Stratigraphy and NOmenclature of Some Upper Cretaceous and Lower Tertiary Rocks in South-Central Wyoming By]. R. GILL, E. A. MEREWETHER, and W. A. COBBAN
~ GEOLOGICAL SURVEY PROFESSIONAL PAPER 667 .. Regional stratigraphic studies and ammonite zonat~·on are used in interpreting complex intertonguing and subtle facies changes in· rocks of Late Cretaceous and early Tertiary age
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UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1970 ,:0: !
UNITED STATES DEPARTMENT OF THE INTERIOR
WALTER J. HICKEL, Secretary
GEOLOGICAL SURVEY
William T. Pecora, Director
.... Library of Congress catalog-card No. 72-604715
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·<. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.. C. 20503- Price 65 cents (paper cover) •
CONTENTS
Page Page Abstract------1 Mesaverde Group and Mesaverde Formation-Con. Introduction and acknowledgments ______1 Allen Ridge Formation ______- ______---- 24 Historical background ______2 Pine Ridge Sandstone __ - ___ ------_--- ___ --_---_ 29 Almond Formation ______- --- Southwestern Colorado ______2 31 Lew~ Shale ______Northwestern Colorado ______2 36 Fox Hills Formation ______- _____ ----- _____ ---- 41 South-central Wyoming ______3 Medicine Bow Formation __ ---_------_------__ ---- 43 SuminarY------5 Foote Creek and Dutton Creek Formations ______45 Steele Shale _____ -- ___ -_---- ______-- ___ - __ --- __ 7 Ferris Formation ______46 Mesaverde Group and Mesaverde Formation ______11 Hanna Formation ______- ______---- 47 Haystack Mountains Formation ______12 References cited ______-_----_---_--- __ ---- 48 Index ______Rock River Formation ______20 51
ILLUSTRATIONS
Page FIGURE 1. Index geologic map of south-central Wyoming ______----_--- ___ - ___ -_ 4 2. Stratigraphic diagram showing intertonguing relations of Upper Cretaceous rocks in south- central Wyoming------8 3-15. Photographs: 3. Haystack Mountains Formation ______---_-- ____ - __ --_ 12 4. Hatfield Sandstone Member of Haystack Mountains Formation ______13 5. Thin-bedded O'Brien Spring Sandstone Member of Haystack Mountains Forma- tion------14 6. O'Brien Spring Sandstone Member______14 7. Allen Ridge Formation at Pine Tree Gulch ______25 8. Outcrop of an unnamed marine member of Allen Ridge Formation ______25 9. Pine Ridge Sandstone ______30 10. Almond Formation------33 11. Concretionary sandstone in Lewis Shale ______36 12. Lewis Shale------37 13. Cliff-forming sandstone of the Dad Sandstone Member of the Lewis Shale_- ____ -_ 38 14. Rocks of the Hanna Formation resting unconformably on the Medicine Bow For- mation------44 15. Hanna Formation unconformably overlying the Lewis Shale ______48
TABLE
Page TADLE 1. Chart showing correlation of Upper Cretaceous rocks in south-central Wyoming and nearby
areas------~------6
m STRATIGRAPHY AND NOMENCLATURE OF SOME UPPER CRETACEOUS AND LOWER TERTIARY ROCKS IN SOUTH-CENTRAL WYOMING .,..
By J. R. GrLL, E. A. MEREWETHER, and W. A. CoBBAN
ABSTRACT marine origin. It grades eastward into the dominantly nonsandy Upper Cretaceous rocks described and correlated in this report Pierre Shale. In southeastern Wyoming, the Mesa verde Group is conform are the Steele Shale, Mesa verde Group (consisting of the Rock River l!'ormation (new name), Haystack Mountains )formation ably overlain ·by the Lewis Shale. The Lewis, 2,200-2,600 feet thick, is chiefly dark-gray marine shale but contains sandy units. (new name), Allen Ridge Formation, Pine Ridge Sandstone, and In the Hanna Hasin, the Lewis is divided into three parts by the Almond Formation), Lewis Shale, E'ox Hills Formation, Medi eine Bow ll..,ormation, and the lower part of the Ferris Forma Dad Sandstone l\Iember, which is as much as 1,400 feet thick. ·The Fox Hills Formation conformably overlies the Lewis tion. '.rhe lower Tertiary rocks described consist of the upper Shale. It is chiefly ridge-forming yeJNowish-gray to light-brown part of the Ferris ll..,ormation of Paleocene age and the overlying shallow-water marine sandstone and ranges in thickness from Hanna ll..,ormation of late Paleocene and Eocene age. 'l'he oldest unit Jnvestigated, the Steele Shale, consists of 2,300- less than 200 to more than 700 feet. The Medicine Bow Formation, 3,000-6,500 feet thicl{, rests 8,800 feet of dark-gray marine shale that contains limestone conformably on the Fox Hills. Lenticular beds of sandstone, concretions, beds of bentonite as much as '5 feet thick, and· thin siltstone, and shale, ·and persistent beds of coal make up the layers of siltstone ami very fine grained sandstone. It becomes sandy upward nnd grades into the overlying Mesaverde Group. formation. Most 1 2 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. We acknowledge the assistance of Drs. D. L. Black ment sandstone as the Point Lookout Sandstone and re stone, Jr., and R. S. Houston, of the University of Wyo ferred the three new formations to the Mesa verde ming, in reviewing this report and in discussing per Group. tinent stratigraphic and nomenclature problems. G. H. NORTHWESTERN C'OLORADO Horn, M. "\¥. R.eynolds, and R. H. Tschudy, of the U.S. Geological Survey, also provided valuable assistance. Geologists of the IGng and the Hayden Surveys N. F. Sohl, of the U.S. Geological Survey, identified mapped Cretaceous sedimentary rocks in Routt County, the marine gastropod collections. northwestern Colorado, a.nd adopted the stratigraphic classification previously established in the upper Mis HISTORICAL BACKGROUND souri River region by Meek and Hayden ( 1862, p. 419). The classification used in the Missouri River region, SOUTHWESTERN COLORADO based on lithology and fossils, was applied to Cretaceous In 1875, W. H. Holmes studied the geology of the rocks throughout much of the Rocky Mountain region. San Juan district in southwestern Colorado and con Nomenclature used by these surveys is as follows tiguous parts of New Mexico, Utah, and Arizona. He (adapted from Fenneman and Gale, 1906, p. 18): recognized sedimentary rocks of Cretaceous age and Tertiary .... determined their thickness to be about 5,000 feet 6. Laramie (Holmes, 1877, p. 242). He called the lowermost Cre 5. Fox Hills ) taceous rock unit the Dakota Sandstone, or No. 1, fol 4. Pierre Montana Group lowing the nomenclature of Meek a.nd Hayden ( 1862, p. Cretaceous 3. Niobrara } 419 ; for a summary of Hayden's nomenclature, see Cob 2. Benton Colorado Group ban and Reeside, 1952, p. 1014). Holmes thought that 1. Dakota the overlying marine shale and minor limestone, 1,200'- 1~500 feet thick, represented Hayden's units 2 and 3 and The early geologists generally assumed that the main part of unit 4 (the Fort Benton Group, Niobrara divi Cretaceous coal-bearing units were in the Laramie and sion, and Fort Pierre Group). Holmes ( 1877, p. 245) that the minor coal-bearing units were in the Dakota. named stratigraphically higher nonmarine and marine This assumption resulted in the inclusion of the main rocks the Mesa Verde Group, in which he recognized coal-bearing rocks of northwestern Colorado in the a threefold division-an upper escarpment sandstone, Laramie Formation. a middle coal group, and a lower escarpment sandstone. In 1905, Fenneman and Gale studied the Yampa coal He did not name an overlying 400- to 800-foot-thick field of Routt Co.unty where they recognized marine and marine shale, but he called the next higher massive nonmarine Cretaceous rocks, about 8,000 feet thick, over marine sandstone the Pictured Cliffs Group. Holmes lying the Dakota Sandstone. They ( 1906, p. 17-31) were ( 1877, p. 243, pl. 15) equated the 1narine shale and over unable to apply the classification and nomenclature used lying Pictured Cliffs Group with Cretaceous units 4 and previously in the area and believed that the established 5 of Hayden (Fort Pierre Group and Fox Hills beds). nomenclature was incorrect and only generally relevant. The thick marine shale unit between the Dakota Sand Concerning this problem they stated (p.19) : stone and the Mesa Verde (Holmes, 1877) was named Below the Laramie and above the Dakota the succession of the Mancos Shale by Cross ( 1899) for exposures near formations as summarized in the foregoing table .is not applicable the town of Mancos, Colo., north of Mesa Verde N a to the Yampa field except in a most general .and indefinite way. In the Montana group the Fox Hills sandstone and the Pierre tiona! Park. The marine shale between the Mesa Verde shale are not found as distinct formation or lithologic units, and and the Pictured Cliffs Sandstone was named the Lewis similarly the Colorado group cannot be said to be composed of Shale by Cross and Spencer (1899) for exposures near the Niobrara limestone and the Benton shale as distinguished in Fort Lewis, Colo., east of Mesa Verde National Park. other fields. Moreover, the line between the Montana and Colo rado groups also becomes an indefinite or abitrary boundary The current spelling of the name Mesaverde was ap as the distinction between Pierre and Niobrara is lost. There is, parently introduced by Cross and Spencer in 1.899. however, a certain fossil fauna which has been recognized as In 1919, A. J. Collier investigated the coal deposits in characteristic of the Montana formation, and similarly a lower Holmes' middle coal group of the Mesa Verde south of fauna which is as characteristic of the Colorado. It is, however, more convenient and logical to drop the grouping as Colorado the town of Mancos in the region of Mesa Verde. Collier and Montana and adopt a new basis for subdivision of the (1919, p. 296) recognized Holmes' threefold division of combined stratigraphic interval thus represented. This has al the Mesaverde and designated ·the upper escarpment ready been done by the geologists who have worked in south western Colorado [Cross, 1899], where the succession shows sandstone as the Cliff House Sandstone, the middle coal such marked similarity to that of the Yampa field that the names group as the Menefee Formation, and the lower escarp- there adopted have been incorporated in this report. HISTORICAL BACKGROUND 3 In summary, Fennemnn and Gale recognized a thick SOUTH-CENTRAL WYOMING unit of marine shale containing fossils of Benton and "'\Vhile examining coal deposits in east-central Carbon Niobrara age overlying the Dakota Sandstone and un derlying a thick unit of marine sandstone and shale con County, "'\Vyo. (fig. 1), in 1906, Veatch (1907) recog nized a thick succession of Upper Cretaceous rocks. The taining a fauna of Pierre and Fox Hills age; this latter main difference between these rocks and Upper Cre unit grades upward into nonmarine rocks including coal, taceous rocks of northwestern and southwestern and these, in turn, are overlain by a thick body of marine Colorado was the presence of formations of the shale. Fenneman and Gale acknowledged the apparent homotaxic equivalence of these beds to the Cretaceous Colorado and ~1ontana Groups in "'\Vyoming, units that had been indistinct or unrecognizable in the southern sequence in southwestern Colorado and, therefore, in areas. Veatch ( 1907, p. 246) assigned the Da.lmta, troduced the names ~1nncos Shale, ~1esaverde Forma Benton, and Niobrara Formations to the Colorado tion, and Lewis Shale into northwestern Colorado. In Group and the Pierre, ~1esaverde, and J.....ewis Forma regard to the introduction of the names, Fenneman and tions to the ~1ontana Group. Overlying the ~1ontana Gale ( 1906, p. 28) stated "and the na.me is provisionally Group was the "Lower Laramie," a. thick sequence of adopted as in the case of the ~1ancos shale and Mesa Cretaceous nonmarine rocks. Veatch's Benton, Niobrara., verde formntion, in the expectation that future geologic and Pierre Formations .are probably equivalent to work will definitely establish the correlation between the Fenneman and Gale's ~1a.ncos Shale ( 1906), and the two." Mesaverde and Lewis Formations in each a.rea are The equivalence of the ~1esavercle and Lewis of north u.pproximately equivalent. Regarding the use of the western and southwestern Colorado anticipated by Fen neman and Gale has not been confirmed. Geologic in name Pierre in "'\Vyoming, Veatch (1907, footnote on p. 246) stated: vestigations in western Colorado clearly demonstrate a. lack of continuity between the ~1esnverde and Lewis at It is the belief of Dr. '1'. \V. Stnnton that the Mesnverde and part of the Lewis also belong to the Pierre, ns that formation their type localities and the ~1esaverde and Lewis of is developed east of the Rocky Mountains. A local name will northwestern Colorado and "'\Vyoming. Reeside (1924, therefore probably be applied to this lowest division of the p. 18) stated that the Lewis Shale of the northern areas l\fontana in this region. was definitely not the same age as the Lewis of the The name Steele Shale was introduced by Darton, San Juan district. ~lore recently, "'\~Teimer (1959, p. '11) Blackwelder, and Siebenthal ( 1910, p. 10), to re-place has shown a similar relationship. Pierre as used by Veatch (1907). Their description • At its type locality in southwestern Colorado, the follows: ~1esaverde Group is a thick unit of marine sandstone and nonmarine rocks. It thins northeastward, becomes The lower portion of the Montana group in the Laramie Basin consists of about 3,000 feet of dark shale with some thin finer grained, and finally loses its identity within the beds of sandstone and numerous nodular concretions, mostly ~1ancos Shale. At the lntitude of ·~1ontrose, Colo., the .sandy. These rocks are believed to represent the Steele shale, entire ~1esaverde Group is represented by the middle named for the type locality, Fort Steele, on the North Platte part of the ~1ancos Shale, and the overlying Lewis Shale River. .is an indistinguishable part of the ~1ancos (Dickinson, In 1918, Bowen reported on the stratigraphy of the 1965). In this urea the ~1ancos is overlain by the Pic I-Ianna Basin. l-Ie described the Steele Shale as a 4,000- tured Cliffs Sandstone, which :in northwestern Colorado foot-thick dark-gray shale with interbedded sandstone becomes the bnsal part of the ~1esa verde as defined by and shaly sandstone, some of which forms conspicuous Fennemnn and Gale ( 1906) and by others. The Lewis ledges near the top of the formation (Bowm~, 1918, p. Shale of the Yampa district of northwestern Colorado 229). He described the Mesaverde Formation as 2,700 is not represented by marine rocks in western and feet thick and divisible into three members. The upper soutl)'vestern Colorado. 1nember consists of whitish sandstone interbedded with In 1912 and 1913, I-Iancock ( 1925) investigated the gray and carbonaceous shale and thin irregular beds of geology and coal resources of the Axial and Monument coal. The middle member is composed of brown to gray Butte quadrangles in ~1offat County in northwestern sandstone, carbonaceous shale, u.nd thin irregular beds of Colorado. IIe divided the ~1esaverde into the lies and coal; it contains a fresh- and brackish·water fauna. The the overlying vVilliams Fork Formations and elevated lower member is gray to white sandstone and gray shale; the Mesaverde to group status (Hancock, 192·5, p. 13- it lacks coal and contains a. marine fauna. Bowen ap 14). Publication of the report formally describing these parently redefined the upper and lower boundaries of two new formations was delayed, and the names first the Mesaverde of Veatch and included some of the lower appeared in the U.S. Geological Survey Press part of the Mesaverde in the Steele Shale (Veatch, 1907, Memorandum 16037, October 1,1923. p. 246; Bowen, 1918, p. 229). 108' ~ . ______!_ ¥' ------106' PaUifinder Res~rvoir ------~--r---E~PLANATION______l I D ! '~"}% , I ~ I Outcrop of Ferris and Outcrop of Mesaverde I I Hanna Formations Group 1 .....~ C) ::0 I I ~ :., 1 Outcrop of· Lewis~ Shale, Fox Hills, Lance, I a nd Medicine Bow Formations I ~ Includes L ance along east flank of > o Io Washakie and Great Divide Basins 1 z (.) 1(.) l '=' sj~ Contact__ __ _ z ~I ;:i Dashed where approximately located; 1 0 42' < o-l dotted w here concealed l ~ u...: 6 -<>- z Medicine M 0 Bow 1 Location of section Oil and gas well I Wheatland tfr?J I ~::0 I Reservoir?{? I l?j GREAT DIVIDE ...,/) I BASIN "" (> Ul { 0 -;>' ; J ~ LJ> I l?j 0 ::0 I l?j ~ :i ~ I 0 ~ (".J'\ z I l?j ""d~ ;;{ 0 r--J(. \ l/) 1- 0 \ ) "-:>) z I Ul ::J I '"'\'""' \ ~J\ 0 Saratoga <.... '?._...> ;-.I ~ ~ '=' ~ "' / -.j I "--;, >-3 "''!;, ~() f) . I l?j '0 ~~v- ::0 '1-1 '--' I :j __-;Laramie J -w I > :) ::0 ~~~ ~ <( -< I o'z. v/ Q: I ::0 BIGHORN ~... <( 0 BASIN <;., _J I 0 BASIN I -;,0 P'1 I G- I ~Ul I Ul 1 1-~ 0 0 I '1-\S' I ~ 41 ' / 1 0 JCS-, '?(! naggs ~,j,t(. ,,, .,., ·· I I '"'1 I \1 ...J l?j z >-3 0 10 20 30 40 MILES ::0 ~ FIGURE 1.