough, or in other overlying favorable stratigraphic units to which fluvial unit 1 is connected by superj acent chan- nels. Consideration should be given to exploring this syncline where it extends downdip under the Skull Creek Shale along the toe of the Sheep Canyon mono- cline and south on the Chilson anticline. Northeast-trending secondary structures also influ— enced the position of the main and tributary streams and the deposition of fluvial sandstones that transmit ground water through the Inyan Kara. Within both the Long Mountain and Dewey structural zones, re- current deformation continually affected sedimenta- tion during Lakota and Fall River time by causing a deflection of the northwest-flowing streams and by de- fining the courses of tributary streams. Later folding and faulting in these two structural zones also signifi- cantly affected ground-water movement. Elsewhere, deformation along northeast-trending structures was more sporadic, but the structural influence on sedi- mentation, although more limited, does indirectly affect ground-water movement. The effect of these secondary, northeast-trending structures upon ground water movement should be considered when an area is evaluated for possible exploration. Within the more deeply incised drainages, artesian water from the Inyan Kara Group locally discharges as springs or recharges alluvium and gravel. Near the points of discharge, ground-water flow in the Inyan Kara is accelerated. The possible effect of these high rates of ground—water movement upon mineralization should be considered both for the present drainages and for the ancestral drainages, which are indicated by stream terrace gravels and erosional features. Ground-water analyses and field measurements of redox potential and pH indicate areas below the Skull Creek Shale where uranium probably is being precipitated now. The analyses suggest that most of the uranium is transported by calcium sulfate water and that it precipitates at the margin of a strong reducing environment, such as the hydrogen sulfide- bearing sodium bicarbonate water. The transition zone between calcium sulfate and sodium bicarbonate waters at the Long Mountain structural zone should therefore Ice considered as a favorable area for ex- REFERENCES CITED ploration. containing Sonversely, the central part of the area hydrogen sulfide-bearing sodium bicar- bonate water should be considered unfavorable for exploration unless indications of local recharge of the Inyan Kara by uraniferous water are found. During the evolution from calcium- and magne- sium-rich water, ura precipitati sulfate water to the sodium-rich sulfate iium is precipitated. Perhaps more rapid )n of uranium, and therefore higher grade deposits, occur at the margin of the hydrogen sul- fide-bearing sodium bicarbonate water. Studies of water; samples collected from water wells and exploration drill holes should supplement the usual stratigraphic, mineralogic, lithologic, and radiometri and they p c studies conducted during exploration, robably would aid a systematic search for uranium dieposits present below the water table. Adolphson, variatio Geologi Paper 6 Baker, C. L REFERENCES CITED D. G., and LeRoux, E. F., 1968, Temperature 15 of deep flowing wells in South Dakota, in a1 Survey research 1968: U.S. Geol. Survey Prof. 0—D, p. D60—D62. , 1947, Deep borings of western South Dakota: South Dakota Geol. Survey Rept. Inv. 57, 112 p. Bartram, J. ern Wy Soc. Gu Bell, Henry G., 1940, The stratigraphy and structure of east- ming and the Black Hills area, in Kansas Geol. debook 14th Ann. Field Conf., 1940: p. 113—120. III, and Post, E. V., 1957a, Preliminary geologic map of the northwest part of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—61. 1957b, Preliminary geologic map of the northeast part of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—62. 1957c, Preliminary geologic map of the east-central part of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—63. 1957d, Preliminary geologic map of the west-central part of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—64. _1957e, Preliminary geologic map of the southwest part of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—65. 1957f, Preliminary geologic map of the southeast part of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—66. 1971, Geology of the Flint Hill quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Bull. 1063—M p. 505—586. 55 Bolyard, D. W., and McGregor, A. A., 1966, Stratigraphy and petroleum potential of Lower Cretaceous Inyan Kara Group in northeastern Wyoming, southeastern Montana, and western South Dakota: Am. Assoc. Petroleum Geol- ogists Bull., v. 50, no. 10, p. 2221—2244. Bowles, C. G., and Braddock, W. A., 1963, Solution breccias of the Minnelusa Formation in the Black Hills, South Dakota and Wyoming, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475—0, p. C91—C95. Braddock, W. A., 1963, Geology of the Jewel Cave SW quad- rangle, Custer County, South Dakota: U.S. Geol. Survey Bull. 1063—G, p. 217—268 [1964]. Brobst, D. A., 1958a, Preliminary geologic map of the north- east part of the Dewey quadrangle, Custer County, South Dakota, and Weston County, Wyoming: U.S. Geol. Sur- vey Mineral Inv. Field Studies Map MF—77. 1958b, Preliminary geologic map of the east-central part of the Dewey quadrangle, Custer County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—78. 1961, Geology of the Dewey quadrangle, Wyoming— South Dakota: U.S. Geol. Survey Bull. 1063—B, p. 13—60 [1962]. Brobst, D. A., and Epstein, J. B., 1963, Geology of the Fanny Peak quadrangle, Wyoming—South Dakota: U.S. Geol. Survey Bull. 1063—1, p. 323—377 [1964]. Brod, L. G., Jr., 1964, Artesian origin of fissure caves in Missouri: Natl. Speleol. Soc. Bull., V. 26, no. 3, p. 83—114. Brown, C. B., 1944, Report on an investigation of water losses in streams flowing east out of the Black Hills, South Dakota: U.S. Soil Conserv. Service Spec. Rept. 8, 45 p. Cadigan, R. A., 1959, Sedimentary petrology, in Stewart, J. H., Williams, G. A., Albee, H. F., and Raup, O. B., Stratig- raphy of Triassic and associated formations in part of the Colorado Plateau region: U.S. Geol. Survey Bull. 1046—Q, p. 529—571. 1961, Geologic interpretation of grain—size distribu- tion measurements of Colorado Plateau sedimentary rocks: Jour. Geology, v. 69, no. 2, p. 121—144. Chamberlin, R. T., 1945, Basement control in Rocky Mountain deformation: Am. Jour. Sci., v. 243—A (Daly volume), p. 98—116. Chayes, F. A., 1946, A correction factor for specific gravity and volume differences in fragment analysis: Econ. Geol- ogy, v. 41, no. 7, p. 749—760. 1949, Some notes on the point counter: Am. Min- eralogist, v. 34, nos. 7—8, p. 600—601. Connell, W. E., and Patrick, W. H., Jr., 1968, Sulfate reduc- tion in soil — Effects of redox potential and pH: Science, v. 159, no. 3810, p. 86—87. Connor, J. J., 1963, Geology of the Angostura Reservoir quad- rangle, Fall River County, South Dakota: U.S. Geol. Survey Bull. 1063—D, p. 85—126. Cuppels, N. P., 1963, Geology of the Clifton quadrangle, Wyo-‘ ming and South Dakota: U.S. Geol. Survey Bull. 1063—H, p. 271—321. Darton, N. H., 1896, Preliminary report on artesian waters of a portion of the Dakotas: U.S. Geol. Survey Ann. Rept. 17, pt. 2, p. 603—694. 1901, Preliminary description of the geology and water resources of the southern half of the Black Hills and adjoining regions in South Dakota and Wyoming: U.S. Geol. Survey 21s‘t Ann. Rept., pt. 4, p. 489—599. 56 INYAN KARA STRATIGRAPHY AND URANIUM LOCALIZATION, SOUTHERN BLACK HILLS 1909, Geology and underground waters of South Da- kota: U.S. Geol. Survey Water-Supply Paper 227, 156 p. Darton, N. H., and Paige, Sidney, 1925, Description of the central Black Hills quadrangle [South Dakota]: U.S. Geol. Survey Geol. Atlas, Folio 219. Davis, R. W., Dyer, C. F., and Powell, J. E., 1961, Progress report on wells penetrating artesian aquifers in South Dakota: U.S. Geol. Survey Water-Supply Paper 1534, 100 p. Fenneman, N. M., 1931, Physiography of western United States: New York, McGraw-Hill Book Co., 534 p. Folk, R. L., 1957, Petrology of sedimentary rocks: Austin, Tex., Hemphill’s Book Store, 111 p. Foster, M. D., 1950, The origin of high sodium bicarbonate waters in the Atlantic and Gulf Coastal Plains: Geochim. et Cosmochim. Acta, v. 1, no. 1, p. 33—48. Gott, G. B., 1956, Inferred relationship of some uranium de— posits and calcium carbonate cement in southern Black Hills, South Dakota: U.S. Geol. Survey Bull. 1046—A, p. 1—8. Gott, G. B., and Schnabel, R. W., 1956a, Preliminary geologic map of the northwest part of the Edgemont NE quad- rangle, Custer and Fall River Counties, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—55. 1956b, Preliminary geologic map of the northeast part of the Edgemont NE quadrangle, Custer and Fall River Counties, South Dakota: U.S. Geol. Survey Min- eral Inv. Field Studies Map MF—56. 1956c, Preliminary geologic map of the east-central part of the Edgemont NE quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—57. 1956d, Preliminary geologic map of the west-central part of the Edgemont NE quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—58. 1956c, Preliminary geologic map of the southwest part of the Edgemont NE quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—59. 1956f, Preliminary geologic map of the southeast part of the Edgemont NE quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—60. 1963, Geology of the Edgemont NE quadrangle, Fall River and Custer Counties, South Dakota: U.S. Geol. Survey Bull. 1063—E, p. 127—190. Gries, J. P., 1954, Cretaceous rocks of Williston Basin: Am. Assoc. Petroleum Geologists Bull., v. 38, no. 4, p. 443—453. Gries, J. P., and Crooks, T. J., 1968, Water losses to the Madison (Pahasapa) limestone, Black Hills, South Da— kota, in Wyoming Geol. Assoc. Guidebook 20th Field Conf., Black Hills area, South Dakota, Montana, Wyo- ming, 1968: p. 209—213. Griffiths, J. C., 1967, Scientific method in analysis of sedi- ments: New York, McGraw-Hill Book Co., (Internat. Ser. Earth and Planetary Sci.), 508 p. Hostetler, P. B., and Garrels, R. M., 1962, Transportation and precipitation of uranium and vanadium at low tempera- tures, with special reference to sandstone-type uranium deposits: Econ. Geology, v. 57, no. 2, p. 137—167. Imlay, R. W., 1947, Marine Jurassic of Black Hills area, South Dakota and Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 31, no. 2, p. 227—273. Inman, D. L., 1952, Measures for describing the size distribu- tion of sediments: Jour. Sed. Petrology, v. 22, no. 3, p. 125—145. Jensen, M. L., 1958, Sulfur isotopes and the origin of sand- stone-type uranium deposits [Colorado Plateau and Wyo- ming]: Econ. Geology, v. 53, no. 5, p. 598—616. Krumbein, W. C., and Pettijohn, F. J., 1938, Manual of sedi— mentary petrography: New York, D. Appleton-Century Co., 549 p. Lisitsyn, A. K., and Kuznetsova, E. C., 1967, Role of micro- organisms in development of geochemical reduction bar- riers where limonitization bedded zones wedge-out: Akad. Nauk SSSR Izv. Ser. Geol. no. 1, p. 31—44; English trans- lation, Internat. Geology Rev., v. 9, no. 9, p. 1180—1191. McKee, E. D., 1957, Flume experiments on the production of stratification and cross-stratification: Jour. Sed. Petrol— ogy, v. 27, no. 2, p. 129—134. McKee, E. D., and others, 1956, Paleotectonic maps, Jurassic system, with a separate section on Paleogeography, by R. W. Imlay: U.S. Geol. Survey Misc. Geol. Inv. Map I—175. Mackenzie, D. B., and Poole, D. M., 1962, Provenance of Da- kota Group sandstones of the western interior, in Sym- posium on Early Cretaceous rocks of Wyoming and adjacent areas—Wyoming Geol. Assoc. Guidebook 17th Ann. Field Conf., 1962: p. 62—71. Mapel, W. J., Chisholm, W. A., and Bergenback, R. E., 1964, Nonopaque heavy minerals in sandstone of Jurassic and Cretaceous age in the Black Hills, Wyoming and South Dakota: U.S. Geol. Survey Bull. 1161—C, 59 p. Mapel, W. J., and Gott, G. B., 1959, Diagrammatic restored section of the Inyan Kara group, Morrison formation, and Unkpapa sandstone of the western side of the Black Hills, Wyoming and South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—218. Meuschke, J. L., Johnson, R. W., and Kirby, J. R., 1963, Aero- magnetic map of the southwestern part of Custer'County, South Dakota: U.S. Geol. Survey Geophys. Inv. Map GP—362. Noble, J. A., 1952, Structural features of the Black Hills and adjacent areas [South Dakota—Wyoming] developed since pre-Cambrian time, in Billings Geol. Soc. Guidebook 3d Ann. Field Conf., Sept. 1952: p. 31—37. Osterwald, F. W., and Dean, B. G., 1961, Relation of uranium deposits to tectonic pattern of the Central Cordilleran foreland: U.S. Geol. Survey Bull. 1087—1, p. 337—390. Page, L. R., and Redden, J. A., 1952, The carnotite prospects of the Craven Canyon area, Fall River County, South Dakota: U.S. Geol. Survey Circ. 175, 18 p. Piper, A. M., 1944, A graphic procedure in the geochemical interpretation of water-analyses: EOS (Am. Geophys. Union Trans.) 25th Ann. Mtg., pt. 6, p. 914—923. Pipiringos, G. N., 1968, Correlation and nomenclature of some Triassic and Jurassic rocks in south-central Wyoming: U.S. Geol. Survey Prof. Paper 594—D, 26 p. Post, E. V., 1959a, Preliminary geologic and structure map of the southwest part of the Cascade Springs quad- rangle, Fall River County, South Dakota: U.S. Geol. Sur- vey Mineral Inv. Field Studies Map MF—211. 1959b, Preliminary geologic and structure map of the southeast part of the Cascade Springs quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—212. 196', Geology of the Cascade Springs quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Bull. 106 3—L, p. 443—504. Post, E. V., Lakota Wyomin and Bell, Henry III, 1961, Chilson member of the formation in the Black Hills, South Dakota and g, in Short papers in the geologic and hydro- REFERENCES CITED logic sc ences: U.S. Geol. Survey Prof. Paper 424—D, p. D173—D178. Post, E. V., and Cuppels, N. P., 1959a, Preliminary geologic and structure map of the northwest part of the Cascade Springs quadrangle, Fall River County, South Dakota: U.S. G(ol. Survey Mineral Inv. Field Studies Map MF—207 195 )b, Preliminary geologic and structure map of the west-central part of the Cascade Springs quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—209. Post, E. V., and Lane, D. W., 19593, Preliminary geologic and structure map of the northeast part of the Cascade Springs quadrangle, Fall River County, South Dakota: U.S. Gxol. Survey Mineral Inv. Field Studies Map MF—208 ' 195)b, Preliminary geologic and structure map of the east-central part of the Cascade Springs quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—210. Redden, J. A ., 1963, Geology and pegmatites of the Fourmile quadrangle, Black Hills, South Dakota: U.S. Geol. Sur- vey Prof. Paper 297—D, p. 199—291. 196 3, Geology of the Berne quadrangle, Black Hills, South Dakota: U.S. Geol. Survey Prof. Paper 297—F, p. 343—408. Rubey, W. V Cretace U.S. Ge Russell, W. Geology Ryan, J. D., River C 1063—J, Schnabel, R. central County, Field Si V., 1931, Lithologic studies of fine-grained Upper us sedimentary rocks of the Black Hills region: 01. Survey Prof. Paper 165—A, p. 1—54. L., 1928, The origin of artesian pressure: Econ. v. 23, no. 2, p. 132—157. 1964, Geology of the Edgemont quadrangle, Fall ounty, South Dakota: U.S. Geol. Survey Bull. p. 379—426. W., 1958, Preliminary geologic map of the east- part of the Burdock quadrangle, Fall River South Dakota: U.S. Geol. Survey Mineral Inv. udies Map MF—74. 1963, Geology of the Burdock quadrangle, Fall River and Cu ter Counties, South Dakota: U.S. Geol. Survey Bull. 1063—F, p. 191—215. Schnabel, R W., and Charlesworth, L. J., Jr., 1958a, Prelimi- nary geologic map of the northeast part of the Burdock quadrangle, Fall River and Custer Counties, South Da— kota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—72. 1958b, Preliminary geologic map of the west-central part of the Burdock quadrangle, Fall River County, 57 South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—71. 1958c, Preliminary geologic map of the southeast part of the Burdock quadrangle, Fall River and Custer Counties, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—75. 1958d, Preliminary geologic map of the northwest part of the Burdock quadrangle, Fall River and Custer Counties, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—73. Shawe, D. R., and Granger, H. C., 1965, Uranium ore rolls— An analysis: Econ Geology, v. 60, no. 2, p. 240—250. Stewart, G. L., and Hoffman, C. M., 1966, Tritium rainout over the United States in 1962 and 1963: U.S. Geol. Survey Circ. 520, 11 p. Swenson, F. A., 1968a, New theory of recharge to the artesian basin of the Dakotas: Geol. Soc. America Bull., v. 79, no. 2, p. 163—182. 1968b, Recharge and movement of water in the ar- tesian basin of the Dakotas, 1'12 Wyoming Geol. Assoc. Guidebook 20th Field Conf., Black Hills area, South Dakota, Montana, Wyoming, 1968: p. 199—207. Waagé, K. M., 1959, Stratigraphy of the Inyan Kara group in the Black Hills: U.S. Geol. Survey Bull. 1081—B, p. 11—90. Whitcomb, H. A., Morris, D. A., Gordon, E. D., and Robinove, C. J., 1958, Occurrence of ground water in the eastern Powder River basin and western Black Hills, northeast- ern Wyoming, in Wyoming Geol. Assoc. Guidebook 13th Ann. Field Conf., 1958: p. 245—260. Wilmarth, V. R., and Smith, R. D., 1957a, Preliminary geo- logic map of the west-central part of the Minnekahta quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—67. 1957b, Preliminary geologic map of the east-central part of the Minnekahta quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—68. 1957c, Preliminary geologic map of the southeast part of the Minnekahta quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—69. 1957d, Preliminary geologic map of the southwest part of the Minnekahta quadrangle, Fall River County, South Dakota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—70. Wolcott, D. E., 1967, Geology of the Hot Springs quad- rangle, Fall River and Custer Counties, South Dakota: U.S. Geol. Survey Bull. 1063—K, p. 427—442. Wolcott, D. E., Bowles, C. G., Brobst, D. A., and Post, E. V., 1962, Geologic and structure map of the Minnekahta NE quadrangle, Fall River and Custer Counties, South Da- kota: U.S. Geol. Survey Mineral Inv. Field Studies Map MF—242. U.S. GOVERNMENT PRINTING OFFICE : 1974—0-537-784 3 ti #12,..‘1‘l‘ffilnixc7xyv . UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 763 PLATE 1 (NORTH HALF) GEOLOGICAL SURVEY R. 61 W. 104°07’30” 43°52’30” R. 1 E. 104°OO’ R.60W. 435230 EXPLANATION 5; Qa II i 3 < 0 Alluvium Windblown deposits Colluvium > a a: . . > E ”7 < ‘ . . — < z Spearflsh Formatlon 2 0—: _ > 0: Esu, upper unit: reddish-brown siltstone D: I— ' E Psm, middle unit: gypsum and reddish—brown siltstone E “A 4: PSI, lower unit: reddish-brown siltstone A V\ 99 I) S . . Q? . . . O \V \ Terrace dep051ts k \ th,fluvial terrace IIWWI Minnekahta Limestone Z T 45 N th’flqul terrace conglomerate / Thin-bedded gray to pink limestone <_E ‘ h \ >- > 2 T. 2 S D: [r . w E LLI . Terrace gravel _ F E Opeche Formation 0' \ o A May include younger g "“16le may be equivalent to part LLI Reddish-brown to purple fine-grained sandstone, of Oligocene White River Group [- siltstone, and shale \ 0 Pierre Shale ‘ ' ‘ 3 Z Kp, undifferentiated; only on Fanny Peak quadrangle \\ \: < 50’ Kpss, Sharon Springs Member: black shale containing §\\\\\\\\R§\\\\\\\ Z concretions; bentonite at base Minnelusa Formation it Z Kpg, Gammon Ferruginous Member: black shale con- ‘ . Z S taining siltstone concretions Pml, amt 1: brecCiated red to yellow sandstone and < 2 yellow to gray limestone; in subsurface, unit may be > I]: - anh ydritic and unbrecciated : LIJ Isz, unit 2: slightly brecciated yellowish—gray dolomite D. . . and yellow calcareous sandstone; in subsurface, unit (é) FLUVIAL SANDSTONE Kfuse Nlobrara F or matlon may be anhydritic and unbrecciated Z v35 Gray to white marl 07“ chalk IF’m3 . unit 3: gray cherty limestone and yellow sand— LLI A $ 99 stone 0. S . V 7’” IPm units 4—6" 00,me l d 't fl' t i a) 4-6 , . y co ore uni s o imes one "6 § ”fl and dolomite; minor amounts of shale, mudstone, and Z g J . calcareous sandstone < ‘9 .— S D. s D . 0. e Carllle Shale . ‘ . (T) g. Kcs, Sage Breaks Member: dark-gray shale . Pahasapa leestone u) b Kct, Turner Sandy Member: dark-gray shale, fine— Cream to gray fossiliferous limestone a grained sandstone, and carbonaceous siltstone (I) Kcu, unnamed shale member: gray shale containing E thin limestone beds and fossiliferous concretions Contact U ——— ----- . D Greenhorn Formatlon Fault Kfiiqififrzozzg 0150726313223; limestone lenses and Dashed where approximately located; dotted where con- Kgl lower unit‘ calcareous shale cealed. U, upthrown side; D, downthrown side. On ’ ‘ maps in isometric projection,faults displacing Mes- - ozoic strata are shown only in structural zones 4____I—____ Belle Fourche Shale .‘ . FLUVIAL SANDSTONE T~ 44 N- Black shale; ferruginous concretions in lower part Antlcllne Showing crestline and direction of plunge T. 3 s. A Kct , , -————————}—— K | . KgTJ Mowry Shale Monocline Gray siliceous shale; nonsiliceous in eastern part of Showing trace Kcu area. Fish scales and sandstone dikes common Kct @ Kg' Newcastle Sandstone 0 W Lenticular gray sandstone 6000 Structure contours Km - (I) Drawn on base of Fall River Formation. Hachures Skull Creek Shale (3) indicate closed basin. Contour interval 100 feet Black shale containing cone-in-cone concretions LL] 5% > 2 Uranium mine Qa I" LLI X g Uranium deposit 0 C 45' 45' Breccia pipe or collapse R lt l t' o underl in rock 0a 1 es“ ”mm s” u “m f y g FLUVIAL SANDSTONE KIfs4 Fa 1 River Formation ————— _ Upper mm. Areal limit of lithologic unit shown on maps 1n Fluvial mm 6.. isometric projection Kfusa, fluvial sandstone Dashed where approximately located or inferred Kfusm, interbedded sandstone and mudstone Kfum, variegated mudstone Middle unit: I . d d 1 . Fluvial unit 5.. Area where stream erOSIon remove un er ymg on Kfm55, fluvial sandstone 11th010glc unlt 1 g Kfmsm, interbedded sandstone and mudstone On maps in isometric projection only K “5m 3 Lower unit. ' S Kflss, interbedded sandstone and siltstone . E . _ W Probable mam channel of paleostream and direction S < E of current § Length of arrow indicates relative size of stream. On 3 maps in isometric projection only Q ’X 5 Selected uranium mines from each lithologic host unit 2 U Projected to line of cross section and shown c6 on restored section only § < :4 hi- § Selected group or cluster of uranium deposits E; Projected to line of cross section and shown H on restored section only . . . LACUSTRINE SANDSTONE KIISS Lakota Formatlon ‘Since mapping was completed, the Redwater Shale Member Fuson Member‘ has been revised. Approximately the lower 25 feet of the Red- . . ‘ _ water, as mapped in this report, is equivalent to the Pine Butte Fluvial unit 4 Klf d .t h l 'll Member, and the thin slabby sandstone at the top is equivalent m4, mu. 3 one 0 anne fl’ to the Windy Hill Sandstone Member (Pipiringos, 1968, fig. 8 Qa Klf54 . fluvial sandstone and 1,023), . Klfm, mudstone and minor amounts of sandstone KIfs, sandstone; locally mappable (appears on re— T- 43 N- stored section only) Klfss, white massive lacustrine sandstone (appears T 4 S on restored section and isometric projection only) ' ’ Fluvial unit 3: Klfsa, conglomeratic fluvial sandstone KIm, Minnewaste Limestone Member Chilson Member: Fluvial unit 2: ch52 , fluvial sandstone complex chu2 ,fine-grained lateral equivalents offluvial * {f sandstone (chsz) (appears on restored section ‘ 4}!" only) 3* Fluvial unit 1: “ chsl,fluvial sandstone complex chu1 ,fine-grained lateral equivalents offluvial 19*“ sandstone (K|051 ) (appears on restored section 0* y , KC” only) ‘J . .. ‘3 ‘ $3,??? . . ° ‘: ' 1 i «I . - . Morrison Formatlon ‘ _ I j: FLUVIAL SANDSTONE KIf53 Grayish-green shale Unkpapa Sandstone {_ $0 $3 $3 (:1 03A 40' 40’ Varicolored massive sandstone 0" 0‘6 45” ($2 s A A Q and siltstone $8 9‘? 55$] See S (“q Q P3» Just, siltstone unit % ‘3 ‘i 4‘0 Jus, sandstone unit 1‘ 0’ 0,0 5% R § «9 (3‘ (5” QAO '9 e e as cc k 3 s“ e be 5.5: E ‘0 « Q s < ‘ ‘ § 9 INDEX SHOWING U.S.GEOLOGICAL SURVEY E. U) I:24,000 QUADRANGLES FROM WHICH S. > 2 BASE WAS PREPARED AND SOURCES OF . GEOLOGIC DATA Sundance Formation 0:): References are listed in text Jsr, Redwater Shale Memberl: grayish-green shale; _, QUADRANGLE SOURCE OF GEOLOGIC minor amounts of glauconitic sandstone AN D DATE DATA JSI’ Lak Member: reddish-brown Siltsmm Angostura Reservoir, 1950 Connor (1963, pl. 11) Jshs, Hulett Sandstone and Stockade Beaver Shale Burdock, 1950 __________ Schnabel (1963, p1_ 17) Members: yellowish-gray ripple-bedded sandstone Cascade Springs, 1950“ _ Post (1967, pl. 29) underlain by grayish-green shale Clifton, 1951 _________ Cuppels (1963, pl. 23) Jsc, Canyon Springs Sandstone Member: orange sand- Dewey.1951 ——————————— Brobst (1961, p15) stone; minor amounts of light-gray siltstone Edgemont, 1950 ———————— Ryan (1964, p1- 27) .3 Edgemont N E, 1950 ,,,,, Gott and Schnabel (1963, pl. 12) a Fanny Peak, 1951 ______ Brobst and Epstein (1963, pl. 25) E Jg Flint Hill, 1950 ________ Bell and Post (1971, pl. 32) 3 . Hot Springs, 1950 ______ Wolcott (1967, pl. 28) '3 Gypsum Spring Formation Jewel Cave sw,1954_ _ L , Braddock (1963, pl. 20) ~ ~ . k d Mlnnekahta, 1950 ______ Wilmarth and Smith (1957a, b, c, d) § Impure gypsum. ggtizngzzéygzggg: Fanny Pea an Minnekahta NE, 1351— ” v Wolcott, Bowles, Brobst, and Post (1962) MINNEWASTE LIMESTONE MEMBER Klm E R. 1 E. 55. R. 2 E‘ th 103°52'30” 43°37'30” T, 42 N. T. 5 S. FLUVIAL SANDSTONE KIC52 35' HORIZONTAL SCALE 9 MILES 'L A 1 X 0 KILOMETERS FLUVIAL SANDSTONE chs1 Jsc Jshs T. 41 N, ANGOSTURA T, 6 S JEWEL CAVE SW CASCADE SPRINGS RESERVOIR FANNY PEAK QUADRANGLE CLIFTON QUADRANGLE DEWEY QUADRANGLE QUADRANGLE BURDOCK QUADRANGLE EDGEMONT NE QUADRANGLE FLINT HILL QUADRANGLE QUADRANGLE QUADRANGLE A V M Y A Y A V L W A Y L WA DEWEY STRUCTURAL LONG MOUNTAIN ZONE STRUCTURAL ZONE A A! U unit Upper unit _ ' Fall RIver £29422; Middle unit Middle Formation Lower unit Lower unit a Fuson Fuson g Lakota Member Member 3 Formation Chilson Minnewaste Q Member Limestone Lakota 5 Kfmsm X S Morrison Formation Member Formation E Chilson Member FEET METERS O O ' Unkpapa Sandstone OBTtARA_CO . 50 43°30’ , 43°30! 250 104°07’30” R' 60 W' 5 104°00’ er 5- Kfusm . 103°52’30” Datum is base of Fall River Formation VERTICAL EXAGGERATION APPROXIMATELY x 53 '"TWOFGEOLOGML SURVEY‘ WASH'NGTON' 0-0—1974‘672’50 ROI W SECTION EXTENDS 56 MILES 71.3], SCALE 1'48,000 HORIZONTAL SCALE IS VARIABLE s 1 1/2 O 1 2 3 MILES 5 a I—-I I—I l—l I—I I—I g g RESTORED DIAGRAMMATIC CROSS SECTION g 2!; 1 .5 0 1 2 3 KILOMETERS 5 g Ile—I I—l I—I I—I I———-—I l—-—-—l E APPROXIMATE MEAN GEOLOGIC AND STRUCTURE MAPS AND RESTORED CROSS SECTION OF PART OF THE SOUTHERN BLACK HILLS, SOUTH DAKOTA AND WYOMING UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY , I u , 103°22’30” 43.52%.97'30" 104°oo' 52'130” 4'5 37130 30 43°52'30" _ ‘/ x, a r _ . ~ // A X Harney “ 1 / LImIt of Precambrlan rocks / peak // w I (from Darton and Paige, 1925) // K E I l/ \l .I U / 0 / pch / 5 fl» 3 l Gravity axis of the Black Hills r e 147 7 * pCb ‘1 a I pCC A 2 5 e [L E“ 45' 45' / I I l PALEOZOIC AND YOUNGER SEDIMENTARY ROCKS '% I Z\ % Limit of Precambrian rocks (a Gravity axis of the Black Hills 6‘ \ ' (9/ \ / / ‘ l I X _____ , .. 37'30” o [5807 37 3O Pringle 0 I 2030 V 4 , 1 B " I; ‘3 o / 0° <3 2:3: iio \\ \04/ E Q / i' O DEWEY >4 5 A? R TERRACE 3 / 1095 v / D 0 IO % l {W6} X’ ’9 I095 . \ ,. 00 W V _ f" 1095@ PALEOZOIC AND YOUNGER — " 6 g Q/ aye (l1 SEDIMENTARY ROCKS I670 \ 43°3o' - \ 30’ 104°07'30" 6%\ / Ir 6‘ ’9 . / e _ 047 . , // EV // if / Z / 1" 8 / OHot Springs 2 / x» (.9 / 8!” <6 z )< J I F 0/ (J I J Gravity axis of the // I? Black Hills 5 / | / I 43°22’30” 22'30” lO4°OO' / ill 2 9t. EDGEMONT TERRACEA 8 L3) ,9 ”7 < z (5 o / v: E 0 > /0Edgemont " D. 13' IIJ // m 1- I E 5 m‘ S 2 l 2 9 5 5 COTTONWOOD CREEK 5 5:” ANTICLINE E APPROXIMATE MEAN DECLINATION,1974 430157 I N / 43°15, 103°52’30" 45’ 37 30 30 103°22'30" SCALE 1:250 000 5 O 5 10 MILES I I I I | | 5 O 5 10 KILOMETERS 537-784 0 - 74 (In pocket) I I l I I I I MAP OF PART OF THE SOUTHERN BLACK HILLS, SOUTH DAKOTA AND WYOMING, SHOWING MESOZOIC AND CENOZOIC DEF ORMATION ALONG PRECAMBRIAN STRUCTURES EXPLANATI Order lay not reflect age pCm Myo Formation pCc CDW Formation pCb Bugown Formation PROFESSIONAL PAPER 765 PLATE 2 O N .—A—A———L—.?_A__ Possible thrust fault Queried where inferred. Sawteeth on upper plate Concealed fault Showing probable direction of movement. Located by airborne magnetometer survey and by gravity survey ng Lineament Garnetifenus quartz—mica schist z _4_I___ < E Anticline [1] Showing crestline and direction of plunge Quartziteand sillimanite schist I <2: 0 . . .., . . 3:1 Synclme Quartz-mica schist a. Showing "Wilhlme Containing some beds of grmwrite schist fl Overturned anticline Showing direction of dip of limbs Garnetiferous and graphitic schist Monocline Pegmatite and granite Showing trace and direction of plunge. Dashed where indefinite r . . Strike and direction of dip of beds Northeast-trendlng dlke of layered pegmatite I500 Magnetic contours ______.. Showing total intensity magnetic field of Contact the earth in gammas relative to arbitrary Dashed where approximately located or datum HaChm‘ed to indicate closed based on reconnaissance mapping; short areas of lower magnetic intensity. 17W?" dashed where indefinite. Dotted line val 100 gammas shows limit of mapped area 0 \Q’\ . Normal fault Measured maximum or minimum in- Located in structural zone, or northeast of tensity Within closed high or closed mapped area shown on plate 1 low In gammas 104°07'30” o l n 4355230,, 103 22 30 4 3 2 5 6 7 1 1 8 9 10 11 12 13 14 15 16 43°15' J SOURCES OF DATA References are listed in text 1. Meuschke, Johnson, and Kirby (1963) [aeromagnetic data] 2. Redden (1963, pl. 21 and fig. 75) 3. Darton and Paige (1925) 4. Brobst and Epstein (1963, pl. 25) 5. Cuppels (1963, pl. 23) 6. Brobst (1961, pl. 5) 7. Braddock (1963,111. 20) 8. Schnabel (1963, pl. 17) 9. Gottand Schnabel (1963, pl. 12) 10. V. R. Wilmarth, U.S. Geol. Survey (unpub. data) 11. Wolcott, Bowles, Brobst, and Post (1962) 12. Wolcott (1967, pl. 28) 13. Ryan (1964, pl. 27) 14. Bell and Post (1971, pl. 32) 15. Post (1967, pl. 29) 16. Connor (1963, pl. 11) Gravity data by R. A. Black, U.S. Geol. Survey (unpub. data) UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 765 PLATE 5 104°07’30” 104°OO’ 43°45’ V r, 43°45’ QKs Sedimentary rocks of Quaternary to Early Cretaceous age K Inyan Kara Group of Early Cretaceous age JPs Sedimentary rocks of Jurassic to Permian age Contact __1’____ Fault Bar and ball on downthrown side. Dashed where projected 20——— Sulfate and chloride as percent of total» anions Dashed where data are projected .Io——~F Calcium and magnesium as percent of total cations Dashed where data are projected .1 1 Water well Referred to in table 10 103°52’30" EXPLANATI ON PERCENT Carl-Mg Total cations PERCENT M Total anions 37'30" “ , 43°37'30" I *, indicates sample control WATER TYPES for water subtype | | | I 103°45’ 30' w 43°3o' ‘c._ ( "- Q / 44 K “ (v \ e , o W Y). , 4’ " 4 : ) . 4 ' o‘ V ., .. \ , <3... \ . ' o ) 9/ . : 4 .. .. . O I -- o < I I & 14 0) z I x‘ \ I . . I \e/ .'. l v ) /\ , I KI -. ' / 43°22'30” I 2230" 104°07'30" . .2.3_° .‘J\ .. é a ,— 3 .. P; : :5:::L::‘;:f:::: ?: fl Q) IR 0 0 0d QKS Cotton“, 43°15’ , H 43°15’ 104°00' 52 3o 103°45’ SCALE 1:125 000 I2 0 2 4 6 MILES I I | I 2 o 2 4 6 KILOMETERS . I I I I l A. HYDROCHEMICAL MAP SHOWING DIFFERENCES IN GROUND—WATER COMPOSITION IN THE INYAN KARA GROUP CATIONS+ANIONS EXPLANATION 0 Water from Minnelusa Formation Water from Inyan Kara Group WATER TYPES .J o % 65 Ca B. MULTIPLE-TRILINEAR DIAGRAM SHOWING CATION AND ANION PERCENTAGES FOR CALCIUM SULFATE. SODIUM SULFATE. AND SODIUM BICARBONATE TYPE GROUND— WATER SAMPLES CATIONS+ANIONS EXPLANATION 0 Water from Minnelusa Formation ,Kf Water from Inyan Kara Group Kf, Fall River Formation Kl, Lakota Formation X Relative percentages of calcium and mag- nesium precipitated from ground water in the Iyan Kara Group ——.—— Direction of evolution of water composition WATER TYPES .J 0 Ca C1 C.MULTIPLE—TRILINEAR DIAGRAM OF AVERAGE COMPOSITION OF CALCIUM SULFATE. SODIUM SULFATEAND SODIUM BICARBONATE TYPE WATERS SHOWING POSTULATED EVOLUTION OF GROUND WATER COMPOSITION IN THE MINNELUSA. LAKOTA. AND FALL RIVER FORMATIONS HYDROCHEMICAL DIAGRAMS AND MAP SHOWING POSTULATED EVOLUTION OF ARTESIAN CALCIUM SULFATE TYPE GROUND WATER FROM THE MINNELUSA FORMATION AS IT MIGRATES THROUGH THE INYAN KARA GROUP, SOUTHERN BLACK HILLS, SOUTH DAKOTA AND WYOMING 537-784 0 - ’74 (In pocket) PROFESSIONAL PAPER 765 PLATE 4 103°22'30” ..43°52’30” EXPLANATION UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 5230" 45' 37'30" 30‘ 0 Contact Breccia pipe or collapse structure in Spearfish Formation, Minnekahta Limestone, or Opeche Formation 104°OO’ 104°07’30” 43°52’30" Normal fault —A—A—h— Breccxa plpe or collapse structure 1n Possible thrust fault , . Sawteeth (m “whom side anelusa Formation Fault from photographs t Syncline ""' """ #22- """ "" Possibly formed in part by solution subsidence Concealed fault a Showing probable direction of movement. _ . . Located by airborne magnetometer survey Area containing structures of posmble solution origin 45' and by gravity survey CI Lineament , . , . Topographic depress10n 1n Inyan Kara Group or younger rocks <~—I— Anticline Showing crestline and direction 0f plunge Topographic depression in Sundance Formation I Topographic depression in Spearfish Syncline Show“! "oughhm Formation or Minnekahta Limestone ‘ + _ _ <— _ _ .— Paleostream of Tertiary and (or) Monocline Showing trace and direction of plunge. Quaternary age Dashed where indefinite Dashed where inferred, 45’ X 0 Breccia pipe or collapse structure in Uranium deposit Inyan Kara, Group or Morrison Some undeveloped prospects in pre-Inyan Kara rocks also shown Formation 37’30” 3730" o _..1 Breccia pipe or collapse structure in Spring Sundance Formation Showing locality number in table 9 o 7 Water well Showing locality number in table 11 104°07’30” 103-22130" 0' 43°52'30" 43°30’ 104°07’30” 13 la 15 16 2230" 4315’ INDEX TO SOURCES OF GEOLOGIC DATA References are listed in text. Springs located from U.S. Geological Sur- vey topographic maps. Solution collapse structures not mapped in some areas. Uranium deposits— shown on geologic maps referenced below. 1. Bowles and Braddock (1963) 2. Redden (1963, pl. 21) 3. Dart/on and Paige (1925) 4. Brobst and Epstein (1963, pl. 25) 5. Cuppels (1963, pl. 23) 6. Brobst (1961, pl. 5) 7. Braddock (1963, pl. 20) 8. Schnabel (1963, pl. 17) 9. Gott and Schnabel (1963,*pl. 12) 10. V. R. Wilmarth, U.S. Geol. Survey unpub.>data 11. Wolcott, Bowles, Brobst, and Post (1962) 12. Wolcott (1967, pl. 28) 13. Ryan (1964, pl. 27) 4 331 5, 14. Bell and Post (1971, pl. 32) 30' 103°22'30" 15. Post (1967, pl. 29) .6. Connor (1963, pl. 11) 43°22'30” 104°OO’ O Edgemont I r/ S — D Z 9 X k ; COTTONWO D CREEK g ANTICLINE APPROXIMATE MEAN DECLINATION,1974 430157 , 103°52'30" 45 TRUE NORTH 3730” SCALE 1:250 000 10 MILES I 5 O 5 10 KILOMETERS | MAP SHOWING MAJOR TECTONIC ELEMENTS, MINOR FAULT AND SOLUTION COLLAPSE STRUCTURES, SPRINGS, PALEOSTREAMS, AND URANIUM DEPOSITS IN THE SOUTHERN BLACK HILLS, SOUTH DAKOTA AND WYOMING 537-754 0 - 74 (In pocket) 104°00’ 43°30’ ‘X T. 6 5. 43°22’30” UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Kfmsm R. 6 E, 25' PROFESSIONAL PAPER 765 PLATE 1 (SOUTH HALF) 103°22’30” KIm 43 30’ _ CUSTER_ FALL RIV Jsr 104°OO’ 3 MILES . I E. i» ‘55 S ‘3“ A 0 \‘Z\ 0’ fl <3 <2? S ‘0 OS Q S ‘1 §° ‘0 v v °) e O Oct 4‘ ‘7"? ‘56 <2? <5 A9 ‘5 ‘3'“! a? a?) :3” \§ § e 6‘ § A A ~Z~ g- § s“ 52? 55‘ Q‘ /\ a," Q Q Q- 03, 3 0‘” Q} ‘34" 4? «V "3 7%" INDEX SHOWING U.S, GEOLOGICAL SURVEY I:24,000 QUADRANGLES FROM WHICH BASE WAS PREPARED AN D SOU RCES OF GEOLOGIC DATA References are listed in text QUADRANGLE SOURCE OF GEOLOGIC A N D DATE DATA Angostura Reservoir, 1950L Connor (1963, pl. 11) Burdock, 1950 ,,,,,,,,,,, Schnabel (1963, pl. 17) Cascade Springs, 1950L L L L Post (1967, pl. 29) Clifton, 1951 LLLLLLLLLL Cuppels (1963, pl. 23) Dewey, 1951 LLLLLLLLLLLL Brobét (1961, pl. 5) Edgemont. 1950 LLLLLLLLL Ryan (1964, pl. 27) Edgemont NE, 1950 LLLLLL Gott and Schnabel (1963, pl. 12) Fanny Peak, 1951.. I L L L L L Brobst and Epstein (1963, pl. 25) Flint Hill, 1950 LLLLLLLLL Bell and Post (1971, p11 32) Hot Springs, 1950- _ _ L L L L Wolcott (1967, p]. 28) Jewel Cave SW, 1954 LLLLL Braddock (1963, pl. 20) Minnekahta, 1950L L L L L L L. Wilmarth and Smith (1957a, b, c, d) Minnekahta NE, 1951 LLLLL Wolcott, Bowles, Brobst, and Post (1962) [13,: I a 3 3 g 2 i A El If? V; AI’PROXIMATL MLAN DECLINATION 1974 SCALE 1:48,000 1/2 O l 2 :1 'H I——‘ I—.— r—‘ I—-—-—-————-—' W , w 7' '7’ L ‘r 1 .5 O l 2 3 KILOMETERS Kfusm Kfuss ,~Kpg 43°15'Ifj/m 103°52’30” See north half for explanation of geologic symbols GEOLOGIC AND STRUCTURE MAPS AND RESTORED CROSS SECTION OF PART OF THE SOUTHERN BLACK HILLS, SOUTH DAKOTA AND WYOMING D TBS. ) 20’ (W K955 Qw I Q 0 Lo , $5" ' N .t Kt Kg Kct @ Kct Qw T. 9 S. Qa / Kn th Kpg-Kpss § QW Qa Qw Kgu (I b Qa /( ' ' ' 43°15 R.6E. 25’ 103°22'30" INTERIOR—GEOLOGICAL SURVEY, WASHINGTON, D.C.719747672150 Stratigraphy of the Southern Coast Ranges near the San Andreas Fault from Cholame to Maricopa, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 764 252? M Stratigraphy of the Southern Coast Ranges near the San Andreas Fault from Cholame to Maricopa, California By T. w. DIBBLEE, JR. GEOLOGICAL SURVEY PROFESSIONAL PAPER 764 A discussion of the regional stratigraphy of the M cLure Valley area, Temblor Range, Carrizo Plain, Cuyama Valley, Caliente Range, La Panza Range, and Sierra M adre Mountains UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of 0011ng “tales-card No. 72—600327 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC. 20402 Price: Paper cover—80 cents, domestic postpaid; 55 cents, GPO Bookstore. Stock No. 2401-00300 Abstract ________________________________________ Introduction _____________________________________ Scope and purpose ___________________________ Problems of stratigraphic terminology _________ Chronology used _____________________________ Tectonic areas _______________________________ Crystalline plutonic and metamorphic rocks ________ Eugeosynclinal sedimentary and igneous rocks _____ Definition ___________________________________ Franciscan rocks ____________________________ Ultramafic rocks ____________________________ Jurassic(?) and Cretaceous marine sedimentary se- quence ____________________________________ Definition ___________________________________ Gravelly Flat Formation _____________________ Hex Claystone _______________________________ Panoche Formation __________________________ Upper Cretaceous and lower Tertiary marine sedi- mentary sequence __________________________ Definition Marine clastic Sedimentary rocks ______________ Lower Tertiary marine sedimentary sequence _______ Definition ___________________________________ Lodo(?) Formation __________________________ Avenal Sandstone ____________________________ Kreyenhagen Shale __________________________ Point of Rocks Sandstone ____________________ Wagonwheel Formation ______________________ Middle Tertiary sedimentary sequence _____________ Definition ___________________________________ Simmler Formation __________________________ Vaqueros and Temblor Formations ____________ Review of nomenclature __________________ Vaqueros Formation _____________________ Quail Canyon Sandstone Member ______ Soda Lake Shale Member _____________ Painted Rock Sandstone Member ______ Temblor Formation ______________________ Cymric Shale Member ________________ Wygal Sandstone Member ____________ Santos Shale and Agua Sandstone Mem- bers Carneros Sandstone Member __________ Media Shale Member _________________ ___.L _______________________________ CONTENTS *6 n N o mamammwwu—u—n—t WMQO'AO: 10 10 10 10 12 13 13 13 13 14 15 15 17 17 17 18 18 20 20 22 23 23 Middle Tertiary sedimentary sequence—Continued Vaqueros and Temblor Formations—Continued Temblor Formation—Continued Buttonbed Sandstone Member _________ Monterey Shale ______________________________ Review of nomenclature __________________ Stratigraphic units southwest of the San Andreas fault _______________________ Saltos Shale Member ________________ Whiterock Blufi' Shale Member _______ Stratigraphic units northeast of the San Andreas fault _______________________ Gould Shale Member _________________ Devilwater Shale Member ____________ Interbedded shale and sandstone mem- ber McLure Shale Member _______________ Belridge Diatomite Member ___________ Branch Canyon Sandstone ____________________ Santa Margarita Formation __________________ Caliente Formation __________________________ Basalt Bitterwater Creek Shale _____________________ Reef Ridge Shale ____________________________ Upper Tertiary sedimentary sequence _____________ Definition Deposits in the San Joaquin Valley area _______ Terminology Etchegoin Formation _____________________ San Joaquin Formation ______________ Deposits in the Salinas Valley—Cuyama Valley area Unnamed marine sediments ______________ Quatal Formation ________________________ Morales Formation Valley deposits __________________________________ Definition ___________________________________ Paso Robles Formation _______________________ Tulare Formation ___________________________ Surficial deposits ________________________________ Relationship of sedimentary sequences to the San Andreas fault _________________________________ References cited ___--_____-___--____________-___; ILLUSTRATIONS FIGURE 1. Index map of part of central California showing area studied ______________________________________ 2. Generalized geologic map showing distribution of major stratigraphic sequences in the southern Coast Ranges near the San Andreas fault from Cholame and Avenal to Cuyama and Maricopa _________ III Page Page IV FIGURES 3—8. 10. 11. 12. 13. 14. TABLE 1. 2. 3. CONTENTS Stratigraphic diagrams showing: 3. Major Mesozoic and Cenozoic sedimentary sequences of the southern Coast Ranges near the San Andreas fault from Cholame and Avenal to Cuyama and Maricopa _________________ 4. Cretaceous and Cenozoic chronology of the southern Coast Ranges ________________________ 5. Jurassic(‘.’) and Cretaceous marine sedimentary sequence in the southeastern part of the Diablo Range and in the Temblor Range ___________________________________________ 6. Lower Tertiary marine sedimentary sequence in part of the Diablo Range betWeen McLure and Cholame Valleys and in the Temblor Range _________________________________________ 7. Lithologic units of the middle Tertiary sedimentary sequence southwest of the San Andreas fault from Cholame to Cuyama _____________________________________________________ 8. Lithologic units of the middle Tertiary sedimentary sequence northeast of the San Andreas fault from Avenal to Maricopa _____________________________________________________ Map of the Temblor Range showing geographic localities mentioned and areal extent of the Tertiary formations ________________________________________________________________________________ Geologic map of the Chico Martinez Creek area, Temblor Range, showing members of the Temblor Formation and Monterey Shale ______________________________________________________________ Stratigraphic diagram showing sections of the Temblor Formation from Cedar Creek to Zemorra Creek in the Temblor Range ______________________________________ L ______________________________ Map showing probable original and present areal extent of contemporaneous formations or facies of mainly middle and late Miocene age in southern Coast Ranges ________________________________ Diagram showing classification and names applied to the upper Tertiary (Pliocene) sedimentary se- quence in southeastern part of the Diablo Range and Kettleman Hills ________________________ Stratigraphic diagram showing valley deposits and upper Tertiary sedimentary sequence of the San Joaquin Valley area along east side of the southeastern part of the Diablo Range, Kettleman Hills, and the Temblor Range ____________________________________________________________________ TABLES Names applied by other investigators to strata herein assigned to the Vaqueros and Temblor Forma- tions of map region of figure 2 ____________________________________________________________ Local stratigraphic units of the Temblor Formation in the Temblor Range between Chico Martinez Creek and Bitterwater Creek ______________________________________________________________ Members of the Temblor Formation exposed at Devils Den _______________________________________ Page “>00 11 14 15 19 21 22 25 35 36 Page 16 20 24 STRATIGRAPHY OF THE SOUTHERN COAST RANGES NEAR THE SAN ANDREAS FAULT FROM CHOLAME TO MARICOPA, CALIFORNIA By T. W. DIBBLEE, JR. ABSTRACT The upper Mesozoic and Cenozoic sedimentary series within about 20 miles on either side of the San Andreas fault has been mapped and systematically classified. South- west of the fault, the sedimentary series overlies a Mesozoic crystalline basement of plutonic and metamorphic rocks, is from 5,000 to 40,000 feet thick, and is divided into four lithologic sequences. Northeast of the fault, the sedimentary series overlies a Mesozoic basement of eugeosynclinal rocks (Franciscan rocks and serpentine), is from 25,000 to 40,000 feet thick, and is divided into five lithologic sequences. These sequences are in large part separated by regional uncon- formities. The Cretaceous and Tertiary sequences are marine and terrestrial southwest of the fault, marine northeast of it. The youngest sequence, mainly of Quaternary age, is composed of lithologically similar valley sediments on each side of the fault. Most of the sedimentary sequences are divided into litho- logically distinct formations of large areal extent, some of which in turn are divided into local members. A standardized set of names has been designated for the formations and members for this region, using the existing names that are applicable. On opposite sides of the San Andreas fault, not only are the basement rocks contrasting, but the oldest correspond- ing sedimentary sequences are dissimilar; the successively younger sequences are progressively less different. This con- dition appears to be the result of persistent right-lateral movement on the fault since Cretaceous time. INTRODUCTION SCOPE AND PURPOSE The areal geology of about 20 miles on either side of an 80-mile segment of the San Andreas fault from Cholame and Avenal to Cuyama and Mari- copa (fig. 1) has been mapped and compiled at a scale of 1:125,000, or 2 miles to 1 inch (Dibblee, 1973b). The region mapped is in the southern Coast Ranges and includes the extreme southeastern part of the Diablo Range, all the Temblor Range, Carrizo Plain, Caliente and La Panza Ranges, Sierra Madre Mountains, and much of Cuyama Valley (fig. 2). The subsurface geology of this area based on the areal geology mapped and on logs of test holes ‘. ( 1 35° 7 \\ . Sa ta Man \ . n a seam Cuyama \ \/ Santa Barbara b9 40 MILES FIGURE 1.—Index map of part of central California. Area studied, indicated by dashed outline, is shown in figure 2. drilled for oil or gas is shown in five cross sections (Wagner and others, 1973). The purpose of the geologic map (Dibblee, 1973b) and cross sections (Wagner and others, 1973) is to portray the re- gional geology and to provide a geologic background for earthquake investigations and geophysical studies in progress or contemplated along this great active fault. ' 2 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA 10 2'0 MILES lllllllllll what i \ SAN J04 QU/N '1' Th: 'WGQNAPA gg’l MAJ. I 00 EXPLANATION g Contact Surficial deposits Middle Tertiary sedi- Upper J urassic(?) and Fault mentary sequence Cretaceous marine Dotted where concealed sedimentary sequence or inferred Valley deposits - Lower Tertiary marine sedimentary sequence Eugeosynclinal sedimen- tary and igneous rocks Upper Tertiary sedi- /// _ ‘ \ , mentary sequence / ~ I: (31'; ' \C l /: \ Upper Cretaceous and ’ r I” lower Tertiary marine Crystalline plutonic and sedlmentary sequence metamorphic rocks FIGURE 2.—Distribution of major sequence in the Southern Coast Ranges near the San Andreas fault from Cholame and Avenal to Cuyama and Maricopa. The .purpose of this report is to supplement the terminology, it was necessary to (1) designate the description of the rock units on the geologic map major and minor lithostratigraphic units that are (Dibblee, 1973b) with a discussion of their strati- physically recognizable and mappable throughout graphy in this region. To resolve the problems in | the region, (2) review the stratigraphic name or INTRODUCTION names that have been applied to each unit by pre- vious investigators, and (3) suggest the best desig- nation for each unit. PROBLEMS OF STRATIGRAPHIC TERMINOLOGY The map area (fig. 2) is one in which the Meso- zoic and Cenozoic stratigraphy is exceedingly com- plex because of many unconformities and lateral variations in lithology and thickness resulting from deposition concurrent with tectonic movement. Dur- ing pioneer geologic investigations of the oil and gas districts of this region in the early twentieth century, attempts were made to delineate major stratigraphic units on the basis of reconnaissance mapping. Later, more detailed investigations re- vealed stratigraphic complexities not recognized in the earlier investigations. Correlation problems be- came evident and led to the naming of numerous local stratigraphic units. As a result, each district has its own set of locally recognized stratigraphic units, and no major regional stratigraphic units of the California Coast Ranges have been established. Thus, the stratigraphic terminology is somewhat chaotic. The most practical approach to regional mapping was to recognize and map the major stratigraphic divisions with a characteristic lithology of regional extent. These are informally designated herein as sedimentary “sequences” and shown in figure 3. Their areal extent is shOWn in figure 2. All are in large part separated by unconformities. The upper- most sequence is terrestrial; the other sequences are all or largely marine. Each marine sequence represents a complete or nearly complete sedimen— tary cycle of marine transgression, inundation, and regression. These sequences are divided into map- pable units designated as lithologically distinct formations. Where convenient, these in turn are divided into local units, such as members or facies. This report discusses the pertinent terminology and evidence for the age of each stratigraphic unit, as well as discrepancies and problems involved. In figure 3 and in those figures that follow, time boundaries of the standard European systems and series are suggested only by queries. Definite bound- aries are not shown because of (1) uncertainties in the definitions of the European series or epochs, (2) uncertainties involved in the assignment of the faunal stages and “ages” to those epochs, and (3) uncertainties of correlation of the terrestrial ver- tebrate “ages” with the marine molluscan “ages” and microfaunal stages of the Pacific Coast region. The resolution of these controversial correlation problems is beyond the scope of this report; hence the queries. SOUTHWEST OF SAN NORTHEAST OF SAN AGE ANDREAS FAULT TO ANDREAS FAULT T0 RINCONADA FAULT SAN JOAQUIN VALLEY E> SLIrficial deposits I—‘I Pleisto— . 5; Gene Valley dep05Its o 0 7 _7'_} www— _ ' Upper Tertiary Upper Tertiary 8 Pl' sedimentary sedimentary o '0' sequence sequence Z Gene (terrestrial and (marine) 8 marine) 3 ?? Middle Tertiary Middle Tertiary Mio- sedimentary sedimentary >- sequence sequence E 63:16 (marine terrestrial (marine) i: and volcanic) D: OllgO— WW E cene ?? (Absent) Lower Tertiary marine Eocene sedimentary Upper Cretaceous sequence ?? and lower Tertiary marine Paleo— sedimentary cene sequence (Absent) 7 7 ?? W , Upper Jurassuc(?) % CRETA' and Cretaceous CEOUS marine 8 (Absent) sedimentary 3 sequence 2 CRETA- Crystalline Eugeosynclinal CEOUS plutonic and sedimentary AND metamorphic and igneous OLDER rocks rocks FIGURE 3.—Major Mesozoic and Cenozoic sedimentary se- quences of the southern Coast Ranges near the San Andreas fault from Cholame and Avenal to Cuyama and Maricopa. Regional unconformities indicated by wavy lines. CHRONOLOGY USED Each stratigraphic unit is assigned to the “ages” and (or) stages currently recognizable in California on the basis of stratigraphic and paleontologic evi- dence. Tentative correlations from one chronology to another are indicated in figure 4 by horizontal dotted lines. Assignment of the units to the stand- ard European series is controversial and not yet definitely resolved. The terrestrial mammalian “ages” in figure 4 are those proposed by Wood and others (1941) and by Savage, Downs, and Poe (1954), With modifications by Evernden, Savage, Curtis, and James (1964). None were defined with reference to type sections. Volcanic samples from rock units within each “age” have been radiometrically dated by Evernden, Sav- age, Curtis, and James (1964) and Turner (1970), STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA < _ MAMMA— RADIO- FORAMIN- E :3 SERIES LIAN METRIC IFERAL M9,‘-LUS§AN “AGES" AGESl STAGES AGES Holocene cr' ’ .. Lu E Rancho- Upper E < . Iabrean ___________________ Pleistocene" 82 Pleistocene Irving- "‘Lower tonlan Pleistocene" 1.5 ------------ “San Joaquin” Bla _ Upper ncan and “Etchegoin” a.) , ______________________ g Pliocene ‘ 4 D Lower ”WW" “Jacalltos” hllllan ------- 1o ? Claren- “Delmontian"2 “Santa Upper donian Mohnian Margarita" ------ 12?‘ 2 . . 13?" Lulsian S 2 Miocene Middle Barsto— 14 O B vian Relman “Temblor” -------- \ E E 2 ‘ _ O 55 Lower Heming- Saucesian ,_. fordlan 5 2-1- -------- 22"; Arika- ' . “Va n *— . Upper reean Zemorrian queros __ Ollgocene 26 Lower Refugian “Gaviota” Upper Narizian “Tejon” L Eocene Middle Ulatisian “Domengine” o 3 ............ 3 Lower Penutian “Capay” Upper Bulitian "Meganos" Paleocene Lower Ynezian ”Martinez" Maestrichtian Campanian m U er Santonian “J (I) pp Coniacian 2 8 Turonian r— - w 9 8 Cenomaman S '<_: Albian 8 3:4 Aptian Lu 0 Barremian <2: 2 LOWer Hauterivian Lu Valanginian 0- Berriasian 3 D o': g . . m 3 (D Upper TIthonIan fl < 1Potassium‘ (D 5 L U L N o a, a. DJ }— QC, L gé ————— U 3 3 .‘2 g 3 UlatISIan (Absent?) Gredal Shale Member — Avenal Sandstone r If, Penutian 7 (Absent) Paleo' Bum?” (Absent) Lodo(.7) Formation // cene Yneznan FIGURE 6.