-Index geologic map of south-central Wyoming showing location of measured sections. Geology modified from Love, Weitz, and Hose (1955). ~0 7 J...... , • ..._ HISTORICAL BACKGROUND 5 In south-central Wyoming, the Lewis Shale and over treating the Blair and Rock Springs Formations, the lying "Lower Laramie" were reported by Veatch ( 1907, Ericson Sandstone, and the Almond Formation o£ the p. 246-249) to consist of marine and continental rocks, Mesaverde Group in southwestern Wyoming. respectively. Bowen ( 1918, p. 228-230) substituted the We propose a revision of the stratigraphic nomencla ... name Medicine Bow Formation for the "Lower ture for some of the rocks of Late Cretaceous age in the Laramie." Dobbin, Bowen, andlloots (1929, p. 22-24) area of the Rawlins uplift and the Hanna, Carbon, and described a unit of interbedded 1narine and nonmarine Laramie Basins in southern Wyoming. These revisions rocks, 400-500 feet thick, between the Lewis and Medi are based on regional stratigraphic and faunal studies cine Bow and reassigned n1ost of these rocks from the and on detailed geologic mapping. upper part of the Lewis to the basal part of the Medicine In the area of this report we herein elevate the Mesa Bow. They correlated this transitional unit plus •an verde Formation to the Mesaverde Group and establish uppermost part of the Lewis Shale with the Fox Hills and accept the following formations within the Mesa Sandstone of eastern ''rymning. The Fox Hills had verde Group in the Hanna and Carbon Basins (in as been named in South Dakota by Meek and Hayden cending order) : Haystack Mountains Formation, Allen (1862, p. 419). Dobbin and Reeside (1929, p. 21-23) Ridge For1nation, Pine Ridge Sandstone, and Almond also recognized .the transitional rocks and stated that Form·ation (fig. 2). The Haystack Mount·ains Forma they were of Fox Hills age. Dorf (1938, p. 4-6) rede tion consists o£ thick and persistent units of marine Hned the ~1edicine Bow assigning the basal 400-+- feet sandstone separated by thick units of marine shale. in the I-Ia.nna Basin to the Fox Hills Fonnation. Three of the sandstone units have been 1napped ·locally Bowen ( 1918, p. ·228) also nnmed the Ferris Forma and are designated as members of the Haystack Moun tion of questionable Tertiary age and the Hanna Fonna tains Formation. They are, in .ascending order: Tapers tion of Tertiary age. Most subsequent workers in the Ranch, O'Brien Spring, and Hatfield Sandstone Mem area have used the nmnenclature of Bowen (in Dobbin, bers. The Hatfield Sandstone Member was proposed by Bowen, and Hoots, 1929, p.17-26). Hale ( 1961, p. 134) and is herein adopted. The Allen The names Foote Creek and Dutton Creek were intro Ridge Formation, proposed by Bergstrom (1959, p. duced by Hyden, McAndrews., and Tschudy ( 1965) for 114) for the dominantly nonmarine part o£ the Mesa rocks of Late Cretaceous and Tertiary age in the north verde underlying the Pine Ridge Sandstone, is herein ern part of the Laramie Basin and southern part of the adopted. Dobbin, Hoots, Dane, and Hancock ( 1929, p. Carbon Basin. Geologic investigations in the area since 134) first described the Pine Ridge Sandstone ·as a mem then indicate that these rocks are remnants of the Medi her of the Mesaverde Formation. 'V e herein elevate it to cine Bow and Hanna Formations, respectively .. formation status. The Almond Formation, first de scribed by Schultz (1907, p. 260) is southwestern Wy SUMMARY oming as the Almond coal group, was later called by Nomenclature established for rocks of Late Cretace Sears ( 1926, p. 16) the Aln1ond Formation of the Mesa ous age in southwestern Colorado should not have been verde Group. This formation confonnably underlies the extended into northwestern Colorado, eastern Utah, and Lewis Shale in much of southern Wyoming. The name Wyoming. Although the stratigraphic sequences are Almond is hereby extended from southwestern Wyom homotaxically equivalent, the Mesaverde Formation and ing into the ·area of this study. Lewis Shale are not laterally continuous among the In the Laramie Basin the ·~iesaverde Group consists areas. It would be desirable to abandon the names Mesa of the Pine Ridge Sandstone and a thick underlying verde and Lewis a way from their type localities, but unit of shallow-water marine sandstone and shale. We their general use for more than 60 years makes such a propose that the latter unit be named the Rock River change impractical. A reasonable solution, based on Formation (fig. 2). The thick and distinctive marine regional geologic studies, is to redefine the Mesa verde rocks of the Rock River Formation grade westward into as a group ·and establish within it lesser stratigraphic the mainly nonmarine rocks of the Allen Ridge Forma unit!:\ that are widely mappable and laterally continuous tion. The lateral transition between the two formations (table 1). A similar approach was used by Hancock is in the northen1 part of the Laramie Basin. (1925, p. 13-14) in defining the Iles and Williams Fork The name Lewis Shale is retained in southern Wyo Formations of the ~iesaverde Group in northwestern ming even though the formation is neither correlative Colorado, by Spieker and Reeside (1925, p. 440); in with, nor lithologically the same as, the type Lewis defining the Star Point Sandstone, Blackhawk Fonna Shale of southwestern Colorado. The name is perpetu tion, and Price River Formation of the Mesaverde ated only because of long-established usage in the region. Group in eastern Utah, and by Sears (1926, p. 16); in In its upper part the Lewis Shale contains a wide- 867-863 Q-70-2 6 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. TABLE 1.-Gorrelation of Upper Cretaceous rocks in south-cent1·al Wyonl!ing aml UPPER CRETACEOUS WESTERN INTERIOR AMMONITE ROCK SPRINGS LARAMIE BASIN STAGES AND HANNA BASIN ZONES UPLIFT (ROCK RIVER) SUBSTAGES 29 Discoscaphites nebrascensis Medicine Bow Medicine Bow Formation Formation 28 Hoploscaphites nicolletii Lance Formation (part) (part) (part) .... 27 Sphenodiscus (Coahuilites) Fox Hills Formation Fox Hills Formation ~ ~ 0 ...J 26 Baculites clinolobatus Fox Hills Sandstone Upper part Upper part ~ 2 5 Baculites grandis .c.: - uad Sandstone- Unnamed Lewis Shale ~~~ sandstone 24 Baculites baculus 1--,..------J ~ Lower part ~ 1------i 2 1 Baculites reesidei ,._.; 20 Baculites cuneatus Pine Ridge Pine Ridge U;:>per part Sandstone Sandstone 1 9 Baculites compnssus 18 Didymoceras cheyennense 1 7 Exiteloceras jenneyi .... ~ c.~ 16 Didymoceras stevensoni c: c. :::> .s 5 Sca.phites hippocrepis III Blair Formation 4 Scnphites hippocrepis II Steele Shale 3 Sca.phites hippocTepis I Baxter Shale (part) c: ------~------7------J------?------~ ro 2 De.c;moscaphites bassleTi ·c: Qj --r 0 c. Airport Sandstone Niobrara Formation Niobrara Formation c c. Member of (part) (part) ro :::> 1 Desmoscaphites erdmanni Smith (1961) C/) STEELE SHALE 7 nearby m·eas SOUTHEASTERN POWDER RIVER BLACK HILLS spread unit of sandstone and shale called the Dad Sand WIND RIVER BASIN (RED BIRD) BASIN (SALT CREEK) stone l\iembe.r by Hale ( 1961, p. 136). This name is ii. herein adopted. Lance Formation Lance Formation Lance Formation (part) (part) (part) At the top of the Lewis Shale or ·a.t the base of the overlying l\iedicine Bow Formation is ·a. thick unit com Fox Hills Sandstone posed 1nainly of sa.ndstone. Rocks of this unit are tran Fox Hills Sandstone Fox Hills Sandstone sitional from ma.rine shale of the underlying Lewis to Lewis Shale Upper part nonmarine rocks of the overlying l\iedicine Bow Forma 1- Upper unnamed tion and include shallow-water marine sandstone and Tongue of Meeteetse shale member Formation ~~ marine to nonmarine siltstone and shale. The name Fox (/) Hills Form.ation is used for these rocks. L------VI 'i Q) Kara Bentonitic The l\iedicine Bow Forma.tion of Late Cretaceous age, .•...... 1 Lower part Member Lewis Shale Lower unnamed named and described in the H·anna Basin, is mostly re shale member stricted to the Hanna and Carbon Basins. The name is (part) herein used-as originally defined. The Ferris Forma.tion of Late Cretaceous and early Tertiary age and the Ill Hanna Formation of Tertiary age were defined in Teapot Teapot (Absent or Sandstone Sandstone very thin) the Hanna Basin and ·are herein adopted as originally Member Member proposed. .gc: Niobrara Formation verde is called Cody Shale. The Cody is equivalent to .>- (part) the Carlile Shale, Niobrara Formation, and Steele Shale. 8 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. FIGURE 2.-Stratigraphic cliagrwm showing intertongu·ing relations 1 2 3 4 5 wz en_ w~ w en a:: 0::< oo w z 01- a:: I < IZ z> i-U ...J ...J -0:: ...J u O::J ::;:w W::J ~ ...JQ wen < z enw Zc.!l a:: ~::;: a:: a:: c .,0 "'E- f· ~ t: 0"' "'.,~ 0. 1- u c ...J"' Formation Almond Formation c ~ c c :J 0 ::;:'ro0 ·- ~ E • u ~ ~"-"' 0 "' I""' STEELE SHALE 9 5 6 7 !: 0 m 0:: w I w w ow ~ a:: I ,_u ::;:z 0:: _J ouu- :.:: W:::J 0 u Zc.!l w 0 a: ::;: 0:: EXPLANATION ., c: c: 0 u 3:"' t :ogE1i ., ~- D ::;: 0 -+ "- Marine shale Fox Hills Formatio n D Persistent beds of thin-bedded to massive sandstone deposited in a marine environment D Organic-rich black shale, ironstone concretions, and thin ., bedded sandstone deposited in a lagoonal environment iii r: Ul Ill - .,~ Lenticular sandstone and shale, carbonaceous shale, and coal _J deposited in a fluvatile• environment .9 Ammonite coll ection from measured section or nearby locality Number refers to arnrnonite sequence shown i1< Wble 1 ~ Unconformity Formation boundary Dashed where approximately located [ 50: Hatfield Sandstone Member I l lOOO FEET 0 10 20 30 MILES of Upper 01·etaceottS rocks in south-central Wyo•ming 10 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. ,_.( LITHOLOGIC CHARACTER with the overlying Haystack l\tlountains Formation is also gradational. The shale of the upper part of the The Steele Shale consists of dnrk-gray shale that con Steele becomes increasingly sandy upward and finally tains sparse layers of gray-weathering limestone con merges with the sa.ndstone of the Haystack ~iountains cretions and thin beds of very fine grained sandstone Formation. 'Ve locate the upper contact at the base of rmd siltstone. In areas where sandstone beds of the the first persistent marine sand.stcne. overlying Haystack Mountains Formation pinch out t l1e eqtnvalent. facies, assigned to the Steele, is very' Both the upper and lower boundaries of the Steele .a..;· sandy shale. rise stratigraphically eastwn.rd., and the formatio11 The Steele Shale is nonresistant and commonly forms grades laterally into the lower part of the Pierre Sha,le broad areas of low relief. It is generally poorly exposed, east of the Laramie Mountains. In the type section of the Haystack Mountains Formation, about 11 miles bt~t the upper part crops out ·where protected by the chff-form1ng sandstone of the Haystack Mountains northeast of Rawlins, the Steele Shale is about 2,400 Formation. feet thick; 22 miles farther south, it is about 3 800 feet In the nortlnvestern part of the Laramie .Basin, the t~1ic~. This thickness change results from a stratigraphic upper part of the Steele includes several persistent r1se In the Steele-Haystack Mountains contact. bentonite beds. One bed, as much as 5 feet thick, has been FOSSILS extensively mined a few miles west of Medicine Bow 'Vyo. This bed and those within a few feet above i~ Fossils ·are moderately abundant in limestone con are probably correlative with the Ardmore Bentonite cretions and thin sanely beds of the Steele Shale, and ~. Bed in the Sharon Springs Member of the Pierre Shale they have been collected at many localities throughout in the Black Hills region of \'Tyoming and South Da southern \Vyoming. The best documented collections kota (Gill and Cobban, 1966a, p. A10). The bentonite with respect to stratigraphic position are those of Smith beds probably also correlate with the thick bentonite ( 1965, p. 21-23) from the Hatfield dome area south of unit overlying the Sussex Sandstone Member of the Rawlins in Carbon County. Fossils fron1 these collec Steele Shale in the Salt Creek oii field of the western tions, which were identified and the names herein up Powder River Basin. · dated by W. A. Cobban, are as follows: THICKNESS USGS D3293. SEtA, sec. 24, T. 19 N., R. 87 W. From a limestone The thickness of the Steele Shale has been reported concretion layer 415 ft below the top of the Steele Shale. by Veatch (1907, p. 246) as 3,000-3,500 feet; by Darton, Inoceram1ts cf. I. proximus Tuomey Pteria linguaetormis (Evans and Shumard) Black,velder, and Siebenthal (1910, p. 10) as 3,000 feet; Cytnbophora sp. by Dobbin, Bowen, and Hoots (1929, p. 17) as 4,000- Thyasira sp. 5,000 feet; and by Bergstrom (1953, p. 59) as 2,600- Baculites obt'ltS'ttS Meek (early form) 3,200 feet. The variation in thickness reported probably Trachysca-phites pracspiniuer Cobban and Scott results mainly from individual preferences in selecting USGS D3290. SEtA, sec. 12, T. 19 N., R. 88 W. From a limestone the upper and lower boundaries for the formation. No concretion layer 405 ft below the top of the Steele Shale. •· Inoceram1ts cf. I. proxinws Tuomey type section of the Steele is described in the literature' Pteria sp. and none was measured by us. Electric logs of oil and gas Lucina subundata Hall and Meek wells show that the Steele is about 2,400 feet thick in the Cym,bophora sp. western part of the Hanna Basin~ where the overlying Baculites sp. (weal\: flank ribs) Trachyscaphites p-raespin·igcr Cobban and Scott Haystack Mountains Formation is well developed. At ..... Hatfield dome, about 10 miles south of Rawlins, Smith Placenticems cf. P. meeki Boehm ( 1965, pl. 3) reported the Steele to be about 3 800 feet Placenticeras cf. P. intercalare Meek thick. In the Rock River area of the Laramie B'asin the USGS D3048. N'V% sec. 34, T. 19 N., R. 86 W. From a limestone formation is about 2,300 feet thick. ' coneretion layer '702 ft .below the top of the Steele Shale Inoce-ram1ts sp. RELATION TO ADJACENT FORMATIONS Pteria sp. Ostrea sp. The contact of the Steele Shale with the underlying Baculites sp. (weak flank ribs) Placenticeras cf. P. meeki Boehm Niobrara Formation is gradational. It is located at the USGS D3047. NE% sec. 34, T. 19 N., R. 86 W. From a limeston~ change from the gray shale of the Steele to the yellow concretion layer 702 ft below the top of the Steele Shale. ish-orange-weathering calcareous shale of the upper Inoceramus sp. part of the Niobrara. The contact of the Steele Shale Baculites sp. (weak flank ribs) •-f' MESAVERDE GROUP AND MESAVERDE FORMATION 11 USGS D3046. SW¥.., sec. 3G, T. 19 N., R. 86 \V. From a limestone tral V\Tyoming, and the Steele Shale of the western concretion layer 912 ft below the top of the Steele Shale. Powder River Basin of northeastern 'Vyoming (table InooemnHtS sp. 1). The lower contact of the Steele rises stratigraphically iJ. Pte-ria n. sp. BaottZites sp. (weak flank ribs) toward the east. 'b·achysoaphites 1)raesphvige1· Cobban and Scott MESAVERDE GROUP AND MESAVERDE FORMATION USGS D3291. NE'It sec. 26, T. 19 N., H. 87 W. From a limestone concretion layer 1,73G-1,7GO ft below the top of the Steele Rocks in south-central V\Tyoming formerly called Shale. ~- .l. ~1esaverde Formation, and hereafter referred to as Lucina, ."'ttbttntlata Hall and Meek Baottlites aff. B. aqttilacnsis Reeside the Mesaverde Group (table 1), are divided into the USG•S D3054. NE¥.., sec. 23, T. 19 N., R. 88 W. From a limestone :follmYing formations, in ascending order: Haystack concretion layer 2,320 ft below the top of the Steele Shale. ~1onntains Form·ation, Allen Ridge Formation, Pine Inocemmtts cf. I. proa:inws Tuomey Ridge Sandstone, and Almond Formation. The Ost1·ea sp. ~1esaverde Group confonnably overlies, and laterally GZyptoa:ocm·as sp. intertongues at the base with, the Steele Shale. It Scaphites hip7Jocrepis (DeKay) conformably underlies, and laterally intertongues at USGS D3053. NW:JA, sec. 14, T. 19 N., R. 88 W. From a limestone concretion layer 2,332 ft below the top of the Steele Shale. the top with, the Lewis Shale (fig. 2). InoccramMts cf. I. 1woa:imus Tuomey In the southeastern part of the area (Laramie Basin), Pte1··ia cf. P. Unguaetormis (Evans and Shumard) the Mesaverde Group comprises the Rock River For Ostrea n. sp. mation and the Pine Ridge Sandstone. The absence of ~· Drepanochilus sp. Bacu.lites sp. the Haystack ~1ountains, Allen Ridge, and Almond • Glyptoa:ocems sp . Formations is due to the eastward change in facies from II m·cs·iceras 1nontanaense ( Reeside) rocks typical of these formations to marine beds of the Sca.phites hippocrepis (DeKay) I Steele and Lewis Shales (fig. 2) . USGS D3095. Center of the N% sec. 23, •r. 19 N., R. 88 \V. From The name ~1esaverde Formation is still applied to a a limestone concretion layer 2,747 ft below the top of the Steele Shale. thick sequence of shallow-water marine and nonmarine Ost?