—Lower Tertiary marine sedimentary sequence in part of the Diablo Range between McLure and Cholame Valleys and in the Temblor Range. Unconformity indicated by wavy line. fig. 1) for Avenal wells in Big Tar Canyon, 6 miles southWest of Avenal (fig. 2). This sandstone was assigned to the Domengine Formation (of Ander- son, 1905, north of Coalinga) by Clark (1929, p. 216) and Gester and Galloway (1933, p. 1167, 1184) . The Avenal Sandstone, which contains orbitoid Foraminifera and abundant mollusks, was mapped and described in detail by Stewart (1946, p. 89—94, pl. 1), who adopted the name and suggested its correlation with the Domengine Formation, which is very similar and is probably the same unit. The Avenal Sandstone is from 300 to 500 feet thick and fine grained, and it contains abundant mollusks assigned to the middle Eocene (Stewart, 1946, p. 92—94) . It was questionably assigned to the Ulatisian Stage, middle Eocene, by Mallory (1959, p. 51, fig. 7). In areas south and southeast of McLure Valley, the basal Tertiary sandstone discussed in the next three paragraphs is herein included in the Avenal Sandstone because of gen rally similar lithology and probably similar stratigraphic position. Local names have been applied to this sandstone because of uncertainty of its correlation with the type Ave- nal Sandstone. In the Diablo Range west of McLure Valley, this basal sandstone is as thick as 400 feet and was called Acebedo Sandstone by Dickinson (1963, p. 48—52). This sandstone contains “Spiroglyphus” and orbitoid Foraminifera, and according to Mal- lory (1959, p. 50—51), it is slightly older than the type Avenal Sandstone and was assigned by him to the Ulatisian or Penutian Stage, middle or lower Eocene. In the Devils Den area, the lowest Tertiary sand- stone unit, as thick as 200 feet, contains “Spiro- glyphus” (Rotulam'a) and was named Mabury Sandstone by Van Couvering and Allen (1943, p. 496—500). Mallory (1959, p. 37, fig. 7) assigned this sandstone to the Lodo Formation and to his Penutian Stage, lower Eocene. In the Temblor Range between Media Agua and Carneros Creeks, the lowest Tertiary sandstone unit forms a lens as thick as 300 feet. It is underlain by clay shale of the Lodo Formation and is overlain by the Gredal Shale Member of the Kreyenhagen Shale. According to Durham (1942, p. 503—510), this sandstone contains (in NEl/4.SE14 sec. 28, T. 28 S., R. 19 E., east of Media Agua Creek) mollusks and corals referred to the Domengine Stage, middle 12 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA Eocene. However, at Media Agua Creek, where the sandstone unit is only 25 feet thick, Mallory (1959, p. 24, 34, fig. 7) designated the sandstone (his mid- dle Lodo) and 20 feet of the underlying shale as his type Penutian Stage, lower Eocene; he correlated the sandstone, which there contains “Spiroglyphus” and orbitoid foraminifers, with the Mabury Sand- stone of Devils Den and assigned both to the Lodo Formation. This assignment is not adopted because at Media Agua Creek this 25-foot-thick “sandstone reef” is overlain by about 90 feet of clay shale which Mal- lory (1959, p. 30, fig. 3, 7) designated as upper Lodo but which he assigned to his Ulatisian Stage, middle Eocene. This assignment would correlate this shale With the Gredal Shale Member of the Kreyenhagen Shale. The underlying “sandstone reef” is therefore probably the same unit as the Avenal Sandstone, to which it is assigned. Although there is some doubt as to exact correla- tion, the Acebedo Sandstone west of McLure Valley, Mabury Sandstone of Devils Den, and the sandstone at Media Agua Creek are herein assigned to the Avenal Sandstone because in each area they are of generally similar lithology and form the basal trans- gressive sandstone unit of the lower Tertiary marine sedimentary sequence; thus they appear to be the same unit. Therefore the local names Acebedo and Mabury are not formally adopted. The Avenal Sand- stone, as herein mapped, is presumably in the Do— mengine molluscan age and Penutian and Ulatisian Stages, early and middle Eocene. KREYENHAGEN SHALE The clay shale and claystone facies of the lower Tertiary marine sedimentary sequence is promi- nently exposed in the Reef Ridge area north of McLure Valley. It was named Kreyenhagen Shale for Kreyenhagen wells at Canoas Creek (7 miles west of Avenal), the type locality, by Anderson (1905, p. 163—168). This name was not used by Arnold and Anderson (1910, p. 58—70) but was adopted by Cushman and Siegfus (1942), who de- scribed the sections exposed at Canoas and Garza Creeks (7 miles west of Avenal) and by Stewart (1946, p. 95, pl. 1), who described and mapped the formation in detail. In the Reef Ridge area the Kreyenhagen Shale is from 950 to 1,250 feet thick, consists of gray clayey to silty shale, overlies the Avenal Sandstone, and is unconformably overlain by the Temblor Sandstone. The major part of the Kreyenhagen Shale contains foraminifers diagnostic of the Nari- zian Stage, late Eocene (Mallory, 1959, p. 71, fig. 7). Cushman and Siegfus (1942, p. 395—397) suggested that the upper part may be as young as Oligocene (Refugian). The lowest 50—110 feet of the Kreyen- hagen Shale is greenish claystone which was named the Canoas Siltstone Member by Cushman and Sieg- fus (1942, p. 390—391) and which contains a foram- iniferal fauna (“Canoas Fauna”) to which they assigned a middle Eocene age. Mallory (1959, p. 51, 71) suggwted that this fauna may belong to his Ulatisian Stage, middle Eocene, but it is not cer- tainly diagnostic. In the Devils Den area the Kreyenhagen Shale is separated into two units of clayey shale by the Point of Rocks Sandstone (fig. 6). The lower unit, as thick as 700 feet, was named the Gredal Forma- tion by Van Couvering and Allen (1943, p. 496— 500). This same unit was designated as the Gredal Member of the Lodo Formation and assigned to the Ulatisian Stage, middle Eocene, by Mallory (1959, p. 45, 51, fig. 7), but it was mapped as the Canoas Siltstone Member of the Kreyenhagen Shale by Marsh (1960, p. 31, pl. 1). Because this unit is much thicker than the type Canoas Siltstone Member of Reef Ridge (too thin to show at the map scale), with which it is correlated by petroleum geologists, the unit at Devils Den is herein adopted as the Gredal Shale Member of the Kreyenhagen Shale. The type section of this member is designated as the section exposed in NEl/4, sec. 10, T. 26 S., R. 18 E., 4 miles south of Devils Den, where it consists of about 750 feet of gray clayey shale with local occurrences of green and red clay, overlies the Ave- nal (“Mabury”) Sandstone, and is overlain by the Point of Rocks Sandstone. In the northwestern Temblor Range, the Gredal Shale Member of the Kreyenhagen Shale is exposed south of Cedar Creek and at Media Agua Creek (fig. 9). In the former area, it is several hundred feet thick and consists of gray, green, and red clay- stone that unconformably overlies the Gravelly Flat Formation. At Media Agua Creek, it overlies the Avenal(?) Sandstone and is overlain by the Point of Rocks Sandstone, as at Devils Den; it is about 90 feet thick and is the same unit as the upper Lodo of Mallory (1959, p. 24, 45, figs. 3, 7), which he assigned to his Ulatisian Stage, middle Eocene. The upper unit of the Kreyenhagen Shale in the Devils Den area is composed of about 600 feet of clayey shale that overlies the Point of Rocks Sand- stone and is overlain by the Wagonwheel Formation. This shale unit was named Welcome Formation by Van Couvering and Allen (1943, p. 496—500). This unit is herein adopted as the Welcome Shale Mem- ber of the Kreyenhagen Shale, with the type section designated as Welcome Valley (SE14, sec. 35, T. 25 MIDDLE TERTIARY SEDIMENTARY SEQUENCE 13 S., R. 18 E., NE%NE% sec. 2 and NW%, sec. 1, T. 26 S., R. 18 E.), just south of Devil-s Den. This unit is poorly and incompletely exposed; it is con- cealed by alluvium to the southeast and is over- lapped by the Temblor Formation to the northwest. It forms the upper part of the type Narizian Stage, upper Eocene, of Mallory (1959, p. 55—56), al- though foraminifers of the Refugian Stage have been reported from the uppermost part of this shale unit by Smith (1956, p. 77—78) and Mallory (1959, p. 71). On the basis of the foregoing evidence, the Gredal Shale Member of the Kreyenhagen Shale is assigned to the Ulatisian Stage, middle Eocene, and the Wel- come Shale Member is assigned to the Narizian Stage, upper Eocene, with the upper part possibly extending into the Refugian Stage, early Oligocene. POINT OF ROCKS SANDSTONE The sandstone of the Eocene sedimentary sequence is prominently exposed in the northwest part of the Temblor Range, where it is as much as 2,000 feet thick, near Devils Den where it is about 2,350 feet thick, and in the Diablo Range, where it is as much as 1,250 feet thick. In the Devils Den area, it was named Point of Rocks Sandstone, for Point of Rocks (SI/2 sec. 2, T. 26 S., R. 18 E.), 3 miles south of Devils Den, by Van» Couvering and Allen (1943, p. 496—500). This name is adopted herein. In the Reef Ridge area, this sandstone either is missing or may be represented by a sandstone lens as thick as 30 feet about 100 feet above the base of the Kreyenhagen Shale (Dickinson, 1966a, p. 711). The Point of Rocks Sandstone rarely contains fossils. “Characteristic Tejon fossils” were reported but not listed from the Point of Rocks area by Arnold and Johnson (1910, p. 38). At Devils Den, the Point of Rocks Sandstone, with the possible exception of the lowest 75 feet, was designated as the type Narizian Stage, upper Eocene, by Mallory (1959, p. 55—56). Foraminifers diagnostic of the Narizian Stage were obtained from thin shale beds in this sandstone at Devils Den and also at Media Agua Creek by Mallory (1959, p. 56). At Devils Den, shale interbeds in the lowest 75 feet of the Point of Rocks Sandstone contain foraminifers as- signed by Mallory (1959, p. 57) to the Ulatisian Stage. The basal part of the Point of Rocks Sand- stone is thereby assigned to the Ulatisian Stage, middle Eocene, and the major part to the Narizian Stage, upper Eocene. WAGONWHEEL FORMATION In the Devils Den area, a basal marine sandstone and a clayey shale unit, about 500 feet thick, were 495-417 0 - '13 - 3 mapped as Oligocene(?) rocks by Arnold and J ohn- son (1910, p. 40). Johnson (1909, p. 63) had pre- viously named this unit the Wagonwheel Formation for exposures near Wagonwheel Mountain, 2 miles south of Devils Den, and had tentatively assigned it to the Oligocene. This name was used by Van Couvering and Allen (1943, fig. 213) and is adopted herein. Atwill (1935, p. 1207) correlated this unit with his Tumey Formation north of Coalinga. The Wagonwheel Formation and its foramini- feral fauna were described and discussed in detail by Smith (1956). He assigned the formation to the Refugian Stage of early Oligocene age and indicated that it lies conformably on the Kreyenhagen Shale and disconformably below the Temblor Formation. Because of these stratigraphic relationships, this unit, which is the only one wholly assigned to the Refugian Stage within this region, is placed arbi- trarily at the top of the lower Tertiary marine sedi- mentary sequence, rather than in the middle Ter- tiary sedimentary sequence. MIDDLE TERTIARY SEDIMENTARY SEQUENCE DEFINITION The middle Tertiary sedimentary sequence is ex- tensive on both sides of the San Andreas fault. It lies unconformably on the older rock units in most areas and is lithologically more variable than the other sedimentary sequences. It represents a com- plete sedimentary cycle of transgression, inunda- tion, and regression. This sequence is mainly of Miocene age, but it is in part Oligocene andvpossibly in part Pliocene. Southwest of the San Andreas fault, this sequence is as thick as 10,000 feet in the central part of the Caliente Range and probably equally as thick under the Carrizo Plain. Within a few miles the whole sequence thins to the northwest, southwest, and southeast to about 2,500 feet or less, with a few local unconformities within it. The lowest unit of this sequence is terrestrial, the remainder is marine; much of this marine part grades laterally northeast- ward into terrestrial deposits apparently derived from a granitic terrane that existed northeast of the San Andreas fault in middle Tertiary time. Most of the marine facies is sandstone and some argillaceous sediments, but the middle part in areas distant from the San Andreas fault is mostly sili- ceous shale. Basaltic intrusions and lava flows occur in both the terrestrial and marine facies in the Caliente Range. This sequence unconformably over- lies the Up-per Cretaceous and lower Tertiary marine sedimentary sequence, overlapping and truncating .14 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA CALIENTE RANGE LIJ r <5 STAGE SEES; nAgfifiZXORUA'LTé‘éNS , CARRIZO PLA|N(?), AND NORTHEAST < RED HILLS AREA 5 . SANTA MARGARITA FORMATlON E Mohnlan ,, (sandstone) \\\ Lu r——-—.?* Basalt o :» “<2" <\ :5 Z Luisian Whiterock Bluff Shale ‘31? (7’ (’2’ g Member ,-=-" I,” BRANCH Q o a, ------- _M0NT EREY x» a,» CANYON ©4325“ (If) c __ __________ 8 Relizian SHALE v" , SANDSTONE \1’ > .9 Saltos Shale Member 05:» I; n: 2 Basalt __ ,_\ _____ >7_ ___7 2, E r—"—‘ z . . , 9 R) CALlENTE m Basalt g FORMATION E Painted Rock ‘3 S ' Sandstone ———————— \\\ <1) SauceSIan VAQUEROS Member <:: .:T:’ \\) >- FORMATION - 11111 ,,:> <\ 5:: -§~\’ r\\ ‘5 _ __,» > <\ _____ ‘\\‘» /// ‘x E , ———————————— ‘- ———————————— (\ Lu ‘7 \‘ (/’/ Soda Lake Shale Member ::>-:3 '— d) 2\\_ T“‘&‘ _____________ Y """—’ (e E C \> ' D 8 Zemorrian Mostly '1. Quail Canyon Sandstone Member 9 O _ ‘2 g) (Absent) “25:: s \ MLER FORMATION Mostly 5 O «E\ sandstone UPPER CRETACEOUS AND LOWER TERTIARY MARINE SEDIMENTARY SEQUENCE, AND CRYSTALLlNE ROCKS FIGURE 7.—Lithologic units of the middle Tertiary sedimentary sequence southwest of the San Andreas fault from Cho- lame to Cuyama. Caliente and Simmler Formations are terrestrial; all other units marine. Unconformity indicated by wavy line. it from south to north onto the crystalline rocks. The lithologic units that make up the middle Ter- tiary sedimentary sequence southwest of the San Andreas fault are shown in figure 7. Northeast of the San Andreas fault, this sequence is virtually all marine. It attains its greatest thick- ness, one of the greatest in California, in the south- eastern Temblor Range, where it is as thick as 15,000 feet. In this area and adjacent parts of San Joaquin Valley, most of it accumulated under bathyal and abyssal conditions (Bandy and Arnal, 1969, p. 794, 814). Northwestward, this sequence gradually thins to as little as 700 feet in the Diablo Range and accumulated under shallower water. The lower part is chiefly sandstone and argillaceous deposits, the upper part mainly siliceous shale. In the southeastern Temblor Range and adjacent parts of the San Joaquin Valley, this sequence lies dis- conformably( ?) on the lower Tertiary marine sedi- mentary sequence, but in the northwestern Temblor Range and Diablo Range it becomes unconformable on this and the older sequences, with increasing dis- cordance westward toward the San Andreas fault. In a few places local unconformities occur within this sequence. The lithologic units that make up the middle Tertiary sedimentary sequence northeast of the San Andreas fault are shown in figure 8. The stratigraphic units of this sequence shown in fig- ures 7 and 8 are discussed in the following sections. SIMMLER FORMATION Southwest of the San Andreas fault, the basal unit of the middle Tertiary sedimentary sequence is composed of terrestrial red to gray conglomerate, sandstone, and siltstone. It was named the Simmler Formation by Hill, Carlson, and Dibblee (1958, p. 2981—2983, fig. 3). The name is adopted herein. This formation lies unconformably on and overlaps the Upper Cretaceous and lower Tertiary marine sedi- mentary Sequence from south to north onto the underlying crystalline rocks. It is conformably over- lain by the Vaqueros Formation. In the Caliente Range, the southeastern part of which includes the type section from 4 to 5 mile-s northeast of Cuyama (Hill and others, 1958, p. 2981), the Simmler Formation is about 3,000 feet thick and consists of hard red and greenish-gray well-bedded sandstone, siltstone, and local basal conglomerate. Its red and greenish colors and lack of marine fossils suggest that this formation is MIDDLE TERTIARY SEDIMENTARY SEQUENCE 15 5 STAGE SOUTHEASTERN NORTHWESTERN SOUTHEASTERN < DIABLO RANGE TEMBLOR RANGE TEMBLOR RANGE BITTERWATER REEF RIDGE SHALE (Absent or not exposed) CREEK SHALE Lu (Absent?) //’ ./” SANTA MARGARITA 2 . —————————————— \g,_ Belridge Diatomite Member FORMAT|ON Lu Mohnlan - r: ________________________________________ (conglomerate) 8 Sandstone/c: (Lb-I McLure Shale Member Ienseb >. c: E ——————— NW? ——--—-—————---=:::———————__.L,_NLQ_N_T_E_R_E_Y_____ E w Luisian Devilwater Shale Member :51" SHALE g 5 ------- (Absent) ——-———————————-—--——_————-" Shake and S 5 Relizian Gould Shale Member sandstone u, E _ _____________ _, E -‘r: _____ <_: e‘\‘ Clay shale _',,,3’ E Sauce- —————————————— \ ,,,, Sandstone Lu . r; \ ’— snan ______________ (Absent) ( —————— /,,> "_‘,J \\\\\ ‘I D —7————-———— ‘r _____________ T‘~\ Q .‘ Conglom- ————————————— TEMBL05,,> FORMATION E [1ng 29010" erate lens .— ::: = q, nan _____________ o o ___________ ‘11—»- :Erfig‘ LOWER TERTIARY MARINE SEDIMENTARY SEQUENCE AND OLDER ROCKS FIGURE 8.——Litholog'ic units of the middle Tertiary sedimentary sequence northeast of the San Andreas fault from Avenal to Maricopa. All units are marine. Unconformities indicated by wavy lines. For named local units of Temblor Forma- tion, see table 2 and figures 10 and 11. entirely terrestrial and may contain some lacustrine beds. In the La Panza Range and the vicinity of Cuyama Gorge, the Simmler Formation consists of red and gray coarse conglomerate and sandstone. It is as thick as 3,400 feet in Cuyama Gorge, but is much thinner in the La Panza Range. This conglomerate was mapped as the Redrock Canyon Member of the Santa Margarita Formation by English (1916, p. 202); as the nonmarine Vaqueros Formation by Eaton, Grant, and Allen (1941, p. 217); as the Sespe Formation by Clements (1950) ; and as Oligo- cene(?) red beds by Vedder and Brown (1968, p. 252—253). It was referred to the Simmler Forma- tion by Hill, Carlson, and Dibblee (1958, fig. 3) because its stratigraphic position is the same as that of Simmler Formation in the Caliente Range and it was presumed to be continuous with that formation. It is, however, much coarser and con- tains much sandstone detritus. The Simmler Formation is unfossiliferous, ex- cept for sparse plant remains and bone fragments. Its possible age range is from late Eocene to early Miocene. Its conformable relationship to the over- lying .beds of Zemorrian Stage of the Vaqueros Formation and unconformable relationship to the underlying sequence suggest that it is most likely Oligocene in age. It is probably mainly in the Ze- morrian Stage, late Oligocene, and possibly in part in the Refugian Stage, early Oligocene. The Simmler Formation is probably correlative with the Berry Formation (of Thorup, 1943) of Salinas Valley and with the Sespe Formation (of Watts, 1897) of the Santa Ynez Mountains and Ventura basin on the basis of similar lithology and stratigraphic position. VAQUEROS AND TEMBLOR FORMATIONS REVIEW OF NOMENCLATURE Marine sandstone and argillaceous sediments, commonly assigned early and middle Miocene ages but now considered to be late Oligocene to middle Miocene, form all or much of the lower part of the middle Tertiary sedimentary sequence on both sides of the San Andreas fault. Two names, Vaqueros and Temblor, have been applied to this marine unit, and both have been in common usage for more than 60 years. The name Vaqueros was applied by Hamlin (1904) when he mapped sandstone exposures of this unit about 10 miles west of King City. This 16 STRATIGRAPHY, SOUTHERN COAST RANGES name was also used by Fairbanks (1904) for equiva- lent rocks near Paso Robles. Anderson (1905) ap- plied the name “Temblor beds” to what was later found to be essentially a stratigraphically equivalent unit in the Temblor Range. Application of both these names followed, as shown on table 1. In early years, TABLE 1.—Names applied by other investigators to strata herein assigned to the Vaqueros and Temblor Formations of map region of figure 2 Northeast of San Andreas fault Southwest of San Andreas fault Investigators Vaqueros Formation _______________________ Fairbanks (1904) Temblor beds _________ Anderson (1905, p. 170—172; 1908, p. 18—20). Vaqueros Formation ___Arnold and Anderson (1908, p. 31—35,pl. 1: 1910, p. 80—88, pl. 1). ______ do-______-__..__ Arnold and Johnson (1910, p. 42—51, pl. 1). Temblor Group ____________________________ Anderson and Martin, - {(1914, p. 37—44, pl. Vaqueros Formation _--Anderson and Pack (1915 p. 80—87). Formation ________________________ English (1916, p. 198— 201, pl. XIX). Vaqueros Formation ___ English (1921, p. 13—21, 11-1 1-) Do __________________________________ 14049;“) and Corey (1932, p. —5 0-) _____________________ Eaton (1939, .,261~266 pl. IV): Eaton, Grant and Allen (1941, p. 216—280, fig. 3) Temblor Formation ____Kleinpell (1938, p. 104- 107, pl. 6.) Temblor Sandstone -___W00dring, Stewart, and Richards (1940, p. 129-—144, pl. 51). _____ Simonson and Krueger (1942, p. 1613—1616). Temblor Formation ____Curran (1943, p. 1365— 1369). Van Couvering and Allen (1943, p. 496— 500) Vaqueros Sandstone ________________________ Bramlette and Daviess Vaqu eros Temhlml and Vaqueros1 Temblor-Vaqueros Escudo and Hannah Formations (1944). Temblor Formation ___—Stewart (1946, p. 97— 103, 13-19% _____ do___-__.-____-__Heikkila and MacLeod 1(1951, p. 6, 7—11, pl. 1)- _____ do_-____________Marsh (1960, p. 31— —32, p1.1) Vaqueros Formation ________________________ Hill, Carlson, and Dibblee (1958, p. 2983—2987 ). Dibblee (1962,p p. 9—10); Do _____________ Temblor-Vaqueros Formation. Fletcher (1962, p. 17). Do __________________________________ Vedder and Repenning (1965). Temblor—Vaqueros Dickinson (119626a,p p. Formation. 711—713, 2.) Temblor Formation _-_ _Foss and Blaisdell (1968, p. 38—41) 1 Used in the time-stratigraphic sense. “Vaqueros” was used by geologists of the US. Geological Survey, and “Temblor” by F. M. Ander- son of the California Academy of Sciences. Paleontological studies of the molluscan and echi- noid faunas from the “lower Miocene” strata by Wiedey (1928, p. 104-107) and by Loel and Corey (1932, p. 45—50) established the presence of two faunal zones, namely a lower or Turritella inezana zone and an upper or Turritella ocoyana zone. Al- though some confusion resulted when it was found that Turritella ocoyana ranges downward far into NEAR SAN ANDREAS FAULT, CALIFORNIA the lower faunal zone in the Caliente Range (Eaton, 1939, pl. IV; Repenning and Vedder, 1961, p. 0237) , the faunal assemblages are distinct. Loel and Corey (1932, p. 45—50), Wilmarth (1938, p. 2127, 2234— 2235), Eaton (1939, p. 259-266, pl. IV), Eaton, Grant, and Allen (1941, p. 216—224) , and Woodring, Stewart, and Richards (1940, p. 129) applied the term Vaqueros to strata that contain fossils of the lower faunal zone because these fossils occur in the type Vaqueros Formation (of Hamlin, 1904) and applied the term Temblor to strata that contain fossils of the upper faunal zone because these fossils occur in most of the type Temblor Formation (of Anderson, 1905). These names were also applied to the faunal zones or “ages,” When the lower faunal zone became known as “Vaqueros age” and the upper zone as “Temblor age” (Weaver and others, 1944, chart 11; Corey, 1954, chap. III, fig. 9), but these molluscan “ages” were never defined. Studies of the foraminiferal faunas in the “lower Miocene” strata by Kleinpell (1938, p. 152—155, fig. 4) indicate that “Vaquer0s age” corresponds roughly to his Zemorrian Stage; “Temblor age” to his late Saucesian Relizian and Luisian Stages; and a “tran- sition zone” to his early Saucesian Stage. Differentiating the “lower Miocene” marine strata into the Vaqueros and Temblor Formations on the basis of their faunal content seemed appropriate, but was impractical because (1) generally the lith- ology does not change within these strata, (2) no definite boundary separates the two faunal “ages,” and (3) in many exposures fossils are scarce or lacking. Even in the most fossiliferous and complete section in the Caliente Range, the formations could not be differentiated with certainty on this basis by Hill, Carlson, and Dibblee (1958) or by Vedder and Repenning (1965), although the faunizones could be recognized. It is here prOposed that in all areas southwest of the San Andreas fault the name Vaqueros Forma- tion be applied to this whole stratigraphic unit and that in all areas northeast of this fault the name Temblor Formation be applied. Because of their long-established usage in this manner (fig. 4), both names are best retained with the fault as an arbi- trary boundary. In the field this marine unit, deposited under a transgressing sea, is differentiable into two principal lithologic types or facies: (1) sandstone and (2) argillaceous sedimentary rocks variously called mudstone, siltstone, claystone, clay shale, silty shale, and shale. Where these two types are interbedded, the facies unit is designated by the predominant rock type. In some areas, especially near oil fields, MIDDLE TERTIARY SEDIMENTARY SEQUENCE 17 the parts of these facies that form local strati- graphic units have been named and described in many publications as members. The age of the Vaqueros and Temblor Formations is generally regarded as early Miocene or Oligocene and Miocene (Weaver and others, 1944, chap. 11). Within the region of figure 2 both formations are mainly within the Zemorrian and Saucesian Stages, and locally the uppermost parts include the lowest part of the Relizian Stage, middle Miocene. The Zemorrian Stage is now considered equivalent to late Oligocene age and the Saucesian Stage to the early Miocene (Bandy and Arnal, 1969, p. 786). If this correlation is accepted, then the Vaqueros and Temblor Formations are late Oligocene to middle Miocene in age. VAQUEROS FORMATION Southwest of the San Andreas fault the Vaqueros Formation is thickest, 7,000 feet, in the central and northwestern parts of the Caliente Range and pos- sibly under the Carrizo Plain. It thins southeast- ward to about 1,000 feet at the southeast end of the range, in part by intertonguing of its upper part into the terrestrial Caliente Formation. To the northwest, west, and southwest, this formatiOn thins to about 1,000 feet or less under Salinas Valley and in the La Panza Range. In western Cuyama Valley and in the Sierra Ma-dre Mountains, it is either absent or very thin. In areas other than the Caliente Range, the Vaqueros Formation is mostly all sandstone and is undivided. In the Caliente Range, this formation was divided by Hill, Carlson, and Dibblee (1958, p. 2983-2988) into a local basal unit called the Soda Lake Sandstone Member, a lower unit called Soda Lake Shale Member, and an upper unit called Painted Rock Sandstone Member. The last two of these names are adopted herein; the first is re— named (fig. 7). QUAIL CANYON SANDSTONE MEMBER The Soda Lake Shale Member in the southeastern Caliente Range is underlain in large part by a thin sandstone unit that was Called the Soda Lake Sand- stone Member by Hill, Carlson, and Dibblee (1958, p. 2984). Because the name Soda Lake is already applied to the overlying shale unit, this sandstone unit is here renamed the Quail Canyon Sandstone Member of the Vaqueros Formation. It is named for exposures in Quail Canyon, Cuyama quadrangle, 1964. The type locality is in the NWIASWl/g sec. 4, T. 10 N., R. 25 W., which is the same as that designated by Hill, Carlson, and Dibblee (1958, p. 2984) for the Soda Lake Sandstone Member. It conformably overlies red beds of the Simmler For- mation and was described by Hill, Carlson, and Dibblee (1958, p. 2984) as follows: The sandstone in the type section attains a maximum thick- ness of 300 feet. It thins westward by a probable gradation into Soda Lake shale and toward the southeast it becomes undifferentiated from the overlying Painted Rock sandstone (T. 10 N., R. 25 W.). At its type locality * * * the Soda Lake sandstone is characteristically gray-white, weathering to light bufi', massively bedded, fine to medium grained, well sorted, and very firmly indurated. It is commonly cross-bedded with fore-set beds dipping in a westerly di- rection. This sandstone member contains Pecten mag- nolia and other forms diagnostic of “Vaqueros age” (J. G. Vedder, oral commun., 1968), Oligocene. According to R. L. Pierce (oral commun., 1970), this sandstone member is probably correlative with the Agua Sandstone Member of the Temblor For— mation, and with the Vaqueros Sandstone of the Santa Ynez Mountains. The Quail Canyon Sand- stone Member is assigned to the late Zemorrian Stage, late Oligocene, on the basis of the foregoing evidence. SODA LAKE SHALE MEMBER The Soda Lake Shale Member consists of dark- gray silty clay shale, claystone, and siltstone. The type section is in the northwestern Caliente Range (NEI/L sec. 6, T. 31 S., R. 19 E., and extreme SE14 sec. 31, T. 30 S., R. 19 E.), 3 miles west of the north end of Soda Lake (Hill and others, 1958, p. 2983, 2985). There, it is about 1,200 feet thick and contains a prominent bed of chert just below the middle. It contains foraminifers diagnostic of the Zemorrian Stage (late Oligocene) below that chert bed and foraminifers of the Saucesian Stage (early Miocene) above it. The Soda Lake Shale Member is also exposed in the southeastern Caliente Range, where the probable time-stratigraphic equivalent of the type section is about 900 feet thick or less. It is of the same lith- ology as at the type section and in one place con- tains a lens of chert a few feet thick, just below the middle. It is in part overlain by as much as 2,000 feet of siltstone and some interbedded sandstone that was included in the Soda Lake Shale Member of this area by Vedder and Repenning (1965) be- cause of its predominant siltstone lithology. Accord- ing to them, this part contains foraminifers diagnos- tic of the Saucesian Stage and mollusks diagnostic of “Vaqueros age.” Near the southeast end of this range, all the strata assigned to the Soda Lake Shale 18 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA Member grade laterally eastward into the Painted Rock Sandstone Member. According to R. L. Pierce (oral commun., 1970), the part of the Soda Lake Shale Member below the chert bed at the type section and the lowest part of this member in the Cuyama Valley oil fields contain a neritic foraminiferal fauna diagnostic of the late Zemorrian Stage and are probably correlative with the Agua Sandstone Member and part of the under- lying lower part of the Santos Shale Member of the Temblor Formation as defined herein; the part above the chert bed at the type section and the upper part in the Cuyama Valley oil fields contain a subabyssal fauna diagnostic of the early Saucesian Stage and are probably correlative with the upper part of the Santos Shale Member of the Temblor Formation as defined herein. The faunas of the Soda Lake Shale Member, according to Pierce, however, are unlike those of the San Joaquin Valley, but are similar to those of the same age in the Santa Ynez Mountains. Thus, the basin in which this member accumulated was probably not connected with the San Joaquin Valley basin at that time, as suggested by Cross (1962, p. 27). PAINTED ROCK SANDSTONE MEMBER The Painted Rock Sandstone Member was named for Painted Rock, a prominent cavernous sandstone outcrop south of Soda Lake, but the type locality is the section exposed in the vicinity of Caliente Moun- tain, 7 miles northwest of New Cuyama (Hill and others, 1958, p. 2986, 2988). In the northwestern Caliente Range this member is nearly all sandstone, but at Caliente Mountain and a few miles eastward it includes as much as 50 percent interbedded silt- stone. In these areas this member is about 5,500 feet thick. It thins to the southeast, in part by lat- eral gradation of its lower beds into the Soda Lake Shale Member and of its upper beds into the terres- trial Caliente Formation and in part by actual thinning of the whole member. At the southeast end of the Caliente Range, the Painted Rock Sandstone Member is only about 600 feet thick. The Painted Rock Sandstone Member in the vicinity of Caliente Mountain and southeastward contains abundant Turm’tella ocoyana and Lyropec- ten miguelensis, especially in its upper and middle parts. In other areas these species occur in sand- stones of “Temblor age.” Eaton, Grant, and Allen (1941) assigned the upper 900 feet of this sand- stone unit to the “Temblor” and the rest to the “Vaqueros.” The fauna throughout this member is now considered to be of “Vaqueros age,” early Mio- cene (Repenning and Vedder, 1961). In the north- western Caliente Range, the uppermost sandstones of this member are somewhat higher stratigraphic- ally than those near Caliente Peak and may be of “Temblor age,” middle Miocene. The Painted Rock Sandstone Member contains undiagnostic shallow-water foraminifers, but foram- inifers diagnostic of the Saucesian Stage, early Miocene, occur in the underlying beds of the Soda Lake Shale Member and west of Caliente Mountain in the immediately overlying beds of the Monterey Shale (Vedder and Repenning, 1965). On the northeast flank of La Panza Range, the Vaqueros Formation is nearly all sandstone and ranges from about 200 to 1,200 feet in thickness. It is assigned to the Painted Rock Sandstone Mem- ber because it is lithologically similar to that unit in the nearby northwestern Caliente Range and is conformably overlain by the Saltos Shale Member of the Monterey Shale. In most places the Painted Rock Sandstone Member rests unconformably on _ crystalline basement rocks or on the Upper Creta- ceous and lower Tertiary sedimentary sequence, against which the lower beds buttress out. In other places this member conformably overlies conglom- erate of the Simmler Formation, and at La Panza Canyon (in sec. 36, T. 29 S., R. 16 E.) it overlies a thin intervening wedge as thick as 200 feet of the Soda Lake(?) Shale Member of the Vaqueros Formation. The upper part of the Painted Rock Sandstone Member of La Panza Range is generally fine grained and fossiliferous, with abundant fossils of the Tur- ritella ocoyana. zone of “Temblor age,” lower or middle Miocene. The lower part is medium to coarse grained, nearly white, and rarely fossiliferous, al- though fossils of the Turm'tella inezana zone or “Vaqueros age,” lower Miocene, were reported and listed by Loel and Corey (1932, p. 107 and correla- tion chart). TEMBLOR FORMATION In the Temblor Range the Temblor Formation is composed of sandstone and lesser amounts of argil- laceous sedimentary rocks. In the southeastern part of the range, as much as 7,000 feet crops out; the base of this unit is unexposed. In the northwestern part this unit is much thinner but of variable thick- ness. At the northwest end of the Temblor Range and on the southwest flank of the Diablo Range near Cholame Valley, the Temblor Formation is nearly all sandstone and is 0—5,000 feet thick but generally less than 2,000 feet. At one place about 5 miles northeast of Cholame, the Temblor Formation con- tains a lens, as much as 500 feet thick, of terrestrial red beds, as mapped by Dickinson (1966a, p. 711, pl. 1). At a locality 7 miles slightly south of east MIDDLE TERTIARY SEDIMENTARY SEQUENCE R18 E. R.19 E. T. 27 s. ‘5'?- SAN ‘ 19 R.ZO E. R.Zl E. I‘l‘x No . ‘. \ Antelope Hulls ‘kfi‘oil field North Belridge iI field J \\ oAQU/N \\ uth \\ Antelope Hills ‘\ :lel field Media . T. 28 S. T. 29 S. 5 MILES |____.___J ."x McDonald Anti— \cllne oul field “3% ‘Creek 959%? ‘ c“ ' l s W £3 EXPLANATION Alluvium Valley deposits Monterey Shale Temblor Formation Point of Rocks Sandstone Kreyenhagen Shale, Avenal. Sandstone, and Lodo Formation Pre-Tertiary rocks FIGURE 9.—Part of the Temblor Range showing geographic localities mentioned and areal extent of the Tertiary formations. of Cholame, the formation contains a basal con- glomerate lens as thick as 500 feet. The Temblor ‘ Formation is largely absent in the McLure Valley area, but is present at Devils Ben and Reef Ridge. Throughout the central and northwestern parts of the Temblor Range and adjacent part of the Diablo Range, the Temblor Formation rests either disconforambly or unconformably on the lower Ter- tiary, Cretaceous, and Franciscan rocks, overlapping them from northeast to southwest with increasing discordance toward the San Andreas fault. In most places the Temblor Formation is differ- entiable only into its facies of (1) sandstone, (2) argillaceous sedimentary rocks, and (3) basal con- glomerate (in one area only). These are unnamed; however, on the northeast flank of the central part of the Temblor Range between Salt Creek and Bit- terwater Creek (fig. 9) and in the nearby oil fields, 2O STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA the Temblor Formation has for many years been divided informally by petroleum geologists into units or members given local names. These units are of little regional significance because they are thin, very lenticular, and in outcrop recognizable only in this part of the range. In the subsurface, however, they are economically very important because the sandstone units contain oil that is produced under favorable structural conditions, and the shale units form the caprocks. Mention is made of these units in articles on descriptions of the nearby oil fields, as well as in reports by Kleinpell (1938, p. 106, fig. 6) and Goudkoif (1943), and the units are described, with pertinent references by Foss and Blaisdell (1968, p. 33—43). These units, herein desig- nated as members, are shown in table 2. TABLE 2,—Local stratigraphic units of the Temblor Forma- tion in the Temblor Range between Chico Martinez Creek and Bitterwater Creek (fig. 9) Thickness Stages Stratigraphic unit (ft) (Kleinpell, 1938) Buttonbed Sandstone Member __________ Media Shale Member Relizian. Lower Relizian and upper Saucesian. Saucesian. Lower Saucesian and Zemorrian. Carneros Sandstone Member ____________ Santos Shale Member 0—450 and Agua Sandstone Member as discontinous lenses as thick as 48 ft within Santos Shale Member. Wygal (:“Phacoides”) Sandstone Member- Cymric (:“Salt Creek”) Shale Member__ Lower Zemorrian. Zemorrian ( ?) Anderson (1905, p. 169—170) originally described the “Temblor Beds” at “Canara Springs” (Car- neros Spring in fig. 10) and at “Temblor.” He never designated a type section, but Kleinpell (1938, p. 107) and Curran (1943, p. 1364) considered the section at Carneros Creek described by Anderson to be the type locality of the Temblor Formation. Klein- pell (1938, p. 107 ), Woodring, Stewart, and Rich- ards (1940, p. 130), and Curran (1943, p. 1369- 1370) described the Temblor Formation exposed 2 miles south in Zemorra Creek, a branch of Chico Martinez Creek (fig. 10), where the Temblor For— mation is thicker and more completely exposed than at Carneros Creek. It is here proposed that the type area of the Temblor Formation be designated as the exposures from Carneros Creek to Zemorra Creek, the type section as that exposed at Carneros Creek in sec. 32, T. 28 S., R. 20 E., and a reference section as that exposed at Zemorra Creek in sec. 9, T. 29 S., R. 20 E. (figs. 9, 10). This type section is also the type section of some members of the Temblor Formation and the reference section for the others, as indi- cated in the following paragraphs. Part of this sec- tion is also the type section of the Zemorrian Stage as defined by Kleinpell (1938, p. 106—108). The member-s of the Temblor Formation in the Chico Martinez Creek area (fig. 10) are herein defined in ascending order (thickness figures at Zemorra Creek as given by Woodring and others, 1940, p. 130). The age of the Temblor Formation in its type area ranges from the early Zemorrian Stage, late Oligocene, through the Saucesian Stage, early Mio- cene, to the lowest part of the Relizian Stage, mid- dle Miocene. This age range probably also applies to the Temblor Formation exposed in the south- eastern Temblor Range and Devils Den. In areas west and northwest of the type area and at Reef Ridge, the Temblor Formation is mainly in the Saucesian Stage, early Miocene, and partly of Reli- zian age, middle Miocene. CYMRIC SHALE MEMBER The lowest shale. member of the Temblor Forma- tion is commonly known as the Salt Creek Shale (Williams, 1936; Goudkoff, 1943, pt. 2, p. 253, fig. 99a; Curran, 1943, p. 1368—1369; Foss and Blais— dell, 1968, p. 40), but this name is preoccupied. This shale is herein renamed the Cymric Shale Member, for the nearby Cymric oil field (fig. 9). This mem- ber is disconformable on the Point of Rocks Sand- stone and consists of dark-gray clayey to silty shale. It is traceable and recognizable in the outcrop only from Santos Creek southeastward to a point 3 miles southeast of Zemorra Creek (figs. 9, 11). The type section is in Zemorra Creek where this member is about 74 feet thick. Northeastward, downdip, it thickens to several hundred feet in the subsurface. It contains sparse foraminifers of the Zemorrian Stage, late Oligocene, and forms the lower part of the type Zemorrian Stage (of Kleinpell, 1938, p. 103—108). Recent fauna] studies by W. O. Addicott (oral commun., 1971) suggest, however, that the Cymric Shale Member may be at least in part in the Refugian Stage, early Oligocene. If this is so, this unit may be correlative with the Wagonwheel Formation near Devils Den. Nevertheless, to avoid complications, its age assignment to the early Ze- morrian Stage is tentatively retained. WYGAL SANDSTONE MEMBER The lowest sandstone member of the Temblor Formation in the Chico Martinez Creek area is commonly known as the “Phacoides reef” (Klein- pell, 1938, p. 107; Goudkofl’, 1943, pt. 2, p. 250; Curran, 1943, p. 1368) or “Phacoides Sand” (Foss and Blaisdell, 1968, p. 40). These names are not valid because they refer to a fossil rather than a locality. Therefore this sandstone is here renamed MIDDLE TERTIARY SEDIMENTARY SEQUENCE FORMATIONS AND MEMBERS Plio- Pleisto- Holo- l Oligocene ? Miocene Alluvium ce m3 Tulare Formation NARY cem Gem Etchegoin Formation Belridge Diatomite Member McLure Shale Member de Devilwater Shale Member ng Gould Shale Member Monterey Shale 7(Dl/UATER— L Ttb Buttonbed Sandstone Member Ttm Media Shale Member TtC Carneros Sandstone Member Tts Santos Shale Member Ttw Wygal Sandstone Member Tty Cymric Shale Member Temhlor Formation TERTIARY Eo- cene Tpr Point of Rocks Sandstone LITHOLOGIC SYMBOLS ° ° Gravel - - . - ': Sandstone Clay shale - —- “ Siliceous shale I J— ; Cherty shale "1+:— Diatomite FIGURE 10.—Chico Martinez Creek area, Temblor Range, showing members of the Temblor Formation and Monterey Shale. the Wygal Sandstone Member, for Wygal Spring (fig. 9). The type section is designated as that at Zemorra Creek, where this sandstone is about 75 495-417 0 - 73 - 4 feet thick and overlies the Cymric Shale Member. This sandstone is gray, and its upper part is glau- conitic; locally a fossiliferous calcareous bed sev- 22 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA CEDAR CREEK NAPOLEON DEVILWATER MEDIA AGUA CARNEROS ZEMORRA MICRO- AT MOUTH TWO MILES SPRING CREEK,1 MILE CREEK,1 MILE CREEK CREEK FAUNAL g EAST OF MOUTH WEST SOUTHEAST STAGES < 2 miles—— -—3 miles—.l ~—2 miles—a1 ——3 miles ~—3 miles Monterey Shale (Gould Shale Member) Reliz« uJ ian E O ? 9 460’ 35 E 180’ l: .9 = - s O 0 g ‘ g 350 300’ ‘3 E Sauce- 0 '4 ~ N O . E _ sf 8 ,_. u. suan x— o S ,, o y L LE 3 S ‘160'5 v-4 120 [x 2 h l\ H .. .D 2 N 100' : E .D .. I 4.) E 80’ :: . 400' - l- a: r I l- 180 EL__ 20 C: n] a z N Zemor- 8 rlan 8 I “ ‘ Point of Rocks Sandstone O VERTICAL SCALE 500 FEET Nariz— LIJ LITHOLOGIC SYMBOLS ian 2 Lu 3:: : o 1: , 8 Siliceous shale Argillaceous shale Sandstone 0 FIGURE 11.—Sections of the Temblor Formation from Cedar Creek to Zemorra Creek in the Temblor Range (fig. 9). Units as follows: (1) Buttonbed Sandstone Member, (2) Media Shale Member, (3) Cameros Sandstone Member, (4) upper part of Santos Shale Member, (5) Agua Sandstone Member, (6) lower part of the Santos Shale Member, (7) Wygal Sandstone Member, and (8) Cymric Shale Member. Thicknesses shown other than for Zemorra Creek are approximate. eral feet thick occurs at or near the base. It is trace- able south to Salt Creek and northwest to Media Agua Creek (figs. 9, 11). At both those places it laps over the Cymric Shale Member onto the Point of Rocks Sandstone. Northeastward, downdip from its outcrop, this member thickens to several hun- dred feet in the subsurface. It contains a molluscan fauna assigned an early “Vaqueros age,” late Oligo- cene (W. 0. Addicott, oral commun., 1968), and the shale immediately above and that below is in the lower part of the type Zemorrian Stage (Kleinpell, 1938, p. 103—108). Recent work on the fauna from this sandstone unit by Addicott (oral commun., 1971) suggests, however, that this unit is somewhat older than the “Vaqu-eros Stage,” but younger than the Refugian Stage. But to avoid complications, its assignment to the “Vaqueros Stage” is tentatively retained. SANTOS SHALE AND AGUA SANDSTONE MEMBERS The middle shale member of the Temblor Forma- tion was named the Santos Shale by Gester and Galloway (1933) for Santos Creek, the type locality (fig. 9). This shale is medium to dark gray, clayey to silty, locally semisiliceous in the upper part, and is conformable on the Wygal Sandstone Member. At Zemorra Creek, the reference section, this shale member is 295 feet thick and is divided into two parts, but the lower part, 180 feet thick, is sepa- rated from the upper part, about 60 feet thick, by the 35-foot-thick Agua Sandstone Member. The upper part of the Santos Shale Member is traceable northwestward to Cedar Creek, where it overlies the Agua Sandstone Member and the Point of Rocks Sandstone (fig. 11). Northeastward, downdip, the Santos Shale Member thickens in the subsurface, and the lower and upper parts are separated by the Agua Sandstone Member (Foss and Blaisdell, 1968, p. 39—40). The Santos Shale Member contains fora- minifers diagnostic of the Zemorrian Stage, late Oligocene, in the lower part and of the Saucesian Stage, early Miocene, in the upper part (Kleinpell, 1938, p. 105—108; Foss and Blaisdell, 1968, p. 40). At Zemorra Creek the lower part forms the upper part of the type Zemorrian Stage of Kleinpell (1938, p. 103-108) , except the lowest 50 feet of that shale, which is assigned to the lower part of that stage (Foss and Blaisdell, 1968, p. 40). The Agua Sandstone Member was named Agua Sandstone by Clark and Clark (1935, p. 137) for MIDDLE TERTIARY SEDIMENTARY SEQUENCE 23 Media Agua Creek (fig. 9). They did not designate a type locality, although they mentioned the out- crop at the mouth of Cedar Creek. This outcrop is designated the type locality as it was mapped by Heikkila and MacLeod (1951, pl. 1).- This is the only other place besides Zemorra Creek, the refer- ence section, where this unit crops out, although at a few places between Cedar Creek and Zemorra Creek, the Santos Shale Member contains a sand— stone bed a few feet thick that may be correlative. In the subsurface (in North Belridge, North and South Antelope Hills, McDonald Anticline oil fields and vicinity, (fig. 9) the Agua Sandstone Member is persistent, is several hundred feet thick, and is assigned to the top of the Zemorrian Stage (Foss and Blaisdell, 1968, p. 40). The Agua Sandstone Member is light gray, arko- sic, and locally pebbly. At the mouth of Cedar Creek it is as thick as 48 feet, occurs at the base of the Santos Shale Member, and is disconformable on the Point of Rocks Sandstone (fig. 11). At this outcrop it contains a few fossils, including Pecte’n magnolia, and is assigned a late “Vaqueros age” (W. O. Addi- cott, oral commun., 1968). At Zemorra Creek this sandstone is 35 feet thick, is unfossiliferous, and is at the top of the type Zemorrian Stage (Kleinpell, 1938, p. 103—108), late Oligocene. CARN EROS SANDSTONE MEMBER The name Carneros was first applied to the mid- dle sandstone member of the Temblor Formation by Cunningham and Barbat (1932, p. 417—421) for Carneros Creek, the type locality (fig. 10). The Car- neros Sandstone Member is conformable on the Santos Shale Member, is light gray and thick bedded, rarely contains fossils, and is about 215 feet thick at Zemorra Creek, the reference section, but as much as 500 feet thick in the area of figure 9. It is traceable as far northwest as Cedar Creek (fig. 11). Northwest of Devilwater Creek the upper part intertongues into the lower part of the Media Shale Member, and the lowest sandstone tongue persists as a layer about 120 feet thick. Northeastward, downdip, the Carneros Sandstone Member thickens to more than 1,000 feet locally in the subsurface. It is within the Saucesian Stage, early Miocene, as indicated by foraminifers from the shales below and above. MEDIA SHALE MEMBER The name Media was first applied to the upper shale member of the Temblor Formation by Cun- ningham and Barbat (1932, p. 417—421), for Media Agua Creek (fig. 9). The Media Shale Member is light gray, clayey to silty, and in part semisiliceous. It is conformable on the Carneros Sandstone Mem- ber, is 920 feet thick at Zemorra Creek, the desig- nated type section (sec. 9, T. 29 S., R. 20 E., Car- neros Rocks quadrangle), and about 500 feet thick at Carneros and Santos Creeks. It is traceable north- west to and beyond the mouth of Cedar Creek (figs. 9, 11). Northwest of Devilwater Creek it thickens as the upper parts of the Carneros Sandstone Mem- ber and lower parts of the Buttonbed Sandstone Member intertongue into it. In the Cedar Creek area the Media Shale Member is as thick as 2,200 feet, and the upper part includes much hard semisiliceous shale. In the Chico Martinez Creek area, the Media Shale Member contains foraminifers diagnostic of the upper Saucesian Stage, early Miocene; the upper- most 50 feet, a sandy siltstone, contains foraminifers diagnostic of the lower Relizian Stage, middle Mio- cene (Foss and Blaisdell, 1968, p. 39). BUTTONBED SANDSTONE MEMBER Anderson (1905, p. 170) referred to the top sandstone unit of his Temblor Beds at Carneros Creek as “button beds.” This term has subsequently been commonly applied informally to this sandstone (Kleinpell, 1938, p. 105; Foss and Blaisdell, 1968, p. 38). The type locality was designated as Carneros Creek (Heikkila and MacLeod, 1951, p. 10), in sec. 32, T. 28 S., R. 20 E. (fig. 10). It is here formally named the Buttonbed Sandstone Member for its exposure on Buttonbed Hill (fig. 10). This sand- stone is light gray, thick bedded, and commonly cal- careous, with numerous shell fragments. It ranges in thickness from 0 to 500 feet (240 ft thick at Zemorra Creek, the reference section). It is pre— sumed to be locally disconformable on the Media Shale Member and may be a transgressive basal sandstone of the Monterey Shale, as indicated by an unconformity locally at its base in the Shale Hills area (Heikkila and MacLeod, 1951, p. 10) and at Devils Den. In other areas, this sandstone mem- ber or its equivalent is not differentiable from the underlying sandstone facies of the Temblor Forma- tion. The Buttonbed Sandstone Member is traceable northwestward from Zemorra Creek to and beyond Bitterwater Creek. Northwest of Devilwater Creek all but the upper part intertongues into the upper part of the Media Shale Member. The Buttonbed Sandstone Member contains mol- lusks and buttonlike echinoids (mostly Scutella mewiami) assigned to “Temblor age,” Miocene, (W. O. Addicott, oral commun., 1967). In the Chico 24 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA Martinez Creek area, the Buttonbed Sandstone Mem- ber is in the early Relizian Stage (middle Miocene), as indicated by the microfauna in the adjacent shale below and above (R. L. Pierce, oral commun., 1968) . At Devils Den, local names were applied to units within the Temblor Formation by Van Couvering and Allen (1943, p. 496—500); none of these are adopted herein. The members recognized in the Chico Martinez Creek area of the Temblor Range are believed to be as indicated in table 3, mainly on TABLE 3.—Members of the Temblor Formation exposed at Devils Den Name applied by Van C‘ouvering and Allen (1943) Average (Members 1~5 thickness assigned to Hannah (ft) Formation) Name of member Buttonbed Sandstone Member ___________ 50 Escudo Formation. Media Shale Member ___________________ 350 Member 1. Cameras Sandstone Member 200 Member 2 (sand- (includu interbedded shale). stone and shale). Upper part of Santos Shale Member _____ 300 Member 3 (shale). Undivided lower members: Member 4 (sand- Agua Sandstone Member ____________ 180 stone). Lower part of Santos Shale Member __ 100 Member 5 (shale). Wygal Sandstone Member ___________ 70 Do. Cymric Shale Member _______________ 50 Do. the basis of similar lithologic sequences, although correlations are uncertain. In the northern expo- sures, the Buttonbed Sandstone Member overlaps the older members of the Temblor Formation. MONTEREY SHALE REVIEW OF NOMENCLATURE A distinctive marine deposit of predominantly siliceous organic shale, of early, middle, and late Miocene age, overlies the Vaqueros and Temblor Formations. In the Temblor Range and part of the Caliente Range, the name Monterey Shale was ap- plied to this unit by Arnold and Johnson (1910, p. 55—62, pl. 1), who adopted the name from the term Monterey Formation applied by Blake (1856, p. 328-331) to a similar siliceous deposit exposed near Monterey. Confusion resulted when part of this siliceous shale unit in the Diablo Range, Temblor Range, and Caliente Range was correlated with and assigned to the Santa Margarita Formation by Arnold and Anderson (1910) and English (1916, p. 202—203), and the name Maricopa Shale was applied to the rest of this shale unit in the Caliente Range by English (1916, p. 198—200, pl. XIX) and in the Temblor Range by Pack (1920, p. 35—41, pl. II). This was done when the terms Monterey Series (of Louderback, 1913, p. 191—214) and Monterey Group (of Lawson, 1914) were applied to most of the Miocene marine sedimentary rocks of the California Coast Ranges. The terms Monterey Series and Maricopa Shale were discarded after 1935, and the term Monterey Shale was adopted for the lithologic unit of “pre- dominantly hard silica-cemented shales and softer shales carrying siliceous microfossils” (Wilmarth, 1938, p. 1407, 1299). The term Monterey Shale was applied to this unit by Woodring, Bramlette, and Kleinpell (1936, .p. 127—146), Kleinpell (1938, p. 7, 105; 122, fig. 6), Woodring, Stewart, and Richards (1940, p. 122—123) , Hill, Carlson, and Dibblee (1958, p. 2988—2991), and Durham (1963, 1964, 1966). The term Monterey Formation was also applied (Simon- son and Krueger, 1942, p. 1616; Bramlette and ,Daviess, 1944; Heikkila and MacLeod, 1951, p. 5, 11, pl. 1; Foss and Blaisdell, 1968, p. 36), but because this unit is characterized by a distinctive shale, the term Monterey Shale is hereby retained. The Monterey Shale is the most extensive unit of the middle Tertiary sedimentary sequence on both sides of the San Andreas fault, in places ex- tending beyond the limits of the Vaqueros and Temblor Formations. It was deposited under con- ditions of maximum inundation during the middle Tertiary sedimentary cycle. STRATIGRAPHIC UNITS SOUTHWEST OF THE SAN ANDREAS FAULT Southwest of the San Andreas fault, the Mon- terey Shale is from 2,000 to 3,000 feet thick on the southwest flank of the Caliente Range and the northeast flank of the La Panza Range, from which it extends northwestward under Salinas Valley. In the Caliente Range, Cuyama Valley, and Sierra Madre Mountains, the Monterey Shale intertongues northeastward into sandstone mapped as the Branch Canyon Sandstone (figs. 7, 12). In the La Panza Range and western Cuyama Valley, the Monterey Shale thins to only a few hundred feet; in places it wedges out. The Monterey Shale exposed in the'areas between the San Andreas and Rinconada faults is composed of two lithologic units: a lower unit of predomi- nantly argillaceous shale of middle and locally in part of early Miocene age and an upper unit of siliceous shale of middle Miocene age. The lower unit has been named the Saltos Shale Member, and the upper unit the Whiterock Bluff Shale Member (fig. 7). In several wells in the valley area between Atas- cadero and Shandon, the uppermost part (as much as 300 feet) of the Monterey Shale contains fora- minifers diagnostic of the late Miocene Mohnian Stage (H. C. Wagner, oral commun., 1970). Part of the Monterey Shale exposed north of Atascadero 25 y middle and to the northwest. and 20, SALTOS SHALE MEMBER MIDDLE TERTIARY SEDIMENTARY SEQUENCE s d d E w u m w n m M m . O tm m Wd 2- L: "n m mtn “Um.” nM aMn aw Fwi T m We 0- 1| - v. I a o» n cvew Mom—«vowm d . a cowooeo w a saw ”swamp w afgx B 0| o Q .M euooooE E n CARRIZQ ‘ ' 1' f of) EXPLANATION Exposed. Eroded away xposed 1 .4 I Eroded away V. e r. e t n 0 i M lady $.61 gut gun EBM m 0 d e r P Predominantly Caliente Formation Predominantly Branch Canyon Sandstone Santa Margarita Sandstone and Monterey Shale south- ! west of San Andreas fault M S f 0 t s a e h t m n b a h S Andreas fault FIGURE 12.——Probable original and present areal extent of contemporaneous formations or facies of mainl late Miocene age in southern Coast Ranges. extensive in Salinas Valley, may also be of Late Miocene age. These are the only places within the area of figure 2 southwest of the San Andreas fault where the Monterey Shale is The Saltos Shale Member was named for Saltos Creek near the type locality (secs. 18, 19, of late Miocene age. M0nterey Shale of that age is 26 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA T. 11 N., R. 27 W., San Bernardino base line and meridian) in the central Caliente Range, 8—9 miles northwest of New Cuyama, by Hill, Carlson, and Dibblee (1958, p. 2989-2990), and the name is herein adopted. According to them, the member is about 2,150 feet thick at the type locality: the lower part, about 1,000 feet thick, is composed of gray clay shale and siltstone and is separated by a sill of basalt about 75 feet thick from the upper part, about 1,100 feet of soft fissile shale and hard, brittle siliceous shale and frequent thin beds of dolomite. The lower part was assigned to the Saucesian Stage, early Miocene, and the upper part to the Relizian Stage, middle Miocene. The Saltos Shale Member exposed northwestward along the Caliente Range and in the La Panza Range is generally similar to that at the type local- ity, but in these placesit lacks the basalt and aver- ages about 1,500 feet in thickness. In the La Panza and northwestern Caliente Ranges, the Saltos Shale Member is composed of soft-weathering yellowish- gray thin-bedded clayey to weakly siliceous or cal- careous shale and contains a foraminiferal fauna of the Relizian Stage, middle Miocene. It conform— ably overlies the Painted Rock Sandstone Member of the Vaqueros Formation, in places with a grada— tional or intertonguing contact. In both these areas this shale unit is lithologically similar to and correl- ative with the Sandholdt Formation of Thorup (1943) in Salinas Valley. Near the west end of Cuyama Valley, the lower 150 feet of the Saltos Shale(?) Member is semi- siliceous shale, and the upper 500 feet is clay shale that is overlain by the Branch Canyon(?) Sand- stone. The shale there contains foraminifers as- signed to the lower(?) Saucesian Stage (R. L. Pierce, oral commun., 1967). Where the Vaqueros Sandstone is missing, the shale overlies the Simmler Formation and underlying rocks of Paleocene(?) age with angular discordance of as much as 45°. This is the only place between the San Andreas and Rinconada faults where an angular unconformity appears within the middle Tertiary sedimentary sequence. On the northeast flank of the Caliente Range, on both flanks southeast of Caliente Mountain, and in the eastern San Rafael Mountains, the Saltos Shale Member becomes mainly siltstone, in places contain- ing sparse foraminifers of the Saucesian and Reli- zian Stages, and thin sandstone beds that contain mollusks of the “Temblor Stage” (Vedder and Repenning, 1965). Included in the Saltos Shale Mem- ber of these exposures is several hundred feet of similar but stratigraphically higher siltstone that contains foraminifers of the Luisian Stage and that grades laterally westward into the Whiterock Bluff Shale Member (fig. 7). The siltstone of the Saltos Shale Member intertongues northeastward into the Branch Canyon Sandstone Within a few miles of the San Andreas fault (fig. 12). WHITEROCK BLUFF SHALE MEMBER In the, Caliente Range, La Panza Range, and Sierra Madre Mountains, the siliceous shale unit was named the Whiterock Bluff Shale Member of the Santa Margarita Formation by English (1916, p. 191—215, pl. XIX). This shaleunit was named for Whiterock Bluff, the type locality (sec. 25, T. 11 N., R. 28 W.), about 8 miles west-northwest of New Cuyama (fig. 1), where this shale is approxi- mately 1,200 feet thick. This name was adopted and applied to this shale unit by Hill, Carlson, and Dib- blee (1958, p. 2990—2991), but the unit was reas- signed to the Monterey Shale. The Whiterock Bluff Shale Member was reported by them to contain foraminifers diagnostic of late Relizian and Luisian Stages, middle Miocene. This name as used by Hill, Carlson, and Dibblee (1958) is adopted herein for this shale unit in the area between the San Andreas and Rinconada faults. The Whiterock Bluff Shale Member consists of hard, brittle thin-bedded siliceous shale and inter- bedded fissile to punky shale. It is as much as 1,500 feet thick, but averages 1,200 feet. It is gradational downward into the Saltos Shale Member and up- ward into sandstone of the Santa Margarita Forma— tion. For about 6 miles on each side of Indian Creek (about 12 miles south of Shandon, fig. 2), a zone about 70 feet thick near the top of the Whiterock Bluff Shale Member contains thin layers of phos— phatic pellets and bentonite (H. D. Gower, oral commun., 1970). This zone is overlain by about 80 feet of siliceous and diatomaceous shale, which is overlain by the Santa Margarita Formation. In western Cuyama Valley and on the southwest flank of the La Panza Range, the Whiterock Bluff Shale Member is absent or may be represented by sand- stone. Elsewhere this shale unit is widely distri- buted, and in Salinas Valley this member and the underlying Saltos Shale Member are recognizable in well logs as far northeast as San Juan Creek. It is noteworthy, however, that within 7—10 miles of the San Andreas fault, as in the Caliente Range, this Siliceous shale unit grades laterally northeast- ward through siltstone of the Saltos Shale Member lithology into the Branch Canyon Sandstone (figs. 7, 12). In many places the Whiterock Bluff Shale Mem- MIDDLE TERTIARY SEDIMENTARY SEQUENCE 27 ber contains abundant calcareous foraminifers. These are diagnostic of the Luisian Stage, middle Miocene. The exposure of the Whiterock Bluff Shale Member in sec. 21, T. 28 S., R. 14 E., 12 miles east of Atascadero (fig. 2) is the type locality of the Luisian Stage, as defined by Kleinpell (1938, p. 121,— 123). In the Indian Creek area, the phosphatic pellet zone near the t0p of the member and 30 feet of the overlying shale also contain foraminifers of the Luisian Stage (H. D. Gower, oral commun., 1970). At the type locality of the Whiterock Bluff Shale Member in C-uyama Valley, this member is mainly in the Luisian Stage, but the lowest part is in the upper Relizian Stage (Hill and others, 1958, p. 2991), middle Miocene. STRATIGRAPHIC UNITS NORTHEAST OF THE SAN ANDREAS FAULT Northeast of the San Andreas fault, the Mon- terey Shale conformably overlies the Temblor For- mation and is about 7,200 feet thick in the south- eastern and central parts of the Temblor Range. Northwestward, it thins to about 2,600 feet in the Diablo Range north of Cholame and to only 600 feet on Reef Ridge and northwest of McLure Valley. The Monterey Shale may be divided regionally into two parts: a lower division mainly of middle Mio- cene age and an upper division mainly of late Mio- cene age. The only place northeast of the San Andreas fault where a complete section of the Monterey Shale is continuously exposed in a homoclinal struc- ture is along Chico Martinez Creek in the Temblor Range (fig. 10). This section is the upward con- tinuation of the Zemorra Creek section of the under- lying Temblor Formation. Therefore this section is designated as the reference section for the Mon- terey Shale and its members, as well as for the Temblor Formation, northeast of the San Andreas fault. This section of the Monterey Shale was de- scribed by Woodring, Stewart, and Richards (1940, p. 125), who measured and divided it into 11 num- bered units. In the southeastern and central parts of the Tem- blor Range, the lower division of the Monterey Shale is 2,000—3,000 feet thick and is composed mostly of siliceous shale that is not lithologically differentiable. On the northeast flank of the central part of the Temblor Range, this division is about 1,300 feet thick: the lower part is siliceous shale that is locally known as the Gould Shale Member, and the upper part is argillaceous shale that is locally known as the Devilwater Shale Member. In the northwestern Temblor Range, southwest foot- hills of the Diablo Range, and in Devils Den area, the lower division of the Monterey Shale is about 1,000 feet thick and is locally absent; it is com- posed only of argillaceous shale. In the McLure Valley—Reef Ridge area, the lower division is largely absent. Because at their type localities at Chico Mar- tinez Creek in the central Temblor Range the Gould Shale Member is a siliceous shale unit and the Devilwater Shale Member is an argillaceous shale unit, the name Gould Shale Member is here adopted and applied throughout the Temblor Range to the part of the lower division of the Monterey Shale that is mainly siliceous shale and is Within the Reli- zian and Luisian Stages, middle Miocene (and in one place late Saucesian Stage); the name Devilwater Shale Member is adopted and applied to the part that is mainly argillaceous shale and is within the Luisian Stage, middle Miocene age, in the Temblor Range and southeastern Diablo Range. These names are thereby applied to lithologic rather than paleon- tologic units. Southwest of the Recruit Pass fault in the south- eastern Temblor Range, the lower division of the Monterey Shale is composed of semisiliceous shale, similar to that of the Gould Shale Member, and about 50 percent of intenbedded sandstone. The upper division of the Monterey Shale is a unit of thin—bedded siliceous shale and (or) siliceous mudstone throughout the region northeast of the San Andreas fault. In the southeastern and central parts of the Temblor Range, it is 4,000—5,000 feet thick. Northwestward it thins to about 1,900 feet in the Diablo Range north of Cholame and to only 550 feet in the McLure Valley—Reef Ridge area. Unfortunately this shale unit has a complex and confused terminology because its identity as a single lithologic unit throughout this region has not been recognized. In the Diablo Range and parts of the Temblor Range, the upper division of the Monterey Shale was originally referred to the Monterey Shale by Anderson (1905, p. 171, pl. 34), but a few years later it was assigned to the Santa Margarita For— mation by Arnold and Anderson (1908, p. 35—39, pl. 1), Arnold and Johnson (1910, p. 63—72), and English (1918, p. 229—230, pl. 2) when that name was applied to all strata of late Miocene age in the Coast Ranges, regardless of their lithology. Still later, this siliceous shale unit in the Diablo Range was named McLure Shale by Henny (1930, p. 403— 410) because he thought that the sandstone that locally unconformably underlies it 14 miles west of 28 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA Coalinga (NWIA, sec. 17, T. 21 S., R. 13 E.) was the Santa Margarita Sandstone on the basis of fossils. That sandstone is now known to be the Temblor. Since then, the name McLure has been so much used for this shale unit that it was adopted by Woodring, Stewart, and Richards (1940, p. 114, 122—125) and Stewart (1946, p. 103—104, pl. 9), and they designated this unit as a member of the Monterey Shale. In the southern part of the Diablo Range, this shale unit was referred to the McLure Shale by Marsh (1960, p. 32—33, pl. 1) and to the Monterey Formation by Dickinson (1966a, p. 713, fig. 4, pl. 2; 1966b, pl. 1). In the Chico Martinez Creek area of the Temblor Range, the upper division of the Monterey Shale was for many years informally divided by petroleum geologists into two local stratigraphic units or mem- bers. The lower unit was called McDonald Shale (Cushman and Goudkofl", 1938, pl. 1) or McDonald Shale Member of Monterey Formation (Simonson and Krueger, 1942, p, 1616—1617; Foss and Blais- dell, 1968, p. 37), presumably for the McDonald anticline oil field. This unit presumably corresponds to Monterey Shale units 4 and 5 (total thickness 1,105 ft) of Woodring, Stewart, and Richards (1940, p. 125) and contains foraminifers diagnostic of the early Mohnian Stage. The upper unit was called Antelope Shale (Noble, 1940, p. 1332, fig. 1) or Antelope Shale Member of Monterey Shale (Simon- son and Krueger, 1942, p. 1611, 1617, fig. 2; Foss and Blaisdell, 1968, p. 37), presumably for Antelope Valley. This unit probably corresponds to Monterey Shale units 6—9 (total thickness 3,815 ft) of Wood- ring, Stewart, and Richards (1940, p. 125) and contains diatom remains and sparse foraminifers assigned to the late Mohnian Stage. The McDonald and Antelope units are composed of siliceous shale and are thus difficult to distinguish. In the adjacent subsurface area they are recognized on the basis of paleontology and electric log correlations. In the Shale Hills area of the northwestern Tem- blor Range (about 8 miles south of Devils Den), the upper division of the Monterey Shale was referred to the McDonald Shale Member by Heikkila and MacLeod (1951, p. 13—14, pl. 1). In the central and southeastern parts of the TemJblor Range, this di- vision was mapped informally as the Antelope- McDonald Shale Member by Simonson and Krueger (1942, p. 1611, 1617) and Dibblee (1962, 1968). The application of four names to the siliceous shale of the upper division of the Monterey Shale or parts of it is the source of much confusion. It was found impractical to differentiate this shale unit in the field, especially where it is complexly folded. Therefore it is appropriate to eliminate all but one name. Santa Margarita has been eliminated for this unit because this name is no longer applied to a shale unit. The names McDonald and Antelope, widely used in the subsurface but mainly as paleon- tologic units, are preoccupied and therefore not adopted. The usage of the term McLure Shale Mem- ber of the Monterey Shale by Woodring, Stewart, and Richards (1940, p. 114, 122—125) and Stewart (1946, p. 303—304) is adopted herein for the sili— ceous shale unit of mainly late Miocene age of the Monterey Shale throughout the entire region north- east of the San Andreas fault. ' The lithologically distinct members or units of the Monterey Shale northeast of the San Andreas fault recognized on the basis of lithology are shown in figure 10 and discussed in the following sections. GOULD SHALE lVIEMBER The siliceous shale that forms the lowest unit of the Monterey Shale exposed at Chico Martinez Creek was named the Gould Shale Member of the Temblor Formation by Cunningham and Banbat (1932, p. 418) for nearby Gould Hill (fig. 10). They desig- nated the type locality as the area between the ex- posure along that creek and 2 miles southeastward (fig. 10). This name was adopted as a member of the Monterey Shale by Woodring, Bramlette, and Kleinpell (1936, p. 127—146), Woodring, Stewart, and Richards (1940, p. 125), Heikkila and MacLeod (1951, p. 11-12), and Foss and Blaisdell (1968, p. 38). The Gould Shale Member is composed of tan- weathering thin-bedded brittle siliceous shale alter- nating with softer fissile shale. It conformably over— lies the Buttonbed Sandstone Member of the Tem- blor Formation and is overlain by the Devilwater Shale Member of the Monterey Shale. At the type locality, the Gould Shale Member is 285 feet thick (Woodring and others, 1940, p. 125), but to the northwest it is as thick as 600 feet. From the type locality, it is traceable northwestward for about 20 miles and then disappears, never to reappear. In all these exposures, the Gould Shale Member contains foraminifers diagnostic of the Relizian Stage, middle Miocene (Kleinpell, 1938, fig. 14; Foss and Blaisdell, 1968, p. 38). In the southeastern part of the Temblor Range and southwest flank of the central part, all the lower division, or middle Miocene part, of the Mon- terey Shale is composed of siliceous shale lithologic- ally similar to the Gould Shale Member of the Chico Martinez Creek area. All this siliceous shale is therefore assigned to the Gould Shale Member on the basis of lithologic similarity, even though the MIDDLE TERTIARY SEDIMENTARY SEQUENCE 29 upper part is presumably correlative in age with the Devilwater Shale Member of the Chico Marti- nez Creek area (fig. 10). In the southeastern Tem- blor Range, this siliceous shale unit was informally called Devilwater—Gould member of the Monterey (Simonson and Krueger, 1942, p. 1611, 1616, 1626— 1627; Dibblee, 1962, 1968). This unit, now desig- nated as the Gould Shale Member, is from 2,000 to 3,000 feet thick; it conformably overlies clay shale of the Temblor Formation and is overlain by the McLure Shale Member of the Monterey Shale. In these exposures, the Gould Shale Member contains foraminifers diagnostic of‘the Relizian Stage in the lower part and Luisian Stage, middle Miocene, in the upper part. In one place in the extreme south- eastern Temblor Range, however, the lowest strata of this siliceous shale unit contain foraminifers diagnostic of the late Saucesian Stage, early Mio- cene (R. L. Pierce, oral commun., 1967). DEVILWATER SHALE MEMBER The argillaceous shale that forms the upper part of the lower division of the Monterey Shale in the northwestern Temblor Range is locally known as the “Devilwater Silt” (Bailey, 1939, p. 317 ; Heikkila and MacLeod, 1951, p. 11—12, pl. 1; Foss and Blais— dell, 1968, p. 38). It is presumably named for Devil- water Creek (fig. 9). This name is adopted herein because of its long established usage but is modi— fied to Devilwater Shale Member because it is not “silt” (an unconsolidated sediment) but is clayey shale with lesser amounts of siltstone and fine- grained sandstone. The type section is here desig- nated as the section exposed at Chico Martinez Creek, where it is composed of 1,190 feet of soft clayey shale, locally containing abundant foramini- fers, and silty mudstone (Monterey Shale units 3 and 4 of Woodring and others, 1940, p. 125) sepa- rating the Gould Shale Member below from the McLure Shale Member above (fig. 10). The Devilwater Shale Member is about 1,000 feet thick in most exposures. It persists northwest of Packwood Creek into the southwest foothills of the Diablo Range east of Cholame Valley, where it was mapped as the upper Temblor Sandstone by Marsh (1960, pl. 1) and as the siltstone member of the Vaqueros—Temblor Formation by Dickinson (1966a, p. 711—713, pl. 2). The Devilwater Shale Member is also present in the Devils Den area, where it is about 700 feet thick. There it was called Alferitz Formation and assigned to the Luisian Stage, middle Miocene, by Van Couvering and Allen (1943, p. 496-500), but the name Alferitz is not adopted. . In the Temblor Range the Devilwater Shale Mem- ber contains foraminifers diagnostic of the middle Miocene Luisian Stage (Foss and Blaisdell, 1968, p. 38). It is presumably of the same age in the Diablo Range. In the subsurface of the Kettleman Hills, it and the correlative of the Gould Shale Mem- ber are represented mostly by sandstone which there was assigned to the Temblor Formation by Woodring, Stewart, and Richards (1940, fig. 8). INTERBEDDED SHALE AND SANDSTONE MEMBER 0n the southwest slope of the southeastern part of the Temblor Range and southwest of the Recruit Pass fault, the conglomerate of the Santa Marga- rita Formation is unconformably underlain by Mon- terey Shale of which as much as 1,500 feet is ex- posed although the base is buried. The shale is semisiliceous and contains about 50 percent inter- bedded light-gray sandstone. The shale contains foraminifers diagnostic of the Relizian and Luisian Stages, middle Miocene (Vedder, 1970), and is therefore correlative with the Gould Shale Member east of the Recruit Pass fault. M’LURE SHALE LIEMBER The McLure Shale Member is composed of white- weathering dark-brown thin-bedded chalky to hard porcelaneous siliceous shale. The type locality, desig- nated by Henny (1930, p. 404, table 1), is in sec. 8 (not sec. 6), T. 24 S., R. 17 E., on the west side of McLure Valley, for which it was named. At that locality, this shale is 800 feet thick and is uncon- formable on the Panoche Formation. In the McLure Valley and Reef Ridge areas, this member ranges from 550 to 1,000 feet in thickness, thinning north— ward, and is unconformable on the Temblor and older formations. In the Reef Ridge area the McLure / Shale Member locally contains a basal conglomerate and sandstone with serpentine clasts (Stewart, 1946, p. 98, 103—104; Adegoke, 1969, p. 20). On the southwest flank of the Diablo Range and in the northwestern part of the Temblor Range, the Mc- Lure Shale Member thickens southeastward to about 5,000 feet and is conformable on the Devilwater Shale Member or unconformable on the Point of Rocks Sandstone or Panoche Formation where the Devilwater Shale Member and Temblor Formation are absent. In these areas the McLure Shale Mem— ber contains one or more lenses of sandstone (Po- lonio Sandstone Tongue in McLure Shale of Marsh, 1960, p. 32—33). The reference section of the McLure Shale Mem- ber of the Monterey Shale is here designated at Chico Martinez Creek in sees. 10 and 11, T. 29 S., R. 20 E. (fig. 10), where it is completely exposed. 30 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA There it conformably overlies the Devilwater Shale Member and grades upward into the Belridge Diato- mite Member. In this section the McLure Shale Member is 4,930 feet thick and corresponds to Mon- terey Shale units 4—9 of Woodring, Stewart, and Richards (1940, p. 125). This siliceous shale mem- ber includes units informally called McDonald Shale, Antelope Shale, and Chico Martinez Chert Members (San Joaquin Geological Society, 1959, p. 13; Foss and Blaisdell, 1968, p. 37; Elliot and others (1968, p. 110—112). These terms are not adopted because all these units are composed of siliceous shale, and outside the Chico Martinez Creek area it is not pos— sible to differentiate them on a lithologic basis with certainty on the surface. The lowest unit, the Mc- Donald of local usage, is recognizable in the Elk Hills and other oil fields on the basis of electric log patterns and early Mohnian foraminifers (J. C. Maher, oral commun., 1970). In the southeastern part of the Temblor Range, the McLure Shale Member is from 3,000 to 5,000 feet thick and grades upward into the Belridge Diatomite Member. It overlies similar siliceous shale of the Gould Shale Member from which it is differentiated mainly by a color change; the McLure Shale Member weathers white, whereas the Gould Shale Member weathers cream to buff and is some- what less siliceous and more fissile. Near Taft and Maricopa, the McLure Shale Member contains sev- eral lenses of sandstone. The McLure Shale Member contains much diatom debris, arenaceous foraminifers, and fish scales. It also contains sparse calcareous foraminifers diag- nostic of the Mohnian Stage, late Miocene (R. L. Pierce, oral commun., 1968). Only in the extreme southeastern part of the Temblor Range do the lowest beds contain foraminifers of the middle Mio- cene Luisian Stage (Vedder, 1970). ' BELRIDGE DIATOMITE MELI BER The Belridge Diatomite Member, designated here— in as the uppermost member of the Monterey Shale, was named informally by Siegfus (1939, p. 29) and Young (1943, p. 523—524) for the South Belridge oil field (fig. 9). The type section is herein desig- nated as the section exposed near the mouth of Chico Martinez Creek (SE14 sec. 2, T 29 S., R 20 E., fig. 10). This member corresponds to Monterey Shale units 10 and 11 (total exposed thickness 830 ft) of Woodring, Stewart, and Richards (1940, p. 125) . It is composed of white-weathering soft fissile to punky diatomite that grades downward into the McLure Shale Member and is overlain unconform— ably by the Tulare Formation. At Bacon Hills, 2 miles north of the type section, and near Gould Hill, 2 miles southeast, this diatomite unit is overlain disconformably by the Etchegoin Formation. In the foothills of the Temblor Range from Mc- Kittrick to Maricopa, the Belridge Diatomite Mem- ber is discontinuously exposed and is similar to the Belridge at Chico Martinez Creek. Just west of Taft, as much as 2,200 feet of this unit is exposed uncon- formably below the Tulare Formation. The Belridge Diatomite Member has been corre- lated with the Reef Ridge Shale and assigned a Miocene and Pliocene age by Foss and Blaisdell (1968, p. 36—37). It is, however, lithologically un- like the Reef Ridge Shale near Reef Ridge. In the exposed sections, the Belridge Diatomite Member contains foraminifers and fish scales diagnostic only of the late Mohnian Stage, late Miocene (R. L. Pierce, oral commun., 1967). From field relations the Belridge Diatomite Mem- ber is considered to be older than the type Reef Ridge Shale because in the extreme southeastern Temblor Range the Santa Margarita Formation, which intertongues into the Belridge Diatomite Member, is overlain by the Bitterwater Creek Shale, which in turn is probably correlative with the type Reef Ridge Shale. If this is so, then the Belridge Diatomite Member may be correlative with the upper part of the McLure Shale Member of the McLure Valley—Reef Ridge area. The relationship of the Belridge Diatomite Mem- ber exposed in the Temblor Range to the unexposed Reef Ridge Shale in the oil fields to the east is un- certain because the exposed Belridge Diatomite Member has not definitely been recognized in the oil field subsurface area. These units have been cor- related on the basis of supposed similar stratigraphic position (Foss and Blaisdell, 1968, p. 36), even though they are different lithologically. Subsurface structural data suggest that the Belridge Diatomite Member correlates wtih the upper part (the Ante- lope Shale of drillers) of the McLure Shale Mem- ber in the subsurface and dips under the subsurface argillaceous( ?) unit referred to the Reef Ridge Shale (H. C. Wagner, oral commun., 1970). If this is correct, the exposed Belridge Diatomite Member is older than the Reef Ridge Shale of the subsurface. Because of the foregoing evidence, the Belridge Diatomite Member exposed in the Temblor Range is assigned to the late Mohnian Stage, late Miocene, and is considered to be older than the Reef Ridge Shale. BRANCH CANYON SANDSTONE Marine sandstone that grades laterally westward into the Monterey Shale in the Sierra Madre Moun- MIDDLE TERTIARY SEDIMENTARY SEQUENCE 31 tains and Caliente Range (fig. 7) was named the Branch Canyon Formation by Hill, Carlson, and Dibblee (1958, p. 2991—2993) for Branch Canyon (3 miles south of New Cuyama), the type section (sec. 2. T. 9 N., R. 27 W.). This usage is adopted herein but the name is modified to Branch Canyon Sandstone. In the Branch Canyon area ,south of Cuyama Valley, the Branch Canyon Sandstone is about 3,200 feet thick. The lower 2,100 feet (“Vaqueros,” “Temblor,” and “Briones,” of Eaton and others, 1941, fig. 13) contains mollusks and echinoids diag- nostic of the “Temblor Stage,” middle Miocene. The upper 1,100 feet (“upper Briones,” “Cierbo,” and “lower Neroly” of Eaton and others, 1941, fig. 13) contains mollusks and echinoids diagnostic of the “Santa Margarita Stage,” late Miocene, and is over- lain by the Santa Margarita Formation. Farther east, the Branch Canyon Sandstone is overlapped by and tongues out into nonmarine formations. In the Caliente Range, the Branch Canyon Sand- stone is as much as 3,000 feet thick. There it con— tains mollusks of the “Temlblor Stage,” middle Mio- cene, only. It intertongues southwestward into the Saltos Shale Member of the Monterey Shale in both northwestern and southeastern parts of the range. In the southeastern part, it is overlain by and tongues laterally eastward into the Caliente Forma- tion. Several wells drilled for petroleum in the western parts of the Carrizo Plain and near the San Juan River to the northwest and a well northwest of Cholame penetrated sandstone of, or correlative with, the Branch Canyon Sandstone. These occur- rences and the exposures of this sandstone along the northeastern flank of the Caliente Range sug- gest that the Branch Canyon Sandstone may be con- tinuous under the southwestern part of the Carrizo Plain to and beyond Cholame. Along this strip, this marine sandstone intertongues southwestward into the Monterey Shale and northeastward toward the San Andreas fault into the Caliente Formation (fig. 12). Similar conditions prevail in the eastern Sierra Madre Mountains and presumably under Cuyama Valley. These relations indicate that the Branch Canyon Sandstone is essentially a strandline deposit between the Monterey Shale deposited offshore to the southwest and the terrestrial Caliente Forma- tion to the northeast. SANTA MARGARITA FORMATION Throughout much of the region southwest of the San Andreas fault, the Monterey Shale is overlain by marine sandstone that was named the Santa Margarita Formation by Fairbanks (1904) for ex- posures at Santa Margarita, the type locality (8 miles southeast of Atascadero, fig. 2). This usage is herein retained for this sandstone unit. The Santa Margarita Formation is about 1,500 feet thick in most places and is composed mainly of white friable sandstone. In some places, such as north of the La Panza Range and also south of Cuyama Valley, it contains thin rhyolitic tuffaceous beds, zones of phosphatic pellets, and one or two thin units of silty diatomaceous siliceous shale. South of Cuyama Valley the Santa Margarita For- mation is underlain by upper Miocene beds of the Branch Canyon Sandstone, from which it is arbi- trarily separated by a shale unit at the base of the Santa Margarita Formation. In one exposure just west of Carrizo Plain, the Santa Margarita Forma- tion tongues eastward into nonmarine red beds. Within a few miles of the San Andreas fault in the southeastern Caliente Range and under Carrizo Plain, the Santa, Margarita Formation is not pres- ent, but is probably represented by the upper part of the Caliente Formation. The sandstone of the Santa Margarita Formation contains shallow-water marine mollusks and echi- noids of the “Santa Margarita Stage,” late Miocene. It was deposited as a littoral marine facies of a regressing sea. Northeast of the San Andreas fault, coarse elastic deposits in the upper Miocene section are present only in the southeastern part of the Tem‘blor Range. In this area very coarse conglomerate, which locally contains mollusks of late Miocene age, was referred to the Santa Margarita Formation by Simonson and Krueger (1942 p. 1619—1621). This usage is re- tained herein. This conglomerate, which also in— cludes lenses of breccia and sandstone, is as much as 2,500 feet thick. It intertongues northeastward, downdip, into the Belridge Diatomite Member of the Monterey Shale. CALIENTE FORMATION In areas southwest of the San Andreas fault, terrestrial deposits that intertongue westward into the marine deposits of Miocene age (fig. 7) were named the Caliente Formation by Hill, Carlson, and Dibblee, 1958 p. 2993-2995) for the Caliente Range. The type locality was designated in the southeastern part of the range in sees. 26 and 23, T. 11 N., R. 26 W., 5—6 miles northeast of New Cuyama. This usage is adopted herein. The Caliente Formation of the Caliente Range is as thick as 4,200 feet and consists of varicolored sandstone, claystone, conglomerate, and four units 32 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA of basalt. It has yielded vertebrate remains diag- nostic of the following ages of the mammalian chronology (fig. 4): Arikareean, late Oligocene(?) and early Miocene; Hemingfordian, middle Mio- cene; Barstovian, middle(?) and late Miocene; Clarendonian, late Miocene(?); and Hemphillian, Pliocene (Repenning and Vedder, 1961; Vedder and Repenning, 1965). It is therefore assigned an Oligo- cene(?), Miocene, and Pliocene age (fig. 7), but it is mostly of Miocene age. The strata of the Caliente Formation that contain mammalian faunas assigned to the Arikareean, Hemingfordian, and early Barstovian ages inter- tongue westward into marine beds that have yielded molluscan faunas diagnostic of the “Temblor Stage” and foraminiferal faunas diagnostic of the Sauce- sian, Relizian, and Luisian Stages in the central Caliente Range. The strata that contain mammalian faunas assigned to the late Barstovian, Claren— donian, and Hemphillian “ages” are overlain by the Quatal Formation and are considered in part if not in whole correlative with the Santa Margarita For- mation, which is also overlain by the Quatal Form-a- tion south of Cuyama Valley and northwest of Car- rizo Plain. If all the upper strata of the Caliente Formation correlate with the Santa Margarita Formation, then the Santa Margarita, of late Mio- cene age of the marine invertebrate chronology, may be in part Pliocene of the mammalian chron- ology. Until the relationship of the mammalian “ages” to the marine “ages” and stages is more precisely known, this problem is unresolved. In the Santa Barbara Canyon area southeast of Cuyama Valley, red beds that underlie the Branch Canyon Sandstone were named the Pato Red Mem- ber of the Vaqueros Formation by English (1916, p. 200, pl. XIX), but assigned to the Caliente For- mation {by Hill, Carlson, and Dibblee (1958, p. 2995) . The latter usage is retained, and the name Pato is considered obsolete. These beds contain sparse mam- malian remains that suggest Arikareean age (J. G. Vedder, oral commun., 1968) . In the Red Hills northwest of Carrizo Plain, the granitic basement is overlain by about 3,000 feet of red to gray coarse boulder-cobble conglomerate of granitic detritus. This conglomerate is questionably referred to the Caliente Formation and is presum- ably of middle or late Miocene age, but it may be in part of early Miocene or Oligocene(?) age. It is overlain by sandstone that has late Miocene fossils and is assigned to the Santa Margarita Formation but that could be correlative with the Branch Canyon Sandstone. A well drilled for petroleum about 2 miles east of the Red Hills penetrated terrestrial beds of the Caliente(?) Formation to a depth of 2,910 feet, then struck granitic basement. Another well about 11 miles northwest of the Red Hills or 21/; miles northwest of Cholame was drilled through terres- trial sedimentary rocks, presumably of the Caliente Formation, similar to those in the Red Hills from depths of 1,950 to 6,523 feet, then entered granitic basement. About 18 miles southeast of the Red Hills, red sandy beds which intertongue(?) southwestward into the Santa Margarita Formation crop out. The widely scattered exposures of the Caliente Formation are probably only a very small part of its total areal extent; it is largely covered by younger formations. This terrestrial unit or facies probably underlies the southeastern part of Cuyama Valley and possibly much of the northeast margin of Carrizo Plain (fig. 12), as suggested by the dis- tribution of the formation in surface exposures and well sections referred to. If the Caliente Formation is continuous along this strip, it intertongues south- westward into the Branch Canyon Sandstone and was deposited along a coastal plain adjacent to the Miocene sea to the southwest. The position of the west margin of the continental facies southwest of the San Andreas fault is about as postulated by Hill and Dibblee (1953, p. 446—448) but extends farther northwest. The granitic detritus that makes up the Caliente Formation was derived from a granitic terrane that presumably lay northeast of the San Andreas fault in middle Tertiary time. BASALT Exposures of volcanic flows, sills, and dikes of olivine basalt are present only in the middle Tertiary sedimentary sequence in the Caliente Range and on the east margin of the La Panza Range (fig. 7). Most of the flows are in the Monterey Shale, Branch Canyon Sandstone, and middle and upper Miocene parts of the Caliente Formation of the Caliente Range. Dikes are locally abundant in the Vaqueros and Simmler Formations near Soda Lake, and sev- eral sills occur in the Vaqueros Formation. In the southeastern Caliente Range, two of three prominent basalt flows (“Triple basalts” of Eaton, 1939; Hill and others, 1958, p. 2994; and Vedder and Repenning, 1965) were radiometrically dated by Turner (1970, p. 115) : the upper flow was dated as about 14.2 and 14.4 million years, and the lower one as about 16.1 million years. Both flows are in the Branch Canyon Sandstone, which contains a “Temblor” fauna and which intertongues eastward UPPER TERTIARY SEDIMENTARY SEQUENCE 33 into the part of the Caliente Formation that con- tains a “Barstovian” fauna. BITTERWATER CREEK SHALE Marine siliceous shale or mudstone that discon- forma'bly(?) overlies conglomerate of the Santa Margarita Formation in the Elkhorn Hills area southwest of Maricopa on the northeast side of the San Andreas fault was named the Bitterwater Creek Shale (Dibblee, 1962, p. 8—11, pl. 1). It was named for Bitterwater Creek, 6 miles southwest of Mari- copa, the type locality, Where as much as 2,000 feet of this shale is exposed and is unconformably over- lain by the Paso Robles Formation. This usage is adopted herein. The Bitterwater Creek Shale was thought to be of Pliocene(?) age (Di‘bblee, 1962) because of its stratigraphic position as indicated; however, it con— tains foraminifers, fish scales, and diatoms diagnos- tic of the Mohnian Stage, late Miocene (R. L. Pierce, oral commun., 1967; Vedder, 1970). This age is the same as that of the Belridge Diatomite Member of the Monterey Shale, but the Bitterwater Creek Shale is stratigraphically higher (fig. 8). The relationship of the Bitterwater Creek Shale to the unnamed Pliocene marine elastic sediments to the northwest, which were formerly included in the Bitterwater Creek Shale (Dibblee, 1962, pl. 1), is not clear because of insufficient exposures and structural complications. North of the Elkhorn Hills the Bitterwater Creek Shale intertong-ues northwest- ward into unfossiliferous sandstone with siliceous shale pebbles. This sandstone is similar to that of the unit mapped as unnamed marine sediment, of early Pliocene age. If the sandstones are the same, the Bitterwater Creek Shale is equivalent to at least the lower part of that unit. It is possible, how- ever, that the Bitterwater Creek Shale and the un- fossiliferous sandstone are overlapped by that unit and if so, are thus older. From the foregoing evi- dence the Bitterwater Creek Shale is considered to be late Miocene (Mohnian) and possibly early Plio- cene in age. REEF RIDGE SHALE In the Reef Ridge and McLure Valley areas, about 500 feet of soft—weathering claystone is ex- posed that is transitional between the underlying Monterey Shale and overlying Etchegoin Formation. It was described and named the Reef Ridge Shale by Barbat and Johnson, 1933, p. 239; 1934, p. 1—17) and by Gester and Galloway (1933, p. 1174—1176). This usage was adopted by Woodring, Stewart, and Richards (1940, p. 119—122) and Stewart (1946, p. 104, pl. 9) and is retained herein. This unit is arbi- trarily placed at the top of the middle Tertiary sedimentary sequence. No type locality was desig— nated, but Barbat and Johnson (1933, p. 4—5) stated that this shale unit is “typically exposed” from Little Tar Creek (9 miles south-southeast of Ave- nal) northwest for 22 miles to Jasper Creek (15 miles west of Avenal). They assigned this shale unit to the uppermost Miocene. The type locality is herein designated as the exposure in Big Tar Creek (about 5 miles south-southwest of Avenal) in secs. 7, 8, and 17, T. 23 S., R. 17 E., where the Reef Ridge Shale is about 550 feet thick. According to Kleinpell (1938, p. 165), the Reef Ridge Shale contains foraminifers assigned to his Delmontian Stage, of latest Miocene age. His Del- montian Stage is, however, now considered to be part of, and inseparable from, his Mohnian Stage (R. L. Pierce, oral commun., 1970). Therefore, the Reef Ridge Shale of the type area is considered by Pierce to be of late Miocene age (Mohnian Stage). This age assignment, however, has not yet been doubtlessly ascertained, as it may range into early Pliocene. Clay shale correlative with the Reef Ridge Shale does not crop out in the Temblor Range. Under the alluviated area to the east, however, wells penetrate between the Etchegoin Formation and Monterey Shale a shale unit from 150 to 900 feet thick that is referred to the Reef Ridge Shale by petroleum geolo- gists. This shale unit was considered to be late Mio- cene and possiblyearly Pliocene in age and corre- lated with both the Reef Ridge Shale of Reef Ridge and the Belridge Diatomite Member of the Monterey Shale in the Temblor Range (Foss and Blaisdell, 1960, p. 36). Correlation with the Reef Ridge Shale is probably valid because of its similar stratigraphic position and because in some wells, such as in the Elk Hills oil field, this unit is gray clay shale (J. C. Maher, oral commun., 1970) similar to the Reef Ridge Shale of Reef Ridge. Correlation with the Belridge Diatomite Member is considered not valid, as the Reef Ridge Shale is thought to be younger than that unit because of reasons as indicated in the discussion of the Belridge Diatomite Member. Accordingly, then, the Reef Ridge Shale is probably correlative with the Bitterwater Creek Shale in the south end of the Temblor Range and is considered to be late Miocene and possibly early Pliocene in age. UPPER TERTIARY SEDIMENTARY SEQUENCE DEFINITION In many places on both sides of the San Andreas fault, the middle Tertiary sedimentary sequence is 34 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA overain by shallow-water marine, brackish-water, and terrestrial sedimentary deposits mainly of Plio- cene age. These deposits are informally designated herein as the upper Tertiary sedimentary sequence. The age of the sequence may range into early Pleis- tocene, depending upon the age interpretation of the fossils in the upper part. This sequence underlies almost all the San Joaquin Valley east of the San Andreas fault. West of the fault it is restricted to Cuyama Valley, Carrizo Plain, and Salinas Valley and is exposed at only a few places along the margins of this alinement of valleys. The sequence must have accumulated in two northwest-trending basins separated by the Temblor Range, against which this sequence thins from both sides. In each of these basins the sequence is different in stratigraphy and thickness, as indi- cated subsequently. DEPOSITS IN THE SAN JOAQUIN VALLEY AREA The upper Tertiary sedimentary sequence of the part of the San Joaquin Valley region of figure 2 accumulated in what developed (after middle Ter- tiary time) into a large marine embayment, in large part bounded on the southwest by uplifts that be- came the Temblor Range and the Diablo Range. Because this embayment covered the area that is now the San Joaquin Valley, it is commonly called the San Joaquin basin. The upper Tertiary sequence deposited in this basin is as thick as 7,000 feet and is composed mainly of fossiliferous interbedded sandstone, siltstone, and claystone of shallow ma- rine origin with Some brackish water and lacustrine beds at the top. The sequence crops out in the Reef Ridge and McLure Valley areas of the Diablo Range, and the upper part is exposed in the Kettleman Hills. In these areas it lies conformably on the Reef Ridge Shale and is overlain conformably by the Tulare Formation. Southeast of McLure Valley and Kettleman Hills, this sedimentary sequence is concealed except for a few very small exposures in the foothills of the Temblor Range. Subsurface well data from east of the Temblor Range indicate that this sequence is about 7,000 feet thick, but it thins abruptly south- westward against previously deformed and eroded Monterey Shale of the Temblor Range. TERMINOLOGY The stratigraphic nomenclature applied to the upper Tertiary sedimentary sequence of the west side of San Joaquin Valley is much confused, as pointed out by Woodring, Stewart, and Richards (1940, p. 26—27). In the area north of Coalinga, Anderson (1905, p. 178-181) originally named the entire exposed sequence “Etchegoin Beds,” for ex- posures on “Etchegoin ranch, some twenty miles northeast of Coalinga” (this plots in the alluvium of San Joaquin Valley), but he called the lower two-thirds “Etchegoin Sands” and the upper third “San Joaquin Clays.” Later, Arnold and Anderson (1910, p. 113—114) located this ranch in NW1/1, sec. 1, T. 19 S., R. 15 E., but designated the type section of the Etchegoin Formation on Anticline Ridge “9 miles north of Coalinga” and defined the forma- tion as consisting of sand, gravel, and clay above “the Glycimems zone.” On the east flank of the Diablo Range south of Coalinga and in the Kettleman Hills, Arnold and Anderson (1908, p. 46—55; 1910, p. 96—124) applied the term “Etchegoin Formation” to the upper two- thirds of this sequence and named the lower third “Jacalitos Formation,” which was inferred from the fossils to be of late Miocene age. This classifica- tion was adopted by Nomland (1916); however, a year later he (Nomland, 1917, p. 197) abandoned the name Jacalitos Formation because that unit is lithologically and paleontologically nearly similar to the Etchegoin, and he applied the term Etchegoin Formation or Group to both units and assigned both to the Pliocene. In later years the San Joaquin Clay again became recognized as the upper third of the upper Tertiary sedimentary sequence in the west-side oil fields and the foothill areas (Reed, 1933, p. 236; Barbat and Galloway, 1934). In the Kettleman Hills this unit was formally defined and mapped as the San Joaquin Formation by Woodring, Stewart, and Richards (1940, p. 26-28) and adopted by Stewart (1946, p. 104—105, pl. 9). In both reports the name Jaca- litos Formation was revived for the lower third, and Etchegoin Formation retained for the middle third of the upper Tertiary sedimentary sequence. They considered all three units to be of Pliocene age. Still later, Adegoke (1969, p. 28—34) recognized only a twofold division of this Pliocene sequence. He assigned the predominantly sandy lower two- thirds to the Etchegoin Formation and the largely clayey upper one-third to the San Joaquin Forma— tion, as shown in figure 13. In the oil field subsurface areas east of the Tem- blor Range, Pack (1920, p. 44—47, pl. 1) and Wood- ring, Roundy, and Farnsworth (1932, p. 32—39) applied the term “Etchegoin Formation” to the entire Pliocene marine sedimentary sequence. Although the lithology of the upper Tertiary sedi- mentary sequence is generally similar throughout, it is proposed to adopt the terminology proposed by UPPER TERTIARY SEDIMENTARY SEQUENCE ThlS report \ / UOHELUJOJ /\ \\ / UOI euuo unoSa o ugnbeor U98 \ / \\ .1 :1 . ll 13 \ / \ l \/ V/ I auoxspues en|a : 1 Adegoke, 1969 uoneuuog ugnbeor ues uouewjod ugoSauog Woodring, Stewart. {3’ LU ~ : Saga U -;"' -—O 01 n:-.~°.-.o¢ --°u°o°.---.... I-... ._ .-—- .............. .90 ”Goo-:..‘.:§ ° _ _ >“g .3 5 “3° 0 . .. w. Tulare Formation_ _ _ g ‘3 EU OODD'OO°a~-°°°. o ——b 9% ??? :z: 0—0 °9.'-;-g.a o-ao o. .e‘o_e-o_o‘«; - - D 7 7 ---- -* L“ ”'— _ ; Etchegoin Formation '_- PHocene Upper Tertiary sedimentary sequence Miocene formations FIGURE 14.—Valley deposits and upper Tertiary sedimentary sequence of the San Joaquin Valley area along east side of the southeastern part of the Diablo Range, Kettleman Hills, and the Temblor Range. ETCHEGOIN FORMATION The Etchegoin Formation, as redefined by Nom- land (1917), Barbat and Galloway (1934), and Adegoke (1969, p. 26—28), is a series of semifriable sandstone and interbedded siltstone, claystone, and minor pebble conglomerate, all deposited under shallow-water marine conditions and presumably of Pliocene age. In a few places it contains thin strata of tuff. In the Reef Ridge it is about 5,200 feet thick, overlies the Reef Ridge Shale or the Mon- terey Shale, and is overlain by the San Joaquin Formation. The type locality of the Etchegoin Formation has not been clearly designated. The formation was named by F. M. Anderson (1905) for “its char- acteristic development in the vicinity of Etchegoin ranch” (in T. 19 S., R. 15 E.) north of Coalinga. He did not designate a type section, but Arnold and Anderson (1910, p. 113) stated: “The nearest local- ity to the Etchegoin ranch for which a description or section was given is 9 miles north of Coalinga, and this may therefore be taken as the type sec- tion.” But on their map (Arnold and Anderson, 1910, pl. 1) this “locality” plots several miles west of what they mapped as the Etchegoin Formation. From this confusion it may be said that the type section is within T. 19 S., R. 15 E., north of Goa- linga, but its exact designation will not be made until that area, which is far north of the area of figure 2, is more carefully mapped. The most complete and best exposed section, which is herein designated as the reference section, is that north of Reef Ridge between Big Tar and Garza Creeks, Garza Peak quadrangle, or from 3 to 5 miles southwest of Avenal (figs. 1, 2). The section there is about 5,200 feet thick and is conformable between the Reef Ridge Shale below and San Joaquin Formation above. In this section the Etchegoin For- mation is composed of two parts, as recognized by Adegoke (1969, p. 28). The lower part (Basal Brown Sandstone Member of Adegoke, 1969, p. 28), about 3,500 feet thick, is mainly bedded commonly nodular brownish-gray sandstone and interbedded siltstone in about equal amounts and contains few fossils. This unit corresponds roughly to the unit formerly called Jacalitos Formation by earlier workers (fig. 13). The upper part (Upper Blue Sandstone Member of Adegoke, 1969, p. 28), about 1,700 feet thick, is similar to the lower part; how— ever, sandstones predominate and are somewhat coarser and commonly pebbly and (or) fossiliferous, and many of them are blue. This unit corresponds roughly to the formerly restricted Etchegoin For- mation of Stewart (1946, p. 105, pl. 9). It is similar to and nearly equivalent to the “blue bed facies” mapped farther northwest by Rose and Colburn (1963, p. 33). Other places where this unit is ex- posed are in McLure Valley and Kettleman Hills. On the geologic map (Dibblee, 1973b) only parts of the Upper Blue Sandstone Member of Adegoke (1969, p. 28) that are composed predominantly of blue sandstone are mapped separately from the rest of the Etchegoin Formation (fig. 14). In the Reef Ridge area there are several blue sandstone units, some as thick as 500 feet. Southeastward along strike all thin out or lose their distinctive blue color east of the Pyramid Hills. In McLure Valley the whole upper part of the Etchegoin Formation is composed of unfossilifero-us massive blue sand- stone, about 1,500 feet thick. In the Kettleman Hills UPPER TERTIARY SEDIMENTARY SEQUENCE (North and Middle Domes) several thin blue sand- stone strata are present. The blue sandstones are medium grained and commonly contain pebbles of black and variegated chert and andesite. The blue color of the sandstone is the effect of a thin blue coating on the grains. The Etchegoin Formation of the Reef Ridge and Kettleman Hills areas contains abundant marine mollusks and echinoids of Pliocene age (Woodring and others, 1940, p. 102—103). In the Kettleman Hills (North Dome) and at a locality 10—12 miles north of Coalinga, a few mammalian remains from the upper part of the Etchegoin Formation are assigned to the late Hemphillian age, Pliocene (D. E. Savage, written commun. to C. A. Repenning, 1968). In the Reef Ridge area, the few molluscan fossils from the lower part of the Etchegoin Forma- tion are considered to be early Pliocene, and those from the upper part are considered to be late Plio- cene (W. 0. Addicott, oral commun., 1969). SAN JOAQUIN FORMATION In the Kettleman Hills the San Joaquin Forma— tion, as mapped by Woodring, Stewart, and Richards (1940, p. 26—28, pl. 1), is from 1,200 to 1,800 feet thick and is mainly gray soft claystone, siltstone, and fine-grained sandstone. The base was taken as the base of a 50-foot-thick bed of gray to blue sand- stone and pebble conglomerate (Cascajo Conglom- erate Member of Woodring and others, 1940, p. 49—53). The San Joaquin Formation overlies the Etchegoin Formation and grades upward into the Tulare Formation. The type locality of the San Joaquin Formation is on the northeast flank of Ket- tleman Hills, in sec. 23, T. 22 S., R. 18 E., 8 miles east of Avenal (fig. 1), as suggested by Barbat and Galloway (1934, p. 478—480); however, Woodring, Stewart, and Richards (1940, p. 27) suggested a better standard section 3 miles northwest in sec. 8, T. 22 S., R. 18 E. In the foothills north of Reef Ridge, the San Joaquin Formation is about 2,000 feet thick and is similar 'to its exposure in Kettleman Hills. The base is taken as a thin pebble bed that overlies blue sandstone of the Etchegoin Formation. The San Joaquin Formation grades upward into the Tulare Formation through interbeds of conglomerate simi- lar to that of the Tulare Formation. Southeastward along strike, the contact with the Tulare Forma- ion becomes difficult to map because the upper 1,200 feet of the San Joaquin Formation contains increas- ing amounts of sandstone and many layers of shale- pebble conglomerate, a composition like that of the Tulare Formation. 37 The San Joaquin Formation in the Kettleman ,Hills contains marine, brackish-water, and laws- trine fossils considered to be of late Pliocene age by Woodring, Stewart, and Richards (1940, p. 103) . They reported (1940, p. 97—98) mammalian fossils from the “Pecten zone” about 600 feet below the top of this unit. These were considered by Durham, Jahns, and Savage (1954, p. 69) to be of Blancan age or late Pliocene and early Pleistocene age and by Hibbard, Ray, Savage, Taylor, and Guilday (1965, p. 512) to be early Blancan age or late Pliocene. Adegoke (1969, p. 51) suggested that part or all of the San Joaquin Formation may be of Pleistocene age. In the Reef Ridge foothills the San Joaquin Formation contains molluscan fossils that Addicott (oral commun., 1968) considered to be of late Pliocene age. The unit is tentatively assigned a late Pliocene age, but could range into the Pleisto- cene, depending on the interpretation of the Plio- cene-Pleistocene boundary. DEPOSITS IN THE SALINAS VALLEY— CUYAMA VALLEY AREA The upper Tertiary sedimentary sequence of the southeastern part of Salinas Valley, Carrizo Plain, Caliente Range, and Cuyama Valley is as thick as 5,000 feet, but generally thinner. It accumulated in what developed after Miocene time into a large troughlike basin between the Temblor Range uplift on the northeast and an extensive uplift to the southwest that evolved into the Santa Lucia, La Panza and Sierra Madre Mountains (fig. 2). This trough apparently extended northwestward through Salinas Valley and may therefore be referred to as the Salinas basin. Most of the upper Tertiary sedi- mentary sequence lies southwest of the San Andreas fault; a small part is on the northeast side of the fault in a narrow strip between the fault and the Temblor Range uplift. The upper Tertiary sedimentary sequence is ter- restrial, except under Salinas Valley and in part of the strip on the northeast side of the San Andreas fault, where it is marine. In the central parts of the Salinas basin, this sequence conformably overlies the Santa Margarita or Caliente Formation, but along the flanks, especially the southwestern flank, it lies unconformably on all older formations, includ- ing the crystalline rocks. Where exposed, this se- quence is unconformably overlain by the Paso Robles Formation. UNNAMED MARINE SEDIMENTS Several test holes drilled for petroleum in the Shandon area of the Salinas Valley southwest of the San Andreas fault passed through as much as 38 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA 2,000 feet of marine sandstone and siltstone of probable Pliocene age below the Paso Robles Forma- tion and above the Santa Margarita Formation. Because of its comparable age and stratigraphic position, this unit may be equivalent to the Pancho Rico Formation, as redefined by Durham and Addi- cott‘ (1964, p. E4; 1965, p. A2—A5) in Salinas Valley northwest of figure 2. In the narrow strip on the northeast side of the San Andreas fault east of Soda Lake is exposed about 2,000 feet of marine sandstone that overlies conglomerate of the Santa Margarita Formation and grades laterally northward and upward into the terrestrial Morales Formation. The relationship of this sandstone to the Bitterwater Creek Shale is discussed under that formation. This marine sand- stone unit contains early Pliocene mollusks (Arnold and Johnson, 1910, p. 89; W. O. Addicott, oral ‘com-mun., 1967). It may be correlative with the marine unit in the Shandon area described pre- viously and also with part of the lithologically simi- lar Etchegoin Formation of San Joaquin Valley and the Diablo Range. QUATAL FORMATION In the eastern Caliente Range, red beds of the Caliente Formation are overlain conformably by as much as 700 feet of lacustrine gray claystone. This claystone is believed to correlate, on the basis of similar lithology and stratigraphic position, with the Quatal Formation named by Hill, Carlson, and Dibblee (1958, p. 2996—2997) for Quatal Canyon near the type locality, in the Cuyama badlands south- east of the Caliente Range and beyond the southeast border of figure 2. This name is herein adopted for this claystone in both exposures. The Quatal Formation, which conformably under- lies the terrestrial Morales Formation, is exposed at only a few places other than in the Caliente Range. In the Cuyama badlands it is composed of about 400 feet of reddish—brown claystone and gypsum that overlies the Caliente Formation. South of Cuyama Valley it is composed of 200—400 feet of white sand- stone and red clay that disconformably overlies the Santa Margarita Formation and Branch Canyon Sandstone. In San Juan Creek, northwest of Carrizo Plain, about 200 feet of gray clay assigned to the Quatal Formation disconformably overlies the Santa Margarita Formation. The Quatal Formation was presumed by Hill, Carl- son, and Dibblee (1958, p. 2996) to be of late Mio- cene age because of its stratigraphic position. In the Caliente Range the uppermost beds of the Caliente Formation that underlie the Quatal contain mam- malian remains diagnostic of Hemphillian age, Plio- cene (Savage, 1957, p. 1845), and beds about 1,600 feet above the base of the overlying Morales Forma- tion contain a few mammalian remains of Blancan age (James, 1963, p. 11; Repenning and Vedder, 1961). The relationship of the Quatal Formation to the Pliocene(?) marine sediments of the Shandon area to the northwest is concealed, but the Quatal is presumably younger. Because of its stratigraphic position, the Quatal Formation is herein inferred to be of Hemphillian age and is assigned to the Plio- cene. MORALES FORMATION In the Cuyama Valley, Caliente Range, and in the area northwest of Carrizo Plain is exposed a de- formed valley deposit, as much as 5,000 feet thick, of light-gray gravel, sand, and silt that conformably overlies the Quatal Formation and unconformably laps onto the middle Tertiary sedimentary sequence. This valley deposit was named the Morales Member of the Santa Margarita Formation by English (1916, p. 203, pl. XIX) for Morales Canyon (10 miles north- west of New Cuyama) , the type locality. This deposit was redefined as a formation by Hill, Carlson, and Dibblee (1958, p. 2990, 2996—2998) because it differs lithologically from the Santa Margarita Formation and in the type locality in unconformably overlies the Santa Margarita Formation with angular dis- cordance. The usage of Morales Formation of Hill, Carlson, and Dibblee (1958) and Vedder (1970) is retained herein. . The Morales Formation was inferred to be of Plio- cene age by Hill, Carlson, and Dibblee (1958, p. 2996—2998) on the basis of its stratigraphic position above the Quatal Formation and Miocene strata and because of its unconformable relationship below equivalents of the Paso Robles Formation in western Cuyama Valley and eastern Caliente Range and at San Juan Creek northwest of Carrizo Plain. A tooth of Equus (Pleisohippus) sp. (large horse), considered diagnostic of Blancan age (Plio- cene or Pleistocene) of the vertebrate chronology, was found near the middle of the 5,000-foot-thick Morales Formation in the eastern Caliente Range (Vedder and Repenning, 1965; Vedder, 1970). The profound deformation of this formation, however, as compared to the much less deformed uncon- formably overlying Paso Robles Formation indicates that the Morales Formation probably is late Plio- cene in age, to which it was assigned by Vedder (1970). ' In the Panorama Hills and southwestern foothills of the Temblor Range just northeast of the San Andreas fault, as much as 2,500 feet of terrestrial VALLEY DEPOSITS ' 39 gravel named Panorama Hills Formation by Dibblee (1962, p. 8, pl. 1) gradationally overlies sandstone of the unnamed marine sediments and is uncon- formably overlain by the Paso Robles Formation. The name Panorama Hills Formation is herein abandoned, and this unit is assigned to the Morales Formation because it is of similar lithology and is probably in large part correlative. Presumably this valley deposit accumulated in the same basin as the Morales Formation now exposed in the Caliente Range and Cuyama Valley. VALLEY DEPOSITS DEFINITION Alluvial deposits of Pleistocene and possibly late Pliocene age form the uppermost and youngest thick sedimentary unit of the map area. These are informally designated herein as valley deposits. They accumulated in the San Joaquin and Salinas basins after the sea completely withdrew from this region near or at the end of Pliocene time. These basins thereby became valleys, separated by the Temblor-Diablo Range uplift, which was rising on the northeast side of the San Andreas fault. The valley deposits southwest of this uplift are com- monly called the Paso Robles Formation; these accumulated in a long valley that extended from what is now the Salinas Valley southeastward through Carrizo Plain into Cuyama Valley. The valley deposits northeast of the Temblor-Diablo Range uplift are commonly called the Tulare Forma- tion, and they accumulated in the San Joaquin Val- ley. PASO ROBLES FORMATION Dissected locally deformed valley deposits in up- per Salinas Valley were named the Paso Robles For- mation by Fairbanks (1898, p. 565—566) for expo- sures near Paso Robles (fig. 1). This name has since been applied to these deposits beyond the Paso Robles area by Fairbanks (1904) , Arnold and J ohn- son (1910, pl. 1), Bramlette and Daviess (1944), Dibblee (1962, p. 6—10, pl. 1), and Durham (1963, 1964, 1966) and is used herein. In the Salinas Valley lowland area north of the La Panza Range, the Paso Robles Formation is as much as 1,500 feet in exposed thickness; it attains a total maximum thickness of more than 4,000 feet in the subsurface west of Shandon as indicated from well logs. In this lowland area this valley deposit is composed of pebble gravel, sand, and clay, derived from the LaJPanza Range and from mountainswest of Salinas Valley. In the subsurface near Shandon it conformably(?) overlies the un- named Pliocene marine sediments (Pancho Rico(?) Formation) as indicated by well logs. In the La Panza Range and Red Hills, this valley deposit thins and unconformably laps over the previously de- formed middle Tertiary sedimentary sequence onto the crystalline basement complex. Under the Carrizo Pain, the Paso Robles Forma- tion is as thick as 2,000 feet near the San Andreas fault as indicated from well logs, and is composed largely of shale-pebble gravel, sand, and clay, de- rived mainly from the Temblor Range. Southwest- ward this valley deposit thins and buttresses out against previously deformed Morales and Quatal Formations and the middle Tertiary sedimentary sequence of the Caliente Range. At and near the southeast end of the Caliente Range and southwest of the San Andreas fault, the Paso Robles Formation (“deformed fanglomerate from eastern sources” of Vedder and Repenning, 1965, and “deformed alluvial deposits” of Vedder, 1970) is as thick as 1,000 feet and is unconformable on previously deformed lower, middle, and upper Tertiary sequences, including the Morales Forma- tion. The Paso Robles Formation is there composed of gravel and some landslide debris of rocks exposed in the San Emigdio Mountains across the fault, but now is some 20 miles southeast of this area, owing to that much strike-slip on the fault since deposi— tion of this detritus. Northeast of the San Andreas fault, the Paso Robles Formation is as thick as 2,000 feet and more adjacent to the fault, but thins out rapidly northeastward against the Temblor Range. It un- conformably overlies rocks of the Temblor Range, including the Morales Formation, and was derived entirely from the Temblor Range. In Cuyama Valley, equivalents of the Paso Robles Formation are thought to be the old dissected locally deformed alluvial fan deposits, such as sev- eral on the southwest side of the Caliente Range and one southwest of New Cuyama. These deposits are as thick as 600 feet and are composed of coarse locally derived detritus. The top of