·ea sp. beds in the Powder River, Bighorn, and 'Vind River BaculUes sp. Basins o:f 'Vyoming. Regional stratigra.phic studies in Sca1Jhites hip1worcpis (DeKay) I dicate that the formation is composed of severa.l wide USGS D3051. NW¥.., sec. 26, T. 19 N., R. 88 \V. From clayey spread and distinctive units tha.t can be recogt1ized in limestone concretion layer 3,565 ft below the top of the Steele each of the basins. Some of these units, such as the Tea Shale. Uintacrinus sooial·is Grinnell pot and Parkman ~Sandstones, a.re formal members of Ost?·ca oongcsta Conrad the ~1esaverde Formation, but other equally distinctive Inocemn1.1ts cf. I. balticus Boehm units are unnamed. Bacttlitcs tho1ni Reeside In the southeastern part of the vVind River Basin, Desmoscaphites bassled Reeside Barwin ( 1959, p. 141) named the lower regressive • AGE AND CORRELATION tongue of the ~1esaverde Formation the Phayles Reef ~t[e.mber and later modified the name to Phayles Mem The fauna listed above from the Steele Shale in the ber (Ba.rwin, 1961, p. 174). 'Ve reexa.mined Ba.rwin's I-Iatfield dome area., south of Rawlins, is common to the area and type section in the S'V1.4 sec. 4, T. 33 N., R. 87 Telegraph Creek and Eagle Formations and the lower ,V., and found that the correct spelling of "Phayles" is part of the Claggett Formation of central Montana Fales, as shown on the Garfield Peak 7112-minute quad (Cobban and Reeside, 1952, p. 1019-1020). In the area rangle map. Inasmuch as "Phayles" is not a well north ·and northeast of Rawlins, the top of the Steele js established and repeatedly published name, we are ac older and apparently does not contain beds younger cepting the correct spelling of Fales. than about the middle part of the Eagle; beds in the :Marine rocks overlying the Fales were called the 'Val lower part of the overlying I-Iaystack Mountains For lace Creek Tongue of the Cody Shale (Barwin, 1959, .... mation contains late Eagle and Claggett fauna. p. 142) . The type section of the '~r allace Creek is also in The upper part of the Steele Shale in the area north the s·"r14 sec. 4, T. 33 N., R. 87 W. The 'Va.llace Creek of Rawlins correlates with the upper part of the Mancos Tongue of the Cody and the Fales ~1ember of the ~1esa Shale of northwestern Colorado, the upper part of the verde are distinctive stratigraphic units in the south Blair Form·ation of southwestern vVyoming, the upper eastern part of the 'Vind River Basin and are herein part of the Cody Shale in the vVind River Basin of cen- adopted as formal stratigraphic units. for. that area. 12 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH- CENTRAL WYO. FIGURE 3.-Haystack l\Iourutains Formwtion exposed along the west side of the HaystJack Mountains in sec. 18, T. 24 N., R. 86 W., Oarbon County, Wyo. tr, Tapers Ranch Sandstone Member; ob, O'Brien Spring Sandstone Member; ho, Hatfield Sand stone Member; hm, top of Haystack Mountains Formation. HAYSTACK MOUNTAINS FORMATION from O'Brien Spring located in the SWl)!, sec. 9, T. 24 TYPE SECTION AND DISTRIBUTION N., R. 86 W. (Seminoe Dam Southwest 7%-minute quadrangle) . Both members are moderately well ex The Haystack Mountains Formation receives its name posed in the vicinity of these two localities, but they are from an imposing range of hills that occupies the west best developed and exposed at the locality of the 'type half of TS. 22--23 N., R. 86 W., Carbon County, "\Vyo. Haystack Mountains Formation which is designated the (fig. 3) . These hills, ca.lled the Haystack Mountains, type section of the two new members. form the rugged elevated surface along the east side of The Hatfield Sandstone was named a member of the the Rawlins Northwest 7ljz-minute quadrangle, the "lower (marine) Mesaverde" by Hale (1961, p. 130- southern part of the Wild Horse Mountain 7ljz-minute 134) for exposures along the flanks of Hatfield dome quadrangle, and the western part of the Lone Haystack south of Rawlins. The name is here adopted as the Mountain 7ljz-minute quadrangle. yotmgest named member of the Haystack Mountains The type section of the Haystack Mountains Forma Formation. Inasmuch as a type section was not given by tion was measured a short distance west of the place Hale, we designate as the principal reference section the where the Seminoe road passes through the canyon of exposure of the Hatfield Sandstone Member on the west the North Platte River, about 6 miles north of the town side of Hatfield dome in the NE%NE% sec. 18, T. 19 N., of Sinclair (fig. 1) . The section was measured by plane R. 88 W ., Carbon County, Wyo. (Bridger Pass 15-min table and tape in the NE%NE% sec. 22, NE% sec. 23, ute quadrangle) (figs. 1, 4). and SE%SE14 sec. 14, T. 22 N., R. 86 W., Carbon The Haystack Mountains Formation is a widespread County (Sinclair 7ljz-minute quadrangle). The upper and distinctive unit that can be recognized along the part of the underlying Steele Shale was measured in the east margins of the Great Divide and Washakie Basins, NljzSW% sec. 7, T. 22 N., R. 86 W. (Rawlins North on the flanks of the Rawlins uplift, and in the Hanna west 71!z-minute quadrangle). and Carbon Basins (fig. 1). The upper part of the for Three new distinctive members of the Haystack mation is present along the Colorado-Wyoming bound Mountains Formation are recognized and mapped in ary east of Baggs, "\Vyo. It is not recognizable in the this area (table 1; fig. 2) . These members are, in ascend Laramie Basin because of a facies change from ridge ing order: Tapers Ranch Sandstone, O'Brien Spring forming sandstones to soft sandy sha,le. Rocks in the Sandstone, and Hatfield Sandstone. The name Tapers Laramie Basin that are equivalent to the Haystack Ranch is taken from Tapers Ranch in the Sl!z sec. 3, T. Mountains Formation are part of the Steele Shale. The 24 N., R. 86 W. (Wild Horse Mountain 71!z-minute dominant source for the marine sandstones of the Hay quadrangle), and the name O'Brien Spring is taken stack Mountains Formation seems to have been from HAYSTACK MOUNTAINS FORMATION 13 FIGURE 4.-Haystack Mountains Formation at the principal reference section of the Hatfield Sandstone Membe1·, sec. 18, T. 19 N., R. 88 W., Carbon County, Wyo. The Ha.tfield Sandstone Member (H) crops out in the middle of the slope. the north and northwest inasmuch as brackish-water .about 55 feet thick. The Hatfield Sandstone Member at strata occur in association with these beds in that the type section of the Haystack Motmtains Formation direction. is mostly very fine grained, thin bedded, and crossbed LITHOLOGIC CHARACTER ded, ·and it is gradational with the underlying marine The Haystack Mountains Formation is thick and lith shale. The Hatfield Sandstone Member probably orig ologically diverse, consisting mainly of thick units of inated as a marine beach and barrier-bar deposit. marine sandstone, deposited in nearshore a11d offshore The O'Brien Spring Sandstone Member crops out enviroments, interbedded with thick units of marine about 1,350 feet below the top of the Haystack Moun shale, deposited in deeper water environments. The tains Formation north of Sinclair. It consists of pale sandstone of marine origin in the type section generally yellowish-gray very fine grained and fine-grained thin is pale yellowish gray, very fine to fine grained, very bedded sandstone (fig. 5) about 220 feet thick, that thin to thin bedded, a.nd commonly burrowed. Sand forms a prominent cliff (fig. 6). The lower part of the stone units generally have a gradational base and ·are as member grades into the underlying marine shale. The much as 275 feet thick. Units of marine shale range in sandstone contains abundant Ophiomorpha, a fossil thickness from about 25 to 700 feet. The shale is gray crustacean burrow indicative of a shallow-water marine to brownish gray and consists mostly of clay and sandy environment. clay. The shale contains fossiliferous concretions in The Tapers Ranch Sandstone Member is the basal varying abundance, and these may be rusty-weathering sandstone of the Haystack Mountains Formation and, ironstone, limestone, or argillaceous sandstone. at the type section north of Sinclair, is about 270 feet thick. The member consists of grayish-green fine- to At the type section the formation contains eight ledge coarse-grained glauconitic thin-bedded sandstone con forming sandstone beds, three of which ·a.re laterally taining laminae of dark-gray sandy shale. At the type persistent and locailly mapped. The three units are des section, a unit about 50 feet thick of gray sandy shale ignated members of the Haystack Mountains Forma containing laminae of sandstone crops out about 75 feet tion. The uppermost of the members is the Hatfield above the base of the member. The member has a grada which is the most diagnostic .and useful for correlation. tional base. The Tapers Ranch Sandstone Member prob It crops out about 450 feet below the top of the forma ably originated in an environment of deeper water than tion north of Sinclair. The Hatfield consists of pale either the Hatfield or the O'Brien Spring. yellowish-gray cliff-forming sandstone about 167 feet thick at the principal reference section on Hatfield THICKNESS dome. At this locality, it is overlain by a unit of brack ish-water and sha.llow-marine carbonaceous shale, silt The Haystack Mountains Formation ranges in thick stone, and sandstone, about 100 feet thick. At the type ness from 2,550 feet at the type section to 850 feet at Hat section of the Haystack Mountains Formation, the Hat field dome. This thinning toward the southwest results field is a cliff-forming marine sandstone, about 120 feet from facies changes in the lower part of the formation; thick, that is overlain by rocks of brackish-water origin sandstone at the type section grades into shale at Hat- 3e7-soo o-70---<3 14 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. gradational. The basal sandstone of the Haystack Moun tains grades into sandy shale in the upper part of the Steele. The marine shale members of the Haystack Moun tains Formation are genetically tongues of the Steele Shale. The units of marine sandstone in the Haystack Mountains Formation, if traced laterally eastward and southward, lose their identity within equivalent parts of the Steele Shale. The contact of the Haystack Mountains Formation with the overlying Allen Ridge Formation is sharp and conformable. It is generally located by a change from marine sandstone to carbonaceous shale or coal The upper part of the Haystack Mountains Formation mn.y locally contain a few beds of carbonaceous sha.Ie, but the lower part of the Allen Ridge Formation does not con tain beds of marine sandstone. The contact of the two formations represents a change from a mainly shallow marine environment to a brackish-water or fluviatile environment. The contact descends stratigraphically to FIGURE 5.-Thin-bedded character of the O'Brien Spring Sand the west and northwest. stone Member of the Haystack Mountains Formation at its type -section in the NE:i4 sec. 23, T. :::2 N., R. 86 W., Carbon FOSSILS County, Wyo. Fossils are moderately abw1dant in the sandstone and shale of the Haystack Mountains Formation. Those in field dome. In sees. 2, 3, and 11, T. 24 N., R. 89 \¥., at the shale are commonly enclosed in calcareous, sandy, Separation Rim, the formation is 930 feet thick. The thickness difference between this locality and the or iron-rich concretions and rarely occur individually. type section to the east results from different inter Fossils are generally sparse in the sandstone w1its but pretations of the base of the Mesaverde Group. North are locally abundant on the upper surfaces of a few from Separation Rim, the Haystack Mountains Forma sandstone beds. The following sequence of index am tion thins to a featheredge, partly by depositional thin monites was established from scattered localities in the ning and facies change to nonmarine rocks and partly Haystack Mountains Formation: by uplift and erosion before deposition of the Pine Bacttlites pe1·pleams (youngest) Ridge Sandstone and the Lewis Shale (Reynolds, 1966). asperitormis The formation thins eastward and is not present in the mclearni central part of the Laramie Basin. obtusus sp. (weak flank ribs) RELA'J,'ION TO ADJACENT FORMATIONS sp. (smooth) (oldest) The contact of the Haystack Mountains Formation Additional fossils are listed with the descriptions of with the underlying Steele Shale is conformable and the measured sections. AGE AND CORRELATION At the type section the Haystack Mountarins Forma tion contains fossils indicative of late Eagle, Claggett, and early Judith River ages (Gill and Cobban, 1966a, pl. 4; Cobban and Reeside, 1952, p. 1019-1020). The Tapers Ranch Sandstone Member contains an unde scribed smooth baculite which is also found in the Shan non Sandstone Member of the Steele Shale in the FIGURE 6.-0'Brien Spring Sandstone Member of the Haystack Mountains Formation at its type section in the NE:i4 sec. 23, Powder River Basin and which is restricted to rocks of T. 22 N., R. 86 W., Carbon County, Wyo. late Eagle age. The thick shale overlying the Tapers .~ HAYSTACK MOUNTA,INS FORMATION 15 H.anch Sandstone l\1e.mber conta.ins an undescribed Type section of the Haystack Mountains Fot·mation and its O'Bt·icn Spring ancl Ta1wt·s Ran-ch Sandstone Members ·~ baculite that has. weal~ flank ribs. Thi.s species, which is indicative of a, very late Eagle age, has also been [l\Iensured with plnnetable nnd tape by J. R. Gill and R. L. Fleisher, .August 1966. Fossils identified by W. A. Cobban. Measured in the :found in the shale between the Shannon and Sussex NEI,4NEI,4 sec. 22, NEI_4 sec. 2,3, and SEI,4SEI,4 sec. 14, T. 22 N., Sandstones l\1embe.r in the. Powder River Basin. The. R. 86 W., Carbon C-ounty, Wyo. (S•lnclalr 71JJ-mlnute quadrangle), loc. 4, fig. 1.] · O'B1~ien Spring Sandstone Member oontains Baoulites Allen Ridge Formation: Feet obt~t8~t8, n. guide fossil to rocks of ea.rly Claggett age. 36. Sandstone and shale intevbedded ; sandstones T'his member has the a.ppearance and fossils of the Sus~ are lenticular, nonpersistent, and weather sex Sandstone Me1111ber of the Steele Shale in the Pow brown ; shales are gray to brown and der River Basin. Ammonites have not been collected locally carbonaceous ; ironstone concretions common. Unit is dominantly fluviatile in from the IIa.tfield Sandstone l\1ember, but they were origin ------1,475 collected from the underlying and overlying shale. ';I'he 35. Shale, 'brown to black, carbonaceous to lig- IIatfield apparently was deposited during the time of nitic ------50 B. a."l]Jerijor1nis or ea.rly during the time of B. per ]JlermtS. This indicates a late Claggett or early Judith Total Allen Ridge Formation ______1, 525 River a.ge for these rocks. Haystack Mountains Formation: The Hatfield Sa.ndstone Member and the overlying Upper unnamed member: rocks of bra.ckish-water origin resulted from a wide 34. Sandstone, pale-yellowish-gray, fine-grained, spread regression of the sea in southern Wyoming, thin-bedded ; contains clay pebbles and Ophiomorpha~· forms ledge______15 northwestern Colorado, and northeastern Utah. This 33. Sandstone ·and shale interbedded, greenish- regression was followed by an ad vance of the sea rep gray to yellowish-gray ; sandstone in beds resented by the marine rocks of the uppermost part of 0.1-1 ft thick; forms slope______34 the I-Iaystack Mountains Formation. In the southern 32. Shale, gray; contains a few thin beds of sand- pa.rt of the vVind River Basin, regressive deposits com ·&tone in lower 20 ft______85 USGS D5573, from near base of this unit parable to the I-Iatfield Sandstone Member are repre in the SE% sec. 6, T. 23 N., R. 86 W. : sented by the Fales l\1ember of the l\1esaverde Lingula subspatulata Halll and Meek Formation, ttnd transgressive deposits equivalent to the Pinna sp. upperm,ost part of the Haystack Mountains Formation Inocet·anHts sp. are represented by the vVa.llace Creek Tongue of the Owytoma sp. Syncyclonema? sp. Cody Shale. Modiolus sp. The regression of the sea that resulted in the deposi Oymella montanensis (Henderson) tion of the I-Iatfield Sandstone :Member and the over Olisocolus? sp. lying brackish-water beds is represented in northwest Ethnwcardimn sp. ern Colorado and in the Book Cliffs area of eastern Tellina sp. \ Baculites perplemus Cobban Utah ttnd western Colorado by the Castlegate Sand Hoploscaphites sp. stone. The marine shale overlying the Castlegate Sand Ptace-ntice1·as sp. stone is called the Buck Tongue of the Mancos Shale 31. Shale, medium-gray______15 ·and is equivalent to the uppermost part of the Hay 30. Sandstone, pale-yellowish-gray, fine-grained, medium- to thin-bedded with some flow- stack Mountains Forma.tion. The Buck Tongue was angle crossbeds ; contains local masses of described by Fisher ( 1936, p. 15) in the Book Cliffs coal brown-weathering concretionary sandstone fi.eld and, more recently, by Cullins (1968) in the near top. 01Jhionwrpha abundant______65 Rangely ttrea of northwestern Colorado. 