the Paso Robles Formation, where preserved from erosion, is a surface of deposition, or an old valley surface that was never buried. Carrizo Plain, where it is preserved under a thin cover of alluvium, is a remnant of this former very extensive valley surface of deposition. To the north- west and west this old valley surface becomes in- creasingly dissected and largely destroyed by down- cutting stream channels of the present Salinas River drainage system. Along its margins this old valley 40 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA surface of deposition blends into the old erosion surface of the La Panza, Caliente, and Temblor Ranges as the Paso Robles Formation thins out against those previously elevated areas. The age of the Paso Robles Formation can only be inferred from its stratigraphic position and from geomorphic relations because, except in one place, no diagnostic fossils have been found. This formation has been variously inferred to be Plio- cene, Pleistocene, or Pliocene and Pleistocene in age. Durham (1966, p. B22) and Galehouse (1967, p. 955-956) considered it to be Pliocene and possibly Pleistocene in age because of the apparent inter- tonguing relationship with the underlying marine Pancho Rico Formation (lower Pliocene) east and southeast of King City. In that part of Salinas Val- ley (northwest of fig. 2), however, the Paso Robles Formation is thin, and some of the lower beds into which marine beds intertongue may be equivalent to the Morales or Quatal Formations farther south- east. The Paso Robles Formation must be at least in part of Pleistocene age because its top surface of deposition, which blends into the Pleistocene erosion surface of the adjacent mountains where this sur- face is cut on units as young as the Morales Forma- tion, is in large part preserved, whereas no surface of deposition of any Tertiary formation remains unburied and uneroded. The angular unconformable relationship of the Paso Robles Formation to all older units, including the Morales Formation of late Pliocene age, suggests that all the Paso Robles For- mation in areas in which this relationship exists is of Pleistocene age. The single locality in which fossils were found in the Paso Robles Formation is 2 miles east of Atascadero in a roadcut about 300 feet west of middle of west line of sec. 7, T, 28 S., R. 13 E. At that place, brackish~marine mollusks were found (by J. S. Galehouse) in shale-pebble gravel about 20 feet above the base of the Paso Robles Forma- tion. W. O. Addicott (written commun., 1971) con- sidered them probably Pliocene, possibly middle Pliocene. Also found at this locality, and in basal cobble gravel of this formation within 3 miles south- east of Santa Margarita, are cobbles with mollusk- bored holes. Although the Paso Robles Formation is generally regarded as Pliocene and Pleistocene(?) in age, the formation within the area of figure 2 is considered by the writer to be of Pleistocene age and in places partly of probable late Pliocene age because of the stratigraphic relations and fossil data as indicated. TULARE FORMATION Locally deformed dissected valley deposits com- posed of gravel, sand, and silt in the hills on the southwest side of the San Joaquin Valley near Coalinga were named Tulare Formation by Ander- son (1905, p. 181) for nearby Tulare Lake. No type locality was then designated, but Woodring, Stewart, and Richards (1940, p. 13) suggested the exposures on the northeast flank of the northern part of Kettle- man Hills North Dome as the type section. The name Paso Robles Formation was also applied to these valley deposits by Anderson and Pack (1915, pl. 1) and to those in the Temblor Range by Pack (1920, pl. II, p. 47—52). These deposits in the Tem- blor Range, however, were included earlier by Arnold and Johnson (1910, pl. 1) in a unit they named McKittrick Formation. These valley sedi- ments were redesignated the Tulare Formation by Woodring, Roundy, and Farnsworth (1932, p. 16— 30), Dibblee (1962, p. 8—10, pl. 1), and Foss and Blaisdell (1968 p. 35) because, even though they are lithologically similar to and occupy the same stratigraphic position as does the Paso Robles For- mation, they were deposited in a different basin or valley. This usage is retained herein. In the foothills of the Diablo Range and in the Kettleman Hills, the Tulare Formation is about 2,700 feet thick and grades downward into the San Joaquin Formation. Well data in the subsurface of the Elk Hills, Buena Vista Hills, and east of the Temblor Range indicate that it is similar. In the foothills of the Temblor Range it thins out west- ward against the unconformably underlying Etche- goin Formation and Monterey Shale. The top of the Tulare Formation is a valley surface of deposi- tion that forms the present undissected surface of San Joaquin Valley under a thin mantle of alluvium but is severely dissected, though partly preserved, where it is elevated by deformation in the Elk Hills, Buena Vista Hills (east of Taft), and foothills of the Temblor Range. The age of the Tulare Formation is inferred to be late Pliocene and Pleistocene (Arnold and Ander- son, 1910, p. 140, 154; Pack, 1920, pl. 11; Woodring and others, 1932, p. 27, and 1940, p. 104; Stewart, 1946, p. 105; Wahrhaftig and Birman, 1965, p. 314— 316) or Pleistocene (Goudkoff, 1943, p. 248—249; McMasters, 1947, fig. 34; Foss and Blaisdell, 1968, p. 35). A few mammalian fossils found in the San Joaquin Formation just below the base of the Tu- lare Formation in the Kettleman Hills and near McKittrick are diagnostic of the Blancan' age, late Pliocene or Pleistocene (C. A. Repenning, oral SURFICIAL DEPOSITS 41 commun., 1968). On the basis of diatom studies, the Tulare Formation is considered to be of Plio- cene and Pleistocene age (K. E. Lohman, written commun., 1968). The Tulare Formation within the area of figure 2 is probably correlative with most of if not all the Paso RoblesFormation on the basis of its similar lithology, stratigraphic position, and geomorphic relations and is likewise tentatively assigned a late Pliocene(?) and Pleistocene age. SURFICIAL DEPOSITS Surficial deposits consist of older alluvium, allu- vium, and landslides. These deposits are generally undeformed, except along or near the San Andreas fault. They are generally unconformable on older formations, except in much of the San Joaquin Valley and Carrizo Plain, where they may be con- formable on the Tulare and Paso Robles Forma- tions where these formations are undeformed. The older alluvium, which is as thick as 400 feet and includes terrace deposits, is dissected where elevated. At the tar seeps a mile south of McKit- trick, terrace sands yielded a large mammalian fauna (Schultz, 1938) of Rancholabrean age late Pleistocene (C. A. Repenning, oral commun., 1969). The alluvium forms a thin cover, generally less than 100 feet thick, on the valleys and flood plains of canyons. The alluvium and landslides are mainly of Holocene age, but may be in part latest Pleisto- cene, depending upon the interpretation of when the Holocene started. RELATIONSHIP OF SEDIMENTARY SEQUENCES TO THE SAN ANDREAS FAULT It may be noted throughout this report that the successively older sedimentary sequences are in- creasingly different on opposite sides of the San Andreas fault and that the basement complex upon which they rest is totally different. This condition appears to be the result of cumulative right-lateral displacement on this fault since Cretaceous (or Jurassic) time, along which areas of dissimilar older sequences and rocks have been juxtaposed, almost exactly as inferred by Hill and Dibblee (1953). In the environs of the Carrizo Plain, it was found that the Paso Robles Formation on the northeast side of the San Andreas fault and also just south- west of it is composed of detritus derived from the mountains on the northeast side and that these detrital sediments on the southwest side have been shifted some 10—15 miles northwest from their sources on the northeast side (Hill and Dibblee, 1953, p. 446; Dibblee, 1973b). The Pliocene marine sediments (Pancho Rico(?) Formation and its equivalent) on the northeast side of the fault extend some 50—60 miles farther south- east than they do on the southwest side, suggesting a right-lateral shift of that amount since they were deposited. The spectacular difference in stratigraphy of the middle Tertiary sedimentary sequence on opposite sides of the fault, with sudden changes of facies at the fault as shown in figure 12, is almost certainly due to lateral juxtaposition of once distant areas. The juxtaposition of the all-marine (in part bathyal) facies of the northeast block against coarse terrestrial facies, which in large part grades later- ally westward into shallow marine facies on the southwest block, is difficult to account for otherwise. A right-lateral offset of about 65 miles on the fault since late Miocene time was estimated by Hill and Dibblee (1953, p. 446—448) from the offset on the fault of the transition facies zone where the terrestrial sediments grade laterally westward into marine sediments. On the northeast block this zone is in the San Emigdio Mountains (southeast of Maricopa, fig. 1); on the southwest block, it is some 100 miles farther northwest, just northwest of Cholame, suggesting a right-lateral displacement of that amount. Further evidence suggesting that much displacement is the occurrence, in the upper Miocene Santa Margarita Formation of the Temblor Range northeast of the fault, of landslide ( ?) masses and coarse detritus of crystalline basement rocks presumably derived from those rocks in the Gabilan Range (north of King City, fig. 1) southwest of the fault but now more than 80 miles to the northwest (Dibblee, 1962, p. 8). This post-Miocene right- lateral displacement may be as much as 150 miles, as inferred by Huffman (1970, p. 105—106) from matching the coarse conglomerate and breccia of this formation in the Temblor Range with their probable bedrock source in the Gabilan Range west of the San Andreas fault. Right-lateral offset of some 175 miles since early Miocene time was suggested by Hill and Dibblee (1953, p. 448—449) on the basis of a similar assem- blage of volcanic rocks and terrestrial and marine sedimentary rocks of early Miocene age in the northern Gabilan Range on the southwest side of the fault and in the San Emigdio Mountains on the northeast side. Radiometric age dates of 21.5 million years obtained from the volcanic rocks in both areas by D. L. Turner (1970, p. 101; oral commun., 1970) reaffirm this inferred offset. 42 STRATIGRAPHY, SOUTHERN COAST RANGES The lower Tertiary and Cretaceous sedimentary sequences, although composed almost entirely of marine elastic rocks, are very unlike in stratigraphy, thickness, and age range on opposite sides of the fault within the region of figure 2. This condition must also be the result of juxtaposition along the fault of areas once far distant. To ascertain Hill and Dibblee’s (1953, p. 448—449) estimated right- lateral offset on the fault of possibly 225 miles since Eocene time, 320 miles since Cretaceous time, and 350 miles since Jurassic time, it is necessary to go far beyond the borders of figure 2, which is also beyond the scope of this report. It may be concluded that the stratigraphy of the region within figure 2 is closely related and greatly affected by movements on and near the San Andreas fault and that the available evidence suggests that this fault was active, either recurrently or continu- ously, since Jurassic or Cretaceous time. In summary, it may be said that the northeast block is one of oceanic basement of eugeosynclinal sedimentary and mafic igneous rocks overlain by four sequences of bathyal to shallow-water marine sedimentary rocks, whereas the southwest block is one of continental basement of granitic and meta- sedimentary rocks overlain unconformably by three sequences of shallow-water marine and terrestrial sedimentary and minor volcanic rocks. It seems evi- dent that the southwest block was shifted north- westward relative to and along the northeast block by many tens of miles of cumulative right-slip on the San Andreas fault during the Cenozoic Era. REFERENCES CITED Adegoke, O. S., 1969, Stratigraphy and paleontology of the marine Neogene formations of the Coalinga region, Cali- fornia: California Univ. Pubs. Geol. Sci., v. 80, 241 p., 13 pls., figs., maps. Anderson, F. M., 1905, A stratigraphic study in the Mount Diablo Range of California: California Acad. Sci. Proc., 3d ser., Geology, v. 2, p. 155—248. 1908, A further stratigraphic study in the Mount Diablo Range of California: California Acad. Sci. Proc., 4th ser., v. 3, p. 1—40. Anderson, F. M., and Martin, Bruce, 1914, Neocene record in the Temblor Basin, California, and Neocene deposits of the San Juan district, San Luis Obispo County: Calif. Acad. Sci. Proc., 4th ser., v. 4, p. 15-112. Anderson, Robert, and Pack, R. W., 1915, Geology and oil resources of the west border of the San Joaquin Valley north of Coalinga, California: U.S. Geol. Survey Bull. 603, 220 p. Arnold, Ralph, and Anderson, Robert, 1908, Preliminary re- port on the Coalinga oil district, Fresno and Kings Counties, California: U.S. Geol. Survey Bull. 357, 142 p. 1910, Geology and oil resources of the Coalinga dis- trict, California: U.S. Geol. Survey Bull. 398, 354 p., 52 pls. NEAR SAN ANDREAS FAULT, CALIFORNIA Arnold, Ralph, and Johnson, H. R., 1910, Preliminary report on the McKittrick-Sunset oil region, Kern and San Luis Obispo Counties, California: U.S. Geol. Survey Bull. 406, 225 p. Atwill, E. R., 1935, Oligocene Tumey formation of California: Am. Assoc. Petroleum Geologists Bull., v. 19, no. 8, p. 1192—1204. Bailey, E. H., Irwin, W. P., and Jones, D. L., 1964, Fran- ciscan and related rocks, and their significance in the geology of western California: California Div. Mines and Geology, Bull. 183, p. 1—177. Bailey, W. C., 1939, Wasco oil field [California] California Oil Fields—Summ. Operations, v. 24, no. 3, p. 66—71 [1941]. Bandy, O. L., and Arnal, R. E., 1969, Middle Tertiary basin development, San Joaquin Valley, California: Geol. Soc. America Bull., v. 80, p. 783—819. Barbat, W. F., and Galloway, John, 1934, San Joaquin clay, California: Am. Assoc. Petroleum Geologists Bull., v. 18, no. 4, p. 476—499. . Barbat, W. F., and Johnson, F. L., 1933, Stratigraphy and foraminifera of the Reef Ridge shale, upper Miocene, California [abs.]: Pan—Am. Geologist, v. 59, no. 3, p. 239; also, 1934, Jour. Paleontology, v. 8, no. 1, p. 1—17. Blake, W. P., 1855, Notice of remarkable strata containing the remains of Infusoria and Polythalmia in the Ter- tiary formation of Monterey, California: Acad. Nat. Sci. Philadelphia Proc., v. 7, p. 328—331. Bramlette, N. M., and Daviess, S. N., 1944, Geology and oil possibilities of the Salinas Valley, California: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 24. Chipping, D. H., 1972, Early Tertiary paleogeography of central California: Am. Assoc. Petroleum Geologists Bull., v. 56, no. 3, p. 480493. Church, C. C., 1968, Lower Cretaceous Foraminifera of the Orchard Peak—Devils Den area, California: California Acad. Sci., Proc., 4th ser., v. 32, no. 18, p. 523—580, 8 pls. Clark, B. L., 1929, Tectonics of the Valle Grande of Cali- fornia: Am. Assoc. Petroleum Geologists Bull., v. 13, no. 3, p. 199—238. Clark, B. L., and Vokes, H. E., 1936, Summary of marine Eocene sequence of western North America: Geol. Soc. America Bull., v. 47, no. 6, p. 851-878. Clark, L. M., and Clark, Alexander, 1935, The Vaqueros in the Temblor Range [abs.]: Am. Assoc. Petroleum Geologists Bull., v. 19, no. 1, p. 137. Clements, T. D., 1950, Geology of Cuyama Gorge, California [abs.]: Read before Am. Assoc. Petroleum Geologists, Los Angeles, Calif., October 20, 1950. Corey, W. H., 1954, Tertiary basins of southern California, pt. 8 in chap. 3 of J ahns, R. H., ed. Geology of southern California: California Div. Mines Bull. 170, p. 73—83. Cross, R. K., 1962, Geology of the Carrizo-Cuyama Basin, in Guidebook to the geology of Carrizo Plain and San Andreas Fault, San Joaquin Geol. Soc. and Pacific Secs. Am. Assoc. Petroleum Geologists and Soc. Econ. Paleon- tologists and Mineralogists: p. 27—35. Cunningham, G. M., and Barbat, W. F., 1932, Age of produc- ing horizons at Kettleman Hills, California: Am. Assoc. Petroleum Geologists Bull., v. 16, no. 4, p. 417—421. Curran, J. F., 1943, Eocene stratigraphy of the Chico Mar- tinez Creek area, Kern County, California: Am. Assoc. Petroleum Geologists Bull., v. 27, no. 10, p. 1361—1386. REFERENCES CITED 43 Curtis, G. H., Evernden, J. F., and Lipson, J. I., 1958, Age determination of some granitic rocks in California by the potassium-argon method: California Div. Mines Spec. Rept. 54, 16 p. Cushman, J. A., and Goudkofi', P. P., 1938, New species of Pulvinulinella from the California Miocene: Cushman Lab. Foram. Research, Contr. v. 14, pt. 1, pl. 1. Cushman, J. A., and Siegfus, S. S., 1942, Foraminifera from the Kreyenhagen Shale of California: San Diego Soc. Nat. History Trans., v. 9, no. 34, p. 385—426, pls. 14—19. Dibblee, T. W., J r., 1962, Displacements on the San Andreas rift zone and related structures in Carrizo Plain and vicinity, in Guidebook to the geology of Carrizo Plain and San Andreas fault, San Joaquin Geol. Soc. and Pacific SecsfiAm. Assoc. Petroleum Geologists and Soc. Econ. Paleontologists and Mineralogists: p. 5—12, pl. 1. 1968, Geologic map of Temblor Range, San Luis Obispo and Kern Counties, California, in Guidebook to geology and oil fields of west side southern San Joaquin Valley, Am. Assoc. Petroleum Geologists and Soc. Econ. Paleontologists and Mineralogists, Pacific Secs., Ann. Field Trip, 1968: In pocket. 1973a, Geologic map of the Shandon and Orchard Peak quadrangles, California, showing Mesozoic and Cenozoic rock units juxtaposed along the San Andreas fault: U.S. Geol. Survey Misc. Geol. Inv. Map I—788 [in press]. 1973b, Regional geologic map of San Andreas and related faults in Carrizo Plain, Temblor, Caliente, and La Panza Ranges and vicinity, California: U.S. Geol. Survey Misc. Geol. Inv. Map I—757 [in press]. Dickinson, W. R., 1963, Tertiary stratigraphic sequence of the Hancock Ranch area, Monterey and Kings Counties, California, in Guidebook to the geology of Salinas Val- ley and the San Andreas fault, Am. Assoc. Petroleum Geologists and Soc. Econ. Paleontologists and Mineralo- gists, Pacific Secs., Ann. Field Trip, 1963: p. 47—53. 1966a, Structural relationships of San Andreas fault system, Cholame Valley and Castle Mountain Range, California: Geol. Soc. America Bull., v. 77, no. 7, p. 707—726. 1966b, Table Mountain serpentine extrusion in Cali- fornia Coast Ranges: Geol. Soc. America Bull., v. 77, no. 5, p. 451—472. Diller, J. S., and Stanton, T. W., 1894, The Shasta-Chico series: Geol. Soc. America Bull., v. 5, p. 435—464. Durham, D. L., 1963, Geology of the Reliz Canyon, Thomp- son Canyon, and San Lucas quadrangles, Monterey County, California: U.S. Geol. Survey Bull. 1141—Q, p. Q1—Q41. 1964, Geology of the Cosio Knob and Espinosa Canyon quadrangles, Monterey County, California: U.S. Geol. Survey Bull. 116l—H, p. H1—H29. 1966, Geology of the Hames Valley, Wunpost and Valleton quadrangles, Monterey County, California: U.S. Geol. Survey Bull. 1221—B, p. Bl—B53. Durham, D. L., and Addicott, W. 0., 1964, Upper Miocene and Pliocene marine stratigraphy in southern Salinas Valley, California: U.S. Geol. Survey Bull. 1194—E, p. E1—E7 [1965]. 1965, Pancho Rico Formation, Salinas Valley, Cali- fornia: U.S. Geol. Survey Prof. Paper 524—A, p. A1— A22. Durham, J. W., 1942, Reef corals from the California middle Eocene: California Acad. Sci. Proc., 4th ser., v. 23, no. 34, p. 503—510. 1954, The marine Cenozoic of southern California, pt. 4, in chap. 3 of Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, p. 23-32. Durham, J. W., Jahns, R. H., and Savage, D. E., 1954, Marine-nonmarine relationships in the Cenozoic section of California, pt. 7, in chap. 3 of Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, p. 59—71. Eaton, J. E., 1939, Geology and oil possibilities of Caliente Range, Cuyama Valley and Carrizo Plain, California: California Jour. Mines and Geol., v. 35, no. 3, p. 255— 274. Eaton, J. E., Grant, U. S., and Allen, H. B., 1941, Miocene of Caliente Range and environs, California: Am. Assoc. Petroleum Geologists Bull., v. 25, no. 2, p. 193—262. Elliot, W. J., Tripp, Eugene, and Karp, S. E., 1968, Road guides, in Guidebook to geology and oil fields of west side southern San Joaquin Valley, Am. Assoc. Petroleum Geologists, Soc. Econ. Geophysicists, and Soc. Econ. Paleontologists and Mineralogists, Pacific Secs., Ann. Field Trip, 1968: p. 102—142. English, W. A., 1916, Geology and oil prospects of Cuyama Valley, California: U.S. Geol. Survey Bull. 621—M, p. 191—214. 1918, Geology and oil prospects of the Salinas Val- ley—Parkfield area, California: U.S. Geol. Survey Bull. 691—H, p. 219—250. 1921, Geology and petroleum resources of north- western Kern County, California: U.S. Geol. Survey Bull. 721, 48 p. Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T., 1964, Potassium-argon dates and Cenozoic mamma- lian chronology of North America: Am. Jour. Sci., v. 262, no. 2, p. 145—198. Fairbanks, H. W., 1898, Geology of a portion of the south- ern Coast Ranges: Jour. Geology, v. 6, no. 6, p. 551—576. 1904, Description of the San Luis quadrangle [Cali- fornia]: U.S. Geol. Survey Geol. Atlas, Folio 101, 14 p. Fletcher, G. L., 1962, The Recruit Pass area of the Temblor Range, San Luis Obispo and Kern Counties, California, in Guidebook to the geology of Carrizo Plain and San Andreas fault, San Joaquin Geol. Soc. and Pacific Secs. Am. Assoc. Petroleum Geologists and Soc. Econ. Paleon- tologists and Mineralogists: p. 16-20. Foss, C. D., and Blaisdell, Robert, 1968, Stratigraphy of the west side of southern San Joaquin Valley, in Guidebook to geology and oil fields of west side southern San Joaquin Valley, Am. Assoc. Petroleum Geologists, Soc. Econ. Geophysicists, and Soc. Econ. Paleontologists and Mineralogists, Pacific Secs.,Ann. Field Trip, 1968: p. 33—43. Gabb, W. M., 1869, Cretaceous and Tertiary fossils: Cali- fornia Geol. Survey, Paleontology, v. 2, 299 p. 36 pls. Galehouse, J. S., 1967, Provenance and paleocurrents of the Paso Robles Formation, California: Geol. Soc. America Bull., v. 78, no. 8, p. 951—978. Gester, C. G., and Galloway, John, 1933, Geology of Kettle- man Hills oil field, California: Am. Assoc. Petroleum Geologists Bull., v. 17, no. 10, p. 1161—1193. 44 STRATIGRAPHY, SOUTHERN COAST RANGES NEAR SAN ANDREAS FAULT, CALIFORNIA Goudkofi’, P. P., 1934, Subsurface stratigraphy of Kettles man Hills oil fields: Am. Assoc. Petroleum Geologists Bull., v. 18, no. 4, p. 435—475. 1943, Correlation of oil field formations on the west side of San Joaquin Valley [California]: California Div. Mines Bull. 118, p. 247—252. 1945, Stratigraphic relations of upper Cretaceous in Great Valley, California: Am. Assoc. Petroleum Geol- ogists Bull., v. 29, no. 7, p. 9564007. Hamlin, Homer, 1904, Water resources of the Salinas Val- ley, California: U.S. Geol. Survey Water-Supply and Irrigation Paper 89, 91 p. Hay, E. A., 1963, Age and relationships of the Gold Hill pluton, Cholame Valley, California, in Guidebook to the geology of Salinas Valley and San Andreas fault, Am. Assoc. Petroleum Geologists and Soc. Econ. Paleontolo- gists, Pacific Secs.,Ann. Field Trip, 1963: p. 113-115. Heikkila, H. H., and MacLeod, G. M., 1951, Geology of Bitter- water Creek area, Kern County, California: California Div. Mines Spec. Rept. 6, 21 p. vHenny, Gerard, 1930, McLure shale of the Coalinga region, Fresno and Kings Counties, California: Am. Assoc. Petroleum Geologists Bull., v. 14, no. 4, p. 403~410. Hibbard, C. W., Ray, C. E., Savage, D. E., Taylor, D. W., and Guilday, J. E., 1965, Quaternary mammals of North America, in The Quaternary of the United States: Princeton, N. J., Princeton Univ. Press, p. 509—525. Hill, M. L., and Dibblee, T. W., Jr., 1953, San Andreas, Big Pine, and Garlock faults, California—a study of the character, history, and tectonic significance of their dis- placements: Geol. Soc. America Bull., v. 64, no. 4, p. 443—458. Hill, M. L., Carlson, S. A., and Dibblee, T. W., Jr., 1958, Stratigraphy of Cuyama Valley—Caliente Range area, California: Am. Assoc. Petroleum Geologists Bull., v. 42, no. 12, p. 2973—3000. Huffman, O. F., 1970, Miocene and post-Miocene offset on the San Andreas fault in central California [abs.] : Geol. Soc. America Abs. with Programs, v. 2, no. 2, p. 104—105. James, G. T, 1963, Paleontology and nonmarine stratigraphy of the Cuyama Valley badlands, California; Pt. 1, Geology, faunal interpretations, and systematic descrip- tions of Chiropte-ra, Insectivora, and Rodentia: Cali- fornia Univ. Pubs. Geol. Sci., v. 45, 154 p. Jennings, C. W., 1958, Geologic map of California, Olaf P. Jenkins edition, San Luis Obispo Sheet: California Div. Mines Map Sheet. Johnson, H. R., 1909, Geology of the McKittrick-Sunset Dis- trict, California [abs.]: Science, v. 30, p. 63—64. Kleinpell, R. M., 1938, Miocene stratigraphy of California: Tulsa, Okla., Am. Assoc. Petroleum Geologists, 450 p. Lawson, A. C., 1914, Description of the San Francisco dis- trict Tamalpais, San Francisco, Concord, San Mateo and Hayward quadrangles [California]: U.S. Geol. Sur- vey Geol. Atlas, Folio 193. Loel, Wayne, and Corey, W. H., 1932, The Vanqueros Forma- tion, lower Miocene of California; Pt. 1, Paleontology: California Univ. Pubs., Dept. Geol. Bull. v. 22, no. 3, p. 31—410. Louderback, G. D., 1913, The Monterey series in California: California Univ. Pubs., Dept. Geol. Bull., V. 7, p. 177— 214. McMasters, J. H., 1947, Cymric oil field, Kern County, Cali- fornia, in Field trip guidebook, Am. Assoc. Petroleum Geologists, Soc. Econ. Geophysicists, and Soc. Econ. Paleontologists and Mineralogists, Pacific Secs., Ann. Field Trip, 1947 : p. 100—105. Mallory, V. S., 1959, Lower Tertiary biostratigraphy of the California Coast Ranges: Tulsa, Okla., Am. Assoc. Petroleum Geologists, 416 p. Marsh, 0. T., 1960, Geology of the Orchard Peak area, Cali- fornia: California Div. Mines Spec. Rept. 62, 42 p. Noble, E. B., 1940, Rio Bravo oil field, Kern County, Cali- fornia: Am. Assoc. Petroleum Geologists Bull., v. 24, no. 7, p. 1330-1333. Nomland, J. 0., 1916, Fauna from the lower Pliocene at Jacalitos Creek and Waltham Canyon, Fresno County, California: California Univ. Pubs., Dept. Geology Bull., v. 9, p. 199—214. 1917, The Etchegoin Pliocene of middle California: California Univ. Pubs., Dept. Geology Bull., v. 10, no. 14, p. 201—202. Pack, R. W., 1920, The Sunset-Midway oil field, California; Part 1, Geology and oil resources: U.S. Geol. Survey Prof. Paper 116, 179 p. Page, B. M., 1970, Sur-Nacimiento fault zone of California: Continental margin tectonics: Geol. Soc. America Bull., v. 81, p. 667—690. Reed, R. D., 1933, Geology of California: Tulsa, Okla., Am. Assoc. Petroleum Geologists, 355 p. Repenning, C. A., and Vedder, J. G., 1961, Continental verte- brates and their stratigraphic correlation with marine mollusks, eastern Caliente Range, California, in Short papers in the geologic and hydrologic sciences, 1961: U.S. Geol. Survey Prof. Paper 424—0, p. 0235—C239. Rose, R. L., and Colburn, I. P., 1963, Geology of the east- central part of the Priest Valley quadrangle, California, in Guidebook to geology of Salinas Valley and San Andreas fault, Am. Assoc. Petroleum Geologists and Soc. Econ. Paleontologists, Pacific Secs., Ann. Field Trip, 1963: p. 38—45. San Joaquin Geological Society, 1959, Guidebook, field trip, Chico Martinez Creek area, California, May 9, 1959: 15 p., geol. map. Savage, D. E., 1957, Age of the Caliente Formation, Caliente Range, California [abs.]: Geol. Soc. America Bull., v. 68, no. 12, pt. 2, p. 1845. Savage, D. E., Downs, Theodore, and Poe, 0. J., 1954, Cenozoic land life of southern California, pt. 6 in chap. 3 of Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, p. 43—58. Schultz, J. R., 1938, A late Quaternary mammal fauna from the tar seeps of McKittrick, California: Carnegie Inst. Washington Pub. 487, p. 113—215. Siegfus, S. S., 1939, Stratigraphic features of Reef Ridge Shale in southern California: Am. Assoc. Petroleum Geologists Bull, v. 3, no. 1, p. 24—44. Simonson, R. R., and Krueger, M. L., 1942, Crocker Flat Landslide area, Temblor Range, California: Am. Assoc. Petroleum Geologists Bull., v. 26, no. 10, p. 1608—1631. Smith, H. P., 1956, Foraminifera from the Wagonwheel Formation, Devils Den district, California: California Univ. Pubs. Geol. Sci., v. 32, p. 65—126. Stewart, Ralph, 1946, Geology of Reef Ridge, Coalinga dis- trict, California: U.S. Geol. Survey Prof. Paper 205—0, p. 81—115 [1947]. REFERENCES CITED 45 Taliaferro, N. L., 1943, Geologic history and structure of the central Coast Ranges of California: California Div. Mines Bull. 118, p. 119—162. Thorup, R. R, 1943, Type locality of the Vaqueros Forma- tion [California]: California Div. Mines Bull. 118, p. 463—466. Turner, D. L., 1970, Potassium-argon dating of Pacific Coast Miocene foraminiferal stages: Geol. Soc. America Spec. Paper 124, p. 91—129. Van Couvering, Martin, and Allen, H. B., 1943, Devils Den oil field [California]: California Div. Mines Bull. 118, p. 496—501. Vedder, J. G., 1970, Geologic map of the Wells Ranch and Elkhorn Hills quadrangles, San Luis Obispo and Kern Counties, California showing juxtaposed Cenozoic rocks along the San Andreas fault: U.S. Geol. Survey Misc. Geol. Inv. Map I—585. Vedder, J. G., and Brown, R. D., 1968, Structural and strati- graphic relations along the Nacimiento fault in the southern Santa Lucia Range and San Rafael Moun- tains, California, in Dickinson, W. R. and Grantz, Arthur, eds., Proceedings of conference on geologic prob- lems of the San Andreas fault system: Stanford Univ. Pubs. Geol. Sci., v. 11, p. 243—258. Vedder, J. G., and Repenning, C. A., 1965, Geologic map of the southeastern Caliente Range, San Luis Obispo County, California: U.S. Geol. Survey Oil and Gas Inv. Map 0M—217. Wagner, H. C., Bartow, J. A., Pierce, R. H., and Dibblee, T W., Jr., 1973, Geologic sections across the San Andreas fault in the Carrizo Plain and the Temblor, Caliente, and La Panza Ranges and vicinity, California: U.S. Geol. Survey Misc. Geol. Inv. Map [in press]. Wahrhaftig, Clyde, and Birman, J. H., 1965, The Quaternary of the Pacific Mountain system in California, in Wright, H. E., and Frey, D. G., eds., The Quaternary of the United States—A review volume for the 7th Congress of International Association for Quaternary research: Princeton, N. J., Princeton Univ. Press, p. 299—340. Watts, W. L., 1897, Oil and gas yielding formations of Los Angeles, Ventura and Santa Barbara Counties, Cali- fornia: California State Min. Bur. Bull. 11,94 p. Weaver, C. E. ., chm., and others, 1944, Correlation of the marine Cenozoic formations of western North America [Chart 11]: Geol. Soc. America Bull., v. 55, no. 5, p. 569-598. White, R. T., 1938, Eocene Lodo formation and Cerros mem- ber of California [abs.:] Geol. Soc. America Proc. for 1937, p. 256—257. Wiedey, L. W., 1928, Notes on the Vaqueros and Temblor Formations of the California Miocene with descriptions of new species: San Diego Soc. Nat. History Trans., v. 5, no. 10, p. 95—182. Williams, R. N., 1936, Recent developments in the North Belridge oil field [California]: California Oil Fields—- Summ. Operations, v. 21, no 4, p. 5—16. Wilmarth, M. G., 1938, Lexicon of geologic names of the United States (including Alaska): U. S. Geol. Survey Bull.'896, 2396 p. Wood, H. E., chm., and others, 1941, Nomenclature and cor- relation of the North American Continental Tertiary: Geol. Soc. America Bull., v. 52, no. 1, p. 1—48. Woodring, W. P., Bramlette, M. N., and Kleinpell, R. M, 1936, Miocene stratigraphy and paleontology of Palos Verdes Hills, California: Am. Assoc. Petroleum Geolo- gists Bull., v. 20, no. 2, p. 125—159. Woodring, W. P., Roundy, P. V. and Farnsworth, H. R., . 1932, Geology and oil resources of the Elk Hills, Cali- fornia (including Naval Petroleum Reserve No.1): U.S. Geol. Survey Bull. 835, 82 p. Woodring, W. P., Stewart, R. B., and Richards R. W., 1940, Geology of the Kettleman Hills oil field, California, stra- tigraphy, paleontology, and structure: U.S. Geol. Sur- vey Prof. Paper 195, 170 p. Young, Umberto, 1943, Republic area of the Midway-Sunset oil field [California]: California Div. Mines Bull. 118, p. 522—525. U. S. GOVERNMENT PRmTENG OFFICE : 1.978 O - 495-417 / 7 EAY E} PT“ -sf‘.',. xix fr “My ‘ may? E 75’ ,7 A? Geology of the Oxidized Uranium Ore Deposits of the Tordilla HiH—Deweesville Area, Karnes County, Texas; A Study of a District Before Mining GEOLOGICAL SURVEY PROFESSIONAL PAPER 765 Prepared on ibehalf 0f the U.S. Atomic Energy Commission "axf -. Pifihzzfi-H ‘ ’ ‘-'i',‘-IC:‘~.‘:"Q qr; DUiJ‘Q‘i‘UjiLFiEQ LJL MAM ‘973 i ~V UHWFPSHY _r_-.;: CJHUQIH-lln mm 1973 9‘ 1' V3“ \ SCIENCE My 52.13)? Geology of the Oxidized Uranium Ore Deposits of the‘Tordilla Hill-Deweesville Area, Karnes County, Texas; A Study of a District Before Mining By G. M. BUNKER and J. A. MACKALLOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 765 Prepared on behalf of the US Atomic Energy Commission A description of the lithologic and structural relations of shallow uranium deposits in nonindurated sediments UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600375 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 Stock No. 2401-00292 CONTENTS Page Page Abstract __________________________________________ 1 Uranium deposits—Continued Introduction _______________________________________ 1 Subsurface radioactivity studies ________ . ______.___ 20 History of investigations ________________________ 1 Comparison between chemlcal and radiometric Physiography and climate _______________________ 4 analyses of drill-hole samples ______ T ______ 20 Methods of investigation ________________________ 4 Eff“: 3f radon on gamma-ray log inter- 21 pre a ion ________________________________ Acknowledgments ______________________________ 5 Relations between surface and subsurface radio- General stratigraphy and environment _______________ 5 activity ______________________________________ 22 Eocene —————————————— —— 5 Size and shape of radioactive layers _____________ 22 Whitsett Formation ———————————————————————— 8 Individual deposits _____________________________ 24 Dilworth Sandstone Member ____________ 8 Hackney (3050) deposit ____________________ 24 Conquista Clay Member ———————————————— 9 Bargmann-Hackney (Superior-Rare Metals) Deweesville Sandstone Member __________ 9 deposit ___________________________________ 25 Dubose Member ———————————————————————— 15 Nuhn (Climax or Korzekwa-Lyssy-Gembler) Tordilla Sandstone Member _____________ 15 deposit __________________________________ 25 Quaternary ———————————————————————————————————— 16 Luckett (Continental or Lyssy-Neistroy) de- Structure ___________________________________________ 16 ms“ ———————————————————————————————————— 28 , , , , Ore controls ________________________________________ 29 Sillc1fication ““““““““““““““““““““““ 17 Origin of the uranium deposits _____________________ 30 Uranium deposits __________________________________ 18 Transportation and deposition of uranium _______ 31 Mineralogy ____________________________________ 19 Geologic development of the deposits ____________ 33 Production and reserves ________________________ 20 References cited ____________________________________ 35 ILLUSTRATIONS Page PLATE 1. Sections and fence diagram showing lithology and distribution of uranium _______________________ In pocket FIGURE 1. Generalized geologic map of the Tordilla Hill-Deweesville area ______________________________________ 2 2. Map of the Karnes County uranium district showing general geology of the Whitsett Formation _______ 6 3. Structure-contour and lithofacies map and sections of the Deweesville Sandstone Member, Lyssy and Korzekwa properties ____________________________________________________________________________ 12 4. Longitudinal diagrammatic sections showing development of clay-filled-channel facies of the Dewees- ville Sandstone Member ________________________________________________________________________ 14 5. Geologic sections along walls of trench in the Hackney deposit _________________________________________ 18 6. Photograph showing principal ore-bearing zone of the Tordilla Hill-Deweesville area ______________________ 19 7. Graph showing relation between chemical and radiometric analyses for uranium content of drill-hole samples _______________________________________________________________________________________ 21 8. Gamma-ray logs of hole B—39 showing radon contamination and the effects of time and of air flushing ____ 22 9. Map showing ore deposits and generalized surface radioactivity in the Tordilla Hill-Deweesville area ____ 23 10. Photographs showing detailed lithology of channel sample localities from a trench at the Nuhn deposit ____ 26 11. Diagrammatic section, north wall of pit on the Windmill ore body, Nuhn deposit _____________________ 28 12. Geologic section of the Whitsett Formation across the Nuhn deposit ____________________________________ 29 13. Histogram showing relation between uranium grade and rock type ____________________________________ 30 14. Graph showing depth of burial of Deweesville Sandstone Member from Dubose time to present ________ 33 15. Diagrammatic section at the end of Catahoula time, showing movement of ground water _______________ 34 III GEOLOGY OF THE OXIDIZED URANIUM ORE DEPOSITS OF THE TORDILLA HILL-DEWEESVILLE AREA, KARNES COUNTY, TEXAS; A STUDY OF A DISTRICT BEFORE MINING By C. M. BUNKER and J. A. MACKALLOR ABSTRACT Shallow, oxidized uranium ore deposits in the Tordilla Hill- Deweesville area lie in a gently dipping, warped block be- tween the F'ashing and Falls City faults. These faults trend northeast, parallel to the regional strike, and may have acted as barriers to the normal downdip movement of ground water. Upward seepage of sulfurous gas through the fault systems may have provided the precipitant for uranium contained in ground water in the areas where fluid movement was hin- dered. The Deweesville Sandstone Member of the Whitsett Forma- tion (upper Eocene) is the most important host rock of the shallow, oxidized uranium deposits known at the completion of fieldwork, but not yet mined. The Deweesville commonly consists of tuffaceous sand, which grades into silt at the base; however, in the Tordilla Hill-Deweesville area in western Karnes County, its lithologic sequence changes sig- nificantly. Most of the important ore bodies are in, or updip from and adjacent to, a clay-filled channel cut deeply into or through the Deweesville. The channel roughly parallels the north to northeast strike of the Deweesville, is from 210 to 400 feet wide, and is about 25 feet deep. Adjacent and par- allel to the mudstone channel, the Deweesville consists of a sequence of alternating sandstones, siltstones, and mudstones (mixtures of clay and silt-sized particles); in contrast, sand dominates elsewhere. The most important uranium deposits are in the lower part of the Deweesville in a sequence of varied lithology, rather than in the more permeable sandy facies; the uranium in the underlying Conquista Clay Mem- ber of the Whitsett Formation is generally of lower grade. The deposits are within or just below the zone of oxidation. Many of the ore deposits are manifested on the surface by radioactivity anomalies updip from the deposits. However, the presence of a surface anomaly may not everywhere indi- cate an ore deposit. INTRODUCTION HISTORY OF INVESTIGATIONS In the fall of 1954, uranium was discovered about 2 miles northeast of Tordilla Hill, western Karnes County, Tex. (fig. 1), by G. H. Strodtman, of Jafl’e- Martin and Associates of San Antonio, while he was making an airborne radioactivity survey for oil structures. At about the same time, uranium miner- als were found at the foot of the northernmost point of Tordilla Hill (fig. 1, Hackney deposit) by Carroll Ewers, of San Antonio, who was prospecting with a hand-portable counter. These discoveries of uran- ium, the first in the Gulf Coastal Plain province, led to intensive prospecting, leasing, and exploratory drilling, which soon established the existence of com— mercial quantities of uranium ore in the area. Most prospecting consisted of locating surface anomalies with radiation-detection equipment; this was gener- ally followed by trenching or drilling. The intense search centered around, but was not confined to, the Tordilla Hill-Deweesville area. More than a dozen uranium occurrences were fOund in Gonzales, Karnes, and Atascosa Counties (Steinhauser and Beroni, 1955; Eargle and Snider, 1957, fig. 1). Be- fore 1970, the largest known deposits were in the Tordilla Hill-Deweesville area. From 1955 to 1957, the most extensive exploration and drilling program within the Tordilla Hill-Dew- eesville area was conducted by the Climax Molybde- num Co. (operating under the local name of the San Antonio Mining 00.), but the Continental Oil Co., the Texas Co., the Superior Oil Co., the Newmont Mining Co., and others were also active. The Nuhn deposit, on the Korzekwa, Lyssy, and Gembler tracts, and the Luckett dep0sit northeast of Dewees- ville, on the Lyssy and Neistroy tracts, as well as some smaller uranium deposits, were discovered. According to deVergie (1958, p. 23) more than 500,000 feet of exploration drilling was completed in 1 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA w BARGMANN-HACKNEY / DEPOSIT / 0 1000 2000 3000 4000 5000 FEET l . . . . l | | 1 4' FIGURE 1,—Genera1ized geologic map showing exploratory drill-hole locations, Tordilla Hill-Dewees- ville area, Karnes County, Tex. Modified from MacKallor, Moxham, Tolozko, and Popenoe (1962). Holocene Eocene A INTRODUCTION EXPLANATION >. D: ‘z‘ 03 m Lu '3: Alluvium 3 O { \ th Q : Twc g >- 0 Twcf E §1 E :43 l Twc LIJ .q l- dei i Whitsett Formation l th. Tordilla Sandstone Member deu, Dubose Member de, Deweesm'lle Sandstone Member Twc, Conquista Clay Member Twcf, fossiliferous sandstone dei. Dilworth Sandstone Member Contact .7 --------- .7 2 -------- ? Anticline Syncline Folds, approximately located Dotted where concealed; queried where doubtful Uranium deposit )_4 X Trench Prospect pit O U.S. Geological Survey auger drill hole .K—2 U.S. Geological Survey core hole .‘ LYSSY KORZEKWA Approximate location of property line and names of land owners FIGURE 1.—Continued 4 OXIDIZED URANIUM ORE DEPOSITS, Karnes County between the fall of 1954 and the summer of 1956. Preliminary geologic investigations by the US. Geological Survey were begun in the Tordilla Hill- Deweesville area in the spring of 1955 (Eargle, 1955; Finch, 1955; Fix, 1955, 1956; Eargle and Sni- der, 1957). Geophysical studies were started in No- vember 1955 with an airborne radioactivity survey of the area (Moxham and Eargle, 1961). These were followed by more comprehensive geological and geo- physical studies of this area and by a much broader study in 1956 to 1959 to examine the relation be- tween uranium deposits in a sedimentary environ- ment and regional and local radioactivity, stratigra- phy, lithology, and geologic structure (Moxham, Eargle, and MacKallor, 1957 ; Moxham, MacKallor, and Tolozko, 1957; MacKallor and others, 1958; Manger, 1958; Eargle, 1958; Moxham and others, 1958; Weeks and others, 1958; MacKallor and Bunker, 1958; Eargle, 1959a, b; Moxham and Ear- gle, 1961; Eargle and Weeks, 1961a, b; Brown, Ear- gle, and Moxham, 1961a, b; Eargle, Trumbull, and Moxham, 1961a, b, c; Trumbull, Eargle, and Mox- ham, 1961; Weeks and Eargle, 1963). One of the objectives of this work was to study unmined depos- its and to survey a district before mining disturbed its radioactivity pattern and intensity and before the geology was revealed by mining, so that compari- sons with still unmined undisturbed areas could be made. The studies described in this report were made from 1956 to 1958. Surface and subsurface geology and subsurface radioactivity were studied to determine how the geologic setting of the mineral deposits is related to ore depositional control and to mechanisms of ore origin. The area studied here ex- tends from the Hackney deposit at Tordilla Hill to the Luckett deposit northeast of the old Village of Deweesville. The area is about 5 miles long and is #2474 mile Wide. PHYSIOGRAPHY AND CLIMATE The uranium deposits in Karnes County are in the Texas coastal plain between San Antonio and Corpus Christi. The topography ranges from gently rolling hills in the northern part of the coastal plain to very flat plains near the coast. In the area of this report, the lowest altitude, 350 feet above sea level, is on Tordilla Creek. The highest point, 520 feet above sea level, is on top of Tordilla Hill, a cuesta that has 120 feet of relief on the northwest side and is the most prominent landmark in the area. A series of low, rounded hills, northeast trending near Dew- eesville, separates the headwaters of Scared Dog TORDILLA HILL-DEWEESVILLE AREA Creek and Tordilla Creek. Scared Dog Creek drains northeastward into the San Antonio River, and Tor- dilla Creek drains southwestward into the Nueces River by the way of Borrego Creek and the Atascosa River. The mean annual rainfall in Karnes County is about 30 inches, but yearly variations are large. Much of the land is used for grazing, but cotton and other crops are cultivated. Most of the cultivated land depends on natural rainfall, but some is irri- gated. The county is between two belts of markedly different climates, subarid to the southwest and sub- humid to the northeast. The climate of the county is characterized by long, hot summers and short, mild winters. To the southwest, caliche is forming at the surface, and vegetation is sparser than that to the northeast and is of a different type. METHODS OF INVESTIGATION The topography was mapped to provide an accu- rate base for surface and subsurface radioactivity studies of the uranium deposits, the enclosing bed- rock, and the overlying soil. The area was mapped by planetable method from September 1956 to March 1958 by J. A. MacKallor, assisted by E. S. Santos, P. P. Popenoe, and others. A base line was established from two locations on the right—of-way of Farm Road 791, which had just previously been surveyed by engineers of the Karnes County office, Texas Highway Commission. Measurements of the attitudes of rock beds were usually determined by the three-point method, because the beds dipped gently and a few beds of hard rock were exposed. Attitudes thus determined are accurate within 5 feet per 1,000 feet and for strike within 20° to 30°. About 2,000 survey points were established within the area of approximately 5 square miles. Exploratory drill holes provided (1) subsurface samples for lithologic determinations and for chemi— cal and radiometric analyses and (2) access to sub- surface strata for gamma—ray logging. A power auger was used to drill 130 drill holes about 4 inches in diameter and as much as 70 feet deep. The cut- tings obtained with the auger were sampled at 1- to 5-foot intervals, depending on the complexity of the strata. Cuttings or sample descriptions from 200 holes drilled by the San Antonio Mining Co. were made available to and were used by the authors. Five holes (those with a “K” prefix) were drilled to depths of as much as 300 feet with a core bit and oil-base drilling fluid to obtain maximum recovery of unaltered and undisturbed cores that represented the natural state of the beds from which they were GENERAL STRATIGRAPHY AND ENVIRONMENT 5 obtained and of the fluids they contained. These samples were sealed in plastic tubes to preserve their original physical and chemical properties until analyses could be completed. Physical properties of the cores and electric logs of the drill holes have been reported by Manger and Eargle (1967). All the samples were classified lithologically by visual exam— ination. Gamma-ray logs were made in all available drill holes to determine the depth, thickness, areal limits, and grade (percent equivalent uranium oxide, eU303) of radioactive rock. These data were used to study the relation between subsurface and surface radioactivity, lithology, and ore deposits. The log- ging system was calibrated in simulated uranium- ore bodies before this investigation and was stand- ardized often to maintain the original calibration. Extensive laboratory and field studies showed the following accuracies of the interpreted data: thick- ness is within 0.1 foot for layers thicker than 0.8 foot, depth is within 0.5 percent, and values for grade of ore are within 20 percent. The gamma-ray logging equipment, calibration procedures, and data-interpretation methods are similar to those de- scribed by Bell, Rhoden, McDonald, and Bunker (1961). ACKNOWLEDGMENTS The technical assistance and suggestions of our many coworkers, especially R. M. M0xham, D. H. Eargle, and A. M. D. Weeks are gratefully acknowl- edged. Elmer S. Santos, Peter P. Popenoe, and Don- ald Peterson assisted with the geologic mapping. D. R. Cunningham aided with the drilling, sampling, and gamma-ray logging. Paul C. deVergie, of the US Atomic Energy Commission, furnished infor- mation on the Luckett deposit and other uranium deposits outside the report area. D. H. Eargle fur- nished information on mining operations. Especially appreciated was the pleasant and helpful coopera- tion of the landowners and mining-lease holders who permitted mapping, drilling, and sampling on their properties and provided drill-hole location maps and samples from their exploration drilling programs. Chemical and radiometric analyses of uranium con- tent of samples were made by J. W. Budinsky and B. A. McCall, of the US. Geological Survey. This work was done on behalf of the Division of Raw Materials, US. Atomic Energy Commission. GENERAL STRATIGRAPHY AND ENVIRONMENT The regional stratigraphy of the southeastern Texas coastal plain is described by Eargle (1959a). The elastic sedimentary rocks (sandstone, siltstone, and clay) which underlie the Tordilla Hill-Dewees— Ville area dip gently southeast and are a part of the thick homoclinal sequence of the Gulf Coastal Plain province. Time-equivalent rock units generally thicken and grade from north to south, changing from continental, through nearshore, to an offshore facies downdip toward the present Gulf of Mexico. The formations exposed within the area of this report, with the exception of the alluvium, belong to the Jackson Group of Eocene age. Excluding the Tordilla Sandstone Member, which in most places is a moderately to highly silicified sandstone, the Whit- sett Formation exposed in the area of this report (fig. 2) consists chiefly of sand, silt, and clay. The Dubose Member contains some beds of poorly indur- ated, friable sandstone and siltstone. Locally, some of the sands in the Deweesville Sandstone Member have been silicified into a well-indurated sandstone (MacKallor and others, 1962). Within the area many holes several tens of feet deep were drilled with a vehicle-mounted soil auger through sand, silt, and clay without piercing lithified rock such as sand— stone or siltstone. Southeast and downdip from the uranium deposits several deep core holes (the “K” holes of fig. 1) did at depth penetrate beds of poorly to well-indurated sandstone. Most of the Dubose and Deweesville interval, as shown by the core holes, consists of friable, poorly indurated sandstone and siltstone and of sand, silt, and clay (Manger and Eargle, 1967). The Catahoula Tuff of Miocene age overlies the Jackson; it is exposed a short distance southeast. Eargle (1959b, p. 2626; 1972) has divided the Jack- son Group of south-central Texas from bottom to top into the Cadell- Formation, Wellborn Sandstone, Manning Clay, and Whitsett Formation and has sub- divided the Whitsett Formation into the Dilworth Sandstone, Conquista Clay, Deweesville Sandstone, Dubose, Calliham Sandstone and its equivalent, the Tordilla Sandstone, and Fashing Clay Members. EOCEN E Field evidence is in agreement with the conclu- sions of Shepard and Rusnak (1957, p. 12) that the intercalated lenses and beds of tuffaceous sand— stones, siltstones, and clays of the Jackson Group of Eocene age in the area were deposited under shal- low-water nearshore marine or brackish-water con— ditions similar to those in present-day bays and la- goons between San Antonio Bay and Corpus Christi in the Gulf of Mexico. Evidence that supports the 29° 00' 28° 45’ OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA MC MULLEN COUNTY \ 98°15’ 98°00, | , | 4 _ Falls City ‘Q/gxon field \ o‘%® Falls City \ \ 0 0c 4, ,7»? ‘\ \ > x y \ / 4:3, ‘ \ Q ‘ .739? Q P‘ w Area of $6 4 TWdi map\ (9 00 é// O\ {1, O 0‘ O 50 (P O V9 0 V000 gFV/ - 0843’ 0 Two ’1» J‘ dei 0 /- a .\o 3* \ De e Vllle \ / , \ I \ / \ I \< dei / \ "7% § Tordilza (bur? C) Creek Approximate s outline of £9 figure 1 /// ‘0‘ //// // ‘3 C 3 O Campbellton (1:7); _ _ —_'| 4 6 MILES FIGURE 2.—Map of the Karnes County uranium district and vicinity, showing the general geology of the Whitsett For- mation of Eocene age. Modified from Eargle (1972). GENERAL STRATIGRAPHY AND ENVIRONMENT r—"—_l COUNTIES A Atascosa G Gonzales K Karnes L0 Live Oak Mc M McMullen W Wilson o 200 400 MILES \_____|—___| EXPLANATION de Twc dei Whitsett Formation wa, Fashing Clay Member Twca, Calliham Sandstone Member th, Tordilla Sandstone Member deu, Dubose Member de, Deweesm’lle Sandstone Member Twc, Conquista Clay Member dei, Dilworth Sandstone Member Contact U Fault Dashed where approximately located or inferred. U, upthrown side; D, down- thrown side Q 0... Ore body Ore roll FIGURE 2,—Continued 8 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA conclusions reached concerning the depositional en- vironment in this area includes personal observa- tions and reports by others that (1) macrofossils (mostly gastropods and pelecypods) were found in Karnes and Atascosa Counties (F. S. MacNeil, writ- ten commun., 1958), (2) shallow-water Foramini_ fera were found in the immediate vicinity of the study area (Ellisor, 1933), (3) although Textulam’a hockleyensis was found in the Conquista Clay Mem- ber near the deposits (P. S. Morey, in Eargle and Snider, 1957), microfossils generally were scarce in the study area, (4) glauconite was not detected in the rocks near the uranium deposits, (5) Ophiomor- pha major, a facies fossil that indicates brackish- water conditions, is common in sandstones of the Jackson Group, (6) a bed of oyster shells is found at the top of the Deweesville Member at the Luckett deposit, and (7) silicified wood is found in Several units of the Jackson Group. Eargle (1959a) pre— sented subsurface evidence that an offshore bar formed in Deweesville time about 10 miles downdip from the uranium deposits. The rate of deposition or the length of time that the sediments remained exposed to the marine wa- ters of the bays and lagoons may have been a major factor in the development of the uranium deposits. Shepard (1953) calculated that sediment at the rate of about 3 feet per century, which will form 1.5-1.8 feet of rock, is presently being deposited in Texas bays. Shepard’s calculation is based upon an average depth change during 65 years determined from more than 20,000 observations made in all Texas bays and is corrected for an estimated 1.7 feet of submergence per century. The present rate of sedimentation cannot be ap- plied to the entire marine Tertiary of the Karnes County uranium area, because there have been times of little or no deposition. The rate, however, might be of value if modified and applied with caution to individual members..For example, the average thick- ness of the Deweesville Sandstone Member is about 45 feet in the area of the deposits; Shepard’s mini- mum figure of 1.5 feet of rock per century would indicate that this member was deposited within a period of 3,000 years. The present rate of deposition probably is faster than the rate was in the preceding few centuries because cultivation of land has in- creased runoif and erosion and because dumping of sewage and industrial wastes into the rivers has in- creased their load. During Deweesville time, how- ever, the rate of deposition almost certainly was faster than it was just before the settling of the Texas coastal plain, and probably was faster than the present rate. Volcanic ash was being deposited and provided additional material for an increased rate of accumulation. The presence of unaltered feldspar grains supports the idea of rapid deposition and burial. Therefore, it is estimated that the Dew- eesville Member was deposited between 2,500 and 3,000 years. The following description of the composition, grain size, and shape of the detritals applies in gen- eral to all members of the Whitsett Formation of the Jackson Group exposed in the Deweesville-Tordilla Hill area and is not repeated in the discussion of the individual members. Most of the sand—sized grains are fine to very fine, according to the classification of Wentworth (1922), and angular to subangular. Approximately 50 per- cent of the sand-sized particles are quartz, 25 per- cent are volcanic grains, which are probably of in- termediate or acidic composition, and 25 percent are grains of almost unaltered feldspar, both orthoclase and plagioclase. Under crossed nicols, tiny microlites are visible in the volcanic grains. Glassy shards are locally common. A. M. D. Weeks of the US. Geologi- cal Survey (oral commun., 1962) has identified grains of chert, zircon, biotite, moonstone, pyrite, and clinoptilolite (zeolite) in thin section. A normal suite contains a small amount of rutile, ilmenite, garnet, and other common accessory heavy minerals. Cementing material, where present, consists of opal, chalcedony, or clinoptilolite. Crystals of gypsum, al- though not abundant, have been observed in silty and clayey beds of the various members. Gypsum is much scarcer below the zone of oxidization (as indi— cated by a change of color of the clay) than it is above. According to A. M. D. Weeks (oral commun., 1962), spectrographic analyses show that the clay- sized material is dominantly clinoptilolite and mont- morillonite. WHITSETT FORMATION DILWORTH SANDSTONE MEMBER Only the top of the uppermost bed of the Dilworth Sandstone Member of the Whitsett Formation is ex- posed in the mapped area. The sandstone is gray to yellowish brown and very fine to fine grained; it is composed chiefly of quartz, moderately fresh frag- ments of volcanic rocks and feldspar, and silt-sized particles of tuffaceous material. Outcrops of white to light-gray silicified sandstone were observed north- west of Tordilla Creek on the Bargmann property. GENERAL STRATIGRAPHY AND ENVIRONMENT 9 Vertical, parallel, and nearly straight casts, 1/16—% inch wide and several inches long, that resemble plant roots are common. The upper few feet of the Dilworth, as determined by drill holes, is thin bed— ded and contains beds of maroon, brown, and gray mudstone (a mixture of clay- and silt-sized parti- cles), in addition to sandstone, as at the Carriger property north of Tordilla Hill (fig. 1). CONQUISTA CLAY MEMBER In the mapped area the Conquista Clay Member is 75—90 feet thick. The clay or mudstone is reddish to grayish brown in the zone of oxidation, which ex- tends to a depth of 30—35 feet below the surface, and dark gray to bluish black below the zone of oxida- tion. The depth of the base of the oxidized zone is generally related to the topography (section H—13 to B-24, pl. 1). The clay is tufl’aceous, and the upper part is silty. Locally, the contact with the overlying Deweesville Sandstone Member is transitional. The upper 20 feet of the member contains a few small lenses of sandstone, and throughout most of the area the top is marked by a zone of calcium carbonate concretions as much as 3 feet in diameter. The mem- ber is carbonaceous and locally contains some silici- fied wood. The contact between the oxidized and unoxidized zones is not as apparent in other rock types as it is in the Conquista Clay Member. In sandstone, the color change may not be readily apparent, and the contact instead of being sharply defined may be gra— dational vertically through several feet. In the early exploration of the area, the oxidized (yellow or brown) clay and the unoxidized (medi- um-gray) clay, the “blue” clay of the drillers, were believed to be separate lithologic units. The base of the oxidized zone, however, approximately parallels the present topographic surface, except where over- lying impermeable layers have retarded infiltration of oxidizing surface waters, and therefore the two color zones are now recognized to be one lithologic unit. In most of the holes drilled, the anomalous ra— dioactivity is confined to the oxidized zone and the radiation intensity generally decreases at or below the oxidized-unoxidized contact. For this reason the contact can often be identified on a gamma-ray log. The Conquista Clay Member contains a sandstone unit 25—30 feet below the top. The sandstone has an average thickness of about 10 feet along the outcrop, but drill-hole data indicate that it pinches out down- dip in the southeastern part of the area. The sand- stone is gray to yellowish brown and fine-grained to very fine grained. It is composed mainly of quartz, moderately fresh feldspar, and fragments of vol- canic rocks and is uniformly speckled with limonite. Casts of pelecypod and gastropod shells are common. Concretions of calcium carbonate found locally in the sandstone are similar to those at the top of the member. The sandstone unit contains two persistent silicified beds, each about 4 inches thick, that make excellent marker beds. The other sandstone strata of , the unit are poorly indurated. The lowermost mud- stone lies on the plant-root sandstone bed of the Dilworth and represents a change of environment, probably a slight deepening of the water. The calcium carbonate concretions consist of a dense core and an outside zone of prisms or wedges of aragonite. These prisms are about 2 inches long and half an inch thick, and many are oriented radi- ally, with the long axis pointed toward the center of the concretion. The concretions are slightly flattened along the general plane of bedding. Although expo- sures are poor and bedding is indistinct, the surfaces of the beds immediately below one of the better ex— posed concretions were observed to be slightly concave upward, and some of the beds appeared to be truncated along the sides of the concretion. In many places, even where bedrock is covered by as much as 2 feet of soil, the location of a carbonate concretion is marked by the presence of residual aragonite prisms. The carbonate concretions apparently are synge- netic in origin, formed on the bottom of a bay, la- goon, or estuary under slightly arid climatic condi- tions. The calcite that replaced the shells and filled the intergranular spaces may have been penecontem- poraneous, derived from the overlying calcareous no- dules. The uranium deposits in the Karnes area are apparently unrelated to calcium carbonate, as Gott (1956) found to be true in the Black Hills, S.D. DEWEESVILLE SANDSTONE MEMBER The Deweesville Sandstone Member, the principal uranium ore-bearing rock in the area, consists chiefly of sand and silt but contains some siltstone and some sandstone and clay. The member con- tains calcium carbonate concretions, Ophiomorpha maj0r( ?), oyster shells, silicified tree stumps in situ, and casts of nearly vertical plant roots; silicified logs are common. The Deweesville ranges in thickness from 20 to 50 feet and averages 40 feet. It forms a band of outcrop 250—300 feet wide in the mapped area. Local thin- ning is accompanied by thickening of the underlying 10 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA Conquista Member, and the combined thickness of the two members remains about constant. The grain sizes of the sandstones in the Dewees- ville are similar to the grain sizes of other sand- stones in the Jackson Group; the grains are predom- inantly fine to very fine and semiangular. Fine- to medium-grained subangular material is found occa— sionally throughout the member. The base of the member near the Hackney deposit is composed mostly of medium-grained sandstone, and many of the grains are semirounded to rounded. The grains are principally quartz and fairly fresh fragments of volcanic rock and feldspar. In most sandstone beds, montmorillonitic clay forms a ma- trix for the grains (Eargle and Snider, 1957, p. 17). Most of the sandstone is grayish to pale yellowish brown or buff and is locally stained with small amounts of limonite. At the Hackney deposit some of the outcrops of silicified sandstone and of uncon- solidated sand are deep yellowish brown from in- tense impregnation of limonite; these outcrops con- tain conspicuous streaks of yellow uraniferous min- erals. At other outcrops a few feet away, an equiva- lent bed is highly silicified and is dark gray to black. Beds from 1 inch to 1 foot thick, predominantly of altered vo‘canic ash, are randomly distributed in the Deweesville. At most outcrops these beds are white, hard, and silicified. At the Hackney deposit some of the silicified ash is pink and some chocolate colored; in places, color banding parallels the bedding. Below the surface the ash beds are soft, unsilicified, and purplish black. Impressions of leaf and stem frag- ments are abundant, but little organic material re- mains in the unsilicified parts of the beds. Thin sec- tions of the silicified rock show numerous pinpoints of birefringent materials, brown streaks of plant material( ?), and opal. According to A. M. D. Weeks (oral commun., 1962), spectrographic analyses of the silicified material show silica to be the only con— stituent present in quantities greater than 1 percent, and she identified only opal by X-ray analyses. In the field this, type of rock has been called tuif, car— bonaceous turf, carbonaceous clay, ash, lignitic clay, and tufl’aceous clay. The last name is the most de- scriptive, but is not diagnostic because it also applies to most of the other clays of the Jackson Group. Carbonaceous tuff is a good descriptive term, but the actual carbon content is low, even though impres- sions of stems and leaves are abundant. These beds probably were formed by alteration of extremely fine volcanic dust that fell into a Tertiary bay or lagoon. Some of the beds of tuff can be traced for a few thousand feet along the strike, but many pinch out within a few tens of feet. The uppermost unit of the Deweesville is a zone of sandstone and clay. On the Niestroy and Bargmann properties, a zone of carbonate nodules, similar to those in the Conquista Clay Member, and a zone of oyster shells are at or near the top of the Dewees- ville (MacKallor and others, 1962). On the Hackney and Thane properties, the upper 2 feet of sandstone contains numerous casts of plant roots similar to those in the top beds of the Dilworth. Scattered car- bonate nodules mark the top of the Deweesville at the Lyssy property. Between the Hackney and Lyssy properties, good marker beds are absent, but the upper sandstone bed contains some plant roots. On the Jandt property, about 10 feet below the top of the Deweesville, several silicified vertical tree stumps were observed, indicating that the trees had grown there. The characteristics of the upper Dew- eesville indicate that at the end of Deweesville time the bay was nearly filled with sediments and that deposition was probably proceeding at a slower rate. In much of the area, the Deweesville Sandstone Member contains a zone 10 or more feet thick of clay and siltstone that divides the member into an upper and a lower sandstone unit. Near the Hackney deposit, the clay and siltstone zone is covered by a thin layer of soil and lies between two ledges of silicified sandstone. On the Korzekwa property, nu- merous drill holes have penetrated the clay and silt- stone zone. Silicified outcrops are common throughout the area of a sandstone bed near the base of the Dewees- ville that in many places contains Ophiomorpha major. In some places, this bed rests directly on the Conquista Clay Member; in others, the contact is transitional—predominantly silty sandstone or silt- stone above and silty or sandy mudstone below. The location of the contact was chosen on the basis of grain size. The lensing and the channeling of the basal beds cause the contact to be irregular. The lower part of the Deweesville and the upper few feet of the underlying Conquista contain all the uranium ore deposits shown in figure 1. Even where no ore is present, the radioactivity is greater in the lower few feet of the Deweesville and the upper few feet of the Conquista than in the rocks stratigraphi- cally above and below (pl. 1). The Deweesville Sandstone Member has been di- vided into three lithofacies units in the vicinity of the Nuhn deposit (fig. 3, section A-A’). Information from surrounding areas indicates that these units GENERAL STRATIGRAPHY AND ENVIRONMENT 11 extend throughout the mapped area and probably beyond it. A sandstone lithofacies as much as 50 feet thick consists entirely of sandstone except for siltstone and clay lenses in the basal 5—10 feet. The sandstone is mostly loose and unconsolidated; locally it is slightly indurated but, except for a few outcrops, is not sili— cified. A second lithofacies (hereafter called the interca- lated facies) consists of ( 1) a lower sandstone zone, 10—20 feet thick, that contains some claystone and siltstone lenses near the base, (2) a middle zone, 10—20 feet thick, of intercalated lenses of sandstone, siltstone, and clay, and (3) an upper zone, 10—20 feet thick, of sandstone. In most places this facies laterally adjoins a third, a clay-filled-channel, litho- facies, but where the intercalated facies is locally absent, the sandstone lithofacies adjoins the channel. Although available information is insufficient to de- lineate the exact boundaries of the intercalated facies, it undoubtedly extends, probably with only minor gaps, from the Luckett deposit southward to the Hackney deposit. All the uranium deposits are in or very near this intercalated facies.- The third lithofacies is a clay-filled-channel facies. The channel locally contains a few very small lenses of siltstone, sandstone, and tufi', and a 1— to 2—inch- thick bed of weathered tufi“. Drill-hole samples of the clay cannot be distinguished from samples of the Conquista Clay Member, and where the channel in- tersects the Conquista, a definite boundary cannot be determined on the basis of lithology. The channel occupies much of the Deweesville in- terval. A few feet of sandstone is usually above and below the clay, but in some places the channel base is near or cuts through the base of the Deweesville. Tongues of clay, which are transitional between the channel facies and the intercalated facies, locally ex- tend outward from the t0p of the channel. The channel is 200—400 feet wide andvfrom 20 to more than 40 feet thick in the middle; its sides slope about 20°. It trends southwestward, generally paral- leling the strike of the beds, and has been traced from near Deweesville southward past the Nuhn de- posit on the Lyssy and Korzekwa properties to a point about 400 feet southeast of the Bargmann- Hackney deposit. The only known outcrop is along Farm Road 791 about 3,500 feet east of the Barg- mann-Hackney deposit. DeVergie (1958, fig. 3), who examined some drill cuttings of the Luckett deposit, did not find the typical clay-filled—channel facies around that deposit, but he did find a persistent zone of clay, lignite and lignitic clay, and siltstone, which corresponds closely to the intercalated facies of the Korzekwa-Lyssy area. DeVergie’s work on the Luck- ett deposit suggests that the clay-filled channel ter- minates between Deweesville and the Luckett ore body but that the associated intercalated facies of the Deweesville continues to the northeast. Inasmuch as the clay—filled channel and aSSociated intercalated beds are a major ore control, considera- tion of the processes that could have produced these features is economically and scientifically important. The stratigraphic position of the channel (pl. 1; fig. 3) shows that the channel was formed and filled after the beginning of and before the end of Dewees- ville time, but the details of how it was formed are not easily determined. The relatively great depth of the channel, without slumping of the sides of unc0nsolidated sand and clay, cannot be explained by the simple process of subaerial stream erosion and, during a later period of marine transgression, the filling of the eroded channel with clay. One possible origin of the channel is that it was cut subaqueously at the mouth of a delta-forming river and later filled with clay. A fea— ture of the same magnitude, Joseph Bayou outlet of the Mississippi River, has been described by Russell (1936, p. 39). In 1896, Joseph Bayou was 100 feet wide and 26 feet deep; in 1907 it was 175 feet wide and 11 feet deep; and it is now 50 feet wide and less than 10 feet deep. Although the middle zone of inter- calated clay, siltstone, and sandstone of the Dewees— ville Member could be deltaic, the evidence favors an origin other than deltaic, possibly lagOOnal. Additional evidence of scouring and channeling was observed by Eargle; he noted a coarse sand and clay-ball conglomerate fill exposed by mining opera- tions in a pit on the Gembler property. The pit is described in the section of this report on the Nuhn deposit. The scouring and channeling and the intercalation of sand, silt, and clay are suggestive of a tidal flat and strong tidal currents within the deeper chan- nels. The environment during the deposition of clay and intercalated clays and sands probably was simi- lar to that for the present tidal flats of the Wadden Sea area of the Dutch 'and northwestern German coasts. Van Straaten (1949; 1951) gave an excellent description of the Dutch Wadden Sea area, and Lu- ders (1934) of the German area. These tidal flats have well-developed drainage systems consisting of large channels, approximately parallel to the shore, which drain smaller channels or prielen (Van Straa- ten, 1949, pl. 2; 1951, fig. 2). The remarkably 12 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA Deweesville Sandstone Member 2000 FEET I FIGURE 3.——Map and sections of the Nuhn deposit showing lithofacies of the Deeweesville Sandstone Member and structure contours drawn on its base. GENERAL STRATIGRAPHY AND ENVIRONMENT 1000 FEET l | l I l J VERT|CAL EXAGGERATION 8 X EXPLANATION WHITSETT FORMATION deu, Dubose Member _ - I — -. ' _ de, Deweesville Sandstone Member Cla—sy-filiedzhan—ml Inéercalamd sand Sand dec, clau-filled-channel famles and clay desc, intervalated sand-and-clay Facies of Deweesville Sandstone Member famies __ ______ _ H T Twcés, gem-d; Cl: M mb Contact Trench exposing uranium wc' 011,un . y e e'r Dashed where approximtely located Twcf,foss’ll'lferous sandstone . l 400—— — - 0n map On section Structure contour Drill hole Drawn on base qf Dewees’ville Sandstone Illélcember Dashed where approximately LYSSY ated Conan" interval 5 feet. Datum ——— is mean sea level KORZEKWA '._.._ __ _ _ Approximate location of property line thhofacles boundary with names of land owners Short dashed where projected beneath Dubose Member FIGURE 3.—Continued 14 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA SSW FARM ROAD 79/ AT BARGMANN— DRgLL HOLE NNE A KORZEKWA CORNER J_3 LUCKETT ORE BODY A, PDRILL HOLE LYSSY-NIESTROY AREA H—18 . ........ Sanois'fone 'Memrbe Deweesville Sandstone Member ‘ Deweesville Sandstone Member < ______________ Conquista Clay Member —- ‘ Deweesvil le Sandstone Member __ _____ _,_._._\ r‘r—o—FLL—'———-‘———— — Present erosional surface— —- — E o - 5000 FEET l | | | I I VERTICAL EXAGGERATION 100x GENERAL STRATIGRAPHY AND ENVIRONMENT 15 straight courses of the large channels are in contrast to the meandering courses of the prielen, which according to Van Straaten (1949, p. 139) are compa- rable to rivers on land. The large channels are filled with water even during low tide, but the prielen run dry during low tide. As indicated by aerial pho- tograph (Van Straaten, 1949, pl. 2), the large chan- nels are of the same magnitude as the clay—filled channel of the Deweesville—Tordilla Hill area. Lu- ders (1934) reported channels extending as much as 6 meters below mean sea level. The clay-filled chan- nel of the Tordilla Hill-Deweesville area corresponds to the large channels of the Wadden Sea, and the numerous smaller channels (pl. 1; fig. 11) may cor- respond to the prielen. (For detailed description of lithology, fig. 11, see section entitled “Nuhn (Climax or Korzekwa-Lyssy—Gembler) deposit”) MacKallor’s interpretation of the development of the clay—filled channel within the Deweesville Mem- ber is shown in figure 4. After the lower sandstone was deposited throughout the area, strong tidal cur- rents scoured out a channel in the loose sand. Then the clay zone, locally intercalated with sand and silt, was deposited throughout much of the area. During this time the large channel was receiving clay depos- its, but the channel was not completely filled. The environment was similar to that of the present area of the Wadden Sea. After the period of scouring and the deposition of the middle zone of clay, calmer conditions prevailed, the channel was completely filled, and the upper sandstone unit of the Dewees- Ville was deposited throughout the area. DUBOSE MEMBER The Dubose Member consists of 80—90 feet of in- tercalated clay, poorly indurated sandstones and silt- stones, and carbonaceous tufl’. Most of the beds are 2—5 feet thick. Sandstone is less common than silt- stone or claystone; it is fine grained and is composed of quartz, feldspar, and volcanic rock fragments; it is only locally indurated. The sandstones are me— dium grained and are gray to yellowish brown, stained in various degrees with limonite. The car- bonaceous tufi‘ beds, which are less than 1 inch thick to several inches thick, contain abundant impres- sions of leaves and stems of plants, but the actual organic content is very low. Most of these beds are silicified at the outcrop and are white to pink. Where unsilicified, the beds are clayey and are chocolate brown to maroon. The tuffaceous clay and the silt- stone are various shades of brown and green. The Dubose contains abundant silicified wood and several beds of very carbonaceous tuff and clay. Ophiomorpha major, a facies fossil indicative of brackish-water conditions and a common fossil throughout the more massive Tordilla Sandstone Member above the Dubose, is not common in the Dubose. The change from Deweesville to Dubose time was marked by increased volcanic activity, as shown by the greater number of thin ash beds. Although it is thought that both Deweesville and Dubose deposi- tion took place in bays, the Dubose contains much more clay than the Deweesville,and its more variable lithology is indicative of multiple environments, and generally of fresh-water, rather than brackish-wa- ter, deposition, in contrast to the Deweesville below and the Tordilla above. The many thin lenses of sand and clay suggest that the Dubose may have been partially formed under deltaic conditiOns. TORDILLA SANDSTONE MEMBER Above the Dubose Member is a sandstone unit about 30 feet thick, the Tordilla Sandstone Member. The sandstone is gray to yellowish brown and is mostly fine grained; it is composed of quartz, moder- ately fresh feldspar, fragments of volcanic rock, and some tuffaceous material. The lower part of the Tor- dilla consists of thin platy beds of tuffaceous very fine grained sandstone and siltstone. Exposed sur- faces are generally silicified but locally are poorly indurated. At Tordilla Hill, the sandstone is very hard, and it forms the caprock of this prominent topographic feature. It forms distinctive rubble of whitish plates and small blocks. This rubble and some bedrock cap small rounded hills or knolls on the Gabrysch and Culpepper tracts (MacKallor and FIGURE 4.—Longitudinal diagrammatic sections showing de- velopment of clay-filled-channel facies of the Deweesville Sandstone Member. Line of section is shown in figure 1; map of clay-filled channel is shown in figure 3. A, After deposition of lower sand of Deweesville Member on Con- quista Clay Member. B, After erosion of much of lower sand of the Deweesville in channel. Erosion of loose sand probably by tidal action but possibly by fluvial currents. C, After filling of channel in the Luckett area with clay and a few sand lenses. D, Beginning of deposition of upper sand of Deweesville Member in the Luckett area and the continuation of the filling of channel. Original channel has been filled, but tidal currents maintain a shallow channel in which sediments are being deposited in, at the sides of, and at the head of the channel. E, After deposition of all the Deweesville Sandstone Member and beginning of Dubose time. 16 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA others, 1962). Above the platy beds the sandstone appears massive, but it contains beds 1 foot or more apart and has some low-angle croSsbedding. The thick sandstone sequence of the Tordilla is very different from the variable lithologic sequence of the underlying Dubose, and there is nothing about the Tordilla to suggest a deltaic environment, al- though the presence of Ophiomo'rpha proves that the sandstone was deposited near shore under marine conditions. QUATERNARY Alluvium of Quaternary age that consists of silt, clay, and organic material occupies most of the val- ley bottoms; locally along Tordilla Creek, these de- posits are covered by a thin veneer of gravel. The thickness of the alluvium ranges from about 4 to 10 feet. Most of the alluvium is covered with a dense, almost impenetrable, growth of thorny bushes. The surface remains muddy for weeks after a heavy rain. STRUCTURE The Tordilla Hill-Deweesville area (fig. 1) lies in the warped downthrown block between the ends of two normal, northeast-trending en-echelon faults (fig. 2; MacKallor and others, 1958, fig. 20). The Falls City fault, north and northeast of the deposits, beyond the limits of the area of figure 1, is down- thrown to the southeast; the Fashing fault, south and southwest of the deposits, is downthrown to the northwest. Both of these major faults have asso— ciated oil and gas fields; the Falls City field (Crutch- field and Bowers, 1950) produces oil from the Wilcox Group of Eocene age and the Fashing field produces oil from the Carrizo Sand of Eocene age and gas distillate from the Edwards Limestone of Cretaceous age (Knebel, 1957). No faults were ob- served within the area by geologic surface and sub- surface mapping nor were any detected by seismic and resistivity surveys, but the lenticuiarity of the beds prevents detection of faults that have only a few feet displacement either by geologic or by geo- physical methods. The beds within the area of the deposits strike generally north-northeast, but in the immediate vi- cinity of Tordilla Hill, the beds locally strike north or even a little west of north. In the northeastern part of the area, the strike is east-northeast. The beds within the area depicted in figure 1 dip to the southeast from 20 to 60 feet per thousand (1°—4°), which is less than the regional dip of the Jackson beds for most of the coastal plain. Apparent local variations in the attitude of the beds are the result in part of very gentile anticlinal and synclinal flex— ures and in part of irregularities in the thickness of sand units. On the Bargmann property (fig. 1) an anticlinal axis and a synclinal axis trend perpendicular to the regional strike. Interpretations of the structure-con- tour map drawn on the base of the Deweesville Sandstone Member (fig. 3) include (1) the presence of two possible folds on the Korzekwa property (fig. 1), (2) the local thickening and extension down into the Conquista Clay Member by the Deweesville, and (3) a lesser possibility of the presence of faults. The fold axes (or the local thickenings of the Dewees- ville) may extend southeastward from the Korzekwa property through the J andt and the Gabrysch prop- erties (fig. 1). Many silicified outcrops have one or two, rarely three, well-developed sets of almost vertical joints. The joints of any one set at a single outcrop are straight and within a few degrees of being truly parallel. Individual joints normally are from about 1 to 3 feet apart. The strike of the most common and best developed set is north-northeast to east-north east, parallel to the regional strike of the beds; a second conspicuous set of joints strikes perpendicu- lar to the strike of the beds. A third well-developed set of vertical joints intersects the other two sets at approximately 30° and 60° angles, but this set was observed only near the Hackney deposit (MacKallor and others, 1962). In a few places, poorly developed nonplanar vertical joints from 4 to 8 feet apart in- tersect the two major joint sets. Because the differ- ence in strike of individual joints, or even of the strike along the same joint, was as much as 30°, these poorly developed, irregular joint sets were not plotted. Where the local strike of the beds deviates from the regional strike, as on the Lyssy property east of Deweesville, the strike of the two major joint sets continues to parallel the regional strike and the dip direction of the beds. In agreement with the conclusions by McKinstry (1948, p. 291—295) and Billings (1946, p. 101—103) regarding the structural interpretation of joints and shears, the joint system in the area (MacKallor and others, 1962) indicates horizontal, rather than verti- cal forces. By being in a downthrown block, the area would have been subjected to horizontal compressive forces by either horizontal or vertical movement along the Falls City and Fashing faults. SILICIFICATION 17 SILICIFICATION Patches of well indurated silicified sandstone and carbonaceous tuff are spotty but widespread throughout the area of uranium deposits (MacKallor and others, 1962). Attention was given to silicifica- tion in both the large-scale and quadrangle mapping programs because of the proximity of silicified sand- stone to most of the uranium deposits. Highly silicified sandstone is extremely hard, breaks across the grain, gives a ringing sound when struck with a hammer, and has a shiny luster; less hardened sandstone and tuffaceous material are clas- sified as indurated. Induration by silica is common; but according to A. M. D. Weeks (oral commun., 1960), zeolitic alteration is responsible for much of the moderate induration. Most of the sandstone in the area is friable, and some sandstone is as nonin- durated as recent beach sand. Silicified siltstone was rarely observed. Thin sections of silicified fine-grained sandstone and tuff show the cementing material to be opal; no uranium minerals were observed. In highly silicified sandstone that contains secondary uranium miner— als, bands of opal and chalcedony are intercalated; those bands in contact with the sand grains are opal. The cement of medium-grained sandstone that does not contain uranium minerals consists of opal bands only. A tentative conclusion is that the formation of chalcedony, rather than opal, is in some way related to the deposition or occurrence of secondary uran- ium minerals. Within the report area (figs. 1, 2), silicified rock is found within all exposed members of the Eocene Whitsett Formation. The upper plant-root bed of the Dilworth and two thin beds, one at the top and one near the base of the fossiliferous sandstone unit of the Conquista, are silicified at every outcrop. Some outcrops of the Deweesville are silicified. The lower, middle, and upper parts of the Deweesville are all locally silicified, but the entire section is not silicified in any one place. Most outcrops of the Tordilla are silicified. The Dubose contains m0stly mudstone and siltstone, rocks that are not favorable for silicifica- tion, but the few sandstone beds and thin tuif beds in this part of the section are silicified at some out- crops. In outcrops, silicified sandstone grades downward within a few feet to poorly indurated nonsilicified sandstone, and the contact between silicified and nonsilicified sandstone is irregular and cuts across bedding. Excellent examples of the relationship be— tween silicified and nonsilicified sandstones of the Tordilla are visible along the rim of Tordilla Hill (MacKallor and others, 1962). Several small cut- crops of well—silicified Deweesville Sandstone Mem- ber just north of Tordilla Hill on the Hackney prop- erty have been removed by mining operations. The silicified rock was only a foot or two thick and was underlain with slightly indurated sandstone or un- consolidated sand. The layer of silicified sandstone did not extend downdip under soil and bedrock at the Hackney workings, although an exploration trench did expose silicified ribs (fig. 5). Some of the sandstones of the Tordilla and Deweesville contain nodules which have a 1/3-inch-thick rim of grayish, punky, poorly indurated sandstone enclosing a shiny, hard, bluish-gray silicified core. In some places prongs of poorly indurated sandstone extend into the silicified sandstone along joints. An interpreta- tion, suggested by D. H. Eargle (oral commun., 1958), is that the silica cement is now being re- moved because of climatic conditions. Inasmuch as the auger drill could not penetrate a silicified layer even a few inches thick, no auger holes were started on silicifed sandstone; but many holes were started near silicified outcrops. The drill seldom encountered silicified rock in these holes. A very few holes had to be abandoned at a depth of about 30 feet because of a silicified layer perhaps no more than 2—3 inches thick. Silicification below the surface is scarce and spotty—one hole may contain a thin silicified layer and adjoining holes at the same interval may be unsilicified. In the five core holes (K—l to K—5), only a few scattered small stringers of silicified rock were found below the zone of oxida- tion. The evidence from outcrops, trenches and pits, and drill holes is that most silicification occurs in the oxidized zone at or within a few feet of the surface. After examining the distribution of silicified sand- stone near Tordilla Creek, the authors concluded that the present drainages existed at the time of silicifi— cation but that they have been widened and deep- ened since that time. The large patch of silicified sandstone just north of the Korzekwa trench in the Nuhn deposit (fig. 1; MacKallor and others, 1962) apparently forced Tordilla Creek to make a big loop around the resistant rock and confined it to a nar— row valley in this area. Another type of silicification, the replacement of wood by silica, probably occurred before the silicifi— cation of the rocks just discussed. Silicified logs and tree stumps have been observed in the Conquista Clay, Deweesville Sandstone, and Dubose Members of the Whitsett Formation. The logs retain their 18 SW 404' e 402' 400’ 398’ 396' C OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA Southeast wall 394’ 404' ~ 402’ 400’ 398’ 396’ 394’ Northwest wall 20 30 FEET I EXPLANATION Tuffaceous rock Sand Silicified rock Contact C, carbonaceous material U, yellow uranium minerals L. limonite M, manganese minerals O, opal G, gypsum CG, clay galls FIGURE 5.—Geologic sections along southeast and northwest walls of trench in the Hackney deposit. original shape in cross section, which suggests that silicification took place shortly after deposition and burial of the logs. If the logs had been silicified after a few hundred feet of overlying sediments was de- posited and after a considerable lapse of time, the cross section of the logs would have been modified by the compressive force of the overlying sediments. Outside of the study area of figure 1, a few silicified logs contain small encrustations of yellow uranium minerals on the outside and in small cracks, but the logs do not approach ore-grade material. The conclusion is that the spotty silicification, con- fined almost entirely to 5 feet of the present surface, is of recent geologic age (that is, Pleistocene), pre- ceding only the late deepening of stream valleys. The lack of deformation of silicified wood, however, indi- cates early penecontemporaneous replacement. Therefore, silica has been in the sediments and water since the early deposition of ash. URANIUM DEPOSITS Uranium minerals in Texas have been found in the Oakville Sandstone (Miocene), in the Catahoula Tuff (Miocene), and in several members of the URANIUM Whitsett Formation (Eocene). The significant de- posits in the Tordilla Hill-Deweesville area occur where the permeable Deweesville Sandstone Member lies on the relatively impermeable Conquista Clay Member (fig. 6). The uranium minerals occur mostly within the lower 10 feet of the Deweesville, but al- most invariably extend down into the upper few feet of the Conquista; and where the upper part of the Conquista is unusually silty, the uranium concentra- tion may be greater below than above the c0ntact. The host rocks in the vicinity of the deposits are characterized by diastems, channels, crossbedding, and intercalated lenses of sandstone, clay, and silt- stone. Furthermore, the largest deposits occur within a few hundred feet updip from a major clay- filled channel (fig. 3). The larger deposits either crop out at or extend to within 20 feet of the surface, but economically im- portant deposits may exist at greater depths. Al- though the nearness to the surface affects the miner- alogy of the deposits, it is not an ore control. Downdip from the principal ore bodies, three of the cored holes penetrated areas of anomalous ra- dioactivity at depths below 100 feet. K—1 had an FIGURE 6.—Principal ore-bearing zone of the Tordilla Hill- Deweesville area straddles the contact (to which the man is pointing) between the Deweesville Sandstone Member and the underlying laminated Conquista Clay Member of the Whitsett Formation and extends upward to the sur- face. Trench is in the northwestern part of the Windmill deposit on the Gembler property. Photograph by D. H. Eargle, 1960, after mining began in the area. DEPOSITS 19 anomaly of 0.12 percent equivalent uranium oxide (eU308) from a depth of 157.6 to 158.8 feet; K—3 an anomaly of 0.22 percent eU308 from 140.2 to 141.8 feet; and K—5 anomalies of 0.12 and 0.15 percent eU308 from depths of 103.0 to 104.2 feet and from 112.1 to 113.0 feet, respectively. Equivalent uranium oxide is the amount of U303 that would have con- tained enough uranium to decay to the amount of daughter products that emit the measured radioac- tivity. The chemical uranium in the cores was con- siderably less than the equivalent uranium. The anomalies in K—5 were in the Tordilla Sandstone Member; the other anomalies were in the lower part of the Deweesville Member (Manger and Eargle, 1967). The radioactivity anomaly in hole K—5 was later shown to be on the updip fringe of the largest uranium deposit in the region (D. H. Eargle, written commun., 1969). No discrete uranium minerals were identified in the cores, and inasmuch as the radioac— tivity was disseminated in the light fraction of the rock, the radioelements may be absorbed on the clay minerals (A. M. D. Weeks and A. H. Truesdell, writ- ten commun., 1959). The uranium deposits are, in general, tabular; their shape was determined from the results of the fieldwork and verified by subsequent mining. The interpretation of horizontal shape (fig. 1 and plate 1) is based on data from the ground radioactivity study by L. R. Tolozko (in MacKallor, 1962), gam- ma-ray logs, and outcrops and exposures in pits. The general dimensions of the Luckett deposit were ob- tained from deVergie (1958, fig. 2) and from the pattern of drill-hole locations noted during plane ta— bling of the area. Although the exact shapes of ore bodies are not shown on detailed maps made by min— ing companies, the maps do show the larger ore bod- ies to be elongated along the strike of the beds. Small protuberances parallel with and perpendicular to the general strike of the beds coincide with the orientation of the most conspicuous joint systems. MINERALOGY The deposits contain a great variety of high-val- ent uranium minerals, many of which are unstable. On the Gembler property, uraninite occurs in the Conquista Clay Member below the zone of oxidation but forms a very minor part of the deposit. Eargle and Weeks (1961a, p. 26) stated, The minerals are chiefly varieties of yellow to greenish-yellow, oxidized uranium minerals. They include uranyl phosphates, arseno- phosphates, silicates, phospho-silicates, molybdates, and vanadatcs. Locally in silty clays beneath the thickest and richest deposit a small amount of uraninite ore has been found. The uranyl phos- phate minerals, autunite or meta-autunite, are the most abundant. 20 OXIDIZED URANIUM ORE DEPOSITS, In general, the mineralogy resembles more the oxidized near- surface deposits in the Tertiary of Wyoming than it does those of the Colorado Plateau which are high in vanadium and contain carnotite as the dominant mineral. The Kames County area ores are low in vanadium content, but traces of the uranyl vanadates, carnotite and tyuyamunite‘ are widely distributed. Most of the uranium minerals are oxidized be- cause the deposits are within or just below the zone of oxidation. In addition to the one occurrence of uraninite, A. M. D. Weeks (unpub. data) reported one other mineral that may be in part low valent— an unidentified purplish—black uranium molybdate found in an outcrop of highly silicified sandstone at the Hackney deposit. MacKallor systematically collected 33 samples from a prospect trench (fig. 1) on the Korzekwa property at the south end of the Nuhn deposit for chemical and equivalent uranium analyses and for semiquantitative analyses of other elements. A. M. D. Weeks (oral commun., 1958) compared the re- sults with the composition of average sandstones and found that the MacKallor samples show-ed con- siderable to slight enrichment in uranium, molybde- num, arsenic, vanadium, and lead. She believed that a moderate enrichment of these elements was caused by volcanic debris in the sandstone. J. N. Rosholt, of the US. Geological Survey, made radiochemical analyses of three suites of samples, two from a shallow trench on the Korzekwa prop- erty and one from a depth of about 40 feet from an ore body along the Gembler-Lyssy property line. The samples have a wide range of disequilibrium, and Rosholt interpreted the radiochemical analyses as indicating considerable migration of uranium within the last 250,000 years (Rosholt, 1963). Uranium minerals occur as thin layers along bed- ding planes and joints and are disseminated throughout the host rock, coating grains and filling interstices. Some uranium minerals have replaced volcanic rock fragments and feldspar grains along cleavage cracks. Ore-grade material has been found from the surface to a maximum depth of about 40 feet. PRODUCTION AND RESERVES In 1958, after the period of intense prospecting but before any mining operations were begun, the US. Atomic Energy Commission (S. R. Steinhauser, oral commun., 1958) estimated the reserves of uran- ium in Karnes, Atascosa, and GOnzales Counties, Tex., to be 280,000 tons of ore which would average 0.22 percent U308. The first production of uranium ore from the southeastern Texas coastal plain was from the TORDILLA HILL-DEWEESVILLE AREA Hackney deposit in December 1958, when a few tons of selectively mined ore containing 2.16 percent uranium was trucked to the uranium mill at Grants, N. Mex. In July 1959, preparation for open—pit mining was begun by the San Antonio Mining Co. on the Nuhn deposit (Maxwell, 1962, p. 123) ; and by April 1961, the company had fulfilled its contract to deliver 100,000 tons of ore containing about 0.2 percent U308. By July 1961, Susquehanna-Western Inc. had mined about 80,000 tons of ore containing about 0.2 percent U308 from the Luckett deposit (Maxwell, 1962, p. 126). The same company mined the Barg- mann-Hackney (formerly Rare Metals) deposit in 1963, greatly enlarged the Korzekwa mine in 1964, and reopened the Hackney deposit and mined about 10,000 tons of ore in 1965 (D. H. Eargle, written commun., 1969). In 1968, production from Susque- hanna-Western’s mill at Deweesville was about 1.2 million pounds of U308 (Eargle, 1970). SUBSURFACE RADIOACTIVITY STUDIES COMPARISON BETWEEN CHEMICAL AND RADIOMETRIC ANALYSES OF DRILL-HOLE SAMPLES Gamma-ray log interpretations are based on the assumption that the uranium is in equilibrium with its daughter products ; therefore, it was necessary to determine whether the radioactive material in the report area fulfilled that condition. Samples from auger cuttings and drill cores were analyzed chemically for uranium content and radi- ometrically for equivalent uranium content. The re- sults of these analyses may not agree, because of secular disequilibrium, statistical error, or error in both chemical and radiometric analyses. Disequilibrium can be caused by normal geologic processes. Because the parent and daughter radioele- ments have different chemical characteristics, they can be separated by ground-water movement. Either the parent or the daughter products may predomi- nate in a uranium deposit. Disequilibrium may also occur through radon loss during the grinding process preceding radiometric analysis either because the gas is driven off by fric- tional heat or because it escapes from pore spaces in the rock as a result of fracturing of the pores. Un- less the sample is allowed to stand for several days after grinding to regain equilibrium, as was done here, the measured radioactivity may be less than that required for a true radiometric analysis. Statistical error is inherent in all radiometric analyses and is a function of the total number of events or counts observed. The error can be mini- URANIUM mized in laboratory analyses by increasing the meas- urement time interval for samples of low activity. For count-rate meters used with gamma-ray logging equipment, the magnitude of the fluctuation from an average value depends on the count rate and the time constant of the instrument. The relation between chemical and radiometric analyses of drill-hole and pit samples was estab- lished by plotting the uranium data obtained by the two methods (fig. 7). All the chemical analyses are assumed to be correct, though some errors believed to be relatively insignificant undoubtedly exist, par- ticularly in analyses of low-grade material. The re- sults show a Wide range (about 0.5—2.0) in ratios between chemical and radiometric analyses, espe- cially for values less than 0.05 percent chemical uranium. Above this value, the range is not as Wide, and the chemical uranium analyses are about 11/2 times higher than the radiometric analyses. The radiometric analyses are generally higher than the chemical analyses in the range of 0.001 to 0.01 percent U. Some of the discrepancy in the two sets of data in this range may be the result of the contri— bution of radioactivity from the natural radioisotope of potassium, K“. The gamma-radioactivity emitted by K“ in a sample containing 1.5 percent K is equivalent to the radioactivity from 0.001 percent U (J. N. Rosholt, US. Geological Survey, oral IIIIIIIII IIIIIII O O O IIIIIT o J Radioactive equilibrium | I 9 o ... lilbIIIIII IIIIII RADIOMETRIC ANALYSIS, IN PERCENTAGE OF EQUIVALENT URANIUM 380° I IIII| 0.10 I IIIIIII I I 0.01 CHEMICAL ANALYSIS, IN PERCENTAGE OF URANIUM FIGURE 7.—Relation between chemical and radiometric analyses for uranium content of drill-hole samples. 0, auger sample; x, diamond-drill core sample obtained with oil-base mud. DEPOSITS 21 commun., 1958). Semiquantitative spectrographic analyses by A. M. D. Weeks show that rocks of the Deweesville Sandstone and Conquista Clay Members of the Whitsett Formation range from 1 to 3 percent K (D. H. Eargle, written commun., 1964). A comparison of equivalent uranium and chemical uranium analyses was made by A. M. D. Weeks on more than 530 samples ranging from high-grade ore down to a content of 0.001 percent U. The results indicated that the average equivalent uranium is about 5 percent higher than the average chemical uranium (Weeks and Eargle, 1963), though ratios from individual samples vary widely. EFFECT OF RADON ON GAMMA-RAY LOG INTERPRETATION Gamma-ray logs obtained from a few drill holes, especially those on the Korzekwa property, exhibited excessively high anomalous radioactivity through several tens of feet of drill hole. Data from most holes in the area indicated that the maximum thick- ness of mineralized zones was a few feet; therefore, contamination of the few holes by radon gas was suspected. During drilling, radioactive cuttings and dust are sometimes transported up the hole by drill- ing fluid or air and are deposited along some finite interval of the hole. In contrast, radon gas is usually distributed throughout several tens of feet within the drill hole. The effects of radon contamination on the gamma-ray logs in the Tordilla Hill-Deweesville area are similar to those observed in other areas in the United States (Hilpert and Bunker, 1957). To test the inference that radon contamination was present, drill hole B-39 (fig. 8), suspected of being highly contaminated, was used for an experi— ment. The hole had been logged immediately after it was drilled, and the log exhibited anomalously high radioactivity throughout its length (fig. 8, log A). Twelve hours later the hole was relogged. Except for a few feet at each end of the hole, the radioactivity had increased significantly (fig. 8, log B). The ra- dioactivity in a zone about 10 feet thick between the depths of 40 and 50 feet, and just below the uranium ore, had increased by a factor of two. The hole re- mained uncapped for an additional 48 hours and was logged again (fig. 8, log C). The radioactivity in the bottom of the hole had decreased to less than the amount found immediately after drilling. The ra- dioactivity between the depths of 40 and 50 feet had decreased to about 50 percent more than was ob- served immediately after the time the hole was drilled. Although no meteorological data were kept, 22 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA LOG A LOG B LOG C LOG D Run immediately Run 12 hours Run 60 hours Run after air blown after drilling after drilling after drilling for 30 minutes COUNTS PER MINUTE o O 1000 0 1000 0 1000 0 1000 10 —— i — — — X1 — X1 X1 X1 20 — — — — ._ _ X10 X10 x10 X 10 DEPTH BELOW DRILL COLLAR, IN FEET 0‘ b w o C! o l ' ’ l l | | l l l | l l I | I l 8 l l £_ ‘_ _ FIGURE 8.—Gamma-ray logs of drill hole B—39 in the Nulm deposit showing radon contamination and effects of time and of air flushing. Curve X 1, read direct; curve X 10, multiply reading by 10. the authors believe that the radon gas was evacuated from the drill hole by an increase in barometric pressure and wind velocity (Hilpert and Bunker, 1957). An air hose was lowered to the bottom of the hole, and air was pumped into the hole at a rate of about 600 cubic feet per minute for 30 minutes. Sub- sequent logging indicated no significant change in the radioactivity (fig. 8, log D). The lack of change in radioactivity between the depths of 40 and 50 feet probably indicates that a predominant source of the radioactivity here was radioisotopes lead-214 and bismuth-214 adhering to the walls of the drill hole. On drill-hole logs that were recognizably contami— nated by radon, only major anomalies were inter- preted for grade. For these, the instrument readings were reduced by the amount of contamination, doubtlessly causing an underestimation of equiva- lent—uranium content in some zones of lower grade mineralization. RELATIONS BETWEEN SURFACE AND SUBSURFACE RADIOACTIVITY Airborne (Moxham, 1958, 1964; Moxham and Eargle, 1961) and carborne radioactivity surveys in the Texas coastal plain indicate that the gross re- gional radioactivity ranges from about 6,;r (micro- roentgen) per hour to about 9 Mr per hour. The Tordilla Hill-Deweesville area is surrounded for many square miles by an aura of slightly anomalous radioactivity ranging from about 10 to 15 Mr per hour (Moxham, Eargle, and MacKallor, 1957, p. 449; MacKallor and others 1962). The Tordilla Hill-Deweesville area is completely within the aura; therefore, most of the lowest surface radiation in- tensities shown (fig. 9; MacKallor and others, 1962) are higher than the regional radiation intensity. The uranium deposits are reflected by surface anomalies directly over them in some places, eSpe- cially where the uranium is near the surface. An intense surface anomaly overlies the Hackney de- posit at the north foot of Tordilla Hill. Both the surface and the subsurface radioactivities extend downslope (northwest) from the deposit. A surface anomaly of 5,000 [11' per hour was measured in this area and is probably related to a surface accumula- tion of mechanically dispersed ore from the Hackney deposit. Elsewhere, the surface anomalies are found updip from the uranium deposits at the location where the ore-bearing geologic units are exposed at the surface. SIZE AND SHAPE OF RADIOACTIVE LAYERS The sizes and the shapes of the radioactive layers are as varied and complex as those of the lithologic units. The thickness of the layers that show anoma- lous radioactivity ranges from a few inches to sev- eral tens of feet; the thickness of the high-grade (0.5—0.99 percent eUROB) layers is limited to a few feet. In cross section the layers range from ellipsoids to long stringers. The width of the layers ranges from a few feet to a few hundred feet; the width of the high—grade layers is not more than 100 feet. The higher grade zones are surrounded by halos of lower grade uranium. Similar halos in the Colorado Plateau were reported as early as 1950 (A. S. Rog- ers, U.S. Geol. Survey, written commun., 1950). In the Karnes County area, where the mineralized zones are several feet below the surface, the halos follow the topographic slope. The halos generally ex— tend farther downdip than updip from the locus of mineralization. The edges of the horizontal layers in cross section are very irregular. Many layers split into multiple layers at the edges; this splitting is especially notice- able in the low-grade (0.01—0.049 percent eU303) deposits. The shape of the layers is also very irregular in plan view. Some of the apparent irregularity may be URANIUM DEPOSITS 23 a? my“ EXPLANATION O . . LUCKETT Uranlum depOSIt X DEPOSIT 30 microroentgens per hour 1 ’ surface radioactivity contour 2 «1?ch 635%; .5000 (90;. High surface radioactivity _ Shown in ,ur/hr. Valut‘ (Ts gross intensity "\ (includes cosmic component) 19‘ V C- O GABRYSCH @e/ 97% WOLF / <1 9% . . . A ‘9 vo Approx1mate location of property line / $65) and names of landowners / 63 x. BARGMANN— HACKNEY DEPOSIT 2 7" >‘ / g ‘2 f /’ <2 :1 : / a: U 1/ 9‘ E 9 $9 $3“ Y’ C; Q‘Z’ 0 1000 2000 3000 4000 5000 FEET L. i . . | I l | | FIGURE 9.—Ore deposits and generalized surface radioactivity contours in the Tordilla Hill-Dewees- ville area. Modified from MacKallor, Moxham, Tolozko, and Popenoe (1962). 24 OXIDIZED URANIUM ORE DEPOSITS, caused by the pattern of the drill holes and by the subjective interpretation of the radioactivity data. However, in some areas that are pierced by many drill holes, for example, the Korzekwa property, the horizontal limits of the radioactive layers are de- fined reasonably well. The radioactivity in this area follows. a meandering southerly trend within which are elliptical depoSits Of high-grade uranium. INDIVIDUAL DEPOSITS Figure 1 shows the landowners and the names being used in 1958 for the important deposits in the Tordilla Hill-Deweesville area. The Nuhn (Climax) deposit is a collective name for three somewhat sep- arate ore bodies: Korzekwa, Lyssy, and Gembler- Lyssy (or Windmill). During this study, the Nuhn deposit was also known as the Climax or San Anto- nio Mining Co. deposit. The Luckett deposit was also known as the Continental and as the Susquehanna- Western deposits. These two deposits extend across property lines; where a precise location is needed, the name of the landowner follows the name of the deposit in parentheses. The Bargmann-Hackney de- posit, also known as the Superior-Rare Metals de- posit, is divided by the highway. HACKNEY (BOSO) DEPOSIT The Hackney (Boso) deposit at the foot of Tor— dilla Hill was one of the first deposits of uranium minerals to be discovered in the southeastern Texas coastal plain. The mineral lease of part of the Hack— ney tract, including the uranium deposit, was acquired by the late Dr. Fred M. Boso, of San Anto- nio, shortly after the discovery of uranium minerali- zation there (1954). After the upper few feet of material around the deposit was bulldozed, between 8 and 9 tons of se- lected ore, containing 2.16 percent U308, and 1.4 percent lime, was trucked to the mill at Grants, N. Mex., in December 1958. The deposit was mined later, in 1965, by Susquehanna-Western, Inc. The Hackney depoSit is the only one in the Tor- dilla Hill-Deweesville area in which highly silicified sandstone contains uranium. At the time of this sur- vey, three silicified outcrops within the uranium de- posit had been destroyed by bulldozer operations. These three outcrops were part of the sandstone bed of the Deweesville Sandstone Member and lay just above the silty clays of the Conquista Clay Member of the Whitsett Formation. One of the small outcrops was unusual in that the exposed rock had a dark-yellowish-brown ferrugi- nous stain; yellow uranium minerals were abundant. TORDILLA HILL-DEWEESVILLE AREA The exposed sandstone was slightly less than 1 foot thick and lay just above a 1-inch-thick bed of opal- ized tuff. This thin bed of tuif, exposed in a nearby prospect pit, also contained abundant yellow uran- ium minerals. Although float from this tuff was found for several hundred feet along the contact, no mineralized material was found away from the de- posit. The northern outcrop of the deposit, a light-gray fine-grained sandstone, contained a few specks of yellow uranium minerals. In the southern outcrop, the sandstone is highly silicified and is smoky to very dark gray. The southern outcrop is predomi- nantly medium grained; in contrast, most of the other outcrops are fine grained. The cementing mate- rial consists of alternate bands of chalcedony and opal. In a small prospect pit here, visible uranium minerals were scarce, but the mineralogy is unusual. At this outcrop, and no place else, A. M. D. Weeks (oral commun., 1960) identified iriginite, a yellow uranyl molybdate, and a newly discovered purplish- black uranium molybdate mineral, as well as two molybdenum minerals, jordisite and ilsemannite. The yellow uranium minerals found in the Hack- ney deposit were mainly autunite, carnotite, and tyuyamunite. Carnotite was more abundant at this deposit than at the other deposits in the area. In addition to the uranium minerals, the deposit locally contained small amounts of disseminated fine-grained pyrite and marcasite. A. M. D. Weeks (oral commun., 1961) observed these minerals as microscopic subhedral grains in interstitial bands of opal and as replacements of detrital volcanic grains. Limonite stains are common throughout the deposit in both sandy and clayey material. Manganese ox- ides, occurring locally as BB-sized pellets and stains, are common, but elsewhere are scarce or absent. In a trench on the Hackney property (fig. 5), which was bulldozed during mining operations, yel- low uranium minerals were seen to be scattered throughout the sandstone and clays, but were very scarce in the silicified sandstone. The uranium min- erals commonly were concentrated along bedding planes in streaks less than 1 cm thick, and several very thin streaks were locally seen within an inter- val of a few inches. The uranium minerals coat the sand grains and partly fill the interstices with a fine yellow powder. In clay, the minerals form conspicu- ous yellow coatings along bedding planes and mi- nute, nearly vertical, partings or cleavage fractures. Uranium minerals were observed as partial replace- ments of grains of feldspar and volcanic material in thin sections of silicified rock. Limonite, both yellow- URANIUM DEPOSITS 25 ish brown and reddish brown, is more widespread than uranium minerals and imparts the characteris- tic colors to some streaks of sand. In the trench, selenite is common above the silicified sandstone and below the soil and occurs as platy aggregates from less than 1 inch to several inches in diameter. The original ore shipment was obtained from a small area north of the trench—around the small outcrop and prospect pit—and west of the eastern— most outcrop. Although the excavations extended to Conquista, the ore came only from the basal few feet of the Deweesville. This basal sandstone ranges from completely unindurated to indurated and highly silicified. In many places no gradation occurs between highly silicified and unindurated sandstone; in some places from a few inches to as much as 1 foot of indurated, slightly silicified sandstone sepa- rates highly silicified from unindurated sandstone. The highly silicified sandstone is smoky to dark gray. The normal color of the slightly silicified and unindurated sandstones is light gray to pale brown; where theSe sandstones are heavily impregnated with limonite, the color is dark brown. The limonite on the outcrops was a dark yellowish brown, but much of the limonite below the surface was reddish brown. Mottled bright yellow and brown limonitic pockets that are as large as a few cubic feet and that consist almost entirely or only partly of high—grade ore were observed only in unindurated and in slightly silicified sandstone. The digging of a trench, now filled, on the Carri- ger property just across the road from the Hackney deposit uncovered uranium minerals in the Con- quista Clay Member. Such occurrences undoubtedly were similar to those visible along the highway cut between this trench and the Hackney deposit, where uranium minerals occur uncommonly along bedding planes and cleavage fractures. Directly below the mined—out area, in the upper 2 feet of the Conquista, yellow uranium minerals are conspicuous, but even this material does not approach ore grade. The two unmineralized outcrops on the Hackney property are part of the plant—root bed, which is in the uppermost sandstone of the Deweesville. The in- terval between this sandstone bed and the basal sandstone bed consists of unindurated sandstone and clay. At this deposit, the Deweesville is only 20 feet thick, whereas the average thickness in the Tordilla Hill-Deweesville area is 40—50 feet. The local thin— ning of the sandstone is a result of the depositional environment. The difference in thickness of the permeable Deweesville between this area and adja- cent ones certainly aifected the rate of ground water movement and may have been an important ore con- trol. The beds on the Hackney and adjacent properties dip gently southeast except for a local area on the Hackney property, opposite the Bargmann—Carriger property line, Where they locally dip northeast. A north-trending fault, not observable on the surface,. may be present in this region. BARGMANN-HACKNEY (SUPERIOR-RARE METALS) DEPOSIT Closely spaced drill holes on the Bargmann prop- erty near a surface radioactivity anomaly indicate the probable extent of a deposit found by the Supe- rior Oil Co., mineral leasees of the tract. Several holes were drilled by the U.S. Geological Survey near the road on both the Hackney and the Barg- mann properties, and some mineralized material containing less than 0.1 percent eU was found be- yond the deposit, as shown in figure 1. The amount of higher grade material apparently is minimal (pl. 1) and is confined to the Deweesville Sandstone Member. The upper few feet of the Conquista Clay Member contains a considerable amount of radioac— tive material that is less than 0.05 percent eU (holes H—13 to B—24, pl. 1). The uranium deposit lies a few hundred feet updip from a deep clay-filled channel, a major ore control of the area. NUHN (CLIMAX OR KORZEKWA-LYSSY-GEMBLER) DEPOSIT One large deposit, containing several distinct ore bodies, occurs on the Korzekwa, Lyssy, and Gembler tracts, known collectively as the Nuhn lease. The deposit was mined by the Climax Molybdenum Co. operating under the name of the San Antonio Min- ing Co. During the US. Geological Survey’s airborne ra— dioactivity survey in the Texas coastal plain, the ore bodies showed one large anomaly (Moxham and Eargle, 1961) ; this anomaly was perhaps the princi— pal one discovered during the airborne survey by Jafi’ee—Martin and Associates that started the uran- ium rush in the southeast Texas coastal plain. The Climax Molybdenum Co. systematically drilled these three tracts and discovered two small high-grade ore bodies on the Korzekwa property, a larger one on the Lyssy property, and another partly on the Gembler tract and partly on the Lyssy tract. Mining operations did not commence until 1959, after fieldwork for this report had been completed, and as a result figure 1 does not show the location of the open-pit mines. By April 1961, the San Antonio 26 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA SECTIONA East end of trench Unit Lithology Thickness (ft) 1 Soil. 2 Silty clay subsoil; caliche ____________________ 0.9 3 Sand, fine; caliche __________________________ .4 4 Sand, fine; limonitic caliche __________________ 1.2 5 Sand, fine to medium, lignitic, limonitic; caliche .9 16 Sand, fine __________________________________ .4 7 Lignite and sand ____________________________ .6 8 Sand, fine to medium, very limonitic, at top; autunite( ?) _ .4 + 1Unit 6 illustrates the discontinuous nature of the individual lithologic units. FIGURE 10.