29. Sandstone and ·shale interlbedded; san Type section of the Haystack Mountains .Formation and its Type section of the Haystack Mo1mtains Formation and its O'Brien Spring and Tapers Ranch Sandstone Members O'Brien Spring and Ta-pers Ranch Sandstone Members Continued Continued Haystack Mountains Formation-Continued Haystack Mountains Formation-Continued Upper unnamed member-Continued Middle unnamed member.....,....Continued Feet 29. Sandstone and shale interbedded-Con. Feet 20. Sandstone, pale-yellowish-gray, fine-grained, USGS D3347, from ·same level as above thin-bedded ; soft at base and harder and in the NW~NE~NE* ·Sec. 30: cliff forming above; contains in middle Inoceramus subcompresiJus Meek and dark-brown-weathering sandstone concre Hayden tions 1.5 ft thick and 10 ft in diameter ; Oymbophora sp. upper few feet contains abundant Baculites cf. B. perpleaJus C'ooban glauconite and a few iron-replaced fossils__ 95 28. Shale, medium- to dark-grayish-brown ; con- USGS D6266, from top of unit : .4. tains a few ironstone concretions------25 Baculites mclcarni Landes USGS D5550: 19. Sandstone, like unit 20, sof.t; forms low ridge; Dis'Cinid brachiopod (attached to contains at top dark-brown-weathering oyster) sandstone concretions 1 ft thick and 6 ft Ostrea sp. in diameter______40 N1te1tla 1sp. 18. Shale, medium-dark-gray------40 27. Sandstone, pale-yellowi,sh-gray, very fine 17. ·Sandstone, pale-yellowish-gray, fine-grained, grained, thin-bedded; low-angle crossbeds- 5 soft______25 USGS D5549: 16. Sandstone, like unit 17, glauconitic; weathers Nucula 'sp. in 2 low benches; contains abundant Ostrea sp. Ophiomo·rpha and at top dark-brown 26. Shale, medium- to dark-brownish-gray, car weathering sandstone concretions 2 ft thick bona.ceous in pal'lt ; forms slope. At base n and 8 ft in diameter______65 1-ft-thick bluish-gray carbonaceous shale 15. Shale, gray, sandy ; weathers yellowish gray ; overlain by a 0.5-ft-thick impure coaJl____ 65 contains 'spa;rse rusty-brown-weathering 25. Sandstone, light-gray, very fine grained ; con- limestone concretions; forms valley------85 tains a 1-ft-thick 1ignitic shale in middle. 14. Sandstone, pale-yellowish-gray, fine-grained, Pel'lsistent unit but variable in thickness- 4 cliff former; contains a few Ophionwrpha,_ SO 24. Shale, dark-grayi,sh-brown to brownish-gray; 13. Shale, medium-dark-gray; poorly exposed but locally carbonaceous at base; jarosiJtic on contains a 1-ft-thick bentonite at base____ 170 bedding planes______50 Total Middle unnamed member______·760 Total upper unnamed member______428 O'Brien Spring Sandstone Member : Hatfield Sandstone Member: 12. .Sandstone, light-gray, very fine grained, clayey, soft ______23. Sandstone, pale-yeUowish-gray, fine-grained, 45 medium- to thick-bedded at base, thin USGS D5571, from 20 ft below top in bedded at top with low-angle crossbeds; the S~1,4NE~ sec. 7, T. 23 N., R. contains abundant Ophiomorpha in mid 'l'ypo section ot the H aystaok Mountains Formation wnd its Typo section ot the Haystack .Motmtains Formation and its O'Brien Spring and 'Ta1)01·s Ranch Sandsto'no Members O'Bt·ien Spring and Tapet·s Ranch Sandstone .Members Continued Continued Haystack Mountains Formation-Continued Steele Shale (part)-Continued Feet Lower unnamed memlJer-Continued 1. Shale, medium-dark-gray, soft; contains 10. Shale, medium-gray, soft-Continued Feet limestone concretion layers 600 ft and 20 ft USGS D5548, from 80ft below top on line below tOP------600 of section: USGS D5547, from 20ft ·below top: Baoulites sp. (weak flank ribs) Baoulites sp. (smooth) USGS D363, from 2'70 ft below top: USGS D5554, from 600ft below top: BQicztUtes sp. (weak flank ribs) Anisomyon sp. USGS D2994, from 600 ft below top : BacttZites sp. BQicztZites sp. (w1~ak flank ribs) Scaphites hippocrcpis (DeKay) III USG.S D364, from 655 f.t below top : H aresiceras natronense Reeside Bacttlites sp. (weak flank ribs) 9. Sandstone and shale interbedded; weathers Total Steele Shale measured____ 788 yellowish gray and forms slope______40 USGS D2993, 20 ft below top : Rete1·encc sect·ion of the Haystack .M01mtains Formation Bacztlites sp. [Measured by A. D. Zapp, September 1961. Fossils identified by W . .A. Cobban. Measured on the north side of Horsehoe Ridge in the SEIA, sec. 36, T. 25 N., R. 84 W., Carbon County, Wyo. (Seminoe Dam Total lower unnamed member____ 715 Southeast 7 %-minute quadrangle), loc. 6, fig. 1.] Feet Tapers Ranch Sandstone Member : Allen Ridge Formation: 8. Sandstone, pale-greenish-gray, medium- to 34. Sandstone and shale interbedded ; lenticular coarse-grained, thin-bedded with low-angle ridge-forming units deposited in a fluvia cross·beds, calcn.reous, glauconitic, ridge tile environment. Thickness estimated forming; contains some reddish-brown iron from the topographic map ______1, 120 cement------8 7. Sandstone, grayish-green to light-yellowish Total Allen Ridge Formation (ap g.ray, fine-grained; contains thin laminae proximate) ------1, 120 and beds of gray shale with the .thicker beds of shale forming slopes covered with Haystack Mountains Formation : th,in plates of sandstone______60 Upper unnamed member: .,.. 6. Sandstone, gray, fine-grained to very fine 33. Sandstone, pale-yellowish-gray, fine-grained, grained, clayey, thin-bedded with shale massive, soft; weathers light gray to white_ 40 laminae; cleaner and glauconitic in upper 32. Shale, dark-gray ; contains f?everal 0.2- to part; contains some iron cement ; upper 0.5-ft-thick ledges of hard calcareous silt- part forms a ridge and basal part forms a stone 40-45 ft above base______200 slope ------..:.------78 USGS D3323, from shale: 5. Shale, medium-dark-gray, sandy; contains Inoceramus subcornpressus Meek some sandstone laminae ; poorly exposed__ 50 and Hayden 4. Sandstone, pale-yellowish-gray to dark-gray, Ethmocardium sp. glauconitic; contains small dark chert Bacttlites perplemus Cobban granules and limonite-.cemented shale Placenticeras cf. P. intercalare Meek pebbles. Upper part medium to coarse 31. Shale, dark-gray, somewhat carbonaceous; grained and very glauconitic, weathering to may be nonmarine------3 a brown cliff ; lower part clayey and slope 30. Sandstone, pale-yellowish-gray, very fine forming ------75 grained, hard; cliff former; in beds about Total Tapers Ranch Sandstone Mem- 0.5 ft thick; contains abundant oysters____ 20 ber ------271 29. Shale, brownish-gray; appears nonmarine__ 13 28. Sandstone, pale-yellowish-gray, very fine Total Haystack Mountains Formation_ 2, 544 grained ro fine-grained, upper surface a coquina of clams______5 Steele Shale (part) : 27. Shale, dark-brownish-graY------22 3. Shale, medium- to dark-gray, sandy; con 26. Sandstone, yellowish-gray, very fine grained, tains a few layers of gray sandy limestone thin-bedded, very hard; contains abundant concretions in upper part and red-weather- burrows, trails, and oysters______2 ing ironstone concretions in lower part____ 180 25. Shale, dark; appears nonmarine______28 · 2. Sandstone and shale interbedded ; weathers 24. Sandstone, pale-yellowish-gray, fine-grained, pale yellowish gray ; sandstone in beds massive; contains abundant Ophiomorpha nbout 0.1 ft thick or less ; forms low ridge_ 8 at tOP------8 18 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Jleference scet·ion of the Haystack 1li ountains Ji'o~nnaHon-Con. Reference sect·ion of the Haystack Mountains Formation-Con. Haystack Mountains Formation-Continued Haystack Mountains Formation-Continued Feet Upper unnamed member-Continued Feet Lower unnamed member: 23. Shale, purplish-brown, silty; appears non- 13. Shale, brownish-gray, silty to sandy; transi marine ------7 tional with overlying sandstone; contains brown-weathering gray limestone concre- Total upper unnamed member------348 tions ------170 12. Shale, bl·ack, dayey; contains abundant lay- Hatfield Sandstone Member: ers of :ferruginous limestone or ironstone 22. Sandstone, light-gray, fine-g:Pained, iron -concretions ------320 stained 110-140 ft above base; forms mas- USGS D3319, from 15 ft below top: sive ledge______140 Inoceram1ts sp. 21. Shale and siltstone interbedded, dark-gray; Bamtlites sp. (weak flank ribs) increasing amounts of thin beds of sand- USGS D3318, from 150 to 170 ft above stone in upper part______18 base: 20. Sandstone, dull-gray, massive, very resistant; Inoceram'lts cf. I. balticzts Boehm contains abundant scattered round phos- Baculites sp. (weak flank ribs) phate nodules and baculites at top ______30 Placenticet·as sp. USGS D3322: USGS D3317, near base: Inoceramus .sp. Inoceranws cf. I. balticus Boehm Ostrea sp. Baculites sp. (weak flank ribs) Baculites asperiformis Meek Pla cent-iceras sp. 11. Shale, gray, sandy and silty, poorly ex-posed._ 165 Total Hatfield Sandstone Member___ _ 188 Total lower unnamed member ------655 Middle unnamed member : 19. Shale, dark-gray; contains large orange weathering limestone concretions in mid- Tapers Ranch Sanclstone Member: dle; some thin sandstones in lower 5 ft____ 152 10. Sandstone, pale-yellow,ish-gray, very fine USGS D4770, from concretions: grained to fine-graincil, clayey, soft; a few Oxytoma nebraseana (Evans and thin ledge formers. Some beds are. glau- Shumard) conitic ------240 Ostrea sp. Modiolus sp. 9. San-dstone, brownish-gray, very fine grained Baettlites asperijo1·mis Meek :to fine-grained, thin-bedded ; clayey and Hoploseaphites n. sp. .soft in middle; ·contains ·a scattering of 18. Sandstone,_ gra:y, fine-grained to very fine dark chert granules and pebbles to 0.1 ft in grained ; clayey and soft in lower ·part, diameter. Some beds are very glauconitic__ 60 cleaner and harder in upper 6 ft; contains Ophiomorpha ------30 Total Tapers Ranch Sandstone 17. Siltstone and shale, gray; weathers yellow- Member ------300 ish gray ------80 16. Sandstone, pale-yellowish-gray, fine-grained; ... , .ridge forming for the most part ; lower 80 Total Haysback Mountains For- ft ·and intervals 80--95 -and 105-120 ft above mation ------2,265 base are soft and may contain some .shale. ~s.andstone in the interval 35-55 ft ~bove Steele Shale (part) : the base is clayey .and forms a topographic 8. Shale, dark-gray; conta.ins a few very fine depresSion ------132 grained thin sandstone beds; unit is transi 15. Shale, dark-gray ------235 tional into •the overlying sandstone. Lower 45 ft contains several discontinuous ledges Total middle unnamed member------629 of tan-weathering silty limestone with many crushed baculites______328 O'Brien Spring Sandstone Member : 14. Sandstone, gray, very fine grained, clayey; USGS D3316, from limestone concre- upper half massive and very concreti-onary, tions 60 ft above base: top iron cemented and rarely exposed ____ 145 Bac1tlites sp. (·smooth) USGS D3321, from 75 ft a.bove lYase: 7. Shale and siltstone interbedded, very da1rk Baculites obt1tSWJ Meek gray; contains large septa·rioan concretions_ 95 USGS D3320, from 5 ft above base : 6. Sand:stone, grayish-green, very glauconitic, Inoceramw~-sp. hard; contains a scattering of dark chert Bacttlites aff. B. obtusus Meek Total O'Brien Spring S.andstone granules ------2 5. Sandstone, greenish-gray, very fine grained., Member ------145 glauconitic, clayey------105 HAYSTACK MOUNTAINS FORMATION 19 Jlcfc1·enec sect'i,on of the Ilaystack, Mountains li'o1'1nat-ion-Con. Princi.pa.l 1'Cferencc section of the llatficl(l Smulstonc Mcntbe1· of tho II etystetclv M omttains F01'1nat-ion-Continued Steele Shale (part)-Continued Feet 4. Shnle, mostly coYered; contains some massive Haystack Mountains Formation-Continued ~iltstone nenr nnd nt the top______870 Upper unnamed member-Continued Feet USGS D3315, from shale 330 ft above 47. Siltstone, pale-yellowish-gray, laminated, car- base: bonaceous; contains many burrows______4 bwce1·am.'ns cf I. 1n'OX'lnws 'luomey 46. Shale, brownish-gray, flaky ; contains iron- Bac1tlitcs aqud,lacns·is Reeside stone concretions------5 ~·· 3. Snncl,stone, gt-eenish-gray, fine-grained with 45. Sandstone, pale-yellowish-gray, fine-grained; some Yery 1ine grained beds ; thin-bedded weathers light gray; contains large Ophio- ~ becoming massive in upper part; contains 1no1·pha ------2 :.l. nbnnd'ant trails nnd ripple murl\:S on bed 44. Shale, like unit 46------4 cling planes. Capped by a 5-ft-thick bed of 43. Siltstone, like unit 47------5 bnnded silty limestone______80 42. Shale, lil\:e unit 46------10 2. Covered; nppears to be shale______125 41. Siltstone, like unit 47------2 l. Sn ndstoue, pnle-yellowish-g·ray, very fine 40. Shale, brown, carbonaceous______1 grained, thin-bedded; capped by a 5-ft- 39. Siltstone, light-brown, carbonaceous, lami- thick bed of banded silty limestone______55 nated; contains burrows in upper part____ 9 38. Shale, reddish-brown to black, carbonace- Total Steele Shnle measured ______1, 660 ous ------4 Prinoipal 1'Cference scct,ion of the Ilettficl(l San(lstonc Membc1· 37. Sandstone and siltstone, interbedded, light- of the Haystack Mounta-ins Ji'onnat'ion yellowish-gray, very fine grained, ripple- [Mcnsurcd by .T. H. Gtll nnd G. A. Bergmnn, August 1967, with plnne laminated ------5 tnblc null J"ncob's stnlf. :n•osslls identified by W. A. Cobbnn. Measured 86. Shale, olive-gray, poorly exposed; contains 011 the west side or Hn,tfleld dome in the NE~~NEY.t sec. 18 nnd in the ironstone concretions______15 center nnd N\Vl/.tNW.I/.~ sec. 17, 1'. 1!l N., R. 88 W., Cnrbon County, 35. Shale, blacl\:, lignitic______1 Wy,o. (Brltlgcr Pnss :1'5-mlnute qundrnnglc), Ioc. 2, fig. 1.] 34. Sandstone, light-gray to brownish-gray, medi- Allen Ridge l!"'ormation: um-grained, slightly carbonaceous______5 64. Sandstone and shale interbedded; lenticular 33. Sandstone, pale-yellowish-gray, fine-grained; ridge-forming units deposited in a fluviatile contains Ophiomorpha______8 environment; thiclmess not measured. 32. Shale, reddish-brown, carbonaceous, poorly Hnystnck Mountains ll'o.rmation: exposed ------11 !~ • Upper unnamed member: 03. Snnclstone, pale-yellowish-gray, fine-grained, 31. Sandstone, like unit 33------6 thin-bedded; upper part weathers light 30. Sandstone, light-gray, medium-grained; con- tains abundant oysters______2 gray; contains large orange-weathering ..... 29. Shale, olive-gray______3 snnclstone concretions in lowe.r part_ ___ _ 17 02. Shale, gray, sandy------15 28. Shale, dark-brown, carbonaceous______2 61. Sandstone, pale-yellowish-gray, fine-grained, 27. Siltstone, black, coalY------1 thin-bedded; contains 01Jhiomorpha ______2 60. Shale, gray; contains sandstone laminae ___ _ 8 Total upper unnamed member______374 59. Snndstone, like unit 6L ______2 58. Shal~ graY------14 Hatfield Sandstone Member: 57, Sandstone, like unit 6L ______2 26. Sandstone, pale-yellowish-gray, fine-grained; 56. Shale, gray; contains some thin beds of sand- weathers yellowish gray to light gray; stone; poorly exposed ______22 lower 20 ft in . beds 0.5-2 ft thick ; upper 55. Snndstone, pale-yellowish-gra;\T, very fine part forms massive cliff with a slight re grained to fine-grained; in beds 0.2-2 ft entrant 45 ft from top. Contains shale ... thick in lower part becoming massive in pebbles and Ophiom01'1Jha______97 upper part; contains a lnyer of pale-oxange 25. Shale, gray, sanely, poorly exposed______30 snndstone. concretions in lower part______75 24. Sandstone, like unit 26, thin-bedded______30 54. Shale, olive-gray, poorly exposed ______40 23. Sandstone and shale ; weathers yellowish G3. Sandstone, pale-yellowish-gray, fine-grained; contains 01Jhiomo1'1Jha ______1 gray ------10 ~· 52. Shale, olive-gray------1 Total Hatfield Sandstone Member___ 167 ~· 51, Sandstone, like unit 53; contains abundant 01Jhiomorpha and iron-cemented shale Espy Tongue of Hale ( 1961) : pebbles ------34 60. Shale, olive-gray; contains thin-shelled 22. Shale, gray, sandy------65 ·- oysters ------23 21. Limestone concretion; weathers orange_____ 1. 