—Detai1ed lithology of the localities fro~ SECTION G West end of trench Um't Litholoay Thickness (ft) 1 Soil. 2 Subsoil, sandy ______________________________ 1.0 3 Sand, yellow to buff, very fine; clayey streaks of reddish-brown limonite __________________ .8 4 Sand, light-gray above yellow-brown, very fine to fine, tuffaceous, clayey ___________________ .5 5 Clay, chocolate to maroon, lignitic ____________ .4 Sand, light-gray to pale-yellow, very fine, tufl’a- ceous; clayey streaks; yellow uranium min- erals ___ .4 which channel samples A and G were taken from the south wall of the Korzekwa trench, south end of the Nunn deposit. Photographs by J. A. MacKallor, 1957. Mining Co. had produced 100,000 tons of ore con- taining about 0.2 percent U303 from this deposit. One of the small ore bodies on the Korzekwa prop- erty, the Orchard, near the center of the tract was tested by two perpendicular lines of holes drilled by the US. Geological Survey (pl. 1). Plate 1 shows that the mineralized zone is not controlled by the present land surface but by the Conquista-Dewees- ville contact. Although most of the uranium is in the sandstone above the contact, some is in sandy and silty clay below. Another ore body on the Korzekwa property was originally exposed by a shallow trench (figs. 1, 10) near the Korzekwa-Lyssy property line. Gamma-ray logs made by the US. Geological Survey in holes drilled by the Climax Molybdenum Co. show the ore body to be elongated parallel to the strike of the Deweesville. The section exposed in the trench was from 10 to 15 feet above the base of the Deweesville and clearly showed the small-scale scouring, crossbedding, and lensing within thin units of intercalated fine—grained sandstone and claystone. Such intercalations are characteristic of the lowest few feet of the Dewees- ville and to a lesser extent of the upper few feet of the Conquista, the zone that contained all the known oxidized uranium deposits in the Tordilla Hill-Dew- eesville area at the time of this survey. In the sandy material of the trench, bright yellow uranium minerals occur as streaks along bedding planes and as irregularly scattered blobs. The uran- ium minerals coat and fill the interstitial space be- tween sand grains. In the clayey beds, uranium min— erals from coatings along bedding planes and along minute, nearly vertical, partings or cleavage frac- tures. A. M. D. Weeks (oral commun., 1961) has identified the yellow to greenish-yellow uranium minerals autunite, carnotite, tyuyamunite, and po- seyite from the Korzekwa trench. URANIUM Each small unit (fig. 10; see section on “Mineral- ogy”) was spectrographically assayed for uranium and other elements. Unit 8 of channel sample C con- tained 0.3 percent U, which was the highest assay obtained from the south side of the trench. One small pocket of high-grade ore was observed just below the soil on the north side of the trench. This pocket contained a little more than 1 cubic foot of ore and may be a result of the upward movement of ground water by capillary action. Gypsum is very scarce, but stringers and small nodules of caliche are abundant throughout the up— permost few feet of section exposed in the Korzekwa trench. In contrast, in the Hackney trench caliche is scarce, but gypsum is abundant. Limonite is common throughout the beds and occurs both as small specks scattered throughout the sandstone and as streaks along bedding planes. The distribution of limonite and uranium in the beds is apparently unrelated. A large ore body near the center of the Lyssy property belonging to the Nuhn deposit (fig. 1) is elongated parallel to the strike of the beds. A deep trench at the south end of the deposit exposed 10—15 feet of mineralized material, some above and some below the Conquista-Deweesville contact. The ex- posed Conquista section consists of slightly silty clay that underlies a zone of clayey silt. The basal 5—10 feet of Deweesville consists of intercalated sandy and silty beds very similar to those exposed in the Korzekwa trench. Above the basal intercalated zone of Deweesville is a 2- to 3-foot bed of sandstone covered by soil. Uranium minerals are commonly Visible in the sandstone and siltstone of the lower part of the Deweesville and in the clayey siltstone at the top of the Conquista. The occurrences of uranium miner- als, caliche, and limonite in this deposit are similar to those described for the Korzekwa tract. Several closely spaced thin seams of manganese oxide could be traced for several feet along the wall of the Lyssy trench. The seams occur. within the ore zone and are either parallel with the bedding planes or cut across them at a low angle. During its drilling program, the Climax Molybde— num Co. discovered the Windmill ore body alOng the Gembler-Lyssy property boundary. At the time of field mapping, the only surface evidence of this de— posit was a filled-in trench, drill holes, and an in- tense surface-radioactivity anomaly. After the field- work was completed, this ore body was mined by open pit, and geologic sections of the pits and other DEPOSITS 27 geologic observations were made by D. H. Eargle as mining progressed. This ore body was the first to be mined by the San Antonio Mining Co. and furnished much of the total production from the N uhn deposit. Beside the usual yellow, high-valent uranium min- erals, the Windmill ore body contains, at a depth of about 40 feet, an appreciable quantity of sooty pitch- blende. Figure 11 and the following columnar section furnished by Eargle show the stratigraphic position of the pitchblende. Section of the Whitsett Formation in north wall of pit of the San Antonio Mining Co. Windmill ore body, Gembler prop- erty, Nuhn deposit, .9 miles airline southwest of Falls City, 2,000 feet west of Deweesville, Karnes County, Tex. [Beds 1—3 constitute the ore zone. Measured by D. H. Eargle] Deweesville Sandstone Member: Feet 7. Clay-conglomerate (channel-fill); coarse- grained sandstone matrix; clay blocks and boulders as much as 2 ft long, jumbled; sandstone lenses, some sandstone loose, some silicified after deposition; sharp very irregular lower contact, with as much as 4 ft of relief. Maximum thickness to top of cut 6. Clay, bentonite, very light gray; weathers white with irregular conchoidal fracture and smooth surface; faintly laminated, hackly, brittle; sharp contacts on top and bottom, bottom contact regular, manganese dioxide stains along top and bottom. Thick- ness varies with depth of scour preceding deposition of overlying bed _____________ 0—5 5. Sandstone, silty, very light olive gray, very fine grained, tuf’faceous, laminated; con- tains fragments and some impressions of finely disseminated plant fragments; upper 1 ft contains manganese dioxide stains; Ophiomorpha; lenticular, slightly ferrugin- ous, silicified at base, unit averages 6 inches in thickness, but varies 4 in. in thickness in 6 ft laterally ,,,,,,,,,,,,,,,,,,,,,,, 11 4. Siltstone, tufl'aceous, carbonaceous, pale-choc- olate to yellowish-orange—brown, clayey, very finely interlaminated with very fine grained sand; very carbonaceous 1.5—2.4 ft below top; lower contact wavy ,,,,,,,,,,,, 3. Sandstone, very light gray, fine-grained, silty, soft, finely crossbedded, faintly lami- nated; basal contact sharp but wavy, with about 6 in. relief in 6 ft laterally; oxidized uranium minerals fill interstices between grains W, _____________________________ Total Deweesville Sandstone Member exposed 4.5—7 10—12 34.5—39 Conquista Clay Member: 2. Clay, silty, pale—brown, contains finely dis- seminated carbonaceous matter; upper 3 ft thin bedded, beds averaging 1—2 in. in 28 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA Section. of the Whitsett Formation in north wall of pit of the San Antonio Mining Co. Windmill ore body, Gembler prop- erty, Nuhn deposit, 9 miles airline southwest of Falls City, 2,000 feet west of Deweesville, Karnes County, Team—Con— tinued Conquista Clay Member—Continued Feet thickness, maximum of 3 in.; vertically jointed; brown (ferruginous) staining and abundant autunite and other oxidized uranium minerals locally along bedding and joint planes; oxidized zone of bed below 1. Clay, medium-gray, laminated; contains silty streaks and lenses; locally, along bedding- plane surfaces of clay and in thin silty laminae, are smears, or vermiculate mot- tlings, of somewhat irridescent black min- eral matter containing sooty uraninite .,_ 2 Total Conquista Clay Member exposed 6 All the deposits on the Nuhn lease lie along the Deweesville-Conquista contact updip from a deep clay-filled channel in the Deweesville Member (fig. 3). The other two facies of the Deweesville are also present within the Nuhn lease. Where not eroded, the Deweesville Sandstone Member is 40-50 feet thick within the Nuhn lease. The beds strike from about N. 20° E. to N. 60° E. and dip southeast from 20 to 60 feet per thousand, but the slight change in attitude has no apparent effect on the distribution of ore minerals. LUCKETT (CONTINENTAL OR LYSSY-NEISTROY) DEPOSIT The Continental Oil Co. acquired the mineral lease for the Lyssy and Neistroy tracts northeast of Dew- eesville (fig. 1) from A. J. Luckett, of New Braun- fels, Tex., trustee for the mineral rights. The Conti- nental Oil Co. drilled several holes to explore a large surface radioactivity anomaly and discovered a siza- ble deposit, which was mined by Susquehanna-West- ern in 1961—62. Cuttings from the drill holes were examined by Paul deVergie, of the US. Atomic Energy Commis- sion, and much of the following description is based upon his work (deVergie, 1958). The maximum di- mensions of the deposit, extended to include much low-grade material, are about 2,000 feet long, 800 feet wide, and 10 feet thick; the long dimension par- allels the strike of the beds. The uranium ore is confined to a sandstone and siltstone zone of irregu- lar thickness between the clay of the Conquista and an overlying clay zone within the Deweesville. Al- though this clay zone is wider and more sheetlike than the clay-filled channel (figs. 3, 4), the two fea- tures undoubtedly are closely related. The scouring and the lensing within the lower part of the Dewees- ville in the immediate vicinity of this deposit are similar to these features within the Deweesville at other deposits. Soil, sandy, dark-gray. Conglomerate; clay fragments and boulders, course sand matrix. Very irregular base. Clay, bentonitic, very light gray, smooth; very irregular fracture. Sandstone, silty, very light olive gray, fine-grained, tuffaceous, lamin— ated; finely divided organic matter; upper part contains Ophiomorpha. Siltstone, pale— chocolate to yellowish-orange - brown; highly carbonaceous; laminated. Deweesville Sandstone Member Whitsett Formation Sandstone, very light gray, fine- grained, silty, soft, finely cross- bedded, faintly laminated; abundant secondary minerals filling interstices between grains. Irregular base. Clay, silty, pale- brown, carbon- aceous, lamin- ated; abundant autunite along bedding and joint planes. Clay, medium-gray, laminated; silty streaks. Black, vermiculate motiling of sooty pitchblende locally in silty layers. Whitsett Formation Conquista Clay Member, FIGURE 11,—Diagrammatic section, on north wall of pit in Windmill ore body, Gembler property, Nuhn deposit. Note channeling and scouring. Section by D. H. Eargle. Not to scale. ORE CONTROLS 29 ORE CONTROLS The most obvious factors that controlled uranium deposition are lithology, structure, and stratigraphy. In the Tordilla Hill-Deweesville area all the impor- tant known deposits occur near the Conquista-Dew- eesville contact. Most of the ore is within the lower part of the Deweesville Sandstone Member, which is fine grained to very fine grained sandstone with in- tercalated lenses of sandstone, silt, and clay. In some deposits an appreciable amount of uranium occurs locally where beds in the upper several feet of the Conquista Clay Member are mainly silt. The spatial relationship of the three lithofacies of the Deweesville Member is an important local con- trol. The deposits occur in or near the sandstone- silt-clay facies of the Deweesville, or lie within the clay-filled channel, or are found updip on the outer flank of a leveelike structure adjacent to the chan- nel. The relation of the deposits to the channel sug- gests that the levee restricted the movement of uran- ium-bearing solutions through the relatively permea— ble Deweesville and that the resultant change in ve- locity contributed to the uranium precipitation. The channel and the uranium deposits lie in a north- trending belt. The higher grade uranium is in or slightly updip from the channel; no uranium was found nearby on the downdip side. Elsewhere, how- ever, such as in sections 3—60 to 3—39 (pl. 1), Where the levee is only slightly higher than the base of the Deweesville, the levee has no apparent effect On the deposition of the uranium. The lack of influence is emphasized by the extension of the radioactive zone through the clay which forms the levee. The Nuhn deposit on the Lyssy-Korzekwa proper- ties is a few hundred feet updip from the clay-chan- nel facies (fig. 12) and has been emplaced mainly within the sandstone-silt-clay facies. The Barg- mann-Hackney deposit is a few hundred feet updip from the clay-filled channel facies and probably is in the sandstone-silt-clay facies, though this relation- ship has been obscured by erosion. Much of the ur- anium in the Hackney deposit is in a medium- grained sandstOne of the sandstone-silt—clay facies. The clay-filled channel facies has not been detected near the Hackney dep0sit, but a clay zone, exposed by exploration, may be related to the channel. The channel and the sandstone-silt-clay facies ap- parently extend northeastward from Deweesville through the area of the Luckett deposit. Work by deVergie (1958, fig. 3) shows in the middle part of the Deweesville Member a 10- to 20-foot-thick zone of clay and silt that corresponds to the sandstone- silt-clay facies described herein. In the area of the Luckett deposit, the channel filling becomes siltier, thinner, and wider, grading laterally into the sand- stone-silt-clay facies. The deposits are in beds that are transitional (both vertically and horizontally) between strata of moderate permeability and strata of relatively low permeability. The relation between uranium grade (percent eU30g) and rock type was examined statistically (fig. 13). Uranium in the grade range of 0.010—0.049 percent eU308 is about evenly distributed in sand- stone, sandy clay, and clay. Layers of uranium min- erals cross lithologic contacts, thereby indicating no apparent lithologic control over their deposition for this grade. Uranium minerals in the grade range 0.05—0.099 percent eU308 are found in all three lithologies but occur less in clays; thus their deposition may have been controlled to some extent by decreasing perme- ability below the layers of uranium. In some places depositional control is the base of the oxidized zone (pl. 1, section B—56 to B—50); elsewhere, layers of EAST WEST ~25, B/ B E ' Q — 480’ 480 3 DeweesvilleiSandstone Member 440’ § Silicified sandstone cap Dubose Member _ 440 3 , Silt facies . . . . I 400’ E” —'-—‘——~' " " — 400 360’ \Eag‘rn—aryqisifiefis Conagiritseslay Uranium mineralization — 360’ 320, alluvium sandstone 320, 0 i l l 1000 FEET | | l VERTiCAL EXAGGERATION X 2 FIGURE 12.—Geologic section of the Whitsett Formation across the Nuhn deposit, showing relation of the de- posit to the clay-channel facies and to the sand-silt—clay facies. Deweesville Sandstone Member is shown by dot pattern; uranium mineralization by crosshatch. Line of section shown on figure 1. Modified from Mac- Kallor, Moxham, Tolozko and Popenoe (1962). 30 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA PERCENTAGE EQUIVALENT URANIUM OXIDE 0010—0049 0050—0099 010—049 0.50—0.99 Clay Sandy clay =1" 26 E 27 34 E 36 i75 O 100 O 100 O 100 O 100 PERCENTAGE OF OCCURRENCES Sandstone FIGURE 13.—~Re1ation between uranium grade and rock type. this grade cross lithologic contacts with no apparent depositional control. Uranium above 0.10 percent grade is found only in sandstone and sandy clay, thereby indicating lith— ologic control. In sections B—60 to B—39 and B—56 to B—50 (pl. 1), the uranium is in a fairly continuous zone that follows the general dip of the beds. The zone is apparently unaffected by local undulations in the vertical position of the stratigraphic contact. In section 13—56 to B—5O the uranium in the grade range 0.10—0.49 percent eU308 occurs mainly in sand but intersects undulations in an underlying sandy clay. Uranium in the highest grade range, 0.50-0.99 per- cent eU;,O,, occurs in discontinuous zones in sand- stone and sandy clay, but does not occur in clay. The extent of structural control of ore deposition is not easily assessed. Vertical jointing had some minor influence in determining the exact shape of the deposits, and the strike of the beds in most in- stances coincides with the direction of elongation of the deposits. The clay channel that cuts through the Deweesville Member probably impeded or diverted the movement of ground water in a manner that favored a strike-oriented trend for major ore deposi- tion. The concentration of deposits in the warped block between the ends of the Falls City and Fash- ing faults may also reflect the control of ground-wa- ter movement on mineral deposition. In the Tordilla Hill-Deweesville area and in the central coastal plain area as a whole, the principal known uranium deposits are in the basal part of the Deweesville Sandstone Member and the upper part of the Conquista Clay Member of the Whitsett For- mation. Evidently the rocks laid down during this geologic interval provided the environment required for a uranium host, and it is in this sense that the term “stratigraphic control” is used. Perhaps more correctly, such stratigraphic control represents a summation of favorable lithologic factors and the necessary geochemical environment for the forma- tion of uranium deposits. ORIGIN OF THE URANIUM DEPOSITS Volcanic tuff was deposited in a terrestrial or shoreline environment during Jackson time. Glassy material of this sort is fairly unstable, particularly if exposed to alkaline carbonate ground water simi- lar to that now existing in the coastal plain area. It is postulated that uranium and silica were released from the glass during diagenetic processes, as evi- denced by widespread devitrification of the glass, silicification, and zeolitic alteration. The uranium in the interstitial fluid was trans- ported to a favorable depositional environment, ap- parently provided in part by permeability traps and by reducing agents—perhaps organic material, hy- drocarbons, hydrogen sulfide, and pyrite in the host rocks or hydrogen sulfide originating in the Edwards Limestone (associated with the Fashing-Edwards gas-distillate field). The depositional environment would tend to minimize loss of uranium to the open sea. Tertiary volcanic material provides a source of uranium. A theory of leaching of uranium from tuff has been presented by Waters and Granger (1953) and by McKelvey, Everhart, and Garrels (1955, p. 499—501). Denson and Gill (1965, p. 67) concluded that uranium was leached from Oligocene and Mio- cene volcanic ash, transported laterally and down- ward, and then precipitated in carbonaceous rocks (lignite) in the southwestern part of the Williston basin of the northern Great Plains. The Eocene and Miocene rocks of the Texas coastal plain contain a considerable amount of tuff and other volcanic de- bris (Eargle, 1959b). On the basis of a study of idiomorphic zircon, Callender and Folk (1958) stated that volcanism was more pronounced during deposition of the Eocene Yegua Formation (at the top of the Clai- borne Group) and younger formations than during deposition of the Eocene Sparta Sand (near the mid- dle of the Claiborne Group) and older formations. Their study supports the theory that most of the uranium was leached from the Jackson (younger than the Yegua) and younger rocks, rather than from rocks stratigraphically below the ore-bearing Jackson Group. Although chemical analyses of weathered and un- ORIGIN 31 weathered rock outside the mineralized area are not available, an assumption that about 5 ppm U was leached from the more tuffaceo-us units of the Ter- tiary sediments is reasonable. Denson and Gill (1956, p. 417) stated that the Arikaree Formation and the White River Group of eastern Montana and the Dakotas contain an average of about 0.0015 per- cent (15 ppm) uranium, which is 12 times the aver- age for sedimentary rocks. According to Larsen and Phair (1954, p. 75), Denson and Gill (1965, p. 58), Doe (1967, p. 62), and Rosholt and Noble (1969), 6—7 ppm U is a more realistic maximum concentra- tion for silicic glassy igneous rocks. Larsen and Phair (1954, p. 80) stated that as much as 40 per- cent of the uranium in most fresh-appearing igneous rocks is readily leachable. If the tuffaceous rocks of the Texas coastal plain originally contained 6—7 ppm U and if from 1/3 to 1/2 of that uranium were in a state available for leach- ing, about 3 ppm U could be leached from the tuffa- ceous sediments and would be available to form a uranium deposit. The tufi'aceous rocks of the Texas coastal plain are a quantitatively adequate source for the uranium contained in the deposits in the Tordilla Hill-Dew- eesville area. Consider a slab of sandstone of the Deweesville 40 feet thick (the average thickness), extending about 20,000 feet along the strike from the base of Tordilla Hill to the Luckett deposit (fig. 1) and extending updip for 5,000 feet. If the rock averages 14 cubic feet per t0n and if 3 ppm U is readily leached, this one slab would make available more than 840 tons of the element uranium, which is considerably more than the uranium contained in the 250,000 tons of inferred ore (Moxham, 1958, p. 816) for the Karnes County—Atascosa County area. Admittedly, the quantity of uranium in nonore grade rock may be several times as large as the quantity of uranium within the deposits, but the source material was not confined to the Deweesville, and much of the leached uranium well may have moved more than 5,000 feet downdip before redepo- sition. - A magmatic theory was considered, but there are no known igneous intrusions to support such a theory, and an aeromagnetic survey made at the same time as the aeroradioactivity survey (Moxham and Eargle, 1961) did not indicate buried igneous rocks. If uranium were introduced into the Jackson rocks by solutions coming from a deeply buried un- known magmatic source, one might find evidence of the pathways or channels traversed by the magmatic solutions. The Falls City and the Fashing faults are logical pathways, and if they served such a purpose for uraniferous solutions, one would expect to find at least a slight contrast in radioactivity on opposite sides of the faults. Neither these nor any other major faults in the immediate area can be detected from the radioactivity pattern (Moxham and Ear- gle, 1961) ; but several radioactive anomalies, includ— ing a small uranium deposit in Live Oak County to the south, occur along faults. These occurrences may be due to the coincidence of faulting and the retar— dation of ground water plus seepage of a precipitant along the faults. TRANSPORTATION AND DEPOSITION OF URANIUM Much of the present ground water in the area is of an alkaline carbonate type (Anders, 1960, table 7), which is an excellent leaching and transporting agent for uranium. The water probably became alka- line by the leaching of volcanic material in the Ter- tiary rocks, and similar alkaline carbonate waters would have existed in the past. Regardless of the original source of the uranium, it eventually was added to alkaline carbonate ground water, probably as a uranyl (U+603) ion. As the ground water migrated downdip, the uranium pre- cipitated in chemically and physically favorable re- ducing environments. According to A. M. D. Weeks (oral commun, 1958), some reducing agent is needed to trigger precipitation of uranium. Although reduced carbonate content of the ground water may have been an important factor in determining the general area in which uranium was deposited, the actual site of deposition requires the presence of a reducing agent. Carbonate can be lost if by release of pressure, carbon dioxide gas escapes; such loss would cause calcite precipitation, even if the solubil- ity were decreased by the loss of sulfate and carbon- ate radicals. Hydrogen sulfide in natural gas will produce the reducing environment required for pre- cipitating uranium. In the southern Black Hills, Gott (1956, p. 8) found that uranium occurred in carbonate-poor sandstones marginal to sandstones that were well indurated with calcium carbonate cement. This rela- tionship suggests (Gott, 1956, p. 3—4) that solutions that precipitated calcium carbOnate also precipitated uranium. In the Tordilla Hill-Deweesville area, how- ever, no calcium carbonate cement was observed in the ore deposits, and only very small stringers of caliche occur near the surface. Calcium carbonate cement was observed in outcrop only in the sandy, fossiliferous unit of the Conquista Clay Member and 32 OXIDIZED URANIUM ORE DEPOSITS, was not observed in the ore zone, the Deweesville Sandstone Member. If precipitation of calcium car- bonate was a factor in uranium deposition in the Karnes County area, precipitation of the calcium carbonate would have occurred generally updip from the uranium deposits in part of the Deweesville now removed by erosion. Any calcium carbonate depos- ited near the uranium deposits in beds not yet eroded might have been removed by meteoritic water, just as caliche in the Catahoula Tuff a few miles from the deposits is now being destroyed. A few of the deeper sandy cores from the “K” holes, downdip from the uranium deposits, did contain a few stringers of fibrous calcite and calcium carbon- ate cement; mainly from depths greater than 150 feet. A significant quantity of reducing material is re- quired to form an ore deposit. Tests show that natu- ral gases, principally those that contain hydrogen sulfide, but maybe hydrogen to a lesser extent, will precipitate uraninite at the gas-liquid interface (Sims and Smith, 1956). Hydrogen sulfide undoubt- edly was an important reducing agent for the Karnes County deposits. A possible source is the Fashing-Edwards field, which produces a sour-gas distillate from the Edwards Limestone of Creta- ceous age. This field is only about 1 mile downdip from the deposits but is at an elevation of —-—10,380 to —9,780 feet (Pinkley, 1958, p. 40). Sour gas from this field may have migrated up the Fashing fault zone and then updip in permeable beds such as the Deweesville Member. D. H. Eargle (written commun., 1971), however, believes this is an unlikely source of the reducing agent and says, Although migration upward from the Edwards Limestone in the Fashing gas field has been postulated, it is not likely that this was the source of the hydrogen sulfide. The principal argument against this source is that the same fault traps sweet gas in the Carrizo Sand 7,500 feet higher in section. Apparently enough hydrogen sulfide is generated in the higher beds to create the reducing environment necessary to precipitate the uranium. Hydrogen sulfide may have been generated locally from organic matter in the clayey parts of the J ack- son Group rather than brought into the ore beds from the Fashing-Edwards gas field. Either or both sources of hydrogen sulfide are geologically feasible. A strong odor of hydrogen sulfide was detected com- ing from a shallow water well a short distance down- dip from the deposits. The presence of the well in the Whitsett Formation strengthens the idea that hydrogen sulfide played an important role in form- ing the deposits. TORDILLA HILL-DEWEESVILLE AREA . Organic derivatives of either animal or vegetable material may have been reducing agents. Garrels and Christ (1956, p. 300) stated, “It appears that most materials derived from wood are effective pre- cipitants of uranium from migrant solutions * * *.” The evidence is that wood, per se, was not an impor- tant reducing agent in the Karnes County area. Al- though silicified wood occurs in mest of the Jackson beds, it rarely contains anomalous amounts of uran- ium, and the occurrence of uranium mostly in cracks indicates deposition after silicification. Most of the deeper cores (from five holes drilled by the US. Geological Survey) of silt and clay contained organic derivatives, indicated by a petroliferous odor. A par- tial explanation for the occurrence of the uranium deposits in sand and silt overlying clay is that reduc- ing fluids formed in the clay, which was compara- tively rich in organic material, and migrated upward into permeable sands, where they precipitated uran- ium from ground water in those sands. In addition to the previously mentioned gas—distil- late field, there are two oil fields, one producing from the Wilcox GrOup of Eocene age along the same fault zone and another producing from the Wilcox along the Falls City fault. No evidence has been found, however, that petroleum, per se, was an im- portant factor in formation of the uranium deposits, either as a transporting medium or as a reducing agent. Two of the samples collected by Climax Mo- lybdenum Co. from its drill holes near uranium de- posits contained grains of a black vitreous substance that burned with a smoky flame. This asphaltite, probably a petroleum residue, contained no anoma- lous radioactive elements. Scattered small grains of pyrite, a good reducing agent for uranium, were observed with a hand lens at the Hackney deposit and in many of the clayey and silty cores from the “K” holes. Although pyrite is widespread, the percentage of pyrite in the occur- rences observed is too low for the pyrite to have been the major reducing agent for the Karnes County deposits. Locally, where concentrations are high, pyrite might have been an important reducing agent—at the Hackney deposit, for example. Al- though only an insignificant amount of pyrite is now in the rocks there, some of the high-grade material, both silicified and nonsilicified, is heavily coated with deep-yellowish-brown limonite, which may be an alteration product of pyrite. A. M. D. Weeks (oral commun., 1959) suggested that uranium might be removed from ground water by adsorption on clay, but it is difficult to see how ORIGIN 33 this process alone could form a significant deposit in silty or sandy rocks. GEOLOGIC DEVELOPMENT OF THE DEPOSITS The source of the Eocene sediments must have been a combination of erosional debris from olde sedimentary rocks to the northwest or west (D. H. Eargle, written commun., 1969) and of elastic vole canic material. The sediments locally contained con— siderable organic material, as evidenced by lignitic material, molds of plant remains, silicified wood, small round masses of asphalt, and thin chuinas of Corbicula, Ostrea, and gastropods. Volcanic activity to the west and southwest, chiefly in northern Mexico and western Texas, contributed much ash and sand-sized volcanic material to the area. Some of this material fell directly into shallOw bays and estuaries, but most of it was deposited on land. The fine unconsolidated volcanic debris was quickly picked up by streams and, along with other detrital sediments, quickly transported to the shallow ma- rine environment where it was deposited before fresh water had a chance to leach the volcanic mate- rial. Rapid burial prevented uranium from being Deweesville Sandstone Member Dubose Member Tordilla Sandstone Member Fashing Clay Member Erosion(?) Uppermost beds Post-Catahoula to recent erosion Pre-Catahoula erosion 'Catahoula Formation Present time >‘ L” 0 Whitsett ‘9 800 Formation | LT. i | | | l | ‘ .— Lu E 600 _ E _i S n: D 400 — CD 1... O E o. 200 Lu 0 TIME (NO SCALE) FIGURE 14.—Depth of burial of basal part of the Deweesville Sandstone Member from the start of Deweesville time to the present in the Tor- dilla Hill-Deweesville area. Graph line dashed where drawn between two possible depths as shown by heavy dots. leached by the sea water. Slight transgressions and regressions of the sea in Jackson times, as well as the very nature of shallow-water nearshore deposits, "esulted in intercalations of sand, silt, and clay. In Oligocene time, conditions were more stable 'han during Jackson time, and the dominant sedi— ment deposited was clay. Ash in the upper part of the Oligocene( ‘2) Frio Clay is evidence of some vol- canic activity. At the end of Frio deposition, the Deweesville Sandstone Member of the Jackson Group was covered by approximately 600 feet of sediments (fig. 14). Fresh water began to enter the Jackson rocks at about this time, probably shortly before deposition of the Catahoula Tuff. Shallow ground waters flowed laterally toward streams, but deeper ground water flowed downdip, leaching elements from the volcanic material. The waters moving downdip were locally diverted, guided by clayey aquicludes and retarded by perme— ability barriers where there were facies changes and structural anomalies. Sodium was added by a proc- ess of base exchange (Renick, 1924). Eventually a sodium carbonate ground water, containing small amounts of uranium, molybdenum, and other ele- ments, was developed. This ground water was under sufficient hydrostatic pressure to replace some of the connate water. Although most of the movement of ground water was downdip, there was some move- ment between units. For example, some water in the Dubose Member may have entered the sandstone of the Deweesville by flowing from one lens of sand- stone to other contiguous, but lower, lenses until it reached the Deweesville; and the ground water in the Catahoula Tuff of Miocene age may have moved into lower stratigraphic units (fig. 15). Upon passingthrough a physically and chemically favorable environment, uranium and other elements were precipitated. Inasmuch as most of these favor- able environments were below the water table, some of the uranium was precipitated as pitchblende and other minerals in which the uranium has a valence of +4; some of the uranium, however, may have been absorbed by clay. Except in rare cases, the deposited uranium was widely scattered in small quantities. Although the water table fluctuated during cli- matic cycles, the overall tendency was for it to drop in relation to the stratigraphic units, as a result of the lowering of the land surface by erosion. When the water table dropped below the precipitated uran- ium, the minerals were unstable in the oxidizing en- vironment, and new oxidized minerals were formed. Because vanadium was scarce, mostly water-soluble 34 OXIDIZED URANIUM ORE DEPOSITS, TORDILLA HILL-DEWEESVILLE AREA EXPLANATION Contact _> Direction of flow of ground water containing uranium e Deposit of uranium-bearing min» erals, Tordilla Hill area Relatively impermeable clay unit FIGURE 15,—Diagrammatic section along the southwest boundary of Karnes County at the end of Catahoula time, showing movement of ground water. Tc, Catahoula Tufl'. Tf, Frio Clay. Whitsett Formation: Twsc, upper sand- stone and claystone; wa, Fashing Clay Member; th, Tordilla Sandstone Member; de, Deweesville Sandstone Member; Twc, Conquista Clay Member. minerals, rather than carnotite, were formed. These newly formed minerals may have been taken into solution and almost immediately reprecipitated, either as a result of evaporation of the vadose water or by chemical reaction with a nearby reducing ma- terial. Sooner or later, however, the uranium was carried by vadose water back to the ground water where it was again reprecipitated, and another cycle was completed. Under certain conditions uranium was lost or per- manently removed from this cycle of temporary dep- osition and solution. Such a loss is occurring today in the Karnes County area. When the land surface is lowered faster than uranium in the oxidized zone is added to the ground water, some of the uranium eventually reaches the surface to form an outcrop and is then eroded and carried away by surface water. The slower the rate of er0sion, the more time a favorable reducing zone had to deposit or “trap” uranium from migrating ground water. Eventually, however, erosion lowered the surface so that the deposited uranium minerals were in the zone of oxi- dization above the water table. Under these condi- tions the uranium minerals were unstable and were eventually taken into solution and redeposited in an— other favorable reducing environment downdip from the previous site. The trend is for the later deposits to be larger and richer than the first ones formed, for the first ones had a source of uranium only from the tuffaceous material. Later deposits had an addi- tional source of uranium from the preexisting con- centrations or deposits. An arid climate results in less vadose water to carry the uranium to the ground water; if evapora- tion were greater than precipitation, capillary action would move the uranium toward the land surface rather than toward the water table. This has been happening in the Karnes County area, where a high-grade pod of yellow uranium mineral (autunite?) has formed just below the surface at the Korzekwa trench. Isotopic analyses by Rosholt (in Weeks and Eargle, 1963) also show that near-sur- face uranium recentlyrhas been moving. The climate of the last few thousands of years has been such that uranium in the oxidized zone has not been moving down as fast as erosion has lowered the surface. Consequently, some uranium is being car- ried out of the area by both Tordilla Creek and Scared Dog Creek. A water well on the Korzekwa property a short distance downdip from the deposit contains 96 ppb (parts per billion) uranium, which indicates that some of the uranium is being removed by ground water from the deposit. The data (pl. 1, section H—13 to B—24) show some evidence that the radioactive minerals have been de- posited recently and that they are probably in transit at present. Between holes B—24 and H—4, the layer of anomalous radioactivity intersects at least two lithologic contacts, including the contact be- tween the Deweesville and the Conquista Members. The base of the radioactive layer parallels that contact and is restricted to the oxidized zone. Be- tween drill holes H—9 and H-ll the radioactive layer parallels the topographic slope instead of the strati— graphic dip; this relationship suggests that surface water is leaching radioactive minerals from the area near H—9 and that the minerals are being redepos- ited at present in the vicinity of hole H—lO. Evidence of leaching of uranium minerals from a deposit by ground water movement is illustrated at drill hole H—7 (section H—13 to B-24, pl. 1). A de- pression in the base of the Deweesville may cause an REFERENCES CITED 35 accumulation of surface water, thereby permitting a greater quantity to enter the underlying Conquista at this location than elsewhere. The leached minerals appear to have moved downward from the depres— sion into the Conquista and to have proceeded from there downdip. The relative permeability of the host rock and of the underlying rock may have been a controlling factor in the deposition of the uranium minerals. The base of most uranium layers follows an inclined plane which sometimes follows a distinct lithologic contact. In many locations the uranium occurs in a relatively permeable sandy layer underlain by a less permeable clayey layer. Another example of uranium minerals being leached from a deposit and moved down the topo— graphic slope instead of following the geologic dip is shown in section 8—40 to B—28 (pl. 1). The Hackney deposit is about 200 feet east of hole B—28 beyond the left end of the illustrated section. The high-grade ore is in the basal part of the Deweesville Sandstone Member and the lower grade material extends into the Conquista Clay Member. The ore is near the surface of the ground, at an elevation higher than that of the drill collar of hole B—28. Erosion along the topographic slope has truncated the strata that crop out along the section. Fragmental debris from the outcropping strata has been transported by sur- face water westward and redeposited down the slope. The waterborne uranium leached from the Hackney property follows the surficial alluvium lying on the truncated layer of impermeable clay between holes B—28 and S—29. Between S—29 and S—30 the uranium apparently entered the permeable sandstone of the Conquista, and its movement along the topographic slope virtually terminated at hole S—30. The layer of anomalous radioactivity that par- allels the topographic surface at a depth of about 10—15 feet between S—27 and 8—31 seems to origi- nate locally from the fossiliferous sandstone be- tween holes S-27 and S—28. This origin suggests strongly that the uranium has moved downdip from the radioactive layer at-the surface along the contact of the fossiliferous sandstone unit and the clay of the Conquista Member between drill holes 8—29 and 8—28. REFERENCES CITED Anders, R. B., 1960, Ground-water geology of Karnes County, Texas: Texas Board of Water Engineers Bull. 6007, 107 p. Bell, K. G., Rhoden, V. C., McDonald, R. L., and Bunker, C. M., 1961, Utilization of gamma-ray logs by the U.S. Geological Survey, 1954~53: U.S. Geol. Survey open-file report, 89 p. Billings, M. P., 1946, Structural geology (second printing): Prentice~Ha11, Inc., 473 p. Brown, R. D., Jr., Eargle, D.H., and Moxham, R.M., 1961a, Preliminary aeroradioactivity and geologic map of the Falls City NW quadrangle, Atascosa, Karnes, and Wilson Counties, Texas: U.S. Geol. Survey Geophys. Inv. Map GP—249. 1961b, Preliminary aeroradioactivity and geologic map of the Falls City NE quadrangle, Karnes and Wilson Counties, Texas: U.S. Geol. Survey Geophys. Inv. Map GP—250. Callender, D. L., and Folk, R. L., 1958, Idiomorphic zircon, key to volcanism in the lower Tertiary sands of central Texas: Am. Jour. Sci., v. 256, no. 4, p. 257—269. Crutchfield, J. W., and Bowers, E. F., 1950, Performance of the Lower Pawelek Reservoir, Falls City Field, Karnes County, Texas: Am. Inst. Mining Metall. Engineers Trans., v. 189, p. 335—344. Denson, N. M., and Gill, J. R., 1956, Uranium-bearing lignite and its relation to volcanic tufl‘s in eastern Montana and North and South Dakota, in Page, L. R., Stocking, H. E., and Smith, H. B., compilers, Contributions to the geology of uranium and thorium by the United States Geological Survey and Atomic Energy Commission for the United Nations International Conference on Peaceful Uses of Atomic Energy, Geneva, Switzerland, 1955: U.S. Geol. Survey Prof. Paper 300, p. 413—418. 1965, Uranium-bearing lignite and carbonaceous shale in the southwestern part of the Williston basin—a regional study: U.S. Geol. Survey Prof. Paper 463, 75 p. deVergie, P. C., 1958, Some developments in uranium ore studies in Karnes County, Texas, in South Texas Geol. Soc., Fall Field Trip Dec. 1958, p. 23—29. Doe, B. R., 1967, The bearing of lead isotopes on the source of granitic magma: Jour. Petrology, no. 8, pt. 1, p. 51— 83. Eargle, D. H., 1955, Stratigraphy [Karnes County, Texas]: U.S. Geol. Survey Rept. TEI—540, p. 135—139. 1958, Regional structure and lithology in relation to uranium deposits, Karnes County area, Texas [abs]: Econ. Geology, v. 53, no. 7, p. 919. 1959a, Sedimentation and structure, Jackson Group, south-central Texas: Trans. Gulf Coast Assoc. Geol. Soc., v. 9, p. 31—39. ——1959b, Stratigraphy of Jackson group (Eocene), south- central Texas: Am. Assoc. Petroleum Geologists Bull., v. 43, no. 11, p. 2623—2635. 1970, Recent developments in uranium in south Texas: South Texas Geol. Soc. Bull., v. 10, no. 6, p. 3—6. 1972, Revised classification and nomenclature of the Jackson Group (Eocene), south-central Texas: Am. Assoc. Petroleum Geologists Bull., v. 56, no. 3, p. 561— 566. Eargle, D. H., and Snider, J. L., 1957, A preliminary report on the stratigraphy of the uranium—bearing rocks of the Karnes County area, south-central Texas: Texas Univ., Bur. Econ. Geology, Rept. Inv. 30, 30 p. Eargle, D. H., and Weeks, A. D., 1961a, Uranium-bearing clays and tuffs of south-central Texas, in Field excur- sion, central Texas, October 1961: Texas Univ. Bur. Econ. Geology Guidebook 3, p. 19—30. 36 OXIDIZED URANIUM ORE DEPOSITS, 1961b, Possible relation between hydrogen sulfide- bearing hydrocarbons in fault—line oil fields and uranium deposits in the southeast Texas coastal plain, in Short papers in the geological and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424—D, p. D7—D9. Eargle, D. H., Trumbull, J. V. A., and Moxham, R. M., 1961a, Preliminary aeroradioactivity and geologic map of the Floresville SE quadrangle, Karnes and Wilson Counties, Texas: U.S. Geol. Survey Geophys. Inv. Map GP—246. 1961b, Preliminary aeroradioactivity and geologic map of the Stockdale SE quadrangle, Karnes, De Witt, and Wilson Counties, Texas: U.S. Geol. Survey Geophys. Inv. Map GP—248. 19610, Preliminary aeroradioactivity and geologic map of the Karnes City NW quadrangle, Karnes County, Texas: U.S. Geol. Survey Geophys. Inv. Map GP—251. Ellisor, A. C., 1933, Jackson group of formations in Texas, with notes on Frio and Vicksburg: Am. Assoc. Petroleum Geologists Bull., v. 17, no. 11, p. 1293—1350. Finch, W. I., 1955, Karnes County, Texas: U.S. Geol. Survey Rept. TEI—540, p. 134—135. Fix, P. F., 1955, Uranium in natural waters: U.S. Geol. Sur- vey Rept. TEI—540, p. 200—202. 1956, Uranium in natural waters: U.S. Geol. Survey Rept. TEI—620, p. 279—280. Garrels, R. M., and Christ, C. L., 1956, Field studies on the origin of primary uranium ores in the western United States, in Semiannual progress report for June 1 to November 30, 1956: U.S. Geol. Survey TEI—640, p. 300— 301, issued by the U.S. Atomic Energy Comm. Tech. Inf. Service, Oak Ridge, Tenn. Gott, G. B., 1956, Inferred relationship of some uranium de- posits and calcium carbonate cement in southern Black Hills, South Dakota: U.S. Geol. Survey Bull. 1046—A, 8 p. Hilpert, L. S., and Bunker, C. M., 1957, Effects of radon in drill holes on gamma-ray logs [N. Mex.]: Econ. Geology, v. 52, no. 4, p. 438—445. Knebel, R. M., 1957, Deep Edwards reservoir in shallow country: Oil and Gas Jour., v. 55, no. 1, p. 166. Larsen, E. S., Jr., and Phair, George, 1954, The distribution of uranium and thorium in igneous rocks, in Faul, Henry, ed., Nuclear geology: John Wiley & Sons, Inc., p. 75—89. Luders, Von K., 1934, Uber das Wandern der Priele: Abh. Naturwiss., verein zu Bremen, 29, p. 19—32. MacKallor, J. A., and Bunker, C. M., 1958, Ore controls in the Karnes County uranium area, Texas [abs]: Geol. Soc. American Bull., v. 69, no. 12, pt. 2, p. 1607. MacKallor, J. A., Eargle, D. H., and Moxham, R. M., 1958, Texas Coastal Plain geophysical and geologic studies— semiannual progress report, June 1 to Nov. 30, 1958: U.S. Geol. Survey Rept. TEI—750, p. 78—87. MacKallor, J. A., Moxham, R. M., Tolozko, L. R., and Popenoe, P. P., 1962, Radioactivity and geologic map of the Tordilla Hill—Deweesville area, Karnes County, Texas: U.S. Geol. Survey Geophys. Inv. Map GR—199. McKelvey, V. E., Everhart, D. L., and Garrels, R. M., 1955, Origin of uranium deposits, in Part 1 of Bateman, A. M., ed., Economic geology, 50th anniversary volume, 1905— 55: Urbana, 111., Economic Geology Pub. 00., p. 464—533. McKinstry, H. E., 1948, Mining geology: Prentice-Hall, Inc., 680 p. Manger, G. E., 1958, A comparison of the physical properties of uranium-bearing rocks in the Colorado Plateau and TORDILLA HILL-DEWEESVILLE AREA Gulf Coast of Texas [abs]: Econ. Geology, v. 53, no. 7, p. 922—923. Manger, G. E., and Eargle, D. H., 1967, Physical and asso- ciated properties of uranium-bearing rock in five drill holes in Karnes County, Texas: U.S. Geol. Survey open- file report, 19 p. Maxwell, R. A., 1962, Mineral resources of south Texas— Region served through the Port of Corpus Christi: Texas Univ. Bur. Econ. Geology Rept. Inv. 43, 140 p. Moxham, R. M., 1958, Geologic evaluation of airborne radio- activity survey data, in United Nations Survey of raw material resources: U.N. Internat. Conf. Peaceful Uses of Atomic Energy, 2d, Geneva, Sept. 1958, Proc., v. 2, p. 814—819. 1964, Radioelement dispersion in a sedimentary en- vironment and its effect on uranium exploration: Econ. Geology, v. 59, no. 2, p. 309—321. Moxham, R. M., and Eargle, D. H., 1961, Airborne radio- activity and geologic map of .the Coastal Plain area, southeast Texas: U.S. Geol. Survey Geophys. Inv. Map GP—198. Moxham, R. M., Eargle, D. H., and MacKallor, J. A., 1957, Texas Coastal Plain geophysical and geologic studies— semiannual progress report, Dec. 1, 1956 to May 31, 1957: U.S. Geol. Survey Rept. TEI—690, p. 445—457. 1958, Texas Coastal Plain geophysical and geologic studies—semiannual progreSs report, Dec. 1, 1957 to May 31, 1958: U.S. Geol. Survey Rept. TEI—740, p. 217— 227. Moxham, R. M., MacKallor, J. A., and Tolozko, L. R., 1957, Radioactivity surveys and their relation to geologic fea- tures, Texas Coastal Plain [abs]: Geol. Soc. Am. Bull., v. 68, no. 12, p. 1770. Pinkley, G. R., 1958, Geologic studies, surface and subsurface, Fashing field area, Atascosa County, Texas, in South Texas Geol. Soc., Fall Field Trip Dec. 1958, p. 30—41. Renick, B. C., 1924, Base exchange in ground water by sili- cates as illustrated in Montana: U.S. Geol. Survey Water-Supply Paper 520d, p. 53—72. Rosholt, J. N., 1963, Uranium in sediments: U.S. Geol. Survey open-file report, 211 p. Rosholt, J. N., and Noble, D. C., 1969, Loss of uranium from crystallized silicic volcanic rocks: Earth and Planetary Sci. Letters, v. 6, no. 4, p. 268—270. Russell, R. J., 1936, Lower Mississippi River delta, in Re- ports on the geology of Plaquemines and St. Bernard Parishes: Louisiana Geol. Survey Geol. Bull. 8, 453 p. Shepard, F. P., 1953, Sedimentation rates in Texas estuaries and lagoons: Am. Assoc. Petroleum Geologists Bull., v. 37, no. 8, p. 1919—1934. Shepard, F. P., and Rusnak, G. A., 1957, Texas bay sedi- ments: Inst. Marine Sci. Pub., v. 4, no. 2, p. 5—13. Sims, H. M., and Smith, F. L., 1956, Studies regarding the role of Wyoming natural gas in precipitating uranium minerals from pregnant solutions: RME—3143, issued by the U.S. Atomic Energy Comm. Tech. Inf. Service, Oak Ridge, Tenn., 58 p. Steinhauser, S. R., and Beroni, E. P., 1955, Preliminary re- port on uranium deposits in Gulf Coastal Plain, south- ern Texas: U.S. Atomic Energy Comm. Rept. RME—1068, 43 p., issued by Tech. Inf. Service, Oak Ridge, Tenn. REFERENCES CITED 37 Straaten, L. M. J. U., van, 1949, Quelques particularité du relief sous-marin de la mer des Wadden (Hollande): Comptes du Congres de Sediment. et Quat. en France, p. 139—145. 1951, Texture and genesis of Dutch Wadden Sea sedi- ments: Proc. 3d Internat. Cong. Sedimentology, Neder- lands, p. 225—244. Trumbull, J. V. A., Eargle, D. H., and Moxham, R. M., 1961, Preliminary aeroradioactivity and geologic map of the Stockdale SW quadrangle, Karnes and Wilson Counties, Texas: U.S. Geol. Survey Geophys. Inv. Map GP—247. Waters, A. C., and Granger, H. C., 1953, Volcanic debris in uraniferous sandstones, and its possible bearing on the origin and precipitation of uranium [Colorado Plateau]: U.S. Geol. Survey Circ. 224, 26 p. Weeks, A. D., and Eargle, D. H., 1963, Relation of diagenetic alteration and soil-forming processes to the uranium deposits of the southeast Texas Coastal Plain, in Clays and clay minerals, Natl. Conf. clays and clay minerals, 10th, 1961, Proc.: New York, Macmillan 00., p. 23—41. Weeks, A. M. D., Levin, Betsy, and Bowen, R. J., 1958, Zeolitic alteration of tufi'aceous sediments and its relation to uranium deposits in the Karnes County area, Texas [abs]: Geol. Soc. America Bull., v. 69, no. 12, pt. 2, p. 1659; also Econ. Geology, v. 53, no. 7, p. 928—929. Wentworth, C. K., 1922, A scale of grade and class terms for elastic sediments: Jour. Geology, v. 30, no. 5, p. 377—392. 3“? .7 “JL'W m 8 (a, AP PROFESSIONAL PAPER 765 UNITED STATES DEPARTMENT OF THE INTERIOR PLATE 1 GEOLOGICAL SURVEY SOUTHEAST NORTHWEST o m 420, if “I“ 420' m NORTHWEST SOUTHEAST I EXPLANATION 410' w ‘2 8, — 410' 410, 410' .1 '\ H I 77777 QUATERNARY K S T 1': I_ 7 XII HOLOCENE I I T Qal, soil or alluvium 400’ N I — E “ “ ' f» I 400’ TERTIARY . _________________ _ ' ‘ 400 ‘ EOCENE Jackson Group Whitsett Formation 390’ I 39 ’ deu, Dubose Member 390 0 de, Deweesville Sandstone Member Two, Conquista Clay Member BARGMANN- , Twcf,'fossiliferous sandstone HACKNEY DEPOSIT 380’ »:|'wdTH—_ —fi P H — 380’ 380,__—— , V . . ‘ T '__ 380’ dei,D11worth Sandstone Member eUgOI, IN PERCENT — P ch—annel _ " Si|icified : ' ' 370’ — 370’ 370’ a L:— 370' — Two ’: Soil or alluvium 050—099 TEET, L: :: I: 360' T 360' 360’ ._ :: Li _iT ':—~ 360’ ,_ ' Ti 0 500 FEET 7 7 FT __ _————I Sand or sandstone 0.10—0.49 350' — 350 350’ — T7 _: : ' INDEX TO DRILL HOLES IN H_20 _ _ L I_ : _— _L__ :__k_ SOUTHERN PART OF T:E__T_ _T: NUHN DEPOSIT .I . I I , I 340'T TETL: _T _ 340' 340— Two/T; _T — 340' Clayey sand 0.050—0.099 o 500 FEET _ ' T'D‘ 245 ft 33 ' 330' I I INDEX TO DRILL HOLES NEAR O O IOIO 290 FEET 330 O 100 200 FEET 330 . . . BARGMANN—HACKNEY DEPOSIT ‘ I I Silty sand 0010—0049 8‘22 To H‘ZO' HACKNEY PROPERTY SOUTHWEST I3_5o TO 3—39 , KORZEKWA PROPERTY 0 L0 380’ Drill hole 380’ “““““ A LLLLL — 380' _ Multiply scale by 10 or 0—10,000 370, 370, _ ~ T T _ T T T __ _ _ _ : ’ ’ _____ Sllty clay Counts-per-minute range __ EEEEE 370’ _ _ _ # —370' 360’ 360’ :Twc‘; i___' Multiply scale by 100 or 360’ T TET____ _:_—_ — 360' 0—100,000 counts-per-minute _ _ L _ Gamma-ray log range 350’ 350’ (Section B—22 to H—20) 350, _ — 350’ 340' 340’ 100 200 FEET __ L , (I) I J 340' — TwcA; I T 340’ [3—24 TO B-ZO, FARM ROAD 791 ADJACENT TO HACKNEY PROPERTY ”RD. 245 ft NORTH E T 330’ 330’ W S 00 '7 SOUTHEAST O 100 200 FEET 420' —— I I K‘E I— 420 ” I . I g I — TO _ KORZEKWA PROPERTY SOUTHWEST NORTHEAST B 56 B 50' . . ~ I_ 0‘ — 380' 410I__ I ." , _ _v 410, 380 w m 2 I _ I u __ , I 370% 370’ 400 51 _> I _ 400, f 360’ — _ ~ 360’ 390' —: — 390' , : 350'~ 350' 380 —, ~ 380’ , HACKNEY : DEPOSIT : o // / _ O «I / / « .. v A ’Y r—S— —340’ 370’ _I_- _ 370’ @A’p/O , O / 340 _ 0 (Q / I _ c; a» , I T TTTTT (NC, Q/ /( . ' _ I , ELLLLL, L , I _ _ I 360’ — _ F_ 360, 330 _ 330 _L¥_i:__ _ _____ : : _ o 500 FEET T T Li, ,, -_I INDEX TO DRILL HOLES NEAR 320 320 350’ — I— 350' O 100 200 FEET HACKNEY DEPOSIT I I 4] S—37 TO S—39 , CARRIGER PROPERTY SOUTHEAST r 34 I 340 O 100 200 FEET O NORTHWEST | I l J 390, _E’ 390 H—IB TO 8—24, BARGMANN PROPERTY H m g 3 laria fragments residue P—40—61 48°06' 176°32’ 5,500 0—1 75 1 10 4 Sponge (1) ______ Coarse to fine sand. 10—11 70 <1 3 2 _________________ Medium to fine sand. 20—21 70 <1 3 2 _________________ Very coarse to fine sand. 30—31 70 1 5 5 Sponge (<1) _____ Medium to fine sand. 41—61 50°24' 176°30’ 7,230 0—1 75 2 20 ___ Sponge (>1) _____ As h. 10—11 95 __~ 2 2 ___do ____________ 20—21 98 1 1 1 __-do ____________ Ash. 30—31 98 <1 1 <1 ___do ____________ Do. 40—41 80 ___ 10 5 ___do ____________ Fine sand. 48-61 51°41’ 161°07’ 4,650 0—1 85 1 10 ___ _________________ Fine sand. 10—11 90 <1 3 <1 _________________ sh 17—18 75 <1 8 2 _________________ 49—61 49°50’ 160°57’ 5,000 0—1 50 1 3 4 Sponge (2) ______ Ash, 0fine to granule. 