5 49. Sandstone, like unit 53 ______5 USGS D6363: 48. Shale, olive-gray to brownish-gray; contains B acuUtes sp. ironstone concretions ______8 20. Shale, grayish-brown, flaky______20 20 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Principal refet·ence section of the Hatjielcl Sandstone Member Principal reference section of the Hatfield Sandstone Member of of the Haystack Mountains Formation-Continued the Haystack Mountains Formation--Continued Haystack Mountains Formation-Continued Steele Shale (part)-Continued Espy Tongue of Hale (1961)-Continued Feet 6. Shale, gray, poorly exposed; contains at top 19. Shale, grayish-brown, flaky; contains sand- tan-weathering silty limestone concretion stone laminae in upper 2 ft______15 0.5 ft thick and 1.5 ft in diameter______150 USGS D6362: 5. Shale, gray, with thin laminae of very fine Ostrea albertensis Landes grained sandstone; contains at top a 18. Sandstone, yellowish-gray, very fine grained, layer of calcareous sandstone concretions lower 25 ft clayey and friable; contains 6 0.5 ft thick and 1.5 ft. in diameter. Unit is layers of orange-weathering sandstone con equivalent to the top of the O'Brien Spring cretions 2 ft thick and 6 ft in diameter. Sandstone Member of the type Haystack Upper 30 ft is glauconitic and contains Mountains Formation and to Cow Creek iron-cemented nodules with fossils______55 Member of the Steele Shale of Hale USGS D6361, from top of unit: (1961) ------35 Calcareous worm tube USGS D6359, from sandstone concre- Inocerwrntts sp. tions: Ostrea t·usselli Landes Calcareous worm tube JJJthmocardi1tm u.rswniense Landes Inoceramus sp. Oymbophora sp. Oymbophora cf. 0. holmesi (Meek) Baculites cf. B. asperiformis Meek Baculites obtusus Meek 17. Shale, gray, sandy; weathers light gray ___ _ 25 4. Shale, gray, sandy; contains thin sandstone 16. ·Sandstone, pale-yellowish-gray, fine-grained ; laminae, a few gray limestone concretions, ...... weathers light brown ______6 and at top a 0.2-ft-thick bentonite bed __ _ 20 USGS D6360, from base of sandstone : 3. Bentonite and yellow fibrous calcite ______1 4· N ucttla? sp. 2. Shale, gray, slightly sandy, poorly exposed __ 100 Modiolus sp. 1. Sandstone and shale interlaminated ; forms ~ Orenella n. sp. siDall ridge------30 Ethmocardium ursaniense Landes Oymbophora sp. Total Steele Shale measured 15. Shale, gray, sandY------19 (.rounded) ------510 14. Sandstone, pale-yellowish-gray, very fine grained; capped by a 3-ft-thick bed of ROCK RIVER FORMATION medium-grained crossbedded sandstone containing abundant Ophiomorpha ______12 TYPE SE'CTION AND DISTRIBUTION 13. Shale, dark-gray, flaky ______17 12. Sandstone, pale-yellowish-gray, very fine The Rock River Formation of the Mesaverde Group grained, ripple-laminated; contains at base is named herein for exposures in the SE% sec. 8, SW14 siltstone concretions 1.5 ft thick and 1.5 ft sec. 9, and NW14 sec. 16, T. 20 N., R. 76 W., about 2 in diameter------21 11. Shale, gray, fl'aky; weathers light gray to miles southeast of the town of Rock River, Albany pale yellowish gray------35 County, Wyo. The Rock River Formation is mainly confined to the Laramie Basin and consists of alternat Total Espy Tongue of Hale ( 1961) _- 291. 5 ing beds of hard and soft fossiliferous sandstone of marine origin~ The formation is generally poorly Deep Creek Sandstone of Hale ( 1961) : exposed and about one-third of the formation is con 10. Sandstone, pale-yellowish-gray, fine-grained, ·cealed at the type section. The covered intervals prob- thin-bedded; weathers yellowish gray to dusky yellow in lower part and light gray ably contain nonresistant sandstone, but they might to light brown in upper part; contains a consist of soft sandy shale. few burrows------40 Darton and Siebenthal (1909, p. 36-37) first described these beds in the Rock River area and related them to Total Deep Creek Sandstone of Hale the lower part of the Montana Formation. Equivalent (1961) ------40 rocks in the southern part of the Laramie Basin were Total Haystack Mountains Forma- called the Mesaverde Formation (Darton and others, tion (rounded)------870 1910, p. 10). Steele Shale (part) : The Rock River Formation crops out beneath the 9. Shale, gray, upper part sandy------100 Pine Ridge Sandstone and overlies the Steele Shale 8. Bentonite, light-greenish-gray, nonswelling__ 1 along the west margin of the Laramie Basin. The for 7. Shale, gray, poorly expos.ed______75 mation grades eastward into the marine Pierre Shale ROCK RIVER FORMATION 21 nnd does not occur east of the Laramie Range. West (Stanton and J(nowlton, 1897, p. 138-141) identified ·- ward, the Rock River Formation grades into the dom many mollusks from rocks now included in the Rock inantly nonmarine rocks of the Allen Ridge Formation. River· Formation. l\1ost of these (with their names up One or more thin tongues of the Rock River Formation dated) and many others are listed in the type section. can be identified in the upper part of the Allen Ridge The fossils reveal that the lowest part of the Rock Rive:r in the southeastern part of the Carbon Basin. lies in the :uppermost part of the zone of Baculites per·· plexus, and that the formation extends up through the LITHOLOGIC CHARACTER zone of Didynwceras stevensoni and probably a little The Rock River Formation consists of soft sandstone higher. One very fossiliferous sandstone (unit 22 of type n.nd a few beds of soft sandy shale deposited in a marine section) contains Trigonia and other fossils characteris environment. The sandstone weathers light gray to tic of the Gulf Coast Cretaceous. light brown and is generally very fine to fine grained AGE AND CORRELATION and thin bedded to massive. Locally, the sandstone is sha.Iy and crossbedded. Large brown-weathering fossil The Rock River Formation is of Judith River and iferous sandstone concretions are abundant in some beds. early Bearpaw age. It correlates with about the middle These concretions are harder than the enclosing rocks part of the Pierre Shale to the east and with the upper n.nd forn1low ridges where they are numerous. The for part of the l\1itten Black Shale l\1ember, the Red Bird mation is generally poorly exposed, except for the Silty l\1ember, and the lower part of the lower unnamed harder concretionary layers. member of the Pierre Shale in the southern Black I-Iills (Gill and Cobban, 1966a, pl. 4). The Rock River is THICKNESS equivalent to the Parkman Sandstone Member and over The maximmn known thiclrness of the Rock River lying unnamed marine member of the Mesaverde For Formation, 1,565 feet, is at the type section. The forma Ination in the western Powder River Basin (table 1). It tion has not been measured at other localities, but it correlates and intertongues with the Allen Ridge For apparently thins to the east and south. This thinning mation in t)le Hanna and Carbon i Basins and is accompanies a facies change from shallow-water marine equivalent to the lies Formation of northwestern sandstone to deeper water marine shale. Colorado. TYPE SECTION ··)-- RELATION TO ADJACENT FORMATIONS The type section of the Rock River Formation was The basal sandstone of the Rock River Formation measured by G. R. Scott and W. A. Cobban, and fossils grades into the sandy shale of the underlying Steele collected from the formation were identified by Cobban Shale. The contact between the two formations is select and N. F. Sohl. A description of the type section follows. ed where the rocks are dominantly sandstone above and dominantly shale below. The Rock River Formation Type section ot the Rock Rive1· Formation grades laterally eastward into marine shale of the Pierre [l\Ieasured with a Jacob's staff by G. R. Scott and W. A. Cobban, May 1957. l\:leasured about 2.5 miles southeast of Rock River tn the S% and westward into mainly nonmarine rocks of the Allen N% and NE:JA,SElJI, sec. 8, NW:JA,NW:!4SW1JI, sec. 9, and NW:I4 Ridge. NWlJI, sec. 16, T. 20 N., R. 76 W., Albany County, Wyo. (Rock River The Rock River Formation -appears to be overlain un 7%-miruute quadrangle), loc. 8, fig. 1.] conforinably by nonmarine rocks of the Pine Rirlge Pine Ridge Sandstone : Sandstone. In the Rock River area, we have little evi 41. Sandstone, whitish-gray, fine-grained, massive; dence to indicate an angular unconformity at the base forms conspicuous tree-covered bluff. Not t· measured. of the Pine Ridge, but Davis (1966) had sufficient da.ta Rock River Formation : Feet from this area to propose a disconformity. Gill and Cob 40. Concealed ------3~ ban ( 1966b) described a widespread unconformity at 39. Sandstone, light-gray, soft; in massive beds the base of the equivalent Teapot Sandstone Member of separated by darker shale partings______140 the Mesaverde Form·ation in northern 'Vyoming, and USGS D1390, from 60-90 ft above base: ~· Inoceramus sp. Reynolds (1966, 1967) has reported an unconformity at Ostrea russeZli Landes (bored) the base of the Pine Ridge Sandstone nlong the east 38. Sandstone, light-brown, soft, massive; contains margin of the Great Divide Basin. some harder concretionary shaly sandstone that weathers darker brown. A few FOSSILS Ophiomorpha ------30 37. Sandstone, gray, soft, shaly; uppermost few Marine invertebrate megafossils are abundant at feet harder and somewhat carbonaceous; several levels in the Rock River Formation. Stanton some parts of unit concretionary______103 367-863 0-70--4 ,' 22 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 1'11PC section of the Rock River Formation-Continued Type section of the Rock River Formation-Continued Rock River Formation-Oontinued Feet Rock River Formation-Continued Feet 36. Sandstone, light-brown, soft; contains darker 32. Sandstone, like unit 33 ; contains gray- and brown-weathering concretionary s·a.ndstone brown-weathering sandy fossiliferous lime- and, at top, a ridge-forming bed of closely stone concretions. Thickness estimated______30 spaced sandstone concretions 1-2 ft thick and USGS D1387: as much as 8 ft in diameter, commonly M icrabaoia americana Meek and crowded with large Inoce1·am.us ______Hayden 61 ~-· USGS D1391, from top of unit: Calcareous worm tubes Membraniporoid bryozoan (attached Echinoid fragment Dysnoetopora demissa (White) to Inoceramus) Websteria-like bryozoan Inocerwnws cf. I. shikotanensis Nagao Pyriporoid bryozoan (on inocerams and Matsumoto and ammonite living chambers) BacuUtes sp. Solemya n. sp. USGS D1389, from rest of unit: Perrisonota sp. Inoceramus oonvea:us Hall and Meek Nucula cf. N. pla'fltimarginata Meek Ostrea sp. and Hayden TeZlina sp. Ntteula (Pectinucttla) sp. Ba.cuUtes sp. Yoldia? cf. Y.? evansi (Meek and Placenticeras sp. Hayden) Eutrephoceras sp. Nemodon sulcatinus (Evans and Opkiomorpha sp. Shumard) ReptiUan hones Limopsis sp. Gervillia aff. G. recta Meek and 35. Sandstone, light-gray and light-brown, very fine Hayden grained, soft; contains closely spaced large Inoceramus convea:ttS Hall and Meek dark-brown-weathering fossiliferous sand Pteria linuuaetormis (Evans and stone concretions that are commonly 3-4 ft Shumard) thick and 8-10 ft in diameter. Unit forms a Oa:ytoma aff. 0. nebrascana (Evans conspicuous ridge ______10 and Shumard) USGS D1388, from concretions : Ostrea cf. 0. plu-nwsa Morton Membraniporoid bryozoans Syncyclonema kallii Gabb _.., (on inocerams) Oklamys nebrascensis Meek and Inoceram~ts convea:us Hall and Meek Hayden Pteria linuuaetormis (Evans and A.na.timya n. sp. Shumard) V etericardia? sp. Tenea circularis (Meek and Hayden) Ostrea cf. 0. russelli Landes Ottspidaria cf. 0. moreauensis (Meel{ Ostrea cf. 0. plumosa Morton and Hayden) Oymella montanensis (Henderson) Ouspidaria cf. 0. variabilis Warren Luoina sp. Oymbopkora sp. Tellina sp. Dentalium cf. D. pauperculttm Meek Oymbophora sp. and Hayden Gonioohasma sp. Dentalittm? sp. Drepanochilus nebrascensis (Evans A.cmaea occidentalis (Hall and Meek) and Shumard) ? A.tira? nebrascensis (:1\feek and Euspitra? sp. Hayden) Serritusus n. sp. Drepanochiltts nebrascensis (Evans A.nisomyon borealis (Morton) and Shumard) Baculites criolcmayi Williams Euspira obUquata (Hall and Meek) Didymooeras stevensoni (Whitfield) Serritusus aff. S. dako·ten~is (Meek Solenooeras n. sp. and Hayden) Hoploscaphites sp. Oryptorhytis cheyennen~is (Meek and Placentioeras intercalare M~ek Hayden) Crustacean N onactaeonina attenttata (Meek and Fish scales and teeth Hayden) Carnivorous dinosaur tooth Oligoptycha sp. 34. Sandstone, light-brown, soft, very fine grained__ 20 A.cteon sp. 33. Sandstone, gray, very fine grained, soft, shaly; A.nisomyon borealis (Morton) uppermost 1-2ft is harder and forms a low Baculites criclcntayi Williams ridge ------24 Didymoceras stevensoni (Whitfield) ROCK RIVER FORMATION 23 'l'·mw scct·ion ot the Jl,ock River Formation-Continued Type section ot the Rock Rive1· Formation-Continued noel' Ri,·er ]!"'ormation-Continued Rock River Formation-Continued 32. Sandstone, like unite 33-Continued 22. Sandstone, gray, soft, massive-Continued USGS D1387-Continued USGS D1400, from throughout unit: SoZenoceras n. sp. Calcareous worm tubes (attached to Hoploscaphites n. sp. baculites) Placenticeras intercalare Meek Dysnoetopo1·a demissa (White) Crustacean Feet N cnwdon n. sp. I Pinna lakcs·i i' 31. Concealed. Thiclmess estimated------280 White 30. Shale, gray, •silty; contains hard gray limestone Inoceramus cf. I. convca:us Hall and concretions at .tOP------8.5 Meek 29. Sandstone, dark-olive-brown, fine-grained; con Ptcria linguactormis (Evans and tains tan-weathering clay pebbles and forms Shumard) n lo\v ridge ______3 Oa:ytoma cf. 0. neb1·ascana (Evans and 28. Sandstone, soft, massive; weathers tan ___ ., ___ _ 5 Shumard) 27. Bentonite, light-gray; contains tan fibrou~ Ost1·ea russelli Landes Pycnodonte cf. P. nwtabilis (·Morton) calcite ------~---- .5 T1·igonia cf. eufaulensis gabbi 26. Sandstone, soft, massi\'e; weathers tan ______80 '1'. Stephenson 25. Snndstone, dark-olive-brown, •fine-grained, more Syncyclonema? sin"pUciu.s Conrad? or less thick bedded and firm ; forms a ridge __ 4 Lin'!Jatula sp. 24. Sandstone, soft, massive; weathers tan ______57 1lnatimya dodclsi, Henderson 23. Sandstone, brownish, soft, massive; contains Cymella montanensis (Henderson) .~ large darker brown weathering fossiliferous Astarte sp. snndstone concretions commonly 2 ft thick Protodonaa: n. sp. and G ft in diameter. Uppermost 1ft, which is Ethm.ocardi1tm n. sp. hnrd and ledge forming, locally contains clay Legmnen ellipt-icu.m Conrad pellets ------28 Tenea parilis Conrad? USGS Dl401, from throughout unit: Tellina cf. T. munda Stephenson Calcareous worm tube (attached to Lc.ptosolen sp. haculite) Scnis sp. Dysnoet01JOra clem.issa (White) "Oorbula" n. sp. Pte1·ict Unguaet01·nllis (Evans and DentaZium sp. Shumard) Baculites n. sp. Oa:ytoma sp. Didymoceras sp. Ost?·ea 1·1tsselli Landes (common in AnapachycliscttS n. sp. upper few feet of unit) .M enuites n. sp. Syncycloncma? s·im·1Jlicius Conrad? PZacenticeras n. sp. Molliolus sp. Ophiomorpha Cymella montanensis (Henderson) Fish bones, scales, and teeth Feet ,\.. Ethmocm·clhtm Sl>. Reptilian bones Lcgumen elH1Jt-icmn Conrad 21. Sandstone, light-gray; forms series of small Cymbophom sp. ledges of crossbedded sandstone separated by Dt·c]JanochUus sp. (immature) shaly sandstone. Top 2 in. is a conglomerate A1Thoges (Lat-ietla) aff. A. (L.) lobatct- of phosphatic pebbles and oyster fragments in 'Vade tan concretionary siltstone______14.2 E1tspi1·a sp. 20. Sandstone, gray and tan, soft______16 Gra]Jldclnla cf. G. allenri (White) 19. Sandstone, gray, soft; at top are brownish-gray Son·if·ltS1tS '? sp. bard silty concretions about 1 ft ·thick ______74 •· ElU]JSosca]Jha sp. 18. Sandstone, gray and tan, fine-grained, soft ; con 0 UgOlJ tycha sp. tains harder limonitic layers------32 BacuZites n. sp. 17. Sandstone, light-gray, fine-grained, soft; lower Diclymoceras sp. part thin bedded and upper part more mas Oa:ybelocc1·as sp. sive; contains harder masses of tan-weather Pla.ccnt-icc?·a.s sp. ing concretionary sandstone and some brown 22. Sandstone, gray, soft, massive; locally contains carbonaceous partings______162 large brown-weathering sandstone concre USGS D1399, from 95-110 ft above base: tions usually 2 ft thicl' and 4 ft in diameter Inoceramus suboom.m·cssus Meek and and smaller brownish--gray very fossiliferous Hayden sanely concretions. 'rop is locally baculite Ostrea cf. 0. subtrigonalis Meek and ·bearing brown-weathering concretions con- Hayden taining comminuted pelecypods ______27 Shark teeth 24 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. .-4 Type section of the Rock River Formation-Continued Type section of the Rock River Formation-Continued Rock River Formation-Continued Feet Steele Shale (part)-Continued .~· 16. Siltstone, gray; contains large tan-weathering 3. Shale, dark-gray-Continued silty poorly fossiliferous limestone concre- USGS D1394-Continued tions ------3 Inoceramus subcompress'lts Meek and 15. Concealed. Thickness estimated ______150 Hayden 14. Sandstone, tan,, soft, massive; exposed in rail- Bac'ltlites perplea:'lts Cobban Feet road cut------30 2. Shale, dark-gray; contains rusty-weathering 13. Sandstone, tan, soft, massive; contains a few thin shaly, sandy concretions, and tan shaly ·--~ tan-weathering small silty limestone concre- layers of sandstone______30 tions. Bench mark S318 located here______20 1. Shale, dark-gray; contains a few thin layers of ~ USGS D1398, from concretions: shaly very fine grained tan-weathering sand- Inoce1·am1ts ,IJubcompressus Meek and stone ------30+ Hayden " Baculites perplea:us Cobban (transi Total Steele Shale me as u red tional to Baculites gregoryensis (rounded) ------460 'Cobban) 12. Concealed. Thickness estimated ______85 ALLEN RIDGE FORMATION ·,.. 11. Sandstone, tan, fine-grained ______30 PRINCIPAL REFERENCE SECTION AND DISTRIBUTION Total Bock River Formation (rounded)_ 1, 565 Bergstrom (1959, p. 114) applied the name Allen Ridge Form:a;tion to a 1,200-foot-thick sequence of rocks Steele 'Shale (part) : underlying the Pine Ridge Sandstone and overlying the "',-, 10. Concealed. Thickness estimated______75 Steele Sha·le along the northeast flanks of the Hanna 9. Shale, dark-gray ; contains gray limestone con- Basin northeast of Medicine Bow. Bergstrom's de cretions and some baculites------15 USGS D3197: scription consists of -a composite columnar section ac Pyriporoid bryozoan companied by brief remarks regarding.the lithology of MeDlbraniporoid bryozoan the formation. The name was apparently derived from Inoceramus sp. the ridge adjacent to the now-abandoned Allen Station Baculites perplea:us Cobban 8. Shale, dark-gray; contains a few iron-stained on the Union Pacific Railroad ; no topographic feature limestone concretions______85 by this name is shown on the topographic map of the 7. Shale, dark-gray; contains a few iron-stained area ( Saddleback Hills 15-minute quadrangle) . Ac ·-4 limestone concretions and, at top, small cording to Bergstrom, part of the Allen Ridge Form-a masses of "tepee-butte limestone"------27. 5 tion was measured in sec. 9, T. 22 N., R. 79 "\V., which is ·usGS D1396, from top: Pyriporoid bryozoan (in living chaDl near Allen Station, and part was measured in Pine Tree bers) Gulch in sec. 18, T. 23 N., R. 79 W. We were una.ble to Inocera/mus sp. recover Bergstrom's section at these localities, but we Baculites perplea:us Cobban measured a complete section of the Allen Ridge and ad 6. Shale, gray, sandy to silty; contains 7 harder jacent formations along the north and south sides of layers of tan-weathering very fine grained ·-4 shaly sandstone as much as 1 ft thick______72 Pine Tree Gulch in the SlhNE~ sec. 19, T. 23 N., R. 79 5. Shale, dark-gray; contains a few small rusty W., Carbon County (figs.1 and 7, loc. 7) here designated ferruginous concretions and, in upper part, the principal reference section. a thin layer of bentonite with gray fibrous We obtained much the sa.1ne thickness as was reported calcite ------35 by Bergstrom (1,255 compa.red to 1,200 ft), but we dif USGS D1395: fer radica.lly in our interpretation of rock units compos Pyriporoid bryozoans (in living cham- ·• bers) ing the forma.tion. "\Ve found the formation to consist of Inoceramus sp. a lower nonmarine unit of fluviatile sandstone, shale, Baculites perplea:us Cobban and carbonaceous beds about 685 feet thick, .a middle Placenticeras sp. unit consisting of 195 feet of 1narine shale and sand 4. Shale, dark-gray; contains thin rusty ferrugi stone, and an upper unit 375 feet thick consisting domi '-4 nous concretions and sparse layers of tan nantly of rocks of brackish-water origin. Bergstrom ap shaly sandstone______13 parently considered the entire Allen Ridge For1na.tion 3. Shale, dark-gray; contains thin rusty ferrugi- to be nonmarine. nous concretions------80 The Allen Ridge Formation of the Mesaverde Group USGS D1394: Pyriporoid bryozoan is a ,;idespread and distinctive unit that can be recog Membraniporoid bryozoan nized throughout much of south-central Wyoming. It ALLEN RIDGE FORMATION 25 Pine Ridge Allen Ridge Formation Haystack Mountains Sandstone Formation ...._ FIGURE 7.--Allen Ridge Formation nt its principal reference section in Pine Tree Gulch in the NEJA sec. 19, T. 23 N., R. 79 W., Carbon Uo1mty, Wyo. Contact with the underlying ruassi>e sandstone of the Haystack Mountains Formation is shown on the right SJide of the photograph, and the contact with the overlying Pine Ridge Sandstone is shown on the extreme left side of the photograph. I. is the main ridge-forming part of the Mesaverde around the margins of the Carbon and Hanna Basins and the Rawlins uplift, and it is an important part of the Mesa verde along the east margins of the Great Divide and Washakie Basins. In the northwestern part of the Laramie Basin, the Allen Ridge intertongues on a grand scale with marine sandstone and shale of the Rock River Formation. At Rock River the facies change is com plete, and the entire sequence of beds equivalent to the Allen Ridge Formation is represented by rocks of the Rock River Formation. The Allen Ridge Formation is not present elsewhere in the Laramie Basin. LITHOLOGIC CHARACTER At its principal reference section, the Allen Ridge Formation is a diverse lithologic unit. The lower part of the formation is a thick sequence of ridge-forming fluviatile sandstones and shales that weather distinctive shades of brown ftnd rusty brown. These colors contrast FIGuRE 8.-0utcrop of an unnamed marine member in the upper sharply with the yellowish-gray-weathering sandstones part of the Allen Ridge Formation at Pine Tree Gulch, in the NW1,4SEJA sec. 19, T. 23 N., R. 79 W., Carbon County, Wyo. of the underlying Haystack Mountains Formation. The fluviatile sequence is about 685 feet thick and contains fire nonresistant, poorly exposed, and generally form a many beds of carbonaceous shale and numerous iron valley. They were apparently deposited close to the sea, stone concretions but very little coal. perhaps in a lagoon or in some other brackish-water This nonmarine sequence is interrupted in the eastern environment. The marine member and the overlying part of the Hanna Basin by marine strata which are marginal marine beds change character in a west and included in the Allen Ridge, but which connect laterally northwest direction because they grade into nonmarine with the Rock River Formation (fig. 2). This unnamed beds typical of the lower part of the Allen Ridge. marine member consists of 115 feet of fossiliferous mar Along the east edge of the Great Divide and Washakie ine shale and siltstone and 80 feet of marine sandstone Basins, the entire Allen Ridge Format'ion is composed containing abundant 07Jhiomm·pha (fig. 8) . It is over of nonmarine beds, except for a small area west of the lain by reddish-brown-weathering carbonaceous shale, a town of Rawlins, where thin shallow-water marine shallow-water marine sandstone, and a thick unit of sandstones crop out in the upper part of the formation dark-brownish-gray ironstone-bearing shale. These beds (M. W. Reynolds, oral commun., 1968). 367--.863 0-7{}--5 26 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. ~ THICKNESS The second collection, which came from a 5-foot-thic:k: The Allen Ridge Formation ranges in thickness from channel sandstone that crops out 550 feet above the base a featheredge in the northern part of the Laramie Basin of the Allen R.idge Formation in the center of the NE1;4 to 1,255 feet at its principal reference section on the sec. 19, T. 23 N., R. 79 W., is listed in the principal northeast flank of the Hanna Basin; it is as much as reference section. 1,500 feet thick in the Haystack Mountains north of The marine tongue included as a part of the Allen Sinclair; and it ranges in thickness from 0 to about R.idge Formation at the principal reference section con 1,275 feet on the northeast flank of the Great Divide tains abundant marine fossils at 20 and 70 feet above Basin. This variation in thickness is due·in part to uplift the base; these are listed in the section. and erosion before .deposition of the Pine Ridge Sand stone, uplift and erosion in early Lewis time, and pos AGE AND CORRELATIOli sibly in part to depositional thinning. The geologic Inasmuch as the Allen Ridge Formation is domi history of the Upper Cretaceous rocks of this area is nantly nonmarine in most localities, it is difficult to re discussed in deta.il by Reynolds (1966, 1967). late the unit to the Western Interior Late Cretaceous ammonite sequence, except by comparing it with fos RELATION TO A·DJACENT FORM-ATIONS siliferous lateral marine equivalents such as the Rock The Allen Ridge Formation conformably overlies the River Formation. At the principal reference section, the Haystack Mountains Formation. The contact is sharp top of the underlying Haystnck Mountains Formation and is marked by the abrupt change from fine-grained contains Brwulite8 ]Je1•pleayu.s, and we infer that the yellowish-gray-weathering Inarine sandstone below to lower part of the Allen R.idge was probably deposited ~- carbonaceous shale or locally fluviatile channel sand late in the range span of this ammonite. Didymooe1·as stone above. The contact with the overlying Pine Ridge neb1Ytsoen.rse occurs in the lower part of the marine ton Sandstone probably is unconformable. This uncon gue that overlies nonmarine rocks of the lower part of formity is difficult to document at most localities, but the Allen R.idge. A comparison of time-equivalent strata regional stratigraphic and faunal studies strongly·sug at Rock R.i ver shows that these nonmarine beds were gest its presence (Gill and Cobban, 1966b). This un deposited during the range span. of B. gregoryensis and conformity exists on the northeast flank of the Great B. sootti. Divide Basin, as shown by detailed mapping by Rey Similarly, comparisoi1 of the Rock River section with nolds ( 1966, 1967). the Allen Ridge section indicates that the marginal ma Except for minor marine tongues, the Allen Ridge rine.beds above the unnamed marine member were prob ... , Formation is the landward facies of the m·arine Rock ably deposited during, or somewhat later than, the range River Formation that borders it to the east. To the span of Didynwoeras stevensoni. northwest and west the Allen Ridge Formation prob The Allen Ridge Formation is Judith River .and ably merges into the main mass of the nonmarine Mesa early Bea.rpaw in age (Gill and Cobban, 196mt, pl. 4) verde Group. In the southern 'Vind River Basin and in in comparison with the central Montana section. The the Rock Springs uplift, as shown by stratigraphic formation correlates with the Rock River Formation studies, rocks equivalent to the Allen Ridge probably of the Laramie Basin, the Parkman Sandstone Member have been removed by pre-Teapot or pre-Pine Ridge and the lower part of the unnamed marine member of erosiOn. the Mesaverde Formation of the western Powder River FOSSILS Basin, and the lies Formation of the Mesaverde Group Fossils in the nonmarine part of the Allen Ridge For of north western Colorado. 'Ve are uncertain of the cor mation are scarce. Bone fragments were found at a few relation of the Allen R.iclge with rocks of the Mesaverde ·•. localities in the Haystack Mountains, and two collec Group in the R.ock Springs uplift and in the southern tions of invertebrates were obtained from widely sepa .part of the Wind River Basin. rated localities in the Hanna Basin. Invertebrate fossils from the basal part of the Allen Ridge were collected PRINCIPAL REFERENCE SECTION in the S'V1;4SE1;4 sec. 29, T. 24 N., R. 86 W., and were identified by W. A. Cobban as follows: Inasmuch as we were unable to recover Bergstrom's original section ( 1959), we designate the following as USGS D6084: Oampeloma sp. .the principal reference section for the Allen Ridge Tttlotomops cf. T. laevibwwlis Yen Formation. ALLEN RIDGE FORMATION 27 Principal1·etc1·cnce section ot the Allen Ri-dge Formation PrinoipaZ reference section·of the Allen Ridge Formation Continued [1\:lensurcd in July 1067 with planetable and tape by J. R. Gill and R. L. Fleisher. Fossil identifications by W. A. Cobban and N. F. Sohl. Allen Ridge Formation-Continued llensurcd on the not·th nnd south sides of Pine Tree Gulch In the NE1/L sec. 19, '1'. 23 N., R. 79 W., Carbon County, Wyo. (Saddleback Unnamed maTirie member..:....Continued Hills 15-minute quadrangle), loe. 7, fig. 1.] '50. Shale, siltstone and sandstone-Continued USGS D5001, from 70ft above. base: Pine Ridge Sandstone : Serpttla sp. 57. Sandstone, light-gray, fine-grained, high Dysnoetoporoid bryozoan angle crossbeds; contains thin laminae of Inooeramtts cf. I. pertenuis Meek and dark-brown to black carbonaceous shale ; Hayden forms ridge that supports a moderate Oroytoma sp. growth of pine trees; weathers white. Ostrea sp...... Not measured. Syncyclonema sp. Allen Ridge Formation: Pholadomya sp. Upper part: Protocardia? sp. 56. 'Shale, dark-brownish-gray; contains abun Oymella montanensis (Henderson) dant ironstone concretions; poorly exposed Tellina munaa Stephenson on line of section but moderately well Oorbula sp. exposed a quarter of a mile to south along Acmaea? parva (Meek and Hayden) south side of Pine Tree Gulch______180 Acmaea? cf. A. occiaentalis (Meek SQ. S·andstone, yellowish-gray to pale-yellow, fine and Hayden) to medium-grained; weathers in three Oerithioderma? sp. ledges 1-2 ft thick at base, middle, and Tuba.n. sp. top; contains small Ophiomorpha______46 Aporrhais aff. A. biangulata (Meek 54. ·Shale,.medium- to dark-brown~ carbonaceous, and Hayden) flaky, poorly exposed------~------80 Euspira obliquata (Hall and Meek) 53. Sandstone, pale-yellowish-gray, fine- to Gyrodes sp. medium-grained, thin-bedded at base, mas Morea sp. (only apex preserved but sive at top; capped by a 1-ft-thick bed of it belongs in the cancellaria rather brown-weathering sandstone______25 than marylandica species group) 52. Shale, reddish-brown, very carbonaceous, Belliftt8U8 sp. (immature) abundant limonite plates and a few iron- Graphidttla cf. G. alleni (White) stone concretions; sandy in upper part____ 43 Acteon sp. Oligoptycha sp. Total upper part______374 Baculites sp. Didymoceras nebrascense (Meek Unnamed marine member : and Hayden) 51. Sandstone, pale-yellowish-gray, fine- to Placenticeras intercalare Meek medium-grained, lower part ledge forming, Fish scales upper _part soft; contains Ophiomorpha___ 80 50. Shale, siltstone and sandstone, dark-gray to Total unnamed marine member-- 195 dull-olive, soft; sandstone and siltstone laminae are cemented with limonite; poorly Lower part: exposed on line of section but ·well exposed 49. Sandstone, pale-yellowish-gray, fine-grained, n quarter of a mile to south______115 ... ·hard; weathers dark reddish brown; con USGS D5000, from limonite concretions tains a few limonite nodules in lower part 20ft above base : and masses of concretionary-weathering YoZdia·? cvansi (Meek and Hayden) sandstone in upper part______30 NttettZa sp. 48. Shale, light-gray, interbedded with brown Inoce1·mnus aff. I. turgidus Anderson carbonaceous s-hale; contains ·a few light .. Pte1·ia Unqttaeformis (Evans and yellowish-weathering 'beds of soft lenticu Shumard) lar 1Sandstone. A 1-ft-1hick bed of Oroytoma sp. carbonaceous shale at top and a layer of Ost1·ea sp. reddish-brown-weathering ironstone concre-· Goniomya americana Meek and tions 3 ft below top______106 Hayden 47. Sandstone, pale-yellowish-gray, fine-grained, Lttcina sp. crossbedded, lenticular; forms ridge______5 •· Tenea sp. USG-S D4759: - ,... Tellina ntttnda Stephenson Anoaonta propatoris White Oorbttla sp. Plesielliptio sp. Bacttlites sp. Fusconaia? sp. Diclymoceras ct. D. nebrascense .,. . Sphaerittm sp. (:Meel.: and Hayden) V iviparus sp. ... _.,.. ~· 28 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. ... . Pr·incipaZ 1·eference section of the A.Zlen Ridge Forma Pr·indipaZ reference section of the A.Zlen Ridge Forma Uonr-Continued tionr-Con tin ned Allen Ridge Formation-Continued Feet Allen Ridge Formation-Continued Lower part-Continued Lower part-Continued Feet 46. Shale, light- to medium-gray, sandy; oontains 23. Shale, light-gray ; contains thin beds of soft thin lenses of soft sandstone with layers of sandstone and cai'bonaceous shale, soft. A limonite cement and 2 th.in beds of ca.rbo- layer of ironstone concretions 0.8 ft thick naceous ·shale in upper part______45 and 1.5 ft in diameter in middle of unit-___ 15 45. Sandstone, moderate-yellow-brown, fine- 22. Sandstone, pale-yellowish-gray, very fine grained, lenticular; forms ridges; contains grained, thin-bedded ; numerous rusty numerous limonite nodules ______3 'brown .. wea thering limonite-cemented lay 44. Shale, light-gray, sandy; contains numerous ers. Capped by a 1.5-ft-thick bed of hard layers of iron-cemented siltstone or silty reddish ... brown-weathering sandstone______6 konstone. Three 1-ft-thick beds of carbo- 21. Shale, reddish-brown, carbonaceous. Inter naceous •Shale in upper part______29 bedded with light-gray sandy shale; forms 43. Sandstone, pale-yellowish-gray, fine-grained; valley ------35 crossbedded, lenticular; weathers brown 20. Sandstone, pale-yellowish-gray, very fine and forms ridge ______7 grained, thin .. bedded, lenticular; weathers 42. Shale, as in unit 44; contains a few carbo- dark yellowish orange______9 naceous streaks ______21 19. Shale, -as above______30 41. Sandstone, as above ------23 40. Shale, gray and brown interlbedded; in part Total lower part______686 carbonaceous ------59 39. 'Sandstone, pale-yellowish-gray, fine-grained,· Total Allen Ridge Formation ______1, 255 crossbedded, lenticular; forms ridge; con- tains 1.5-ft-th'ic.k :by 3-ft-diameter dark Haystack Mountains Formation : yellowish-orange sandstone concretions at Upper unnamed member: .base ______14 18. Sandstone, pale-yellowish-gray, fine-grained; 38. ·Shale, like unit 40; contains some thin beds forms massive cliff; contains Ophiomor- of soft sandstone ------23 pha ------70 37. Sandstone, like unit 39, except very fine 17. Sandstone and shale intel'bedded ; domi- grained ------5 nantly sandstone in beds 0.1-6 ft thick; 36. Shale, like unit 40, contains ironstone con- shale in ·beds less than 0.1-1 ft thick; forms _.. cretions ------15 valley between 2 cliff-forming sandstones __ 70 35. S·andstone, pale-yellow, very fine grained, 16. S·andstone, pale-yellowish-gray, fine-grained, thin-bedded, soft; numerous layers are ce thin-bedded at 1base to massive at top; mented with limonite ------9 -abundant limonite-replaced shale pebbles in ...... 