10—11 80 <1 1 8 _________________ Ash, fine to very coarse. 20—21 80 <1 1 1 _________________ Do. 30—31 80 <1 1 1 _________________ Do. 40—41 80, <1 1 1 _________________ Do. 50—51 80 <1 1 1 _________________ Do. 60—61 80 <1 1 1 _________________ Do. 52—61 43°47' 160°36’ 5,160 0—1 90 <1 <1 8 _________________ 56—61 39°30’ 160°24’ 5,400 0—1 95 <1 1 1 Sponge (>1) _____ Fine sand. 10—11 95 <1 1 1 _--do ____________ Do 20—21 98 ___ <1 <1 ___do ____________ Do. 30—31 98 ___ <1 >1 ___do ____________ Do. 40—41 99 _-_ <1 1 _________________ Do, 50—51 99 ___ <1 1 _________________ Do. 60—61 99 ___ <1 1 _________________ Do. 70—71 99 ___ <1 1 _________________ Do. 80—81 99 ___ <1 1 _________________ Do 63—61 32°42’ 160°12’ 5,830 0—1 85 <1 ___ <1 _________________ Fine sand 10—11 98 ___ ___ 1 Sponge (1) ______ 20—21 98 ___ -__ 1 ___do ____________ 30-31 98 ___ ___ 1 ___do ____________ 40—41 98 ___ ___ 1 _--do ____________ 50—51 98 <1 ___ 1 ___do _____________ 60—61 98 ___ ___ 1 Sponge, fish bones (1). 70—71 98 ___ ___ -__ ___do ____________ 80—81 98 ___ ___ _-- Sponge (2) ______ 90—91 99 __- ___ ___ _________________ Manganese(?) pellets. 100-101 99 ___ ___ ___ _________________ Do. 110—111 99 ___ ___ ___ _________________ Coarse sand. 120—121 99 ___ ___ ___ _________________ Do. 64—61 30°16’ 160°07’ 5,830 0—1 ___ (1) ___ ___ _________________ 10—11 ___ (2) ___ ___ _________________ 69—61 23°30’ 159°58’ 4,820 0—1 98 <1 <1 1 _________________ 10—11 98 ___ ___ <1 Sponge (<1) _____ Fine sand. 20—21 98 ___ ___ <1 ___do ____________ Do. 30—31 98 -__ ___ <1 ___do ____________ Do. 40—41 98 ___ ___ <1 ___do ____________ Do. 1 Incompletely washed, few Foraminifera. 2Incompletely washed, no Foraminifera. Examination of faunas from the cores showed that, in general, species are sparsely represented but are diverse and mostly arenaceous. No new species are described. Sixty of the 85 species found were illustrated in the Challenger reports (Brady, 1884; Barker, 1960). The few calcareous specimens pres- ent in the deep cores were probably alive at the time of collection, even though not all were stained by rose bengal. The likelihood is not great that such specimens could survive for long after death in their calcite-rundersaturated environment. Table 1 lists the position, depth of water, and per- centage estimates of the constituents of the cores. Most of the material was finer than 0.07 millimeter and contained small percentages of Foraminifera, diatoms, Radiolaria, other organic fragments, and some inorganic residue. This paper is mainly a catalog of species present and their relative abundance. The systematic cata- log includes as complete synonymies as possible, for many of the species have been described from rare occurrences and their systematic descriptions had to 4 FORAMINIFERA OF THE NORTH PACIFIC OCEAN y U.S.S.R. 170. 32. 31° 29° 27 26° 25. e Aleutian Islandsfl“ . . a” - 41. 4o 180° . 38. 50° 35° 33. 40° 30“ E X P LA N AT 1 O N O Core 0 Core-catcher or grab sample '9160 12. [LS.A. “Q @Kodiak 7o 9 10 48' 49 160° 150° 52 56 63 64 69 Hawaiian Islands Q- Q} FIGURE 1.—Location of 1961 Pioneer stations. 60° 40° 20° 0° 140° FIGURE 2.—Distribution of 180° 160° 140° be assembled. Discussion of each species, its mor- phology, and distribution is included. The species are illustrated on plates 1—4. ACKNOWLEDGMENTS Credit is here given to Capts. William Dean, Hor- ace Conerly, and Harley N ygren of the National Ocean Survey (formerly Coast and Geodetic Survey) for supervising the coring. George W. Moore of the US. Geological Survey logged and sampled the cores and collected the grab samples. PREVIOUS WORK Published records of bottom sediments and Fora- minifera from the Pacific Ocean north of lat 20° N. are sparse. The Challenger reports include several samples from this area. The report of the seventh cruise of the Carnegie (Revelle, 1944) includes many more samples and also a comprehensive study of sediment type, the distribution of which is shown in figure 2. Figure 3, showing distribution of CaCos, is taken from Lisitzen (1971). Riedel and Funnell (1965) described several Ter— tiary cores from the area, and several reports of Tertiary faunas from the North Pacific (Bukry and others, 1971; Krashininnikov, 1971; Olson and G01], 1970) have been published as results of the deep-sea drilling project of the Glomar Challenger. EXPLANATION B Terrigenous deposits Hill :0 m :L E m ‘< Radiolarian ooze E Diatom ooze s Globigerina ooze 1 20° 100° 80° marine deposits in the North Pacific Ocean (from ReVelle, 1944). PREVIOUS WORK 4533 SA a 3:85am orlom “w 350.39 omlH .N 3:8th HV 4 .353 .dofimmfi :5me mumwombv £603 93 .5 35:353 533.3 mo nomasnmfiwmnld $5on .8 “.03 no: Dom: no: .03 .8 Pom \sbm .8 .03 .ow v m N H I W § EHE mpcwfiwwwm E Busefig EEQEO Z O _._.< Z <4 n_ Xm .oo Dov com no com .9» com 495—617 0 - '73 - 2 6 FORAMINIFERA OF THE NORTH PACIFIC OCEAN PROCEDURE The top 2 centimeters of each core was preserved in alcohol and stained with rose bengal; the re- mainder of each core was examined at 10-cm intervals. Samples were washed on a ZOO-mesh screen, and all Foraminifera were picked. The number of speci- mens indicated on pages 7—12 represents the actual number of specimens counted. ENVIRONMENT OF THE NORTH PACIFIC Bottom-water temperature in most parts of the area covered by this report ranges from 1° to 2° C. The sediment types are shown in figure 2, taken from Revelle (1944). Samples directly south of the Aleu- tian Islands are composed of terrigenous material; those farther south, to latitude 50° N., are markedly rich in diatoms (see table 1) ; and those still farther south are characterized by red clay. None of the samples are far enough south to reach areas high in CaCOS. (See fig. 3.) Samples taken in fairly shallow water, north of the Aleutian Trench, have a high percentage of cal- careous forms. Table 2 is a compilation of species TABLE 2.—Distribution of Fora’minifera in the North Pacific Aleutian Trench Aleutian Terrace Deep-sea plain Bolivina pseudoplicata _____ Buliminella basicostata ___- Elphidium magellanicum ___ Epistominella exigua ______ Fissum‘na sp ______________ Nom'onella auricula _______ bradyi _______________ Rosalind sp ______________ Virgulina cf. V. complanata Globigem'na bulloides ______ Pseudogaud'ryina atlamtica _ Angulagem’na angulosa ___- Bolivina decussata ________ Cassidulina crassa ________ teretis _______________ tortuosa Cibicides lobatulus ________ refulgens Nonion scaphum _________ Uvigerina cushmomi ______ Tritaxis conica ___________ XXXX XXXXXX XXXXX XXXXX Globotextulam‘a anceps ___- Dorothia exilis ___________ Eggerella bradyi _________ scabra _______________ Ophthalmidium acutimargo pusillum _____________ Quinqueloculina sp ________ Pyrgo sp ________________ X Miliolinella subrotunda ___- Ammomassilina alveolinaformis _____ Bolivina robusta __________ X TABLE 2.—Distm'bution of Foraminife’ra in the North Pacific—Continued Aleutian Terrace Aleutian Trench Deep-sea plain Bulimina aculeata ________ X Globobulimina auriculata __ pacifica ______________ X Uvigerina peregrina _______ X Epistom’inella exigua ______ X umbonife'ra ___________ Elphidium incertum _______ X Elphidiella groenlandica ___ X Globorotalia inflata _______ Globigen’na bulloides ______ X Candeina m'tida ___________ Cibicides bradyi __________ Cassiduli’na subglobosa ___- crassa Ehrenbergina hyst’rix _____ Involutina tenuis _________ X Nonion labradom‘cum ______ X Nonionella turgida ________ Pullem'a subcarinata ______ Gyroidina lamarckiana _ _ _ _ Anomalina globulosa ______ Cibicidoides cf. C. mundulus M elom’s afi‘ine _____________ pompilioides __________ Hoeglzmdina elegans ______ Rhabdami‘na abyssorum -_-_ Rhizammina? sp _________ M arsipella cylindrica ______ Bathysiphon discreta ______ Jaculella acuta ___________ Hyperammina spp ________ Psammosphaera mstica ___- Saccammina sphaem’ca _____ Thurammina papillata _____ Glomospira gord’ialis ______ H ormosina globulife’ra _____ Reophax dentalinaformis _ _ di fi‘lugi f o'rmis _________ dis toms ______________ nodulosus ____________ piluli f er _____________ scorpim‘us ___________ scotti ________________ egocentric-us ___________ Adercotryma glomerata _ _ _ _ Cyclammina cancellata - _ _ _ trullissata ____________ A lveolophragmium m'tidum- cf. A . nitidum ________ ringens ______________ scitulum sub globosum weisnen’ ______________ Alveolophragmium? sp _ _ _ _ Ammobaculites agglutinans- agglutinans filaformis (smooth) agglutinans filafowm's (rough) amem‘canus ___________ Ammomarginulina foliacea _ Placopsilina confusa _______ Spiroplectammina biformis- Bigenem'na minu tissima _ _ _ _ XXXXXX X X XX FORAMINIFERA IN GRAB SAMPLES AND IN TOP 2 CENTIMETERS OF CORES 7 TABLE 2.—Distm'bution of Foraminifera in the North Pacific—Continued Aleutian Terrace Aleutian Trench Deep-sea plain Trochammina grisea ______ x inflata _______________ kellettae malovensis cf. T. malo'uensis ______ nana sp. (chitinous) _______ nitlda ________________ globigerinifo'mnis ______ x Cystammina galeata _______ Nodellum membranaceum __ Haplophragmoides cana/riensis _________ nitida ________________ Oeulosiphon cf. 0. linear-1's" Psammosiphonella sp ______ XXXX XX X X that are present in three areas: the Aleutian Ter- race, the Aleutian Trench, and the deep-sea plain. No indication of relative abundance is given. Sam— ples from the trench itself have surprisingly large numbers of species and specimens, almost entirely arenaceous. One interesting aspect of the trench faunas is that the cement of several species is all or in part composed of pseudochitin, as though there simply was not enough calcitic cementing material available. I | I | IIIII 0 2000 4000 DEPTH OF WATER, IN METERS I IIIII 6000 49 4812 7 1916 69 64 63 56 52 STATION 10 FIGURE 4.—Depth of water for stations along long. 160° W. I I I I I I I I I II 0 (I) 0: Lu _ —2oooLj 2 E 33’ — 44000» < 3 LL 0 e —6oooE 0. Lu 0 I I I I I I I I I II 8000 25 26 27 29 32 33 35 38 40 4113 STATION FIGURE 5.—Depth of water for stations along long. 180° W. Depths of the samples are plotted in figures 4 and 5 and show graphically the great depth from which most of these samples came. It is unusual to find Foraminifera at such great depths because of the low CaCOs concentration. Fauna] lists of the t0p 2 cm of the cores are ar- ranged from north to south. A separate list of faunas found below the surface are arranged serially by sample number. These fossil faunas show an extreme paucity of specimens. FORAMINIFERA IN GRAB SAMPLES AND IN TOP 2 CENTIMETERS OF CORES [Approximate washed volume 10 cm3; depth given in meters below sea level] Kodiak Harbor, Kodiak Island, depth 10 meters [No diatoms, Radiolaria, or sponge spicules seen] Specimens . Total Stained Arenaceous benthomc: Alveolophrayminm subglobosum __________ 1 ______ Eggerella scabra _______________________ 12 ______ Haplophragmoides canariensis ____________ 7 ______ Calcareous benthonic: Buccella friglda _________________________ 69 6 cf. B. inusitata _____________________ 3 ______ Buliminella elegantissima ________________ 1 ______ Elphidium bartletti _____________________ 14 ______ clavatum ___________________________ 37 4 orbiculare __________________________ 13 4 sp. (smooth) _______________________ 4 ______ Nonion labradom'eum ____________________ 1 ______ Virgulina cf. V. complanata ______________ 4 4 Core P—7—61, depth 76 meters. Lat 56°24’ N., long 155°36'W. [One large (l-cm-long) shrimp and about equal volumes of diatoms and Foraminfera] Specimens Total Stained Arenaceous benthonic: Eggerella scab'ra ________________________ 1 ...... Calcareous benthonic: Bolivina pseudoplicata ___________________ 7 ______ Buliminella, basicostata __________________ 1 ______ Elphidlum magellanicum _________________ 7 ______ Epistominella exigua ____________________ 25 ______ Fissum'na sp ___________________________ 1 ______ Nonionella auricula _____________________ 1 ______ bradyi _____________________________ 5 ______ Rosalind sp ____________________________ 1 ______ Virgulina cf. V. eomplanata _____________ 1 ______ Calcareous planktonic: Globige'rina bulloides ____________________ 1 ______ Core P—9—61, depth 121 meters. Lat 54°55’N., long 157°59’W. Specimens Total Stained Arenaceous benthonic: Pseudogaudrylna, atlantica _______________ 2 ______ sp _________________________________ 1 ______ Calcareous benthonic: Anguloyem'na angnlosa __________________ 2 1 Bolivina decussata ______________________ 5 ______ Cassidullna crassa ______________________ 42 8 te'retis _____________________________ 113 ______ tortuosa ____________________________ 76 ______ Clbicides lobatulus ______________________ 17 ______ refulgens ___________________________ 13 ______ Elphidium bartlettl _____________________ 4 ______ cf. E. crispum ______________________ 3 ______ Epistominella exigua ____________________ 1 ______ Lagena spp _____________________________ 6 ______ Loxostomum amygdalz'fo'rmis _____________ 1 ______ N onion scaphum ________________________ 6 ______ Pseudopolymorphina lingua ______________ 1 ______ Um'gem'na cushmani ____________________ 11 ______ 8 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Core P—9-61, depth 121 meters. Lat 54° 55'N long 157° 59 W.—Continued Specimens Total Stained Calcare‘ous planktonic: Globige’rina bulloides ____________________ 21 ______ pachyderma ________________________ 15 ______ Orbulina universal _______________________ 1 ______ Core P—16—61,depth 2,410 meters.Lat 53°53' N.,long 161°40' W. [Diatoms 98 percent; Radiolaria, sponge spicules, Foraminfera compose the remainder, but none very abundant] Specimens Total Stained Arenaceous benthonic: Alveolophragmium subglobosum __________ 2 ______ Eggerella bradyi ________________________ 1 ______ Trochammina globigeriniformis ___________ 1 ______ grisea _____________________________ 1 ______ Calcareous benthonic: Bulimina cf. B. auriculata _______________ 3 2 mexicana ___________________________ 1 ______ Elphidium incertum _____________________ 2 ______ Elphidiella yroenlandica _________________ 24 3 Globobulimina pacifica ___________________ 1 1 H oeglundina elegans _______________ 2 corroded ______ Nonion labradoricum ____________________ 4 4 Nonionella turgida ______________________ 6 6 Pyrgo sp _______________________________ 1 ______ Uvigerina peregrine, _____________________ 3 ______ Virgulina pauciloculata __________________ 3 ______ Calcareous planktonic: Globigerina bulloides ____________________ 7 ______ paehyderma ________________________ 5 ______ Core P—19—61,depth 4,430 meters. Lat 52°41' N.,long 155°36’ W. [Diatoms extremely abundant, a few Radiolaria and Foraminifera] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum ________________ 2 2 Alveolophragmium nitidum ______________ 10 ______ cf. A. nitidum ______________________ 5 ______ ringens ____________________________ 2 ______ subglobosum _______________________ 18 2 weisneri ___________________________ 13 2 Ammobaaulites filaformis (smooth) _______ 1 ______ Ammomarginulina foliacea ______________ 3 ______ Cystammina galeata ____________________ 7 ______ Eggerella bradyi ________________________ 8 ______ Glomospi'ra gordialis ____________________ 2 ______ H aploph'ragmoides cana’riensis ____________ 2 ______ nitida ______________________________ 5 2 Hyperammina cf. H. friabilis _____________ 37 ______ Jaculella acuta (all chitinous) ____________ 13 2 N odellum membranaceum ________________ 5 ______ Oculosiphon cf. 0. linearis _______________ 2 ______ Psammosiphonella sp ____________________ 8 ______ Reophax difllugifo'rmis ___________________ 4 4 excent’ricus _________________________ 9 2 pilulifer ___________________________ 1 ______ Trochammina globigerinifo'rmis __________ 22 4 grisea _____________________________ 7 ______ Sp. (like chitinous) _________________ 2 ______ Calcareous benthonic: Cassidulina crassa ______________________ 1 1 Cibicides bradyi _________________________ 19 3 Miliolinella subrotunda __________________ 3 ______ Pullenia subcarinata _____________________ 3 ______ Calcareous plankto‘nic: Globigerina bulloides _______________ 2 corroded ______ Core P—10—61,depth 4,170 meters. Lat 54°51’ N.,long 155°24 W. [Diamnis and Radiolaria abundant] Specimens Total Stained Arenaceous benthonic: Alveolophragmium subglobosum __________ 2 ______ nitidum ____________________________ 3 ______ Ammomarginulina foliacea _______________ 1 ______ Cyclammina tmllissata __________________ 1 ______ Core P—10—61, depth 4,170 meters. Lat 541°51’ N., long 155°24' W.—C?ontinued Specimens Total Stained Arenaoeous benthonic—Continued Cystammina galeata ____________________ 1 ______ Eggerella bradyi ________________________ 6 ______ Reophax difi‘lugiformis __________________ 2 ______ Spiroplectammina biformis ______________ 2 ______ Trachammina globigeriniformis ______________ 2 Calcareous benthonic: Cassidulina cf. C. subglobosa ____________ 1 1 Core P—12—61,depth 6,560 meters. Lat 53°16’ N., long 161°33’ W. Specimens Total Stained Arenaceo‘us benthonic: Adercotryma glomeratum ________________ 18 ______ Alveolophragmium nitidum ______________ 64 ______ cf. A. nitidum ______________________ 141 ______ subglobosum _______________________ 98 ______ Ammobaculites americanus ______________ 1 ______ agglutinans filaformis (smooth) ______ 70 ______ agglutinans filaformis (rough) _______ 29 ______ Astrorhiza __________________ Fragments sp. A ______ Jaeulella acuta _________________________ 5 ______ Psammosiphonella sp ____________________ 6 ______ Reophaw dentalinafo'rmis ________________ 2 ______ di/flugiformis _______________________ 39 ______ nodulosus __________________________ 22 ______ scotti (chitinous) ___________________ 1 ______ Rhizammina sp ______________ Fragments sp. 5A ______ Trachammina globigeriniformis _________________ Trochammina sp. (like chitinous) ________ 37 ______ Trochammina sp. (chitinous) ____________ 44 ______ Calcareous benthonic: Eponides? sp ___________________________ 3 3 Involutina tennis ________________________ 35 ______ Miliolinella subrotunda __________________ 3 ______ Pullenia subcarinata ____________________ 31 31 Core P—48—61,depth 4,650 meters.Lat 51°41’ N.,long 161°07' W. [Diatoms extremely abundant (<99 percent), Radiolaria and Foraminifera about equal] Total specimens Arenaceous benthonic: Adercotryma glomeratum ____________________ 83 Alveolophragmium nitidum __________________ 21 cf. A. nitidnm __________________________ 47 scitulum _______________________________ 3 subglobosum ___________________________ 52 weisneri _______________________________ 1 Ammobaculites americanus ___________________ 32 agglutinans filaformis (smooth) __________ agglutinans filaformis (rough) ___________ 19 Ammomarginulina foliacea ___________________ 8 Astro'rhiza _______________________________ Fragments Baculogypsina or Thurammina ______________ Cornuspira incerta _____ . _____________________ 14 Cyclammina trullissata ______________________ 3 Cystammina galeata _________________________ 3 Eggerella bradyi ____________________________ 3 scabra _________________________________ 7 Glomospira gordialis ________________________ 2 Hormosina _______________________________ Fragments Hyperammina cylindrica _____________________ 2 Jaculella acute _____________________________ 17 Reophax difilngiformis _______________________ 43 dentalinaformis _________________________ 2 distans _________________________________ 3 scorpiurus _____________________________ 65 Rhabdammina ____________________________ Fragments Saccammina sphaerica _______________________ 19 Spiroplectammina bifo'rmis ___________________ 1 Troehammina globigeriniformis ______________ 28 grisea _________________________________ 1 inflate _________________________________ 25 nitida __________________________________ 10 Calcareous benthonic: Nonion? sp. chitinous ________________________ 2 FORAMINIFER‘A IN GRAB SAMPLES AND IN TOP 2 CENTIMETERS OF CORES 9 Core P—49—61,depth 5,000 meters.Lat 59°50’ N.,long 160°57' W. [Diatoms <95 percent, Radiolaria 4 percent, Foraminifera and sponge skeletons compose the rest] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum ________________ 29 ______ Alveolophragmium cf. A. nitidum _________ 14 ______ ringens ____________________________ 10 ______ subglobosum ________________________ 168 ______ Ammobaculites agglutinans ______________ 88 ______ filaformis (rough) __________________ 6 ______ Baculogypsina or Thurammina ___________ 2 ______ Cyclammina cancellata __________________ 4 ______ trullissata _________________________ 9 ______ Dorothia exilis __________________________ 1 ______ Eggerella bradyi _______________________ 52 ______ Globotextularia anceps __________________ 10 ______ Glomospira gordialis ____________________ 24 ______ Hormosina globulifera _____________ Fragments ______ Hyperammina cylindrica _________________ 99 ______ friabilis ____________________________ 62 ______ Involutina tennis _______________________ 2 ______ Jaculella acuta _________________________ 11 ______ Placopsilina bradyi _____________________ 51 ______ Psammosiphonella sp ____________________ 3 ______ Reophax diffiugifo'rmis __________________ 87 4 excentricus _________________________ 103 30 Spiroplectammina biformis _______________ 18 ______ Trochammina globigeriniformis __________ 35 ______ nana ______________________________ 107 ______ nitida ______________________________ 39 ______ chitinous ___________________________ 1 ______ Calcareous benthonic: Cibicides bradyi ________________________ 2 2 Cibicidoides mundulus ___________________ 1 1 Ehrenbergina hystrix ___________________ 1 ______ Epistominella exigua ___________________ 3 3 umbonife'ra _________________________ 2 2 Gyroidina lamarckiana __________________ 1 1 Hoeglundina elegans ____________________ 1 1 Miliolinella subrotunda __________________ 28 ______ Melonis affine __________________________ 1 ______ Nonion sp. chitinous ____________________ 1 ______ Calcareous planktonic: Globigerina bulloides ____________ 3 corroded ______ Core P—52—61,depth 5,160 meters.Lat 43°47' N.,long 160°36’ W. [Diatoms 50¢ percent, Radiolaria 50: percent, a few Foraminifera and sponge skeletons] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum ________________ 1 ______ Alveolaph’ragmium cf. A. nitidum _________ 5 ______ Ammobaculites agglutinans ______________ 1 ______ Dorothia exilis _________________________ 1 ______ Eggerella scabra _______________________ 1 ______ Glomospira gordialis ___________________ 12 ______ Placopsilina bradyi ______________________ 1 ______ Psammosiphonella sp ____________________ 5 ______ Spiroplectammina biformis ______________ 4 ______ Reophaw difi‘lugiformis __________________ 2 ______ Trachammina globigeriniformis __________ 25 ______ grisea _____________________________ 1 ______ nitida _____________________________ 1 ______ Calcareous benthonic: Cibicides bradyi ________________________ 1 ______ Epistominella exigua ____________________ 3 ______ Miliolinella subrotunda __________________ 5 ______ Ophthalmidium acutima/rgo ______________ 2 ______ Pullenia subcarinata ____________________ 1 1 Core P—56-61,depth 5,400 meters,Lat 39°20' N., long 160°24’ W. [Radiolaria 95 percent, diatoms 4 percent, Foraminifera and sponge skeletons 1 percent] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum ________________ 1 ______ Alveolophragmium nitidum ______________ 6 ______ Ammobaculites amem'canus ______________ 1 ______ Core P—56—61, depth 5,400 meters. Lat 39°20’ N., long 160°24' W.——-Continued “m Total Stained Arenaceous benthonic—Continued Cornuspira involvens ____________________ 2 ______ Glomospira gordialis ____________________ 1 ______ Hyperammina cylindrica _________________ 2 ______ Marsipella cylindrica ____________________ 14 ______ Psammosiphonella ______________________ 1 ______ Reophax dentalinafomis ________________ 2 ______ Troohammina globigeriniformis __________ 7 4 Calcareous benthonic: Cibicides bradyi ________________________ 2 2 Discorbis cf. D. rosea ____________________ 2 ______ Planktonic benthonic: Candeina nitida, ________________________ 1 ______ Core P—64—61,depth 5,830 meters.Lat 30°16' N.,long 160°07' W. [A few Radiolaria, sponge skeletons, Foraminifera] . Total specimens Arenaceous benthonic : Aschemonella sp ____________________________ 3 Bigenerina, minutissima _____________________ 1 Reophax difllugiformis _______________________ 2 Rhabdammina sp __________________________ Fragments Saccammina sphaerica ______________________ 3 Trochammina globigeriniformis ______________ 1 Core P—69—61,depth 4,820 meters.Lat 23°30’ N., long 159°58’ W. [A few Radiolaria, sponge skeletons, Foraminifera] Specimens Total Stained Arenaceous benthonic: Alveolophragmium subglobosum ___________ 3 ______ Ammobaculites agglutinans ______________ 2 ______ Cyclammina sp _________________________ 1 ______ Glomospira gordialis ____________________ 2 ______ Reophaw difilugiformis __________________ 4 ______ scorpiurus _________________________ 3 ______ Rhabdammina sp _______________________ 9 ______ Troohammina globigeriniformis __________ 3 ______ nitida ______________________________ 1 ______ Eponides bradyi ________________________ 2 2 Core P—l3—61,depth 7,000 meters.Lat 51°28’ N.,long 168°38’ W. [Diatoms 98 percent, Radiolaria <2 percent, Foraminifera <1 percent] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum ________________ 1 ______ Alveolophragmium nitidum ______________ 57 ______ scitulum ___________________________ 22 ______ weisneri ___________________________ 1 ______ Cornuspira incerta ______________________ 9 ______ Eggerella scabra ________________________ 1 ______ Hyperammina cylindrica _________________ 14 ______ Marispella cylindrica ___________________ 5 ______ Reophax dentalinaformis ________________ 1 ______ difllugiformis _______________________ 3 ______ excentm'cus _________________________ 12 ______ nodulosus __________________________ 4 ______ scorpiums __________________________ 7 ______ Rhabdammina sp _______________________ 7 ______ Spiroplectamina bifo'rmis _______________ 1 ______ Trochammina globigeriniformis _________ 55 ______ Trachammina (chitinous) _______________ 1 ______ Calcareous benthonic: Pullenia subcarinata ____________________ 5 5 Core P—41—61, depth 7,230 meters. Lat 50°24’ N., long 176°30' W., Aleutian Trench. [Diatoms about 90 percent; Foraminifera 5 percent: sponge spicules and skeletons and Radiolaria make up 5 percent] Specimens Total Stained Arenaceos benthonic: Adercotryma glomeratum ________________ 5 ______ Alveolophragmium c.f. A. nititum ________ 250+ ______ scitulum ___________________________ 12 ______ subglobosum _______________________ 58 ______ 10 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Core P—41—61, depth 7,230 meters. Lat 50°24’ N ., long 176°30’ W., Aleutian Trench—Continued Specimens Total Stained Arenaceous benthonic—Continued Ammobaculites agglutinans filaformis (smooth) ____________________________ 26 ______ Ammobaculites agglutinans filaformis (rough) _____________________________ 1 ______ Ammoscalam'a tenuimargo _______________ 9 ______ Astro’rhiza sp ______________________ Abundant ______ Baculogypsina? sp _____________________ 2 ______ Globotextularia? sp _____________________ 8 ______ Hyperammina friabilis __________________ 150+ ______ Involutina tennis ______________________ 90 ______ Jacnlella acuta _________________________ 19 ______ Placopsilina bradyi ____________________ 36 ______ Reophax difilugiformis __________________ 79 4 excent’ricus _________________________ 103 ______ nodulosus __________________________ 1 ______ Rhabdammina sp ______________________ 55 ______ Saccammina sphaerica __________________ 106 ______ Spiroplectammina biformis _____________ 1 ______ Trochammina charlottensis _____________ 4 ______ globigerini f ormis ___________________ 125 + ______ Trochammina (chitinous) _______________ 504 ______ Calcareous benthonic: Pullenia subca/rinata ___________________ 8 8 Core P—40—61,depth 5,500 meters. Lat 48°06’ N.,long 176°32’ W. [Diatoms about 85 percent; Foraminifera 5 percent; Radiolaria, sponge skeletons, and fish remains make up 10 percent] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum _______________ 2 ______ Alveolophragmium nitidum ______________ 9 ______ subglobosum _______________________ 25 ______ Ammobacnlites agglutinans filaformis (smooth) ____________________________ 15 ______ Bigene'rina minutissima ________________ 5 ______ Cyclammina cancellata __________________ 5 ______ trullissata _________________________ 5 ______ Cystammina galeata ___________________ 2 ______ Eggerella bradyi _______________________ 5 ______ Glomospira gordialis ____________________ 25 ______ Hormosina globulifera __________ 1 + fragments _____ Jaculella acnta ________________________ 2 ______ Miliolinella subrotunda __________________ 4 ______ Reophax difi‘lngiformis __________________ 2 ______ nodulosus __________________________ 6 ______ scorpiurus _________________________ 27 ______ Trochammina globigeriniformis __________ 35 ______ nitida _____________________________ 6 ______ Calcareous benthonic: . Bolivina robusta _______________________ 1 1 Core P—38—61,depth 5,610 meters. Lat 45°50’ N.,long 176°47' W. [Formaminifera about 5 percent; diatoms 75 percent; Radiolaria 15 percent; sponge skeletons and spicules and fish teeth make up 5 percent] Specimens Total Stained Arenaceous benthonic: Adercotryma glomeratum _______________ 8 ______ Alveolophragminm nitidum ______________ 21 ______ cf. A. nitidnm ______________________ 9 ______ subglobosum _______________________ 19 ______ Ammobaculites filaformis (smooth) _______ 23 ______ amerieanus ? _______________________ 1 1 ______ Ammoscalaria tenuima'rgo ________________ 9 ______ Astrorhiza sp ____________ Abundant fragments ______ Bigenerina minutissima __________________ 4 ______ Cyclammina cancellata __________________ 1 ______ tmllissata __________________________ 2 ______ Eggerella fusca ________________________ 3 ______ Glomospi’ra gordialis ____________________ 153 ______ J aculella aeuta __________________________ 3 ______ Placopsilina bradyi _____________________ 5 ______ Psammosiphonella sp ____________________ 3 Core P—38—61, depth 5,610 meters. Lat 45°50’ N., long 176°47’ W.—Continued Specimens Total Stained Arenaoeous benthonic—Continued Reophax difllugiformis __________________ 14 ______ distans ____________________________ 1 ______ excentricus ________________________ 12 6 nodnlosus __________________________ 11 ______ Rhabdammina sp ________________________ 13 ______ Spiroplectammina bifo'rmis ______________ 8 ______ Tritaxis cf. T. conica ____________________ 29 ______ Trochammina globigeriniformis __________ 33 ______ inflata _____________________________ 6 ______ nitida _____________________________ 6 ______ Calcareous benthonic: Miliolinella subrotnnda __________________ 12 ______ Nonion sp _____________________________ 1 1 Quinqueloculina sp _____________________ 1 1 Core P—35—61,depth 5,530 meters. Lat 41°19' N., long 177°02' W. [Radiolaria about 90 percent, diatoms 7 percent, sponge and fish remains 3 percent, Foraminifera <1 percent] Total specimens Calcareous benthonic: Miliolinella subrotunda Ophthalmidium pusillum _____________________ 2 Core P—33—61,depth 5,230 meters. Lat 39°15’ N., long 176°56’ W. [Radiolaria about 90 percent, diatoms 5 percent, Foraminifera 3 percent, sponge and fish remains 2 percent] Specimens Total Stained Arenaceous benthonic: Alveolophragmium nitidum ______________ 2 ______ subglobosum _______________________ 9 ______ wiesneri ___________________________ 1 ______ Ammobaculites americanus ______________ 1 ______ filaformis (rough) _________________ 5 ______ Ammomarginulina foliacea ______________ 5 ______ Astrorhiza sp _____________________ Fragments ______ Eggerella advena _______________________ 10 ______ Glomospira gordialis ____________________ 15 ______ Hormosina normani _____________________ 4 ______ Psammosiphonella sp ____________________ 2 ______ Psammosphaera fusca ___________________ 1 ______ Reophax scorpiurns _____________________ 4 2 distans ____________________________ 3 ______ Rhabdammina sp _________________ Fragments ______ Trochammina grisea ____________________ 1 ______ nitida _____________________________ 7 ______ Calcareous benthonic: Miliolinella subrotnnda ___________________ 7 ______ Ophthalmidium pnsillum _________________ 2 ______ Core P—32—61,depth 5,400 meters. Lat 36°50’ N.,long 177°30’ W. [Radiolaria 90 percent, diatoms 6 percent, Foraminifera 1 percent, sponge and fish remains 3 percent] Specimens Total Stained Arenaceous benthonic: Alveolophragmium nitidum ______________ 3 ______ cf. A. nitidnm ______________________ 4 ______ ringens ____________________________ 1 ______ subglobosnm _______________________ 2 ______ Ammobaculites filaformis (smooth) ______ 5 ______ Ammoscalaria tenuima'rgo _______________ 1 ______ Bigenerina minutissima _________________ 1 ______ Cyclammina tmllissata __________________ 1 ______ Eggerella advena _______________________ 2 ______ Glomospira gordialis ____________________ 7 ______ Hormosina globulife'ra __________________ 5 ______ H yperammina cylindrica _________________ 7 ______ Psammosiphonella sp ____________________ 1 ______ Reophax difi‘lugiformis __________________ 22 _______ scorpiurus _________________________ 6 2 Trochammina globigeriniformis __________ 6 ______ grisea _____________________________ 3 ______ nitida _____________________________ 3 FORAMINIFERA BELOW TOP 2 CENTIMETERS 0F CORES Core P-32—61, depth 5,400 meters. Lat 36°50’ N., long 177 °30’ W.—Continued Specimens Total Stained Calcareous benthonic: Miliolinella circularis ___________________ 9 ______ Ophthalmidium acutimargo _____________ 10 ______ Pullenia, subcarinata ____________________ 2 2 Core P—29—61,depth 4,810 meters.Lat 32°22’ N., long 177°20' W. [Radioleria about 70 percent, diatoms 251 percent, Foraminifera 1 percent, sponges and fish remains 4 percent] Specimens Total Stained Arenaceous benthonic: Ammobaculites filaformis ________________ 5 ______ Ammoscalwria tenuimargo _______________ 1 ______ Cystammina galeata _____________________ 1 ______ Glomospira gordialis ____________________ 35 ______ Homosina globulifera ____________ Fragments ______ Hyperammina cylin’drica _________________ 5 ______ Psammosiphonella sp ____________________ 2 ______ Trachammina globigerinifownis __________ 6 ______ Trochammina cf. T. nitida _______________ 1 ______ Calcareous benthonic: Cassidulina subglobosa __________________ 2 ______ Cibicides bradyi ________________________ 11 2 Hoeglundina elegans ____________________ 8 ______ M elonis pompilioides ___________________ 1 ______ Miliolinella subrotunda __________________ 1 ______ Spiroloculina sp __________________ 1 corrOded Core P—27—61,depth 5,290 meters. Lat 30°06’ N.,long 177°30’ W. [Radiolaria about 85 percent, diatoms 10 percent, sponge or fish remains 5 percent, Foraminifera <1 percent] Specimens Total Stained Arenaceous benthonic: Alveolophragmium nitidum ______________ 1 ______ subglobosum _______________________ 7 ______ Ammobaculites americanus ______________ 1 ______ Cyclammina trullissata __________________ 1 ______ Cystammina galeata _____________________ 1 ______ Glomospira gordialjs ____________________ 2 ______ Psammosiphonella sp ____________________ 4 ______ Calcareous benthonic: Miliolinella subrotunda __________________ 2 ______ Core P—26—61,depth 5,210 meters.Lat 25°55’ N.,long 177°34' W. [Only a few specimens of Radiolaria, sponge skeletons, fish teeth, Foraminifera; all present in nearly equal amounts . Total specimens Arenaceous benthomc: Rhabdammina sp _________________ Abundant fragments Astro’r‘hiza sp _______________________________ 1 Glomosm'ra gordialis ________________________ 4 Reophax difilugifo’rmis ______________________ 3 Core P—25—61,depth 5,120 meters. Lat 23°22’ N.,long 177°54’ W. [No Radiolaria, diatoms, or sponges. few fish teeth, Foraminifera. Northernmost sample with planktonic Foraminifera] Specimens Total Stained Arenaceous benthonic: Reophaoc difi‘lugifo'rmis __________________ 2 ______ Rhabdammina sp _______________________ 1 ______ Calcareous planktonic: Globigerina bulloides ____________________ 1 ______ inflata ____________________________ 1 ______ FORAMINIFERA BELOW TOP 2 CENTIMETERS OF CORES [Core depths given in meters below sea level. Column headings are depths below sea floor in centimeters. Data indicate number of specimens. X indicates presence of fragments] Core P—10—61, depth 4,170 meters Barren Core P—12-61, depth 6,560 meters 10—11 Alveolophmgmium subglobosum ______________ 3 Ammobaeulites filaformis ____________________ ____ Reophax dentalinaformis ____________________ ____ Core P—13—61, depth 7,000 meters _ 10—11 20—01 Alveolophragmium subglobosum _________ 1 ____ Core P—16—61, depth 2,410 meters 10—11 20—21 00—01 40—11 50—51 Bulimina aflinis _____ 1 ____ 2 ____ 3 Elphidium clavatum _ 1 7 ____ 1 ____ U'vigerina peregrina - 1 2 5 ____ 2 ?Ep0nides sp _______ ____ 1 ____ ____ ____ N onion labrado'ricum ____ ____ ____ 1 ____ 2 Lagenid spp _______ ____ ____ 2 ____ ____ Core P—19—61, depth 4,430 meters 10—11 20—21 Cystammina galeata __________________ 6 ____ Jaculella acuta _______________________ 4 ____ Placopsilina confusa __________________ 1 ____ Alveolophragmiwm subglobosum ________ 14 15 Adercotryma glomeratum ______________ 1 ____ Eggerella bradyi ______________________ 1 7 Troohammina nitida ___________________ 1 ____ H ype'rammina fragments ______________ X x Cyclammina cancellata ________________ ____ 1 Ammobaculites cf. A. americanus _______ ___- 1 Miliolinella fragments _________________ ____ X Trochammina sp _____________________ Core P—25—61, depth 5,120 meters 10—11 20—21 30—31 10—11 50—51 60—61 70—71 Globige'rinita voluta _______ 3 3 4 4 1 2 2 Globotmncana sp ___________ 1 ________ 1 ____________ Guembelina globulosa _____ 1 ____________ 2 2 ____ Colomia sp _____ 1 ________________ 2 1 Guembelina costulata _ ___.. 3 ________ 2 ____ 2 sp _________________ 1 2 ____________ Globotmncana marginata ____________________ 3 1 2 Core P—32—61, depth 5,400 meters 10—11 20—21 10—31 40—41 50—51 Eggerella bradyi ____ ___c ____ ____ 2 ____ Miliolinella subrotunda _______ ____ ____ ____ ____ ____ Core P-33—61, depth 5,230 meters 10—11 20—21 30—31 10—41 Reophax fragments _______ ____ X ____ ____ Core P—38—61, depth 5,610 meters 10-11 20—21 30—31 40—41 50—51 60—61 Reophax fragments __ X X X ____ X ____ Alveolophragmium subglobosum ______________________ 1 ____ Miliolinella subrotundum ______________________ 1 ____ Core P—40—61, depth 5,500 meters 10—11 20—21 Alveolophragmium subglobosum ________ 1 1 Reophax dentalinaformis ______________ 2 ____ Hypera'mmina spp ____________________ ____ 8 Core P-41—61, depth 7,230 meters 0—11 20—21 30—31 Alveolophragmium subglobosum __ ____ ____ 1 11 20—21 30—81 60—61 30—81 80—81 80—81 40-41 12 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Core P—48—61, depth 4,650 meters 10—11 17—18 Psammosiphonella sp _______________________ 2 ____ Hormosina globulifera ______________________ 2 ____ Saccammlna sp ____________________________ 2 ___- Ammobaculites cf. A. americanus ____________ ___- Adercotryma glome'ratum ____________________ ___- 1 Reophax difllugiformis ______________________ 2 ____ sp ____________________________________ 1 ___- Alveolophragmium subglobosum _____________ 13 2 scitulum _______________________________ 2 ___- m'tidum ________________________________ 1 3 Trachammina nitida ________________________ ___- 1 Cyclammina cancellata ______________________ ___- Frag- ments Core P—49—-61, depth 5,000 meters 10—11 20721 .9041 10—41 50—51 60—61 Alveolophragmium subgloboswm _____ 13 2 2 9 4 3 Cyclammina cancellata _______ 2 ___- 1 1 ____ 2 Eggerella bradyi ___ 3 __-- ___- -___ ___- ___- Placopsilina confusa _ 1 ___- ___- ____ ___- ___- Glomospira gordialis- 1 ___- ___- ___- ___- ____ Reophaoc fragments _ X ___- ___- ___- ___- ____ dentalinaformis _ ____ ___- __-_ ____ 1 Core P—56—61, depth 5,400 meters 10—11 20—21 30—91 4041 50—51 60—61 70—71 80—81 Arenaceous fragments _-_ >< ____________________________ Core P—63—61, depth 5,830 meters 10—11 20—21, 30—31. 40-41, 50-51. 60—61, 70—71, 80—81, 9041, 100—101, 120—121 Hyperammina? sp ___ 1 _____________________________ Core P—64—61, depth 5,830 meters 10—11 Barren __________________________________________ ____ Core P—69-61, depth 4,820 meters 1o~11 20.21 30—31 40—41 Barren ________________________ SYSTEMATIC CATALOG Family ASTRORHIZIDAE Brady, 1881 Genus RHABDAMMINA M. Sars in Carpenter ,1869 Rhubdammina nbyssorum M. Sars Rhabdammina, abyssorum M. Sars, 1869, Fordhandl Vidensk.- Selsk. Christiania, Aar 1868, p. 248. Barker, 1960, Soc. Econ. Paleontologists and Mineralo— gists Spec. Pub 9, p. 42, pl. 21, figs. 1—13. The species occurs generally as fragments of ex- tremely coarse-grained tubes, sometimes branching. The tubes are coarser grained in the northern sam- ples but are moderately coarse in the southern ones. Distribution—Lat 23° to 51° N. Genus RHlZAMMlNA, 1879 Rhizammina? sp Plate 1, figure 2 The species occurs as tubular fragments. The walls of the tubes are composed of fine sand held together with abundant cement. Distribution—Lat 32° to 53° N. Genus MARSIPELLA Norman, 1878 Marsipella cylindrica Brady Plate 1, figure 3 Marsipella cylindrical Brady, 1882, Royal Soc. Edinburgh Proc., v. 11, p. 714. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 265, 266, pl. 24, figs. 20—22. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 30, figs. 15, 16. Barker, 1960, Soc. Econ. Paleontologists and Mineralo— gists Spec. Pub. 9, p. 48, pl. 24, figs. 20—22. Distribution—Found at two stations (56 and 13) lat 39° to 52° N. Cushman reported it in four North Pacific stations 011' Hawaii and Japan. Genus BATHYSH’HON M. Sars in G. Sars, 1872 Bathysiphon discrete (Brady) Plate 1, figure 4 Rhabdammina discrete Brady, 1881, Micros. Sci. Quart. Jour., new ser., V. 21, p. 48. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 268, pl. 22, figs. 7—10. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 27, 28, fig. 13. Psammosiphonella discreta (Brady). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, pl. 22, figs. 7—10. This species is characterized by its smooth wall texture and light color. Distribution—Lat 30° to 53° N. A few specimens are found at many stations. Genus JACULELLA Brady, 1879 Jaculella acute Brady Plate 1, figure 5 Jaculella acuta Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, p. 35, pl. 3, figs. 12, 13. Brady, 1884, Challenger Repts., Zoology, V. 9, p. 255, pl. 22, figs. 14—18. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 70, figs. 90, 91. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 44, pl. 22, figs. 14—18. ?Jaculella acuta Brady. Heron-Allen and Earland, 1934, Discovery Repts., v. 10, Foraminifera, pt. 3, p. 72, 73, pl. 2, figs. 19, 20. These specimens are identical with Heron-Allen and Earland’s illustrations, and the early part of the test is composed of pseudochitin. Distribution—Lat. 46° to 53° N. Common in the Aleutian Trench area. Genus HYPERAMMINA Brady, 1878 Hyperammina app. Plate 1, figure 6 Probably several species are present. One group seems to be larger and have a coarser wall (cf. H. SYSTEMATIC CATALOG 13 friabilz's Brady, 1884, Challenger Repts., Zoology, v. 9, p. 46, pl. 23, figs. 1, 2, 5, 6). Another group is smaller and more finely arenaceous (cf. H. cylindrica Parr, 1950, Foraminifera, BANZ Antarctic Research Exped., 1929—1931, Repts., ser. B, v. 5, pt. 6, p. 254, pl. 3, fig. 5). However, where they occur together, it is so difficult to draw a line between the two groups that they are considered together. Distribution—Lat 32° to 50° N. Family SACCAMMlNlDAE Brady, 1884 Genus PSAMMOSPHAERA Schulze, 1875 Psammosphaera rustica Heron-Allen and Earlund Psammosphaera rustica Heron-Allen and Earland, 1912, Royal Micros. Soc. London Jour., p. 383, pl. 5, figs. 3, 4; pl. 6, figs. 2—4. Distribution—Found in only one core sample, P- 33-61 (lat 39° N., depth 5,230 m). Genus SACCAMMINA M. Sara in Carpenter, 1869 Saccammina sphnerica M. Sars Saccammina sphaerica M. Sars, 1869, Forhandl. Vidensk.- Selsk. Christiania, Aar 1868, p. 248. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 253, pl. 18, figs. 11—15, 17. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 39, 40, figs. 33—36. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 36, pl. 18, figs. 11—15, 17. Distribution—Lat 30° to 52° N. Abundant in the Aleutian Trench. Genus THURAMMINA Brady, 1879 Thurammina pnpillala Brady Plate 1, figure 7 Thuramrm'na papillata Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, p. 45, pl. 5, figs. 4—8. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 321, pl. 36, figs. 7—18. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 58, fig. 66. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 74, pl. 36, figs. 7—18. Distribution—Lat 48° to 52° N. Reported previ- ously from the North Pacific in Challenger stations from depths of 3,400 to 4,700 meters. Family AMMODISCIDAE Reuss, 1862 Genus GLOMOSPIRA Rzellak, 1885 Glomospirn gordialis (Jones and Parker) Plate 1, figure 8 Trochamrm'na squamata var. gordialis Jones and Parker, 1860, Geol. Soc. London Quart. Jour., v. 16, p. 304. Parker and Jones, 1865, Royal Soc. London Philos. Trans, v. 155, p. 408, pl. 15, fig. 32. Ammodiscus gordlalis (Jones and Parker). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 333, pl. 38, figs. 7—9. 495-617 0 - 73 - 3 Gordiarnmlna gordialis (Jones and Parker). Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 76, 77, figs. 98—100. Glomosplra gord’lalis (Jones and Parker). Cushman, 1918, U.S. Natl. Mus. Bull. 104, pt. 1, p. 99, pl. 36, figs. 7—9. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 78, pl. 38, figs. 7—9. Distribution—Lat 23° to 53° N. Present, often abundantly, at stations just south of the Aleutian Trench. Family HORMOSINIDAE Haeckel, 1894 Genus HORMOSlNA Brady, 1879 Homosina globuliferu Brady Hormosina globulifera Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, p. 60, pl. 4, figs. 4, 5. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 326, pl. 39, figs. 1—6. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 93—— 95, figs. 136, 137. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 80, pl. 39, figs. 1—6. Distribution—Lat 32° to 52° N. Generally present as fragments recognizable by the texture of the wall. Brady described these as fragments of a peculiarly deep-water organism. It was found at 21 Challenger stations, only five of which had a depth of less than 1,800 meters. Genus REOPHAX Montfort, 1808 Reophax dentalinaformis Brady Plate 1, figure 9 Reophax dentalinaformis Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 49. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 293, pl. 30, figs. 21, 22. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 62, pl. 30, figs. 21, 22. Distribution—Occurs from lat 39° to 51° N. Brady listed it from 21 stations, only four of which were Shallower than 1,800 meters. Reopllax difllugiformis Brady Plate 1, figure 10 Reophax difllugiformis Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, p. 51, pl. 4, fig. 3. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 289, pl. 30, figs. 1—4. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 62, pl. 30, figs. 1—4. Proteonina difi‘lugiformis (Brady). Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 41, 42, figs. 40, 41. Distribution—This variable species occurs com- monly at nearly all stations, most abundantly in deep water of the Aleutian Trench. Reophax distans Brady Plate 1, figure 11 Reophax distans Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 50. 14 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Brady, 1884, Challenger Repts., Zoology, v. 9, p. 296, pl. 31, figs. 18—22. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 85, 86, fig. 119. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 64, pl. 31, figs. 18—22. Distribution—Lat 39° to 52° N., rare and fragile. N o specimens with more than three chambers found. Reophax nodulosus Brady Plate 1, figure 12 Reophax nodulosa Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, p. 52, pl. 4, figs. 7, 8. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 294, pl. 31, figs. 1—9. Reophax nodulosus Brady. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 87, 88, fig. 122. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 64, pl. 31, figs. 1—9. This species is generally large and robust. It shows a great deal of variation in chamber shape, as shown in Brady’s (1884) illustrations. Distribution—Lat 46° to 53° N. Reophax pilulifer Brady Reophax pilulifera Brady, 1884, Challenger Repts., Zoology, v. 9, p. 292, pl. 30, figs. 18—20. Reoplax pilulifer Brady. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 85, figs. 117, 118. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 62, pl. 30, figs. 18—20. This species is very distinctive and somewhat simi- lar to Hormosina globullfera Brady (1884, p. 53), but it has a coarsely arenaceous wall. Distribution—Found in core sample P—19—61 (lat 53° N., depth 4,430 m). Reoplnx scorpiurus de Montfort Plate 1, figure 13 Reophax scorpiurus de Montfort, 1808, Conch. Syst, v. 1, p. 331, 83d genre. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 291, pl. 30, figs. 12, 14—17. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 62, pl. 30, figs. 12, 14—17. This is one of the few arenaceous species that shows strong variation in wall texture. In the shore- ward samples (P—13—61, P-19—61, P—38—61, P—41— 61, P—48—61, P—49-61) the wall texture is very coarse; the specimens are large, and the test gener- ally has only three chambers. In the seaward sam- ples (P—32—61, P—33—61, P-63—61, P—69—61), the wall is fine grained, and sponge spicules are often incorporated in the test, which generally has five chambers. Distribution—Lat 23° to 51° N. Reopllax scotti Cluster Reophax scotti Chaster, 1892, lst Rept. Southport Soc. Nat. Sci., 1890—91, p. 57, pl. 1, fig. 1. Hiiglund, 1947, Z001. Bidrag Fran Uppsala, v. 26, p. 94— 96, fig. 72. Cushman and McCulloch, 1939, Allan Hancock Pacific Exped. Repts., v. 6, no. 1, p. 61, 62, pl. 3, fig. 11. Distribution—A single specimen was found in only one core sample (P—12—61, lat 53° N., depth 6,560 m). The extreme fragility of the test may ac- count for its scarcity in prepared samples. Flmily LITUOLIDAE de Blainville, 1825 Genus ADERCOTRYMA Loeblich and Tappan, 1952 Adercolrymn glomenta (Brady) Plate 1, figure 14 Lituola glomerata Brady, 1878, Ann. Mag. Nat. History, ser. 5, v. 1, p. 433, pl. 20, figs. 1a—c. Adercotryma glomeratnm (Brady). Loeblich and Tappan, 1952, Washington Acad. Sci. Jour., v. 42, no. 5, p. 141, 142, figs. 1—4. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, pl. 70, pl. 34, figs. 15—18. These specimens are somewhat broader and have more deeply depressed sutures than those figured by Brady and by Loeblich and Tappan. Distribution—Lat 30° N. to Aleutian Trench. According to Brady (1884, p. 309, 310), this species was found in relatively shallow water in Arctic seas and in deep water (greater than 3,600 m) of tropical and subtropical latitudes. Genus CYCLAMMINA Brady, 1879 Cyclnmmina cancellnla Brady Plate 1, figure 18 Cyclammina cancellata Brady, 1879, Micros. Sci. Quart. J our., new ser., v. 19, p. 62. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 351, pl. 37, figs. 8—16. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 110— 111, figs. 168—171. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 76, pl. 37, figs. 8-16. Distribution—Lat 46° to 50° N. Brady listed this species from two samples from the North Pacific, east from Japan, at depths of 3,400 and 5,300 meters. Cyclammina trullisula (Brady) Plate 1, figure 15 Trochamrm'na trullissata Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, no. 73, p. 56, pl. 5, figs. 10a, b. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 342, pl. 40, fig. 13 (not fig. 14, 15). Cyclammina bradyi Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 113, fig. 174. Cyclammina trulllssata (Brady). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 82, pl. 40, fig. 13. SYSTEMATIC CATALOG 15 Distribution—Widely distributed (lat 30° to 55° N.) , rare. Genus ALVEOLOPHRAGMIUM Shchedrina, 193G Alveolophngmium nitidum (Giles) Plate 1, figure 16 Haplophragmium nitidum Gties, 1896, Harvard Coll. Mus. Comp. Zoology Bull., v. 29, p. 30, pl. 3, figs. 8, 9. Haplophragmo'ldes m'tldum Goes. Cushman, 1920, U.S. Natl. Mus. Bull. 104, pt. 2, p. 44. Haplophragmoides m'tidus (Gaels). Cushman, 1920, U.S. Natl. Mus. Bull. 104, pt. 2, p. 44. Haplophragmoides m‘tidus (Goes). Heron-Allen and Earland, 1934, Discovery Repts., v. 10, Foraminifera, pt. 3, p. 88, 89, pl. 3, figs. 3—6. This species is extremely smooth walled, brown in color, completely involute, with 4 or 41/2 chambers visible. Distribution—Most common north of lat 50° N. in the Aleutian Trench area. Alveolophragmium cf. A. nitidum (OSes) Plate 1, figure 17 Haplophragmoides nitidus (Giles). Heron-Allen and Ear- land, 1934, Discovery Repts., V. 10, Foraminifera, pt. 3, p. 88, 89, last paragraph. This form differs from the typical one in having a slightly coarser wall and more inflated chambers. It occurs with the typical form. Distribution.—Most common north of lat 50° N. Extremely abundant in the deep waters of the Aleu- tian Trench (7,000 m or more). Alveolophrag’mium ringens (Brady) Trochammina ringens Brady, 1879, Micros. Sci. Quart. Jour., new ser., v. 19, p. 57, pl. 5, fig. 12. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 343, pl. 40, figs. 17, 18. Haplophragmoldes ringens (Brady). Cushman, 1910, U.S. Natl, Mus. Bull. 71, pt. 1, p. 109, fig. 166. Alveolophragmium ringens (Brady). Parker, 1954, Harvard Coll. Mus. Comp. Zoology Bull., v. 111, no. 10, p. 487, pl. 1, fig. 19. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 82, pl. 40, figs. 17, 18. Specimens are identical with those figured by Brady. Distribution—Widely distributed, but rare. Brady (1884, p. 344) did not record it from any Pacific stations. Alveolophragmium scitulum (Brady) Plate 1, figure 19 Haplophragmium scitulum Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 50. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 308, p. 34, figs. 11—13. Alveolophragmlum scitulum (Brady). Parker, 1954, Har— vard Coll. Mus. Comp. Zoology Bull., v. 111, no. 10, p. 487. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 70, pl. 34, figs. 11—13. in the Aleutian Distribution—Present only Trench area. Alveolophrngmium subglobosum (G. 0. Sam) Plate 1, figure 20 Haplophragmium latidorsatum (Bornemann). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 307, pl. 34, figs. 7, 8, 10. Haplophragmm’des subglobosum (G. O. Sars). Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 105, 106, figs. 162—164. Labrospira subglobosa (G. O. Sars). Hoglund, 1947, Z00]. Bidrag. Fran Uppsala, v. 26, p. 144, 145, pl. 11, fig. 2, text fig. 126. Alveolophrag'mium subglobosum (G. O. Sars). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 70, pl. 34, figs. 7, 8, 10. Specimens have less deeply depressed sutures than those of Brady. Coarseness of wall is variable. Distribution.—Widely distributed, from lat 23° to 54° N. Brady (1884, p. 308) found it at nine stations in the North Pacific at depths from 3,600 to 7,300 meters. Alveolophngmium weisneri (Parr) Plate 2, figure 1 Trochammina trullissata Brady, 1884, Challenger Repts., Zoology, v. 9, p. 342, pl. 40, figs. 14, 15 (not fig. 13). Labrospira weisneri Parr, 1950, Foraminifera, BANZ Ant- arctic Research Exped., 1929—1931, Repts., ser. B, v. 5, pt. 6, p. 272, pl. 4, figs. 25, 26. Labraszn'ra arctica Parker, 1952, Harvard Coll. Mus. Comp. Zoology Bull., v. 106, no. 9, p. 399, pl. 2, figs. 7, 12. Alveolophragm'lum weis’neri (Parr). Parker, 1954, Harvard Coll. Mus. Comp. Zoology Bull., v. 111, no. 10, p. 488, pl. 1, fig. 23. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 82, pl. 40, figs. 14, 15. Specimens are identical with those illustrated by Brady. Distribution—Lat 39° to 52° N., rare. Alveolophragmium? 3]). Plate 2, figure 2 The form is tiny, slightly evolute; sutures are curv- ing, only slightly depressed; periphery is rounded, only Slightly lobed; wall is smooth, red-brown, pseu- dochitinous; aperture is interio-areal. This is apparently an arenaceous form that has not developed an agglutinating stage (see also Trochammina cf. T. malovensis, p. ). It is very rare. Distribution—Core samples P—48—61 (lat 52° N., depth 4,650 m) and P—49—61 (lat 50° N., depth 5,000 m). 16 Genus AMMOBACULITES Cushman, 1910 Ammobaculites agglutinnns (d’Orbigny) Plate 2, figure 3 Spirolina agglutinans d’Orbigny, 1846, Foram. Fossiles Wien, p. 137, pl. 7, figs. 10—12. Haplophragmium agglutinans (d’Orbigny). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 301, pl. 32, figs. 19—21, 24—26. Ammobaculites agglutinans (d’Orbigny). Cushman, U.S. Natl. Mus. Bull. 71, pt. 1, p. 115, fig. 176. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub.,9, p. 66, pl. 32, figs. 19—21, 24—26. Walls of these specimens are coarser grained than those illustrated by Brady. Distribution—Lat 23° to 50° N. Brady (1884, p. 301, 775) listed it from deep water in the North Pacific. Ammobaculiles agglutinans filaformis Heron-Allen and Earlnnd (smooth form) Plate 2, figure 4 Haplophragmium agglutinans (d’Orbigny). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 301, pl. 32, fig. 23 (not fig. 22). Ammobaculites agglutinans filaformis Heron—Allen and Ear- land, 1934, Discovery Repts., v. 10, Foraminife‘ra, pt. 3, p. 92, 93, pl. 3, fig. 12 (not fig. 11). Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 66, pl. 32, fig. 23 (not fig. 22). This smooth-walled form has low regular cham- bers, and the wall is brown. Distribution—Lat 32° to 53° N., most abundant in the Aleutian Trench. Heron-Allen and Earland listed this form from deep water in the Antarctic Ocean. 1910, Ammobaculites agglutinans filnformis Heron-Allen and Earl-ml (rough form) Plate 2, figure 5 Haplophragmium agglutinans (d’Orbig‘ny). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 301, pl. 32, fig. 22 (not fig. 23). Ammobaculites agglutinans filaformls Heron-Allen and Ear- land, 1934, Discovery Repts., v. 10, Foraminifera, pt. 3, p. 92, 93, pl. 3, fig. 11 (not fig. 12). Barker, 1960, Soc. Econ, Paleontologists and Mineralo- gists Spec. Pub. 9, p. 66, pl. 32, fig. 22 (not fig. 23). The wall is so coarsely arenaceous that chamber arrangement is difiicult to see. Distribution—Lat 39° to 53° N. This form com- monly occurs in the same samples as the smooth— walled form. Ammobaculites americenus Cushman Haplophragmium fontinense Terquem. Brady, 1884, Chal- lenger Repts., Zoology, v. 9, p. 305, pl. 34, figs. 1—4. Ammobaculites americanus Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 117, 118, figs. 184, 185. Barker, 1960, Soc. Econ. Paleontologists and Mineralo— gists Spec. Pub. 9, p. 70, pl. 34, figs. 1—4. FORAMINIFERA OF THE NORTH PACIFIC OCEAN These specimens are similar to those illustrated by Brady and by Cushman but are thicker. Distribution—Lat 30° to 56° N ., most abundant north of lat 50° N. Genus AMMOMARGINULINA Weisuer, 1931 Ammomarginuline foliacen (Brady) Plate 2, figure 6 Haplophragmium foliaceum Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 50. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 304, 305, pl. 33, figs. 20—25. Ammomarginulina foliaceus (Brady). Cushman, 1933, Cush- man Lab. Foram. Research Spec. Pub. 4, pl. 10, fig. 6. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 68, pl. 33, figs. 20—25. Specimens are identical with Brady’s illustrations. Distribution—Widely distributed (lat 39° to 55° N.) but rare. Brady (1884, p. 305) found only a few specimens in the North Pacific. Genus PLACOPSILINA d’Orbigny, 1850 Plncopsilina confuse Cushman Placopsilina confuse Cushman, 1920, U.S. Natl. Mus. Bull. 104, pt. 2, p. 71, pl. 14, fig. 16. Heron-Allen and Earland, 1934, Discovery Repts., v. 10, Foraminifera, pt. 3, p. 94, 95. This tiny form occurs abundantly at several 10- calities. It is commonly attached to diatom frustules. Its small size and distinctive reddish—brown color distinguish it from P. bradyi Cushman and McCul- loch (1939, p. 112). Distribution—Lat 44° to 50° N. Family TEXTULARIIDAE Ehrenberg, 1838 Genus SPIROPLECTAMMINA Cushman. 1927 Spiroplectamminu biformis (Parker and Jones) Plate 2, figure 7 Textularia agglutinans var. biformls Parker and Jones, 1865, Royal Soc. London Philos. Trans, v. 155, p. 370, pl. 15, figs. 23, 24. Spiroplecta blformis (Parker and Jones). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 376, pl. 45, figs. 25—27. Spiroplectammlna biformis (Parker and Jones). Cushman, 1927, Cushman Lab. Foram. Research Contr., v. 3, pt. 1, p. 23. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 92, pl. 45, figs. 25—27. The test is extremely small, fine grained, and brown. Distribution—Lat 46° to 54° N. Genus BIGENERINA d’Orbigny, 1826 Bigenerina minutissima Earlnnd Plate 2, figure 8 Bigenerina minutissima Earland, 1933, Discovery Repts., v. 7, Foraminifera, pt. 2, p. 98, pl. 3, figs. 36—38. SYSTEMATIC CATALOG 17 Heron-Allen and Earland, 1934, Discovery Repts., v. 10, Foraminifera, pt. 3, p. 117, pl. 4, fig. 48. Distribution—Lat. 30° to 48° N., rare. Heron- Allen and Earland rarely found the species in deep waters of the Scotia Sea (lat 55° to 60° 8.). Family TROCHAMMINIDAE Schwager, 1877 Genus TROCHAMMINA Parker and Jones, 1859 Trochammina grisea Heron-Allen and Harland Plate 2, figure 9 Trachamrm'na grisea Heron-Allen and Earland, 1934, Dis— covery Repts., v. 10, Foraminifera, pt. 3, p. 100, 101, pl. 3, figs. 35—37. Distribution—Rare in several stations north of lat 47° N. Trocllsmmina inflnta (Montagu) Plate 2, figure 10 Trochammina inflate (Montagu). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 338, pl. 41, fig. 4. Cushman, 1910, US. Natl, Mus. Bull. 71, pt. 1, p. 121, 122, fig. 188. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 84, pl. 41, fig. 4. Distribution—Specimens identical with those figured by Brady occur in two core samples, P—38— 61 and P—48—61 (lat 46° and 52° N.). Troclmmmina kelletiae Thalmann Plate 2, figure 12 Trocha/mmina peruviana Cushman and Kellett, 1929, US. Natl. Mus. Proc., v. 75, art. 25, p. 4, pl. 1, fig. 8. Trochammina kellettae Thalmann, 1932, Eclogae Geol. Hel- vetiae, v. 25, p. 313. Distribution—A few specimens found at one 10— cality in the Aleutian Trench (core sample P—41—61, lat 50° N., depth 7,230 m) . Trochammina malovensis Heron-Allen and Earlnnd Plate 2, figure 13 Trochammina malovensis Heron-Allen and Earland, 1932, Discovery Repts., v. 4, Foraminifera, pt. 1, p. 345, pl. 17, figs. 14—19. ?Haplophragmium turbinatum var. helicoideum Giies, 1896, Harvard Coll. Mus. Comp. Zoology Bull., v. 29, no. 1, p. 30, 31, pl. 3, figs. 10—13. This species is identical with that in Heron-Allen and Earland’s illustrations The specimen from core sample P—12—61 appears to grade into the pseudo— chitinous T. cf. T. malovensis (below). Distribution—Present at two stations Aleutian Trench. in the Trochnmmina cf. T. malovensis Heron-Allen and Harland Plate 2, figure 11 This species appears identical with T. malooensis except in wall character and in its slightly more irregular shape. The wall is composed of reddish- brown pseudochitin. However, the last few chambers appear finely arenaceous in specimens from core sample P—12—61. Distribution—Found abundantly in the Aleutian Trench, rarely as far south as lat 33° N. Trocllammina nana (Brady) Plate 2, figure 15 Haplophragmium nanum Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 50. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 311, pl. 35, figs. 6—8. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 123, figs. 190—192. Trochammina nana (Brady). Barker, 1960, Soc. Econ. Pale- ontologists and Mineralogists Spec. Pub. 9, p. 72, pl. 35, figs. 6—8. This small species is variable in number of cham- bers. It is characteristically dark reddish-brown. Distribution—Abundant in core sample P—49—61 (lat 50° N., depth 5,000 m) . Trochamminn nitida Brady Plate 2, figure 14 Trochammina nitida Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 52. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 339, pl. 41, figs. 5, 6. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 84, pl. 41, figs. 5, 6. Distribution—Lat 24° to 52° N. This little species is widely distributed but rare. All but one of the occurrences described by Brady are shallower than 390 meters. Trochammina globigeriniformis (Parker and Jones) Plate 3, figure 1 Lituola nautiloidea globigeriniform-is Parker and Jones, 1865, Royal Soc. London Philos. Trans., v. 155, p. 407, pl. 15, figs. 46, 47. Haplophragmium globiger'lniforme (Parker and J ones). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 312, pl. 35, figs. 10, 11. Ammoglobigerina bulloides Elmer and Fickert, 1899, Zeit- schr. Wiss. Zoologie, Leipzig, v. 65, pt. 4, p. 107. Trochammina globigeriniformis (Parker and Jones). Cush- man, 1910, US. Natl. Mus. Bull. 71, pt. 1, p. 124, 125, figs. 193—195. Ammoglobigem‘na globigerinifor’mis (Parker and Jones). Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 72, pl. 35, figs. 10, 11. Distribution—Lat 23° to 54° N. One of the most widely distributed forms. Brady (1884, p. 313) listed it from six stations in the North Pacific, all but one at depths greater than 3,300 meters. Cushman re- corded it as one of the most common deep—water species. 18 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Genus CYSTAMMINA Neumayr, 1889 Cystammina galenta (Brady) Plate 3, figure 2 Trochammina galeata Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 52. Brady, 1884, Challenger Repts., Zoology, V. 9, p. 344, pl. 40, figs. 19—23. Ammochilostoma galeata (Brady). Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 127, 128, figs. 198—201. Cystammina galeata (Brady). Barker, 1960, Soc. Econ. Paleontolo‘gists and Mineralogists Spec. Pub. 9, p. 82, pl. 40, figs. 19—23. Distribution—Lat 30° to 55° N., rare. Brady noted it as rare and found only at great depth in mid- ocean. Genus TRlTAXlS Schubert, 1921 Tritaxis conica (Parker and Jones) Valvalina triangularis var. conica Parker and Jones, 1865, Royal Soc. London Philos. Trans., v. 155, p. 406, pl. 15, fig. 27. Valvulina conica Parker and Jones. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 392, pl. 49, figs. 15, 16. Trltaxis conica (Parker and Jones). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 100, pl. 49, figs. 15, 16. Distribution—Lat 350 N. Family ATAXOPHRAGMHDAE Schwager, 1877 Genus GLOBOTEXTULARIA Eimer and Fickert, 1899 Globotextularia anceps (Brady) Haplophragmium anceps Brady, 1884, Challenger Repts.. Zoology, v. 9, p. 313, pl. 35, figs. 12—15. Globotextularla anceps (Brady). Eimer and Fickert, 1889, Zeitschr. Wiss. Zool., v. 65, p. 679. Cushman, 1910, U.S. Natl. Mus. Bull. 71, pt. 1, p. 125, 126, fig. 196. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 72, pl. 35, figs. 12—15. Distribution—A few specimens found in core sam- ples P—41—61 and P—49—61 (lat 50° N .). Brady noted it in samples from deep water of the Atlantic but not of the Pacific. Genus DOROTHlA Plummer, 1931 Dorothia exilis Cushman Plate 3, figure 3 Gaudryina filaformis Berthelin. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 380, pl. 46, fig. 12. Doroth’ia exilis Cushman, 1936, Cushman Lab. Foram. Re— search Spec. Pub. 6, p. 30. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 94, pl. 46, fig. 12. These extremely minute forms are probably as- signable to the species illustrated by Brady and by Cushman. Distribution—Single individuals found in only two core samples, P—49—61 and P—52—61. Genus EGGERELLA Cushman, 1933 Eggerella bradyi (Cushman) Plate 3, figure 4 Vernem'lina pygmaea (Egger). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 385, pl. 47, figs. 4—7. Vernenilina bradyi Cushman, 1911, U.S. Natl. Mus. Bull. 71, pt. 2, p. 54, 55, fig. 87. Eggerella bradyi (Cushman). Cushman, 1933, Cushman Lab. Foram. Research Contr., v. 9, p. 33. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 96, pl. 47, figs. 4—7. Distribution—Lat 37° to 50° N. Brady reported it as a common deep-water species, occurring in the North Pacific between depths of 3,400 and 5,700 meters. Eggerella scabra (Williamson) Plate 3, figure 5 Bulimina scabra Williamson, 1858, Recent British foramini- fera, p. 65, pl. 5, figs. 136, 137. Verneuilina polystropha (Reuss). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 386, pl. 47, figs. 15—17. Verneuillna scabra (Williamson). Cushman, 1937, Cushman Lab. Foram. Research Spec. Pub. 8, p. 50, pl. 5, figs. 10, 11. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 96, pl. 47, figs. 15—17. Distribution—Rare, found north of lat 43° N. Common in shallow water south of the Aleutian Islands. Deep-water forms are smaller and slightly less regular in shape. Family NUBECULARllDAE Jones, 1875 Genus OPHTHALMlDlUM K’ubler and Zwingli, 1870 Ophthalmidium acutimargo (Brady) Spiroloculina acutimargo Brady, 1884, Challenger Repts., Zoology, v. 9, p. 154, pl. 10, fig. 13 (not figs. 14, 15). Cushman, 1917, U.S. Natl. Mus. Bull. 71, pt. 6, p. 31, 32, pl. 1, fig. 1. Spirophthalmidlnm acutimargo (Brady). Cushman, 1927, Cushman Lab. Foram. Research Contr., v. 3, pt. 1, p. 37. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 20, pl. 10, fig. 13. Distribution—Rare in one core sample, P—52—61 (lat 44° N., depth 5,160 m) . Ophthalmidium pusillum (Earland) Plate 3, figure 7 Spiroloculina tennis (Czjzek). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 152, pl. 10, figs. 9, 10 (not figs. 7, 8, 11). Spirolocuh‘na pusillnm Earland, 1934, Discovery Repts., v. 10, Foraminifera, pt. 3, p. 47, 48, pl. 1, figs. 3, 4. Spirophthalmidium pusillum (Earland). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 20, pl. 10, figs. 9, 10. Distribution—Lat 37° to 41° N. SYSTEMATIC CATALOG 19 Family MILIOLIDAE Ehrenberg, 1839 Genus QUINQUELOCULINA Cushman, 1917 Quinqueloculina sp. This species is very tiny and compressed; the sutures are only very slightly depressed. Only a single specimen was found. Distribution—Core sample P—38—61 (lat 46° N., depth 5,610 m). Genus PYRGO Defiance, 1824 Pyrgo sp. This specimen is possibly referrable to Pyrgo mnrrhyna (Schwager) (1866, Novara Exped, 1857— 1859, Wien, Geol. Theil, Bd. 2, Abt. 2, p. 203, pl. 4, fig. 15), but the aperture is broken on the single specimen found. Distribution—Core sample P—16—61 (lat 54° N., depth 2,410 m). Genus MlLlOLlNELLA Weisner, 1931 Miliolinella subrotunda (Montagu) Plate 3, figure 8 Miliolina m'rcnlaris (Bornemann). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 169, pl. 4, fig. 3; pl. 5, figs. 13, 14. Mlllollnella subrotunda (Montagu) Weisner, 1931, Deutsche Sudpolar Exped., 1901—1903, v. 20 (Zoology, v. 12), p. 107. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 8, 10, pl. 4, fig. 3; pl. 5, figs. 13, 14. Distribution—Lat 30° to 53° N. Brady’s reports are from shallow water. However, under Mlliol'lna labiosa (d’Orbigny) (Brady, 1884, p. 170) he dis- cusses deep-water specimens very similar to M. sab- rotanda, which may be the same species discussed here. Genus AMMOMASSILINA Cushman, 1933 Ammomassilina alveolinaformis (Millett) Splroloeuh‘na asperula Karrer. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 152, pl. 8, figs. 13, 14. Masslllna asperula (Karrer). Cushman, 1921, U.S. Natl. Mus. Bull. 100, v. 4, p. 447, 448. Massilina alveolinaformis Millett. Cushman, 1928, U.S. Natl. Mus. Bull. 104, pt. 6, p. 39. Ammomassilina alveollnaform'ls (Millett). Cushman, 1933, Cushman Lab. Foram. Research Contr., v. 9, pt. 2, p. 32. Barker, 1960, Soc. Econ. Paleontologists and Mineralo— gists Spec. Pub. 9, p. 16, pl. 8, figs. 13, 14. Distribution—One specimen (corroded) found in core sample P—29-61 (lat 32° N., depth 4,810 m) . Famiy TURRILINIDAE Cushman, 1927 Genus BULIMINELLA Cushman, 1911 Buliminella basicostata Parr Bullminella elegantissima d’Orbigny var. seminuda Terquem. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 403, pl. 1, figs. 23, 24. Buliminella basicostata Parr, 1950, Foraminifera, BANZ Antarctic Research Exped., 1929—1931, Repts., ser. B, v. 5, pt. 6, p. 336, pl. 12, figs. 11, 12. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 104, pl. 50, figs. 23, 24. Distribution—Aleutian Terrace. Family BOLlVlNlTlDAE Cushman, 1923 Genus BOLIVINA d'Orbigny Bolivina robusta Brady Bollm‘na robusta Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 57. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 421, pl. 53, figs. 7—9. Cushman, 1911, U.S. Natl. Mus. Bull. 71, pt. 2, p. 36, 37, figs. 59, 60. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 108, pl. 53, figs. 7—9. Distribution—One specimen (stained) from core sample P—40—61 (lat 50° N., depth 5,500 m). Brady described it from generally leSS than 1,500 meters. Bolivina decussaia Brady Bolivina deeussata Brady, 1881, Micros. Sci. Quart. Jour., v. 21, no. 5, p. 58. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 406, p. 423, pl. 53, figs. 12, 13. Barker, 1960, Soc. Econ. Paleontologists and Mineralo~ gists Spec. Pub. 9, p. 110, pl. 53, figs. 12, 13. Distribution—Aleutian Terrace. Bolivina pseudoplicata Heron-Allen and Earland Bollvlna pllcata Brady, 1870, Ann. Mag. Nat. History, ser. 4, v. 6, p. 302, pl. 12, fig. 7. Bolivina pllcata Halkyard, 1889, Manchester Micros. Soc. Trans. and Ann. Rept., v. 6, p. 61, pl. 1, fig. 13. Bollm'na pseudoplicata Heron-Allen and Earland, 1930, Royal Micros. Soc. London, ser. 3, v. 50, p. 81, pl. 3, figs. 36—49. Distribution—Lat 55° to 60° N., occurs only on Aleutian Terrace. Genus BULIMINA d'Orbigny, 1826 Bulimina aculeala d’Orbigny Plate 3, figure 9 Bulimina aculeata d’Orbigny, 1826, Annales des Sci. Natur- elles, v. 7, no. 7, p. 269. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 406, pl. 51, figs. 7—9. Cushman, 1911, U.S. Natl. Mus. Bull. 71, pt. 2, p. 86, 87, fig. 139. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 104, pl. 51, figs. 7—9. Distribution—Rare in one core sample (P—16—61, lat 54° N., depth 2,410 m). 20 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Genus GLOBOBULIMINA Cushman, 1927 Globobulimina auriculaia Bailey Plate 3, figure 10 Bulimina anrieulata Bailey, 1851, Smithsonian Inst, Contr. Knowledge, v. 2, p. 12, p1., figs. 25—27. Distribution—Occurs rarely in core sample P—16— 61 (lat 54° N., depth 2,410 In). Two of the three specimens are stained. Globobulimina pacific: Cushman Bulimina pyrula d’Orbigny. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 339, pl. 50, figs. 7—10. Globobulimina pacific-a Cushman, 1927, Cushman Lab. For- am. Research Contr., v. 3, p. 67, pl. 14, fig. 12. Globobulimina pacifica Cushman?. Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 102, pl. 50, figs. 7—10. Distribution—One stained specimen in core sam- ple P—16—61 (lat 54° N., depth 2,410 m). Family UVIGERINIDAE Haeckel, 1894 Genus UVIGERINA d’Orbigny, 1826 Uvigerina peregrina Cushman Plate 3, figure 11 Uvigem'na pygmaea d’Orbigny. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 575, pl. 74, figs. 11, 12. Uvigerina peregrina Cushman, 1923, U.S. Natl. Mus. Bull. 104, pt. 4, p. 166, pl. 42, figs. 7—11. Euuvigerina peregrina (Cushman). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 154, pl. 74, figs. 11, 12. Distribution—Several specimens found in core sample P—16—61 (lat 54° N., depth 2,410 m). Uvigerina cushmani Todd Um'gerina cushmani Todd, 1948, in Cushman and McCul- loch, 1948, Allan Hancock Pacific Exped. Repts., V. 6, no. 5, p. 257, pl. 33, fig. 1. Distribution—Aleutian Terrace. Genus ANGULOGERINA Cushman, 1927 Angulogerina fluens Todd Angnlogem'na angulosa (Williamson). Cushman, 1948 [not U’vigerina angulosa Williamson], Cushman Lab. For- am. Research Spec. Pub. 23, p. 66, pl. 7, fig. 8. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 576, pl. 74, figs. 15, 16. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 154, pl. 75, figs. 15, 16. Angulogerina fluens Todd, 1947, in Cushman and Todd, 1947, Cushman Lab. Foram. Research Contr., v. 23, pt. 3, p. 67, pl. 16, figs. 6, 7. Distribution—Aleutian Terrace. Family DISCORBIDAE Ehrenberg, 1838 Genus EPISTOMINELLA Husezima and Maruhasi, 1944 Epislominella exigua (Brady) Plate 3, figure 12 Pulm'nulina exigna Brady, 1884, Challenger Repts., Zoology, v. 9, p. 696, pl. 103, figs. 13, 14. Epistominella exigua (Brady). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 212, pl. 103, figs. 13, 14. Distribution—Lat 44° to 55° N. This rare form is generally stained. According to Brady, it is generally found deeper than 1,800 meters. Epistominella umbonifera (Cushman) Plate 3, figure 13 Pulvinulinella umbonifera Cushman, 1933, Cushman Lab. Foram. Research Contr., v. 9, pt. 4, p. 90, pl. 9, fig. 9. not Epistominella? umbonifera (Cushman). Phleger, Parker, and Pierson, 1953, Repts. Swedish Deep-sea Exped., v. 7, no. 1, p. 43, 44, pl. 9, figs. 33, 34. Distribution—Core sample P—49-61 (lat 50° N., depth 5,000 m). Two stained specimens, identical with Cushman’s figures, occur at this station. Phleg— er, Parker, and Pierson’s specimens have more num- erous chambers. Cushman described the form from the South Pacific at a depth of 2,243 meters. Family ELPHIDIIDAE Galloway, 1933 Genus ELPHIDIUM de Monlfort, 1808 Elphidium incerium (Williamson) Polystomella umbilicatula var. incerta Wiliamson, 1858, Recent British Foraminifera, p. 44, pl. 3, fig. 82a. Elphidium incertum (Williamson). Loeblich and Tappan, 1953, Smithsonian Inst. Misc. Colln., v. 121, no. 7, p. 100—102. Distribution—This species occurs only in core sample P—16—61 (lat 54° N., depth 2,410 m) north of the Aleutian Trench. It appears identical with Wil- liamson’s figures. (See discussion in Loeblich and Tappan, 1953.) Elphidium magellanicum Heron-Allen and Finland Elphidinm (Polystomella) magellanicum Heron-Allen and Earland, 1932, Discovery Repts., v. 4, p. 440, pl. 16, figs. 26—28. Distribution—Aleutian Terrace. Genus ELPHlDiELLA Cushman, 1936 Elphidiella groenlandica (Cushman) Plate 4, figure 1 Elphidium grocnlandicnm Cushman, 1933, Smithsonian Inst. Misc. Colln., v. 89, no. 9, p. 4, pl. 1, fig. 10. Elphidiella groenlandica (Cushman). Loeblich and Tappan, 1953, Smithsonian Inst. Misc. Colln., v. 121, no. 7, p. 106, 107, pl. 19, figs. 13, 14. Distribution—This species is abundant in core sample P—16—61 (lat 54° N., depth 2,410 m). Several specimens are stained. Family GLOBOROTALHDAE Cushman, 1927 Geuus GLOBOROTALIA Cushman, 1927 Globorotalia inflata (d’Orbigny) Globigerina inflata d’Orbigny, 1839, in Barker-Webb and SYSTEMATIC CATALOG 21 Berthelot, Histoire Naturelle des l’Iles Canaries, v. 2, pt. 2, Foraminiféres, p. 134, pl. 2, figs. 7—9. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 601, pl. 79, figs. 8—10. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 164, pl. 79, figs. 8—10. Globorotalia inflata (d’Orbigny). Parker, 1962, Micropale- ontology, v. 8, no. 2, p. 236, pl. 5, figs. 6—9. Distribution—One specimen from core sample P— 26—61 (lat 26° N., depth 5,210 m). Family GLOBlGERlNlDAE Carpenter, Parker, and Jones, 1862 Genus GLOBIGERINA d’Orbigny, 1826 Globigerina bulloides d’Orbigny Globigerina bulloldes d’Orbigny, 1826, Annals des Sci. Natur- elles, ser. 1, v. 7, no. 1. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 593, pl. 77; pl. 79, figs. 3—7. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 164, pl. 77; pl. 79, figs. 3—7. Parker, 1962, Micropaleontology, v. 8, no. 2, p. 221, pl. 1, figs. 1—8. Distribution—Lat 23° to 55° N. Rare, often coriroded. Genus CANDEINA d'Orbigny in de La Sign, 1839 Candeinl nitidn d’Orbigny Candelna nltlda d’Orbigny, 1839, in de la Sagra, Histoire physique, politique et naturelle de l’lle de Cuba, Foraminiféres, p. 108, pl. 2, figs. 27, 28. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 622, pl. 82, figs. 13—20. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 170, pl. 82, figs. 13—20. Parker, 1962, Micropaleontology, v. 8, no. 2, p. 253, pl. 8, figs. 27—30. Distribution—One specimen found in core sample P—56-61 (lat 39° N., depth 5,400 m). Family ClBlClDlDAE Cushman, 1927 Genus ClBlClDES do Monlforl, 1808 Cibicides brndyi (Truutln) Plate 4, figure 2 Truncatulina dutemplel (d’Obrigny). Brady, 1884, Chal- lenger Repts., Zoology, v. 9, p. 665, pl. 95, fig. 5. Truncatalina bradyi Trauth, 1918, K. Acad. Wiss. Wien, Math.-Naturw. Cl., Denkschr., Wien, V. 95, p. 235. Ciblcides bradyl (Trauth). Thalmann, 1942, Am. Midland Naturalist, v. 28, no. 2, p. 464. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, 'p. 196, pl. 95, fig. 5. Distribution—Lat 32° to 52° N. Rare but Widely distributed. Except for a few specimens in core sam- ple P-19—61 (lat 32° N.) , all are stained. Cibicides lobatulus (Walker and Jacob) Cibicides lobatalus (Walker and Jacob). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 192, pl. 93, figs, 1, 4, 5. Distribution—Aleutian Terrace. Family CASSIDULlNlDAE d’Orbigny, 1839 Genus CASSIDULlNA d’Orbigny, 1826 Cassidulinn subglobosa Brady Plate 4, figure 3 Cassidulina subglobosa Brady, 1881, Micros. Sci. Quart. J our., new ser., v. 21, p. 60. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 430, pl. 54, fig. 17. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 111, pl. 54, fig. 17. This rare form is smaller than that described by Brady. The specimens may represent immature forms of Brady’s species. Distribution—Lat 55° N., depth 4,430 meters. One specimen, stained. Cassidulina crass: d’Orbigny Cassidulina crassa d’Orbigny, 1839, Voyage dans l’Amerique Meridionale, v. 5, pt. 5, p. 56, pl. 7, figs. 18—20. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 429—430, pl. 54, figs. 4, 5. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 110, pl. 53, figs. 4, 5. Distribution—Aleutian Terrace. Cussidulinn teretis Tappnn Cassidulina laem’gata d’Orbigny. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 428, pl. 54, figs. 1—3. Cassidullna teretis Tappan, 1951, Cushman Found. Foram. Research Contr., v. 2, pt. 1, p. 7, pl. 1, figs. 3a—c. Loeblich and Tappan, 1953, Smithsonian Misc. Colln., v. 121, no. 7, p. 121, pl. 24, figs. 3, 4. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 110, pl. 53, fig. 1. Distribution—Aleutian Terrace. Cassitlulina tortuosl Cushman and Hughes Cassidullna tortuosa Cushman and Hughes, 1925, Cushman Lab. Foram. Research Contr., v. 1, p. 14, pl. 2, fig. 4. Distribution—Aleutian Terrace. Genus EHRENBERGINA Reuss, 1850 Ehrenbergina llystrix Brady Plate 4, figure 5 Ehrenbergina hystrix Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 60. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 434, pl. 55, figs. 8—11. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 112, pl. 55, figs. 8-11. Distribution—One specimen in core sample P— 49—61 (lat 50° N ., depth 5,000 m). Brady described it as occurring rarely only in the deep water of the South Pacific. 22 FORAMINIFERA OF THE NORTH PACIFIC OCEAN Family lNVOLUTlNlDAE Biitscllli, 1880 Genus lNVOLUTlNA Terquem, 1862 lnvolutina tennis (Brady) Plate 4, figure 6 Ammodiscns tennis Brady, 1881, Micros. Sci. Quart. Jour., new ser., v. 21, p. 51. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 332, pl. 38, figs. 4—6. Involutina tennis (Brady). Barker, 1960, Soc. Econ. Pale- ontologists and Mineralogists Spec. Pub. 9, p. 78, pl. 38, figs. 5, 6. Distribution—Lat 39° to 53° N. The test is thin walled and variable in amount of contortion. Family NONIONIDAE Schultze, 1854 Genus NONlON de Montforl, 1808 Nonion labradoricum (Dawson) Plate 4, figure 4 Noniom‘na labradorica Dawson, 1860, Canadian Naturalist, v. 5, p. 191, fig. 4. Nonion labradoricnm (Dawson). Loeblich and Tappan, 1953, Smithsonian Inst. Misc. Colln., v. 121, no. 7, p. 86, 87, pl. 17, figs. 1, 2. Distribution—Only present in core sample P—16— 61 (lat 54° N ., depth 2,410 m), where all specimens are stained. It is also present in shallower water samples south of the Aleutian Islands. Nonion scapllum (Fichtel and Moll) Nonionina scaphum (Fichtel and M011). Brady, 1884, Chal- lenger Repts., Zoology, V. 9, p. 730, pl. 109, figs. 14, 15. Nonion scaphum (Fichtel and Moll). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 224, pl. 109, figs. 14, 15. Distribution—Aleutian Terrace. Genus NONIONELLA Cushman, I926 Nonionella turgida (Williamson) Plate 4, figure 8 Rotalina tnrgida Williamson, 1858, Recent British Fora- minifera, p. 50, pl. 4, figs. 95—97. Nonionina turgida (Williamson). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 731, pl. 109, figs. 17—19. Nonionella tnrgida (Williamson). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 224, pl. 109, figs. 17~19. Distribution—Found only in core sample P—16— 61 (lat 54° N., depth 2,410 m). All specimens are stained. Nonionella bradyi (Chapman) Nonion scapha (Fichtel and Moll). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 224, pl. 109, fig. 16. Nonionella bradgi (Chapman). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 224, pl. 109, fig. 16. Distribution—Aleutian Terrace. Nonionella auricula Heron-Allen and Earland Nonionella auricula Heron-Allen and Earland, 1930, Royal Micros. Soc. London Jour., ser. 3, v. 50, p. 192, pl. 5, figs. 68—70. Loeblich and Tappan, 1953, Smithsonian Misc. Colln., v. 121, no. 7, p. 92, 93, pl. 16, figs. 6—10. Distribution—Aleutian Terrace. Genus PULLENlA Parker and Jones, in Carpenter, Parker, and Jones, 1862 Pullenia subcarinata (d’Orbigny) Plate 4, figure 9 Noniom'na snbcarinata d’Orbigny, 1839, Voyage dans l’Ameri- que Meridionale, v. 5, pt. 5, Foraminiferes, p. 28, pl. 5, figs. 23, 24. Pullenia quinqneloba Reuss. Brady, 1884, Challenger Repts., Zoology, v. 9, p. 617, pl. 84, figs. 14, 15. Pullenia snbcarinata (d’Orbigny). Heron-Allen and Earland, 1932, Discovery Repts., v. 4, Foraminifera, pt. 1, p. 403, pl. 13, figs. 14—18. Barker, 1960, Soc. Econ. Paleontologists and Mineralo- gists Spec. Pub. 9, p. 174, pl. 84, figs. 14, 15. Distribution—Lat 37° to 53° N. Widely dis- tributed in deep water, generally represented by only a few specimens, nearly always stained. Family ALABAMINIDAE Hofker, 1951 Genus GYROIDlNA d'Orbigny, 1826 Gyroidina lamarckiana (d’Orbigny) Plate 4, figure 7 Rotalina lamarckiana d’Orbigny, 1839, in Barker-Webb and Berthelot, Histoire Naturelle des l’iles Canaries, v. 2, pt. 2, Foraminiféres, p. 131, pl. 2, figs. 13—15. Gyroidina lamarckiana (d’Orbigny). Phleger, Parker, and Pierson, 1953, Repts. Swedish Deep-sea Exped., v. 7, pt. 1, p. 40, pl. 8, figs. 33, 34. Distribution—One stained specimen found in core sample P—49—61 (lat 50° N., depth 5,000 m). Phleger, Parker, and Pierson list this species from six stations in the North Atlantic, all deeper than 4,000 meters. Family ANOMALlNlDAE Cushman, 1927 Genus ANOMALINA d'Orhigny, 1826 Anomalina globulosa Chapman and Parr Plate 4, figure 10 Anomalina grosserugosa (Gumbel). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 673, pl. 94, figs. 4, 5. Anomalina globosa Chapman and Parr, 1937, Australasian Antarctic Exped., 1911—1914, Sci. Repts., Ser. C, v. 1, pt. 2, p. 117, pl. 9, fig. 27. Anomalina globnlosa Chapman and Parr. Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 194, pl. 94, figs. 4, 5. A few stained specimens that are apparently re- ferrable to this species occur in core sample P—12— 61, although the sutures are less distinct and the outline is smooth. Distribution—Lat 53° N., depth 6,560 meters. SYSTEMATIC CATALOG 23 Genus ClBlClDOlDES Thelmann, 1939 Cibicidoides cf. C. mundulus '(Brady, Parker, and Jones) Plate 4, figure 13 Truncatulina sp. Brady, 1884, Challenger Repts., Zoology, v. 9, pl. 95, fig. 6. Cibicides mundulus (Brady, Parker, and Jones). Chapman and Parr, 1937, Australasian Antarctic Exped., Sci. Repts., Ser. C, v. 1, pt. 2, p. 120. Cibicr’doides mundnlus (Brady, Parker, and Jones). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 196, pl. 95, fig. 6. This form appears identical to that illustrated by Brady, except for its small size. The single specimen found was stained. Distribution—Lat 50° N ., depth 5,000 meters. Genus MELONIS (le Montfort, 1808 Melanie alfine (Reuss) Plate 4, figure 12 Noniom'na aflinis Reuss, 1851, Deutsche Geol. Gesell. Zeit- schr., v. 3, p. 72, pl. 5, fig. 32. Noniom'na umbilacatula (Montagu). Brady, 1884, Chal- lenger Repts., Zoology, v. 9, p. 726, pl. 109, figs. 8, 9. Nonion afi‘ine (Reuss). Boltovskoy, 1958, Micropaleontology, v. 4, p. 193—200. Gavelinonion barleeanum (Williamson). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 224, pl. 109, figs. 8, 9. Distribution—One small stained specimen found (core sample P—49-61, lat 50° N., depth 5,000 m). Melonis pompilioides (Fichtel and Moll) Plate 4, figure 11 Nautilus pompilr'oides Fichtel and M011, 1798, Testacea Micro- scopica, p. 31, pl. 2, figs. a—c. Nonionlna pompilio'ldes (Fichtel and Moll). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 727, pl. 109, figs. 10, 11. Nonion? pompilio'ides (Fichtel and Moll). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 224, pl. 109, figs. 10, 11. Distribution—One specimen found in core sample P-29—61 (lat 32° N., depth 4,810 m). It is very small but is referred to N. pompilioides because of its thickness and coarsely perforate wall. Family CERATOBULIMINIDAE Cushman, 1927 Genus HOEGLUNDINA Brotzen, 1948 Hoeglundinl elegans (d’Orbigny) Rotalia elegans d’Orbigny, 1826, Annals Sci. Naturelles, ser. 1, v. 7, no. 6, p. 272. Pulm’nnlina elegans (d’Orbigny). Brady, 1884, Challenger Repts., Zoology, v. 9, p. 699, pl. 105, figs. 3—6. Hdglnndina elegans (d’Orbigny). Barker, 1960, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, p. 216, pl. 106, figs. 3—6. Distribution—Lat 32° to 54° N. All specimens are small and, when not stained, appear corroded. REFERENCES CITED Barker, R. W., 1960, Taxonomic notes on the species figured by H. B. Brady in his report on the Foraminifera dredged by HMS Challenger during the years 1873 to 1876: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 9, 240 p. Brady, H. B., 1884, Report on the Foraminifera dredged by HMS Challenger during years 1873—1876: Challenger Repts., Zoology, v. 9, p. i-xxi, 1—814. Bukry, David, Douglas, R. G., Kling, S. A., and Krashin- innikov, Valeri, 1971, Planktonic microfossil biostratigra- phy of the northwestern Pacific Ocean: Deep Sea Drilling Proj. Initial Repts., v. 6, p. 1253—1300. Cushman, J. A., and McCulloch, Irene, 1939, A report on some arenaceous Foraminifera: Univ. Southern Cali- fornia, Allan Hancock Pacific Exped. Repts., v. 6, no. 1, 113 p. Krashininnikov, V. A., 1971, Cenozoic Foraminifera: Deep Sea Drilling Proj. Initial Repts., v. 6, p. 1055—1068. Lisitzen, A. P., 1971, Distribution of carbonate microfossils in suspension and in bottom sediments; The micropale— ontology of oceans: Cambridge Univ. Press, p. 197-218. Olson, R. K., and G011, R., 1970, Biostratigraphy: Deep Sea Drilling Proj. Initial Repts., v. 5, p. 557—567. Revelle, Roger, 1944, Marine bottom samples collected in the Pacific Ocean by the Carnegie on its seventh cruise: Car- negie Inst. Washington Pub. 556, 180 p. Riedel, W. R., and Funnell, B. M., 1965, Tertiary sediment cores and microfossils from the Pacific Ocean floor: Geol. Soc. London Quart. Jour., v. 120, p. 305—368. Page A abyssorum, Rhabdammina _______ 6, 12 Acknowledgments ____________ _ _ - _ 4 aculsata, Bulimina ___ ______ 6, 19; pl. 3 acuta, Jaculella. ______ 6, 8, 9, 10, 11, 19; pl. 1 acutimargo, Ophthalmidium _____ 6, 9, 11, 18 Spiroloculina __________________ Spirophthalmidium _____ Adercotrymu _____________ glomerata, ____ glomeratum _____ 8, 9, 10, 11, 12, 14; pl. 1 advena, Eggerella __________________ 10 afi‘ine, Melam'a _______________ 6, 9, 29; pl. 4 Nom'on _______________________ 23 affinity, Bulimina _ ___- 11 Nonionina. ________________ 23 agglutimma, Ammobaculitea 6, 9, 16; pl 2 biformis, Texcularia ____________ 16 fibuforrmis, Ammobaculitea_ 6, 8, 10, 16: pl. 2 Haplophragmium _______________ 16 Spirolina _____________________ 16 Alabaminidae _________ 22 Aleutian Islands ______ 6 Aleutian Terrace __ 7 Aleutian Trench __________________ 1, 6, 7 alveolinalormis, Ammomassilina. _____ 6, 19 Masailina _____________________ 19 Alveolophragmium m‘tidum __________ 6, 8, 9, 10, 11, 12, 15; pl, 1 ringena _________________ 6, 8, 9, 10, 15 scitulum ____________ 6, 8, 9, 12, 15; pl. 1 subglobosum _ 6, 7, 8, 9, 10, 11, 12, 15; pl. 1 weisnen' ____________ 6, 8, 9, 10, 15; pl. 2 sp ________________________ 6, 15; pl. 2 ame'ricanua, Ammobaculitea __ 6, 8, 9, 10, 12, 16 Ammobaculitea ____________________ 1 6 agglutinans _____________ 6, 9, 16; pl. 2 filaformis _________ 6, 8, 10, 16; pl. 2 americrmus ________ 6, 8, 9, 10, 11, 12, 16 filafo‘r’mia _______________ 6, 8, 9, 10, 11 Ammochiloatomu aaleata 18 Ammodiscidae ________ 13 Ammodiscus aordialis _ 13 Winds ________________________ 22 Ammoglobiyerina bulloides ___________ 17 globigerinifarmis _______________ 17 Ammomarginulina __________________ 1 6 foliavea. _____ __ 6, 8, 10, 16; pl. 2 foliaceuu ___- __________ 16 Ammomassflina __________ _ 6, 19 alvealinafor‘mis ___________ _ 6, 19 Ammoscala‘ria tenuimarya _____ __ 10, 11 amygdaliformia, Lozostomum _ __ 7 anceps, Globoteactularia ______ __ 6, 9, 18 H aplophraymium _______________ 18 Angulogerina _____________________ 20 angulom _____________________ 6, 7, 20 fluem ________________________ 20 anguloau, Angulogerina ____________ 6, 7, 20 U'vigerina _____________________ Anomalina _______________________ globosa _______________________ globulosa ___- uroeseruaoea __________________ INDEX [Italic page numbers indicate major references] Page Anomalinidae ______________________ 29 arctica, Labraspim ________________ 15 Aschemcmella. 5p __________________ 9 aspe’rula, Mauilina _ 19 Spiroloculimz _ 19 Astrorhiza ______ 8 5p ___________________________ 10, 11 Astrorhizidae _____________________ Ataxophmgmiidae _________ atltmtica, Pseudogaudrm‘nu. __ auricula, Nonionella, _______ auriculata, Buliminu ____________ 8, 20; pl. 3 Globobulimim _____________ 6, 20; pl. 3 B Baculogypaina __________ 1 _________ 5D barleeanum, Gavelinonion ___________ 23 bartletti, Elphidium ________________ 7, 8 basicoatata, Buliminella. Bathysiphan ___________ discreta _- ____ Bibliography __ _________________ biformia, Spiroplecta _______________ 16 Spiroplectammina ___- 6, 8, 9, 10, 16; pl. 2 Textularia agglutimma __________ 16 Bigenerina ________________________ 16 minutisaima _ __- 6, 9, 10, 16; pl. 2 Bolivina. _________________ 19 decussata ____________________ 6, 7, 19 plicata _______________________ 19 pseudoplicata _________________ 6, 7, 19 robusta _____________________ 6, 10, 19 Bolivinitidae ___________________ 19 bradyi, Cibicides ___- _ 6, 8, 9, 11, 21; pl. 4 Cyclam’mina. ___________________ 14 Egyerellu _____ 6. 8, 9, 10, 11, 12, 18: pl. 3 Epcmidea ______________________ 9 Nonio'nella ___________________ 6, 7, 29 Placopadina _________________ 9, 10, 16 Truncatulina __ 21 Verneuilina ___ 18 Buccella frigida _.. 7 inusitata ______________________ 7 Bulimina. _________________________ 19 aculeata ___________________ 6, 19; pl. 3 ufiinis ________________________ 11 auriculata --__ 8, 20; pl. 3 measicunu. _______________ 8 pyrula ___________________ 20 acabra ________________________ 18 Buliminella ________________________ 1 9 basicostata _____________ elegantissima seminuda bullaides, Ammoglobigerina __________ 17 Globigerina ____________ 6, 7, 8, 9, 11, 91 O camarieneis, H aplophragmoides _______ 7, 8 cancellata, Cyclammina _____________ 6, 9, 10, 11, 12, 14; pl. 1 Candeina _________________________ 21 m'tidu, _______________________ 6, 9, 91 Page Casaidulina -_ __________ 91 0111380. _______ _.. 6. 7, 8, 21 laem’gata _____________________ 21 subglobosa ____________ 6, 8, 11, 21:121. 4 teretia ______________________ 6, 7, 21 tortuosu. _____________________ 6 , 7, 21 Cassidulinidae ___- 21 Cerawbuliminidae _ 29 charlottenis, Trachammina __________ 10 Cibicides _________________________ 91 bradyi _____________ 6, 8, 9, 11, 21; pl. 4 lobatulua _____________________ 6, 7, 91 mundulus ______________ refulgens _ Cibicididae __ _ _ Cibicidoides ___ mundulus _______________ 6, 9. 29; pl. 4 circularis, Miliolinella ________ 1 _____ 11, 19 clavatum, Elphidium 7, 11 Colomia sp _____________ 11 complanata, Virgulina 6, 7 confuaa, Placopsilina 12, 16 amicu, Tritam'a _________________ 6, 10, 18 Valvulina _____________________ triangularis ________________ Cornuspira. incerta ___- involvem _________ costulam, Guembelinu _ crassa, Casaidulinu _____________ 6, 7, 8, 21 crispum, Elphidium ________________ 7 cushmami, Uvigen'mz ______________ 6, 7, 20 Cyclammimz _______________________ 14 bradyi ___- _________________ 14 cancellata _ ___ 6, 9, 10, 11, 12, 1.6; pl. 1 trulliasata __ _ 6, S, 9, 10, 11, 14; pl. 1 sp __- ________________________ 9 culindrica, Hyperammina _______ 9, 10, 11, 13 Marsipella Custammi’na _______________________ 18 yaleaca ____________ 7, 8, 10, 11, 18:11]. 3 D decussata, Bolivina _________ _. _____ 6, 7, 19 dentalinafo'rmis, Reophaz ___________ 6, 8, 9, 11, 12, 19; pl. 1 Diatoms __________________________ 3 difiiugiformis, Prateonina ___________ 13 Reopham ______ 6, 8, 9, 10, 11, 12, 19; pl. 1 Discorbidae _______ 20 Ducorbia roaea 9 discreta, Bathysiphon ___________ 6, 12; pl. 1 Paammoaipho’nella ______________ 12 Rhabdammina 12 diatoms, Reophaa: ____________ 6, 10, 1.1; pl. 1 Dmothia ________ 18 exdis ____________ 1 ______ 6, 9, 18; pl 3 dutemplei, Truncatulimz ____________ 21 E Eggerella _________________________ 1 8 advent: _______________________ 10 bradyi ________ 6, 8, 9, 10, 11, 12. 18; pl. 3 fused ________________________ 10 propinqua. Pl. 3 acabm ________________ 6, 7, 9. 18; pl. 3 25 26 Page Ehrenbergina ______________________ 21 hyatria; _________________ 6, 9, 21; pl. 4 elegam, H oeylundina ___________ 8, 9, 11. 2.! Pul'vi‘nuli‘nw ____________________ 23 23 ' 7 aeminuda, Buliminella. ___________ 19 Elphidiella ________________________ 20 groenlandica _____________ 6, 8, 20; pl. 4 Elphidiidae _______________________ 20 El,‘ '1' __ _ - 20 bartletti ______________________ 7, 8 ckwatum ______________________ 7, 11 crispum _____________________ 7 groenlandicum _________________ 20 incertum magellanicum __- orbiculure (Palystomella) mayellam‘cum _____ sp ___________________________ 7 Environment, North Pacific _________ 6 Epistominella _____________________ 20 exigua ________________ 6, 7. 9, 20; pl. 3 umbcmife’ra _____ ___ 6, 9. 20; pl. 3 Epzmides bradm' ___________ 9 5p ____________________ 8, 11 Euuvigerina peregrina ______________ 20 excentricus. Reophax ____________ 6, 8, 9, 10 exigua, Epistominella _______ 6, 7, 9, 20; pl. 3 Pulvinulina ____________________ 20 exilia, Dorothia _______________ 6. 9, 18; pl. 3 F filaformis, Ammobaculites ______ 6, 8, 9, 10, 11 Ammabaculites agglutinans ______ 6, 8, 10, 16‘; pl. 2 Gaudruina _____________________ 18 Fissu'rina. 5p ______________________ 6, 7 fluens, Angulogerina ________________ 20 foliacea, Ammomarginulina __ 6, 8, 10, 16‘; pl. 2 foliaceum, Huplophragmium _________ 16 f " . A u ' " 16 fontinenae, Haplophmgmium ________ 16 Foraminifem _____________________ 3 friabilia, Huperammina _____ 8, 9, 10, 13; pl. 1 frigida, Buccella __________________ 7 fuaca, Eggerella ___________________ 10 Psammoaphaera ________________ 10 G galeata, Ammochiloatoma ___________ 18 Cystammina _____ 7, 8, 10, 11, 17,13; pl. 3 Trochammina, __________________ 18 Gaudruina flluformis ________________ 18 C " ‘ bar’ __ 23 Globiyerina bullm'des _ inflata ________________________ 11 pachyderma ___________________ 8 Globigerinidae _____________________ 21 globiyeriniform e, H aplophragmium _ _ _ l 7 globigeriniformia, Ammoylobiyen‘na ___ 17 Lituola nautiloidea _____________ 17 Trachammina _____ 7, 8, 9, 10, 11, 17; pl. 3 Globigerinita voluta. ________________ 11 Globobulimina ___________________ 20: pl. 3 auriculata _________________ 6, 20; pl. 3 pacifica _____________________ 6, 8, 20 Globorotalia __ inflata, ___ Globorotaliidae __________ globoaa, Anomalina ________________ Globotem tuluria _____________________ 1 8 anceps ______________________ 6, 9, 18 sp ___________________________ 10 INDEX Page Globatruncam marginata, ____________ 11 sp ___________________________ 11 globulifera, Hormoeina-_ 6, 9, 10, 11, 12, 1.9, 14 globuloaa, Anomalina ___. glomerata, Adercatrmna ______ 6, 14 Lituola _______________________ 14 glomemtum, Adercotryma ___________ 8, 9. 10, 11, 12. 14:1,]. 1 C’ pi... __- ___ -_ 18 aordialia ______ 6, 8, 9, 10, ll, 12, 18; pl. 1 gordialis, Ammodiscus ______________ 13 Glomospira ___- 6, 8, 9, 10, 11, 12, 1.1; pl. 1 Gordiammina __________________ 13 Troohammina, squamatu _________ 13 Gordiammina gmdialia ______________ l3 yrisea, Tracha/mmina ___- 7, 8, 9, 10, 17; pl. 2 grocnlamdica, Elphidiella ______ 6, 8, 20; pl. 4 groenlandicum, Elphidium _ _______ 20 yraaaerugoaa, Ano‘malina __ -___ 22 Guembelina costulata _______________ 11 globulosa ______________________ 11 sp ___________________________ 11 Gyroidina _________________________ 22 lamarckiana _____________ 6. 9, 22; pl. 4 H H aplophraymium agglutimma ________ 16 (weeps _______________ , 18 foliaceum __ _______ 16 fontineme ____________ 16 globigeriniforme ________________ 17 latidm‘aatum __________________ 15 mmum _______________________ 17 nitidum _______________________ 16 scitulum ______________ _ 15 turbinatum helicoideum __, - 17 H aplophragmoides canariemis _ _ _ ‘7, 8 m‘tida ________________________ 7, 8 mitidum _______________________ 16 nitidua _____ 16 ringens ___- 15 subglobosum 16 helicoideum, Haplophragmium turbinatum _____________ 17 Hoeglundina ______________________ 2.9 elegana ___________________ 8, 9, 11, 2.! H mmosina. _________________ 1.9 alobulifera ___- _ 6, 9, 10, 11, 12. 18, 14 nm‘mam _________________ 10 Homosinidae _____________________ 1.! H yperammina. _____________________ 11, 12 cylindrica ________________ 9, 10, ll, 13 friabilie ______________ 8, 9, 10, 13; pl. 1 am) ________ 6, 11, 12 hystrix, Ehrenberyina _________ 6, 9, 21; pl. 4 I incerta, Cornuspira. ________________ 9 Polystomella. umbilicatula ___ __ 20 incertum, Elphidium ________ __ 6, 20 inflata, Globigerina _________________ 11 Globorotalia ___________________ 6, 20 Troohammina ___________ 7, 10, 17; pl. 1 inmitatu, Buccella 7 Involutina ___________ 22 tennis ______________ 6, 8, 9. 10, 22: pl. 4 lnvolutinidwe ______________________ 22 involvens, Cornuspira _______________ 9 J K Jaculella _________________________ 12 acutu. ___________ 6, 8, 9, 10, 11, 12; pl. 1 kellettae, Trochammina _________ 7, 17; pl. 2 Page Kodiak Harbor ____________________ 7 Kodiak Island _____________________ 7 L labiosa, Miliolina __________________ 19 labradorica, Ntmhmina ............. 22 labradon'cum, Nonion ___- 6, 7, 8, 11, 22; pl. 4 Labrospim arctica _________________ 16 aubgloboaa _____________________ 16 ' n' ___- 16 laevigata, Caasidulina ______________ 21 Lanena spp ______________________ 7 lamarckiana, Gyroidina _______ 6, 9, 22; pl. 4 Rotatina ______________________ latfdorsatum, Haplaphraymium linearis, Oculosiphtm ______________ lingua, Pseudopolymm‘phina _________ Lituola glomerata __________________ 14 nautiloidea alobiyeriniformis _____ 17 Lituolidae ________________________ lobatulus, Cibicides ________ Lomoatomum umugdulifo'rmia _________ M magellum‘cum, Elphidz’um __________ 6, 7, 20 Elphidium (Polystomella) ________ 20 malovenais, Trachammina _____ 7, 16. 17; pl. 2 marginata, Globotmncana ___________ 11 Marsipellu. ________________________ 12 cylindrica _______________ 6, 9, 12; pl. 1 Massilina alveolinaformia -__._ _ 19 aspe‘rula. ______________ _ 19 Melanie ___________________________ 2.! afine ___________________ 6, 9, 23; pl. 4 pompilimldes _________ ..__ 6, 11, 28; pl. 4 membranaceum, Nodellum ________ 7, 8: pl. 1 ... ' , 3 .- - _ 8 Miliolidae _________________________ 19 Miliolina. labioau. ___________ 19 Miliolinella. _______________________ 11, 19 circularis _____________________ 11, 19 aubrotunda ______ 6, 8, 9, 10, 11, 19; pl. 3 minutissima, Bigenerina, __.__ 6, 9, 10, 16; pl. 2 .1 1 ,, C‘L - -_v 23 Cibicidoidea ______________ 6, 9, 2.1; pl. 4 N mma, Trachummina __________ 7. 9, 17; pl. 2 mmum, H aplophragmium ___________ 17 nautiloidea. alobigeriniformis, Lituola" 17 Nautilus pompilioides _______________ 23 m'tida, Candeina _____ Haplophmgmaidea ______________ 7, 8 Troohammina ____ 7, 9, 10, 11, 12, 17; pl. 2 nitidum, Alveolophragmium _________ 6. 8, 9, 10, 11, 12, 15; pl. 1 Haplophraamium _______________ 16 Haplophragmm‘des _____ m'tidus, Haplophragmoidea Nodellum membranaceum nodulosa, Reophaz _________________ nodulosus, Reophax ___ 6, 8, 9, 10. 12, 14; pl. 1 Nom'tm ___________________________ 22 afine _________________________ 23 labmdoricum ________ 6, 7, 8, 11, 22; pl. 4 r r .,. ._, ___ __ 23 scapha ___- 22 scuphum _____________________ 6, 7, 22 5p ___________________________ 9, 10 N " ___ _ 22 auricula _____________________ 6, 7, 22 bradyi ___- ___ 6, 7, 22 turgida __ 6, 8, 22; pl. 4 Nonionidae _______________________ 22 Page Nonianina afim‘a __________________ 23 22 ,, .— 23 ," _ 22 ‘ 3mm ___ _ 22 turgida. _______________________ 22 umbdacatula __________________ 23 normani, H armasina _______________ 10 North Pacific environment __________ 6 Nubeculariidae ____________________ 1 8 0 Oculoaiphan linear-is _______________ 7, 8 073"“ ' "P 18 mtimargo _______________ 6, 9, 11, 18 pusillwm ________ __-_ 6, 10, 18:121. 3 orbiculare, Elphidium ______________ 7 G" " ' w ______ _ 8 P pachuderma, Globigerinu. ___- ___ 8 pacifica, Globobulimina ___- ___- 6, 8, 20 papillam, Thurammimz ________ 1.9, 16; pl. 1 pauciloculata, Virgulina _____________ 8 peregrina, Euuvigerina _____________ 20 Uvigerim ____________ 6, 8, 11, 90; pl. 3 peruvicma, Trachammina ____________ pilulifer. Reopham ________ pilulifera, Reophax Pioneer, U.S. Coast and Geodetic Survey ship _. __________ 1 Placopsilina _______________________ 16 bradyi ______________________ 9, 10, 16 cmfuaa 6, 11, 12, 16 Plain, deep-sea ______________ 7 plicata, Bolivina, ___________________ 19 Polystomella umbflicatula. incerta _________________ 20 (Polystomella) magellcmicum, Elphidium ______________ 20 polyatropha, Verneuflina, ____________ 18 pompilimldes, Melonis _______ 6, 11. 23; pl. 4 Nautilus ___________ 23 Nonion -__ 23 N oniom'mz _____________________ 23 propmqua, Eggerelba _______________ Pl. 3 Proteonina difliugifarmia ____________ 13 Paammosiphonella diam-eta __________ 12 sp __________________ 7, 8, 9, 10, 11, 12 Psammosphaera __ 1.! fusca __ ___________________ 10 mtica _______________________ 6, 1.! Paeudogaudrm'na atlantica ___________ 6, 7 sp ___________________________ 7 pseudoplicata, Bolivim ___ ___- 6, 7, 19 Pseudopolummphina lingua __________ 7 Pullemia 22 quinquelobu. ____________________ 22 subcarinata ______ 6, 8, 9, 10, 11, 22; pl. 4 Pulvinulina. elegans ________________ 23 emigua __________________ 20 Pulvinulinella umbcmife'ra ___________ 20 pusillum, Ophthalmidimn _____ 6, 10, 18; pl. 3 Spiroloculina. __________________ 18 Spirophthalmidium _____________ 18 pygmaea, Uvigerina ________________ 20 Verneuflina, __________ Purge ___________________ SD pyrula, Bulimina __________________ Q q ‘ 1 L ’ P n __ _ 22 INDEX Page Q - ‘ , 1' 19 up _________________________ 6, 10, 19 R Radiolaria ________________________ 3 refulgena, Cibicides - 6, 7 Reophax _____________________ 11. 12, 1.9 dentalimfmmia ___ 6, 8, 9, 11, 12, 13; pl. 1 dirflugiformis __ 6, 8, 9, 10, 11, 12, 13; pl. 1 distans _________________ 6, 10, 1.9; pl. 1 emcentricus _________________ 6, 8, 9, 10 nodulosa ______________________ 14 nodulosus ___- .. 6, 8, 9, 10, 12, 14:91. 1 pilulifer ________ pilulifera ______ acm‘piurua __ scotti _______________________ 6. 8, 14 sp ______________________ Rhabdammim abyssmm discreta ______ sp __________ m. ' ‘ sp _____________________ 6, 8. 12; pl. 1 rinyem, Alveolophragmium ___. 6, 8, 9, 10, 15 Haplophragmoides ______________ 15 Trochammina ___________ 16 robusta. Bolivina ______________ 6, 10, 19 P " sp _ __ _ 6, 7 rosea, Discorbis ____________________ 9 Rotalia elegant; ____________________ 23 Rotalimz lama'rckiwna ______________ 22 turgida, _______________________ 22 rustica, Psammoaphwa ____________ 6, 13 S Saccammina ______________________ 1.1' aphae‘rica. _____________ 6, 9, 10, 1: sp __________________________ 12 Saccamminidae ______________ _ 1 .9 Sample collection ___________ _ 1 Sampling procedure _______ _ 6 acabra, Bulimimz __ _______ 18 Eggerella ______ _ 6, 7, 9, 18; pl. 3 Verneuilina ____________________ 18 scupha, Nom'on ____________________ 22 acaphum, Nonion _________ Nonionina. ____________________ scitulum, Alvelophragmium- 6, 8, 9, 12, 15; pl. 1 Haplophmgmium _______________ 16 scorpiurus, Reopham _______ 6, 9, 10, 14; pl. 1 sooth", Reophaz __________________ 6, 8, 14 seminuda, Buliminella elegantissima ___ 19 sphaen‘ca, Saccammimz _________ 6, 9, 10, 13 Spirolimt. agglutimms _ 16 Spiroloculina. acutima'rgo 18 “pm-141a 19 puaiuum 18 tennis ________________________ 18 sp ___________________________ 11 Spirophthalmidium acutimargo _ 18 pusillum _______________ 18 Spiroplecta. biformia ________________ 16 Spir ,.' ‘ ' 16 bifm‘mis ____________ 6, 8, 9, 10, 16; pl. 2 squamata, gordialia Trochammina, _____ 13 ‘ inata, N ' ' __ 22 Pullem'a, _________ 6, 8, 9, 10, 11, 22; pl. 4 eubolobosa, Cassidulina. _____ 6, 8, 11, 21; pl. 4 Labrospira ____________________ 15 subglobasum Alveolophragmium ______ 6, 7, 8, 9, 10, 11, 12, 15; pl. 1 Haplophraymotdes ______________ 15 aubrotunda, Miliolinella- 6, 8, 9, 10, 11, 19; pl. 3 27 Page '1‘ f ' “go, Amum ’ in, _ 10,11 ‘ ' A-M“ " 22 Involutina __ 6, 8, 9, 10, 22; pl. 4 Spiroloculina __________________ te'retie, Cuaidulim Textula’ria ugglutinam biformis .__ Textulariidae ______________________ 16' Thu! ' ._ __ 8, 9, 13 papillata __________________ 6, 1.1; pl. 1 tartuosa, Cassidulina ____________ 6, 7, 21 triangularis, conica Valvulina ________ 18 Tritaxis ___________________________ comm _________________ Troohammina ____________ charlottenis __ galeata _______ globigen'nifo‘r'mis __ 7, 8, 9, 10, 11. 17; pl. 3 griaea ______________ 7, 8. 9, 10, 17:111. 2 inflata _________________ 7, 10, 17; pl. 2 kellettae _________________ 7, 17; pl. 2 malwmic mma ______ m'tida ______ perwuiana _____________________ squamata. yordialis _____________ 13 w "' *n 14, 15 sp _________________ ___- 7, 8, 11 Trochamminidae 1 7 trulliasata, Cuclammina- 6, 8, 9, 10, 11, 14; pl. 1 Trachammina _________________ 14, 15 Truncatulina bradm' ________________ 21 ’ ‘ ,' ' - , 2!. sp ___________________________ 23 turbinatum helicm'deum, Haplophragmium ________ 17 turgida, N om'o'nellu. ___________ 6, 8, 22; pl. 4 Nonio'ni'na. _____________________ 22 " ‘ " I' 22 Turrilinidae _______________________ 19 U umbilacatula, Nmiom'na. ____________ 23 umbilicatula incerta, Polystomella ___... 20 umbom‘fe'ra, Epistmnineua _____ 6, 9, 20; pl. 3 P...‘...' " " 20 .a, C: 1 " 8 Uvigerina ________________________ 20 angulosa _ 20 cushmcmi ____________________ 6, 7 , 20 peregrina _____________ 6, 8, 11, .90; pl. 3 puumaea 20 Uvigerinidae 20 V Val " ' _.._ _ 18 triangularia conica _____________ 18 Verneuilinu bradm' ______ 18 polystropha ___ _____ 18 puamaea —— 18 scab’ru. ________________________ 18 Virgulina. complanata. ______________ 6, 7 paucilaculata __________ 8 voluta, Globigerinita. 11 W weisneri, Alveolophragmium _________ 6, 8, 9, 10, 15; pl. 2 Labroapira. ____________________ 15_ U.$. GOVERNMENT PRINTING OFFICE : I973 0—495—6I7 PLATES 1-4 Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey Library, Federal Center, Denver, Colorado 80225. ' FIGURE 1. 2. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. PLATE 1 Nodellum membranaceum (Brady). X 115, sample P—19—61, USNM 175142. Rhizammina? sp. (p. 12) X 68, sample P—12—61, USNM 175143. Marsipella cylindrica Brady (p. 12 ). x 70, sample P—13—61, USNM 175144. Bathysiphon discrete (Brady) (p. 12). X 73, sample P—19—61, USNM 175145. Jaculellu. acute Brady (p. 12). x 190, sample P—41—61, USNM 175146. Hyperammina friabilis Brady (p. 12). x 23, sample P—41—61, USNM 175147. Thura’mmina papillata Brady (p. 13). x 80, sample P—48—61, USNM 175148. Glomospira gordialis (Jones and Parker) (p. 13). a, Side view; b, end view; X 43, sample P—40—61, USNM 175149. Reophax dentalinafo'rmis Brady (p. 13). x 55, sample P—56—61, USNM 175150. Reophax difiiugiformis Brady (p. 13). x 436, sample P—41—61, USNM 175151. Reophax distans Brady (p. 13). X 62, sample P—33—61, USNM 175152. Reophax nodulosus Brady (p. 14). X 18, sample P—40—61, USNM 175153. Reophowc scorpiurus de Montfort (p. 14). X 37, sample P—41—61, USNM 175154. Adercotryma glomemtum (Brady) (p. 14). x 214, sample P—41—61, USNM 175155. Cyclammina trullissata (Brady) (p. 14). a, Side view; b. apertural view; X 73, sample P—40—61, USNM 175156. Alveolophragmium nitidum (Giies) (p. 15). a, Side view; b, apertural view; X 200, sample P—19—61, USNM 175157. Alveo‘lophragmium cf. A. mltwlum (G'des) (p. 15). a, Side view; b. ap‘ertural view; x 185, sample P—41—61, USNM 175158. Cyclammina canaellata. Brady (p. 14). x 19, sample P—40—61, USNM 175159. Alveoloph'ragmium scitulum (Brady) (p. 15). a, Apertural view; b. side view; x 102, sample P— 19— 61, USNM 175160. Alveolophmgmium subglobosum (G. 0. Sars) (p.15). a, Side view; b, peripheral view; X 87, sample P—19— 61, USNM 175161. GEOLOGICAL SURVEY PROFESSIONAL PAPER 766 PLATE 1 FORAMINIFERA FIGURE 1. 2. 3. 10. 11. 12. 13. 14. 15. PLATE 2 Alveolophmgmium weisnem' (Parr) (p. 15). a, Side view; b, apertural View; x 155, sample P—19—~61, USNM 175162. Alveolophragmium? sp. (p. 15). X 195, sample P—49—61, USNM 175163. Ammobaculites agglutinans (d’Orbigny) (p. 16). x 61, sample P—41—61, USNM 175164. Ammobaculites agglutinoms filaformis Heron—Allen and Earland (smooth form) (p.16). X 64 sample P—41—61, USNM 175165. Ammobaculites agglutinans filafo'rmis Heron-Allen and Earland (rough form) (p. 16). X 106, sample P—49—61, USNM 175166. Ammomarginulina foliacea (Brady) (p. 16). x 137, sample P—38—61, USNM 175167. Spiroplectammina bifor’rm's (Parker and Jones) (p. 16). X 180, sample P—49—61, USNM 175168. Bigenerina minutissima Earland (p. 16). X 172, sample P—49—61, USNM 175169. Trochammma. grisea, Heron-Allen and Earland (p. 17). a, Evolute side view; b, apertural view; c, involute side view; X 154, sample P—19—61, USNM 175170. Trochammina inflata (Montagu) (p. 17 ). a, Evolute side view; b, involute side view; X 182, sample P—48—61, USNM 175171. Troohammina cf. T. malovensis Heron-Allen and Earland (p. 17). a, Evolute side; b, involute side; X 252, sample P—41—61, USNM 175172. Trachammina kellettae Thalmann (p. 17). a, Evolute side; b, involute side; X 240, sample P—41—61, USNM 175173. Tracha/mmina malovensis Heron-Allen and Earland (p. 17). a, Involute side; b, evolute side; X 320, sample P—12—61, USNM 175174. Trochammina m't’ida Brady (p. 17). a, Evolute side; b, involute side; X 220, sample P—40—61, USNM 175175. Troohammina noma (Brady) (p. 17). a, Involute side; b, evolute side; X 215, sample P—49—61, USNM 175176. GEOLOGICAL SURVEY PROFESSIONAL PAPER 766 PLATE 2 FORAMINIFERA FIGURE 1. 10. 11. 12. 13. PLATE 3 Trachammina globigeriniformis (Parker and Jones) (p. 17). a, Evolute side; b, involute (apertural) side; X 174, sample P—41—61 USNM 175177. Cystammina galeata (Brady) (p. 18). a, b, Side views; X 83, sample P—19~61, USNM 175178. Dorothia exilis Cushman (p. 18). X 190, sample P—49—61, USNM 175179. Egge’rella. bradyi (Cushman) (p. 18). a, Apertural view; b, side view; X 138, sample P—19—61, USNM 175180. Eggerella scabm (Williamson) (p. 18). a, Apertural view; b, side view; X 380, sample P—48—61, USNM 175181. Eggerella propinqua (Brady). a, Apertural view; b, side view; X 204, sample P—6—61, USNM 175182. Ophthalmidium pusillum (Earland) (p. 18). x 113, sample P—32—61, USNM 175183. Miliolinella subrotunda (Montagu) (p. 19). x 166, sample P—49—61, USNM 175184. Bulimina aculeata d’Orbigny (p. 19). X 56, sample P—16—61, USNM 175185. Globobulimma cf. Bulimina auriculata Bailey (p. 20). x 47, sample P—16~61, USNM 175186. Uvigerina peregrina Cushman (p. 20). x 106, sample P——16—61, USNM 175187. Epistominella exigua (Brady) (p. 20). a, Evolute side; b, involute side; x 360, sample P—49—61, USNM 175188. Epistominella umbonifera (Cushman) (p. 20). a, Evolute side; b, apertural view; c, involute side; x 97, sample P—49—61, USNM 1751189. , GEOLOGICAL SURVEY PROFESSIONAL PAPER 766 PLATE 3 F ORAMINIFERA FIGURE 1. 2. 3. 10. 11. 12. 13. PLATE 4 E'lphidiella. groenland’ica, (Cushman) (p. 20). a, Apertural view; b, side view; X 79, sample P-—16—61, USNM 175190. Cibicides bradyi (Trauth) (p. 21). a, Involute side; b, evolute side; X 227, sample P—19—61; USNM 175191. Cassidulim subglobosa Brady (p. 21). X 210, sample P—29—61, USNM 175192. Nonion labradom'cum Dawson (p. 22). a, Apertural view; b, side view; X 100, sample P—16—61, USNM 175193. Ehrenbergina hystm'x Brady (p. 21). X 78, sample P—49—61, USNM 175194. Involut’ina, tenuis (Brady) (p. 22). X 134, sample P-41—61, USNM 175195. Gyroidina lamarckiana (d’Orbigny) (p. 22) a, Evolute side; b, peripheral (aperrbural) View; c, involute side; X 122 sample P—49—61, USNM 175196. Nom‘onella turgida (Williamson) (p. 22). a, Evolute side; b, involute side; X 190, sample P—16—61, USNM 175197. Pullem'a, subca’rinata (d’Orbigny) (p. 22) 3., Peripheral View; b, side view"; X 142, sample P—12—61, USNM 175198. Anomalina globulosa Chapman and Parr (p. 22). a, Evolute side; b, peripheral view; c, involute side; X 109, sample P—12—61, USNM 175199. Melom’s pompilioides (Fichtel and Moll) (p. 23). a, Side view; b, peripheral view; X 160, sample P—29—61, USNM 179200. Melom's afline (Reuss) (p. 23). X 200, sample P—49—61, USNM 179201. Cibica'doides cf. C. mundulus (Brady, Parker, and Jones) (p. 23). a, Evolute side; b, involute side; X 280, sample P—49—61, USNM 179202. ! GEOLOGICAL SURVEY PROFESSIONAL PAPER 766 PLATE 4 FORAMINIFERA