34. Shale, light-gray to reddisrh-brown interbed lower part; contains numerous partially ded; in part carbonaceous; contains tJhin oxidized small pyrite nodules------70 lenticul,ar beds of .sandstone ______22 USGS D5580, from lower part of unit: 33. Sandstone, pale-yellowis'h-gray, fine-grained, BacuZites perpleams Cobban ~ very lenticular; weathers brown and forms 15. S·andstone and shale; weathers yellowish gray; poorly exposed------175 ... ridge ------3 14. Covered; appears to be dark-gray ·sandy 32. 'Shale, like unit 34------29 -4- 31. Sandstone, like unit 33 ; contains limonite,_ shale ------:.------230 cemented shale •pebbles ______35 Total upper unnamed member ______, 475 30. 1Shale and sandstone inte.rbedded; light-gray 'shale interbedded with reddisih-·brown car Hatfield Sandstone Member: bonaceous shale and lenticular beds of 13. Sandstone, pale-yellowish-gray, very fine reddish.Jbrown-weathering .sandstone. Unit grained, thin-bedded, in ·beds 0.1-0.4 ft capped by a 4-ft-thick 'bed of carbonaceous thick, locally cemented with iron -and con- -~ -· ~shale 73 taining fossils; forms ridge ______55 29. Sandstone, like unit 33; weathers dusky yel- USGS D5579: Pyriporoid bryozoan low ------2 28. Shale, like unit 34; contains ironstone con- Inooeramus suboompressus cretions; soft ______23 Meek and Hayden Baculites asperiformis Meek? 27. Sandstone, like unit 33------3 Hoploscaphites sp. 26. Shale, gray; contains thin ironstone layers __ 2 Placenticeras sp. 25. Shale, dark-brown, carbonaceous------3 24. 8-andstone, dark~yellowish-orange, very fine Total Hatfield Sandstone Member_ 55 grained, thin-bedded ______2 PINE RIDGE SANDSTONE 29 Prino,lpal 1'ete1·enoe section ot the Allen Ridge Forma the exposure on Pine Ridge about, 2 miles southeast of Non-Continued tJhe town of Rock River in !{;he northern part of tih.e I-Iaystacl<: Mountains Formation-Continued Feet Laramie Basin, but they did not measure a section at Middle unnamed member : this locality. The section we measured on Pine E.,idge is 12. Covered; appears to be dark-gray shale __ _ 225 considered in tlus report as the princi paJ! reference sec 11. Sandstone, as above; forms massive ridge __ _ 185 USGS D5578: tion for the unit. In tJhis report we eleV'ate the Pine Inooeranvus sp. Ridge Sandstone from a member of the Mesaverde For Baoulites mclea1'ni Landes mation to a formation in the Mesaverde Group. 10. Covered; appears to be dark-gray shale ___ _ ::l70 The Pine Ridge Sandstone is the most conspicuous 9. Shale and sandstone interbedded, gray, soft, formation in the Mesaverde Group. It is a white to poorly exposed; contains thin beds of coarse-grained glauconitic sandstone with light-gray nonmarine sandstone, more resistant and dark phosphate pebbles 50 ft bE!lOw top __ _ 60 lighter colored than the adjacent forma;tions, and gen USGS D5577, from 50ft below top: erally crops out 'as ·a distinotive tree-covered ridge. The Baculites sp. (phosphatized) formation can be recognized along the west and north 8. Shale, gray, sandy; weathers yellowish gray; margins of the Laramie Basin, t!hroughout tJhe Oarhon poorly exposed------ 280 USGS D5576, float 190 ft above base of and Hanna Basins, and along ·the east flank of the Great unit: Divide Basin. It is exposed on the nortJlu~ast side of the BaouUtes cf. B. molem-"'~i Landes W·ashakie Basin near Rawlins, hut has not been identi 7. Shale, poorly exposed; contains a few thin fied on the ·southeast side of the basin near the Wyoming beds of sandstone ______280 Colorado State line. 6. Covered; appears to be sandy shale ______210 LITHOLOGIC CHARACTER Total middle unnamed member ______1, 610 The Pine Ridge Sandstone in much of south-central _ .... O'Brien Spring Sandstone Member: Wyoming consists mainly of pale-yellowish-gray very 5. Sandstone, pale-yellowish-gray, very fine fine grained to fine-grained sandstone that weathers very grained, clayey, soft in lower part becom- ing slightly resistant in upper part; con- light gray to wihite. It includes beds of light-gray car tains thin beds of sandy shale and sparse bonaceous siltstone, sandy carbonaceous sha.le, and thin limestone concretions; poorly exposed____ 250 beds of impure coal. Many bedding surfaces are stained USGS D4757, from 150 ft above base of or ce1nented with iron oxide. High-angle crossbedding unit: that resembles torrential bedding is a striking feature on Oymbopho1·a holmesi (Meek) 1nany outcrops. Some of the sandstone beds in the forma JJaonUtcs obt1ts1ts (Meek) 4. Bentonite, light-gray, slightly swelling_____ 5 tion are closely jointed. These joints and the adjacent 3. Sandstone, pale-yellowish-gray, very fine rock have been cemented with secondary silica resulting grained, thin-~bedded, soft ; capped by a 0.3- in a raised boxwork pattern on weathered surfaces. ft-thick bed of green glauconitic silica- In most areas, sandstones of the Pine Ridge are fine cemented sandstone______70 grained, except where the formation has cut deeply Total O'Brien Spring Sandstone into the underlying rocks. In these areas the grain size Member ------325 of tJhe Pine Ridge ( oalled Tea pot Sandstone Mmnber of tJhe Mesaverde iby earlier workers) reaches granule Total Haystack Mountains Forma- p~bble conglomerate size (Reynolds, 1967, p. D26). tion (rounded)-·------2, 600 Total Mesa verde Group measured THICKNESS (rounded) ------3,860 The Pine Ridge Sandstone is 83 foot thick rut the prin Steele Shale: cipal reference section (fig. 9). It apparently tluns 2. Shale, medium-dark-gray, sandy______175 toward the east, grading into shallow -'water marine 1. Bentonite, like unit 4; contains a 0.2-ft-thick sandstone. This dhange cannot be observed in the Lara silicified sandstone at ba:se______2 mie Basin !but has been seen in ibhe Teapot Sandstone Men1ber (coextensive with the Pine Ridge) of the PINE RIDGE SANDSTONE Mesaverde For1nation in the southern Powder River TYPE LOCALITY AND DISTRIBUTION Basin. The Pine Ridge Sandstone is as muoh as 450 The Pine Ridge Sandstone wrts designated the upper feet thick in the northwestern part of the Rock Creek 1ne1nber of the ~1esaverde Formn,tion and was na.med by oil field in tlhe northwestern part of the Laramie Basin Dobbin, I-Ioots, Dane, and Hancock (1929, p. 140) fur (Dobbin and others, 1929, p. 140), ·and it ranges in 30 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. The Pine Ridge Sandstone is one of the major regres sive tongues of the Mesaverde Group and represents an eastward retreat of the strand. The formation probably thins and changes eastward, first to a shallow-marine unit and then to a part of the Pierre Shale. Following deposition of the Pine Ridge, the sea again advanced westward, and mud of the Lewis Shale was deposited. In the Laramie Basin, the Lewis rests comformably on the Pine Ridge Sandstone; but in the Oarbon, Hanna, Great Divide, and w·ashakie Basins farther west, the Pine Ridge is conformably overlain by, and interfingers with, coal beds, brackish-water shale, and nearshore marine sandstone. The name Almond Formation is ap plied to these rocks which represent the barrier bar or FIGURE 9.-Pine Ridge Sandstone at its principal reference sec barrier island and lagoonal deposits along the western tion in the NE:t,iSW:t,iNW14 sec. 16, T. 20 N., R. 76 W., Albany shore of the advancing Lewis sea. In the western part County, Wyo. Valley to the right side of the area shown in photograph is cut in the Lewis Shale, and sage-covered slope of south-central w ·yoming, where the uppermost strata to the left is formed by the Rock River Formation. of the Pine Ridge Sandstone interfinger with the basal beds of the Almond, the contact of the two formations is placed between the light-gray-weathering nonmarine tJhickness from 250 feet along the east margin of the sandstone and the overlying yellowish-gray to brown Hanna Basin to about 70 feet in the Kindt Basin south weathering sandstone or dark-gray brackish-w·ater of Sinclair (Davis, 1966, p. 68). shale. The sandstone of the lower part of the Almond, On •the northeast flank of the Great Divide Basin, the although similar to the sandstone of the upper part of Pine Ridge is 60-205 feet thick. Reynolds (1967, p. D24) the Pine Ridge at many localities, commonly contains attributed this variation to depositional thinning, to in burrows of marine and brackish-water organisms. The tertonguing with tJhe generally overlying Almond For shale of the lower palt of the Almond, in contrast with mation, and to local truncation beneath the Lewis Shale. the shale of the upper part of the Pine Ridge, contains Regionally, the Pine Ridge rs a thin widespread unit of brackish-water fossils and generally occurs in thicker sandstone deposited by meandering streams upon an units. uplifted and eroded surface of nonmarine and marine l'Ocks. South of Rawlins, along the east margin of the AGE AND CORRELATION W a;shakie Basin, the Pine Ridge Sandstone has lost its The age of the Pine Ridge has been extrapolated from characteristic blanketlike character and is probably the ages of overlying and underlying marine rocks be represented hy thick channel-filling sandstones that cause only poorly preserved plant fossils have been grade laterally into rocks of Allen Ridge lithology. found in the formation. The youngest marine fossils in the underlying Rock River Formation, from 270 feet RELATION TO ADJACENT FORMATIONS below the top, include Didy11wcem s stevensoni. From The nonmarine Pine Ridge Sandstone is thought to the kno"-n range span of this species at other localities, rest unconformably on the Rock River Formation in the it appears that the uppermost part of the Rock River Laramie Basin an~ on the Allen Ridge Formation in Formation could have been deposited during the time the Hanna Basin. The basal beds of the Pine Ridge fill of the next younger index ammonite, E xiteloceras channels in the underlying rocks at many places, but the jenneyi. relief on this erosion surface can be determined at few The lower part of the Lewis Shale, overlying the Pine localities. Apparently, much of central Wyoming was Ridge Sandstone in the Rock River area, contains Bac subjected to regional uplift and erosion before the depo ulites ?'eesidei. This ·ammonite is separated from E xitel sition of the Pine Ridge Sandstone and the coextensive oceras .ienneyi by, from oldest to youngest, the zones of Teapot Sandstone Member of the Mesaverde (Gill and Didymoceras cheyennense, B. compressus, and B. cu Cobban, 1966b). Local areas of intense pre-Pine Ridge neatus in other areas in the Rocky Mountain region. It is folding and erosion in south-central Wyoming were de possible that the Pine Ridge Sandstone was deposited scribed by Reynolds (1966, 1967), and an unconformable during the time span of these three zones, but it is im relationship between the Pine Ridge and older rocks probable because of the unconformity at the base of the in south-central Wyoming was recorded by Davis (1966, formation. The marine equivalent of the Teapot Sand p. 60-62). stone Member of the Mesaverde Formation in the Po,,- ~- ALMOND FORMATION 31. der River Basin contains B. 'l'eesidei (Gill and Cobban, Principal 1'ete1·ence section ot the P·ine Ridge Sandlltone 1966b, p. B21-B24): vVe believe the. Teapot to be coex Continued tensive with the Pine Ridge and, consequently, that the Pine Ridge Sandstone--Continued Feet Pine Hidge wns deposited early in the time of B. 'l'eesi 7. Claystone, light-olive-gray, carbonaceous, very dei. This would indicate that the Pine Ridge Sandstone silty ------5.0 6. Sandstone, like unit 13, but in beds 1-ft thick; is of middle Bearpaw age (Gill and Cobban, 1966a, contains some yellow iron stain______4. 5 pl. 4). 5. Shale, brown to black, coaly in upper foot______4. 0 The Pine Ridge Sandstone correlates with an un 4. Sandstone, like unit 13, but slightly carbonaceous- 2. 4 named sandstone unit in the upper part of the Pierre 3. Shale, olive-gray, carbonaceous______4. 5 Shale at IIorse Creek east of the Laramie. Bange and 2. Sandstone, pale-yellowish-gray, fine- -to medium- grained, hard; abundant plant and root re- with -an unnamed sandstone and shale sequence below .. the Larimer and Rocky Ridge Sandstone l\1embers of mains ------.8 the Pierre Shaile along the east side of the Front Range Total Pine Ridge Sandstone (rounded)__ 83. 0 in Colorado (Scott and Cobban, 1959, p. 129). It prob Rock River Formation (part) : n,bly nJso correlates wi·th the lower part of the 'i\Tilliams 1. Sandstone, very light gray, very fine grained, soft, Fork Formation of the l\1esa.verde Group in north clayey; becomes dusky yellow at .top______75 western Colorado and with the Teapot Sandstone l\1em ber of the l\1esa.verde Formation in the western Powder Rock River Formation measured______75 River Basin, eastern 'i\Tind River Basin, and Bighorn Basin of 'i\Tyoming. The Pine Ridge Sandstone. prob ALMOND FOR¥ATION ably is coextensive with the upper part of the Ericson TYPE LOCALI.TY AND DISTRIBUTION Sandstone of the Rock Springs uplift; the two :form·a The Almond Formation was first called the "Almo11d tions luwe similar lithologies, and both underlie the coal group" of the Mesaverde Formation by Schultz Almond Formntion. (1907, p. 262) and later called the Almond Formation PRINCIPAL REFERENCE SECTION of the Mesaverde Group by Sears (1926, p. 16). Neither geologist designated ·a type locality nor measured a The following section, measured about 2 n1iles south type section. 'Ve assume that the name was derived east of the town of Rock River in the area. where the from the Almond stage station near Point of Rocks, in formn..tion wn,s named, ·is herein designated the principal the SW1,4 sec. 27, T. 20 N., R. 101 W., Sweetwater reference section. County, Wyo. We measured a section nearby, in sec. 25, ., .. where the Almond is about 585 feet thick and consists of P·rimci.1mZ 1·ctc1·encc scct·ion of the Pine R·idge Sandstone two parts. The lower part, 180 feet thick, consists of (l\Iensured with n .Tncob's stuff by J. R. Gill in June 1968. Measured fluviatile sandstone, shale, and coal. The upper part, nbout 2o/.~ miles southenst of the town of Rock River in the NE~ 405 feet thick, consists of marine shale, shallow-water SWIA,NWlJL sec. l(l, T. 20 N., R. 76 W., Albany County, Wyo. Loc. 8, fig. 1.] 1narine sandstone, and lagoonal or brackish-water rocks. Feet The upper part interfingers with the overlying Lewis ... Lewis Shale: Shale, and the lower part is in sharp contact with the 18. Shale, dark-gray to black; not measured. Pine Ridge Sandstone : underlying Ericson Sandstone. 17. Sandstone, light-gray, very fine grained, very thin The Almond Formation is well exposed along the bedded; contnins some yellow iron .stain______1. 0 flanks of the Rock Springs uplift and extends eastward 16. Shale, reddish-brown, carbonaceous______2 in the subsurface through the Great Div.ide and Wash 15. Sandstone, like unit 17------9 akie Basins. The Almond crops out along the east mar ..... 14. Shale, dfH·k-brown to blacl{, coaly in middle; level of prospect pit------15. 8 gins of these basins and is also exposed in the Hanna 13. Sandstone, pale-yellowish-gray, fine-grained; and Carbon Basins to the east. The Almond Formation forms cliff ; contains high-angle crossbeds and is a sequence of fluviatile, brackish-water, and nea~hore •. weathers light gray; weathered surfaces have marine rocks that conformably overlie the Pine Ridge a boxworl( pattern, in part______20. 5 Sandstone and conformably underlie, and intertongue 12. Coal, blnck, impure------1. 4 11. Shnle, dark-brown to black, carbonaceous to with, the Lewis Shale in south-central Wyoming. coaly------2.0? LITHOLOGIC CHARACTER 10. Sandstone, like unit 13------4. 0 In south-central Wyoming, the Almond Formation 9. Shale, dark-brown, carbonaceous, silty; contains a 1-ft-thick siltstone layer in middle______3. 5 consists of a thick sequence of sandstone, shale, and 8. Coni, blncl{, impure______2. 8 minor coal. Sandstone constitutes one-half to one-third .y. 32 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. of the formation. It is pale yellowish gray to dusky yel rine shale-a lower tongue, 215 feet thick, and an low, weathers various shades of brown, and is very fine upper tongue, 75 feet thick. The remainder of the for grained and thin bedded. Locally, the sandstone con mati~n consists of slightly carbonaceous shale con tains Ophiom.orpha, which is evidence of •a shallow taining abundant ironstone concretions, interbedded water marine depositional environment, and abundant sandstone and carbonaceous shale, and beds of shallow oysters and other fossils from a brackish-water deposi water marine sandstone. About 28 miles northeast of ... tional environment. These sandstone units may repre this area, in the southern Haystack Mountains, the Al sent barrier-bar or barrier-island deposits marginal to mond is about 600 feet thick (fig. 10). Remnants of the Lewis Sea. The formation also contains a few sand marine tongues are represented there by shallow-water stone units probably of fluvial origin. The sandstone marine sandstones and shales containing abundant beds of the Almond seem to increase in thickness and brackish-water fossils. This lithology is described in number seaward (east and southeast). reference section 1 of the Almond Formation. Shale units in the Almond are, in a regional sense, Along the northeast flank of the Great Divide Basin tongues of the Lewis Shale and likewise increase in in the Lamont-Bairoil area, the Almond ranges in thickness and number to the east and southeast. The thickness from 0 to 365 feet. This variation resulted Almond contains two types of shale. The first is dark from depositional thinning on a growing Late Creta gray to olive gray ·and devoid of ironstone concretions ceous fold and from erosion along a local unconformity but, locally, contains limestone concretions with marine at the top of the formation (M. 1V. Reynolds, oral fossils. Units of this shale thin to the west and north commun., 1968). !._ west and regionally are tongues of the Lewis Shale. RELATION TO ADJACENT FORMATIONS The second and more typical type is brownish gray to brownish black, carbonaceous to coaly, and contains Dark-gray-weathering shale and sandstone of ·the many ironstone concretions with abundant oysters and lower part of the Almond are conformable with, and al other brackish-water fossils. This sha.le was probably ternate with, lighter colored sandstone of the upper part deposited in a restricted marine or brackish-water envi of the Pine Ridge Sandstone. In some areas the contact ronment, possibly behind barrier-bars or islands. In the is sharp, and in others it is arbitrarily located within extreme northwestern part of the area, on the northeast gradational rocks. The Almond Formation is generally flank of the Great Divide Basin, fluviatile sandstone and conformable with, and grades laterally into, the partly shale form the basal part of the Almond (M. W. Reyn younger Lewis Shale. This contact is generally placed olds, oral commun., 1968). at the top of a shallow-marine sandstone unit that over lies dark-colored brackish-water and fluviatile beds and THICKNESS underlies a marine shale unit. The Almond Formation The thickness of the Almond Formation varies con in south-central Wyoming was deposited along .the mar siderably in south-central Wyoming. The formation gins of the expanding Lewis Sea, which accounts for generally thins toward the east and southeast. The the large-scale intertonguing of the two formations. thinning results from an increase in number and thick FOSSILS ness of marine shale units and from the nonpersistence, in an eastward direction, of the shallow-water marine The Almond Formation contains 1narine and ·• sandstone units chosen to identify the Almond-Lewis brackish-water faunas. The brackish-water fossils are contact. As the sandstone units beneath the Almond mainly associated with carbonaceous shale and iron Lewis contact pinch out and the marine shale units in stone concretions, but reeflike beds of oysters occur with some of the shallow-water marine sandstones. The the upper part of the Almond thicken to the east and marine fossils are in limestone concretions, within southeast, the contact is selected progressively lower in tongues of marine shale, or in shallow-marine sand the rook sequence. stones. Where the Almond Formation crops out along the At Rock River the part of the Lewis Shale that is northwestern margin of the Laramie Basin, it con equivalent to the Almond of the western areas contains sists of 30-40 feet of interbedded carbonaceous shale, the following index ammonites, from oldest to youngest : shallow-marine sandstone, and lenticular coal. The Al B aoulites reesidei, B. ienfleni, and B. eliasi. Of these mond is about 575 feet thick along the south margin forms, B. reesidei and B. eliasi have been found in of the Hanna Basin near the Elk Mountain anticline. marine rocks of the Almond at several places. B. jen.seni In this area the Almond contains two tongues of rna- has not been reported in the Almond, probably because ALMOND FORMATION 33 • ~... •< ----·~.~ · ~-;;·· - ~~ ... ~ FIGURE 10.-Shallow-water marine sandstones and brackish-water shales in the lower part of the Almond Formation near ref erence section 1, sec. 12, T. 22 N., R. 85 W., Carbon County, Wyo. Dip slope to right is formed by the Pine Ridge Sandstone. Looking east. the rocks representing this fossil zone are of brackish seni, and the early ·part of B. eliasi. The type Almond water origin in much of the area. in the Rock Springs uplift took longer to accumulate; In the southern part of the Hanna Basin, in the it appears to encompass the preceding zones plus the NW1,4SW1,4 sec. 27, T. 21 N., R. 81 W., Carbon County, younger zone of B. baculus. The presence of these fos the following fossils were collected from 280 feet above sils indicates that the Almond Formation is of late the base of the Almond : Bearpaw age (Gill and Cobban, 1966a, pl. 4). USGS D6272: The Almond correlates with the lower unnamed shale Calcareous worm tube member and the Kara Bentonitic Member of the Pierre Solemya? sp. Shale in the eastern Powder River Basin, with the lower Nuou.lana sp. part of Meeteetse Formation of the western Bighorn Yoldia? evans·i (Meek and Hayden) and Wind River Basins, and with the upper part of the Breviarca sp. Inocerarmts sp. Williams Fork Formation of the Mesaverde Group in Orcytoma sp. northwestern Colorado. It also correlates with the lower Ethmocm·dittm sp. part of the Lewis Shale in the Laramie Basin and Anisomyon cent1·ale Meek Bac1tlites reesidei Elias with the upper part of the Pierre Shale east of the Laramie Mountains. Additional fossils are listed in reference sections 1 and 2 for the Almond Formation. REFERENCE SECTIONS AGE AND CORRELATION The two following reference sections were measured The Almond Formation in south-central Wyoming about 11 miles apart and document the southerly (sea was deposited during the time range of three am ward) change in the lithology of the Almond monites, in ascending order, Baculites ?'eesidei, B. jen- Formation. 34 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Refe1·ence . ~l'otal Lewis Shale measured______180 light graY------8 30. Covered; appears to be shale______4 AllllOIId lfOI'JliiH t:iOII : f.i3. Sandstone, yellowish-gray, fine-grained; ce- 29. Sandstone, lil{e unit 38, but contains large ..... mented with iron ; contains abundant oysters-- 4 Ophiomo1·pha ------8 USGS D6310: 28. Sandstone, like unit 38, but thin to medium C·mssost1·en ylab1·a (Meek and Hayden) bedded; forms cliff------~------4 G2. Shale, reddish-brown to yellowish-gray; upper 27. Shale, .brownish-gray, carbonaceous______. 5 2 ft very carbonaceous______9 26. Sandstone, like unit 38, but thin beclclecl to mas- sive; forms cliff______18 Gl. Shale, blacl{, coalY------2 riO. Sandstone, pale-yellowish-gray, very fine 25. Sandstone, light-brown, fine-grained, very thin grained, ripple-laminatecL______4 bedclecl ; contains thin laminae of brownish- 4!). Shale, clark- to brownish-gray, flal{y; contains gray carbonaceous shale______7 n layer of ironstone concretions at 10 and 15 24. Sandstone, pale-yellowish-gray, very fine grained, lenticular______3 ft above base------36 48. Sandstone, pale-yellowish-gray, fine-grained, USGS D6307: Inoceranws sp. soft ------5 47. Sandstone, like unit 48; contains numerous 23. Sandstone, light-brown, very fine grained; oyster shells------2 interlaminated with brownish-gray carbon- USGS D6309: aceous shale; muddled bedding______10 - . Cmssost1·ea ylab1·a (Meel{ and 22. Siltstone, pale-yellowish-gray; very thin bedded Hayden)'! at base to massive at top; contains laminae t.l:6. Sandstone, pale-yellowish-gray, fine-grained ; of carbonaceous shale______10 soft in lower part and more resistant near 21. Claystone, medium-light-gray______2 top; nt 60 ft nbove base are orange-weather 20. Sandstone, like unit 23; weathers light yellow__ 3 ing sandstone concretions 2 ft thick and 4 19. Shale, clark-graY------.5 ft in diameter; contains Ophionwrpha______75 18. Siltstone, like unit 22------. 5 45. Sh11le, olive-gray at base becoming clark gray at 17. Shale, dark- to brownish-gray ; weathers splinterY------2.5 top ------10 44. Snndstone, pale-yellowish-gray, fine-grained, 16. Sandstone, pale-yellowish-gray, fine-grained, thin-bedded; local iron-cemented masses of soft ------3 43. Shale, dark-gray to blacl{, flaky ; contains a sandstone in upper part______10 layer of ironstone concretions at 10 ft above USGS D6306: base and at top______22 Inoceramus oblongus White .... 42. Siltstone, pale-yellowish-gray, ripple-lami- 15. Claystone, dark- to brownish-gray______2. 5 . nated ------10 14. ·Sandstone, yellowish-gray, fine-grained; in beds 41. Covered ; appears to be shale ; weathers yellow- 0.1-1.5 ft thick______11 ish graY------17 13. Claystone, medium-light-gray______1 36 · STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Reference section 2 ot the Almond Fonnation---Continued LITHOLOGIC CHARACTER Almond Formation-Continued The Lewis Shale of south-central \Vyoming consists 12. Sandstone, like unit 14------4 of 2,200-2,600 feet of shale, siltstone, and sandstone. 11. Coal, black, impure______1. 5 Much of the variation in thickness may result from dif Total Almond Formation______446 ferences in opinion as to the placement of the upper and lower contacts of the formation. Both the overlying Pine Ridge Sandstone: Fox Hills Formation and the underlying Almond For ,_ 10. Sandstone, light-brown, very fine grained; in mation intertongue -with the Lewis Shale on a regional beds 0.05--0.1 ft thick; contains abundant car scale. In the northern part of the Laramie Basin, the bonaceous fragments and carbonaceous shale to impure coal laminae; weathers dusky Lewis Shale contains many thick beds of sandstone yellow to light gray______17 that are either tongues of the Fox Hills Formation or 9. Shale, brownish-gray, carbonaceous______7 offshore marine units deposited marginal to the Al · 8. Sandstone, like unit 10------6 mond Formation. In this area, Hyden ( 1965) and Mc 7. Claystone, dark-brownish-gray, carbonaceous__ 3 Andrews (1965) included the nonresistant sandstones 6. Sandstone, like unit 10------4 5. Shale, dark-gray; ironstone concretionary layer of the Fox Hills with the Lewis Shale for mapping. at base______4 \Vhere this procedure was follo'"l·ed, the Lewis Shale 4. Sandstone, like unit 10------13 may contain more than 50 percent sandstone. Sandstone of the Lewis is very fine to medium I, Total Pine Ridge Sandstone______54 grained, thin bedded to massive, and pale yellowish Allen Ridge Formation : gray to brown. It is generally nonresistant, but where 3. Shale, medium-dark-gray to brownish-gray; concretionary, it forms ridges that can be traced for contains se1·eral thin layers of sandstone and many miles (fig. 11). Sandstone units in the lower part siltstone ------24 of the Lewis commonly contain molluscan fossils and 2. Sandstone, pale-yellowish-gray, very fine Ophiomm·pha. The middle and upper parts of the for grained, thin•bedded and ripple-marked. mation contain a distinctive and widespread unit o-f in Weathers dusky yellow to light gray; con- terbedded sandstone and sandy shale that ranges in tains some U-shaped btu'l'OWS------4 1. Sandstone and shale interbedded, not measured thickness from 300 to at least 700 feet. This unit is as and described in detaiL------1, 325 signed in this report to the Dad Sandstone Member of the Lewis Shale. Total Allen Ridge Formation (rounded)_ 1, 350 The shale of the Lewis is dominantly dark gray to Total Mesaverde Group measured olive gray, silty to sandy, and nonresistant, and, locally, (rounded) ------1,850 contains fossiliferous limestone or siltstone concretions. LEWIS SHALE TYPE LOCALITY AND DISTRIBUTION The Lewis Shale was named by Cross and Spencer (1899) for exposures of a thick marine shale near Fort Lewis, east of Mesa Verde National Park in south western Colorado. The Lewis Shale of southwestern Colorado is neither an e~tension of, nor the same age as, the Lewis Shale of south-central Wyoming. The name is retained in Wyoming only because of long established usage in the region. (Seep. 3 and 5.) Rocks assigned to the Lewis Shale are widely dis tributed in Wyoming. The Lewis is recognized in the Laramie, Carbon, Hanna, Great Divide, Washakie, Powder River Basins, eastern part of the Bighorn and FIGURE 11.--.Fossiliferous sandstone concretions weathered vVind River Basins, and around the Rock Springs up from a soft friable sandstone in the lower part of the Lewis •Shale, in the NW% sec. 6, T. 22 N., R. 79 W., Oarbon County, lift. In eastern ·wyoming, rocks equivalent to the Lewis Wyo. These distinctive concretions can be traced along the Shale are in the upper part of the Pierre Shale. entire east side of t'he Carbon and Hanna Basins. LEWIS SHALE 37 A distinctive unit of black shale several hundred feet a reference section of the Dad Member in the NW1,4 thick forms the basal part of the Lewis in the north NE1,4SW1,4 sec. 28, T. 15 N., R.. 91 W ., Carbon County, ern part of the Laramie Basin (fig. 12). The siltstone and determined the thickness to be about 585 feet. The of the Lewis is yellowish gray, nonresistant, and poorly Dad Sandstone Member can be traced northward along exposed. the east margin of the Washakie and Great Divide The Lewis Shale is almost entirely marine in origin. Basins, where it has been mapped as the lower part of The shale of. the Lewis represents a marine depositional the Lance Formation (Love, and others, 1955). Ten environment but may contain a few thin units of brack miles northwest of Rawlins, the Dad is 735 feet thick. ish-water origin. The sandstone in the formation con (See reference section of the Lewis Shale.) tains Ophiomorpha in places and was probably The Dad Sandstone Member of the Lewis Shale is deposited in nearshore marine environments. actually a tongue of the Fox Hills Formation. It can A distinctive unit of interstratified sandstone and be trn.ced from near Rawlins northward along the east shale occurs in the middle and upper parts of the Lewis margin of the Great Divide Basin, where the upper Shale in south-central "'Vyomn1g. In the W'ashakie shale unit of the Lewis grades into sandstone and the Basin, these rocks were called the Dad Member of the 1mderlying sandstone beds of the Dad grade into rocks Lewis by Hale (1961, p. 136-137) and were described of the Fox Hills Formation (M. W. Reynolds, oral n.s follows : commun., 1968). Approximrutely seven miles due west in the Dad area, wells The Dad Sandstone Member occurs throughout the have d1illecl ·a total of 2,300 feet of Lewis 'but di S<:lose a series of Hanna (fig. 13) and Carbon Basins and is a thick unit sandstones and minor shales 1,000-1,400 feet thick which divides of poorly exposed sandstone in the northern part of the the Lewis into upper and lower . hale units. This sanely mem Laramie Basin. The Dad Member probably is a result of ber is here called the Dad member of the Lewis shale for typi cal development in the Union Texas Ga s Company Dad Un'it an uplift in central Wyoming and consequent increase 2 well between 6,385 feet '!tncl 7,805 feet. This well is located in in the amount of sediment deposited in the Lewis Sea. sec. 13, T. 16 N., R. 93 W. In the western part of the Powder River Basin, regres We have examined the Lewis Shale along the east sive deposits of sandstone, shale, and coaly rocks in the margin of the ·washakie Basin and can identify the Dad upper part of the Lewis Shale represent the same tec Sandstone Member in this and adjacent areas. The Dad tonic event that caused deposition of the Dad Sand Sandstone Member is much thim1er where exposed than stone Member. Similar rocks divide the Lewis Shale into in the subsurface at the Dad Unit well 2. We measured two parts in the southeasteri1 part of the Wind River .., FIGURE 12.-Dark shale of the lower part of the Lewis Shale exposed along the Pl-atte River, in the NE:IASW:IA sec. 11, T. 20 N., R. 85 W., Carbon Oounty, Wyo. 38 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. FIGURE 13.-Ciiff-forming sandstone of the Dad Sandstone Member of the Lewis Shale, in the SWI,i sec. 14, T. 20 N., R. 83 W., Carbon County, Wyo. Basin. In this area these rocks are called the Meeteetse is about 2,300 feet thick near Rawlins (see reference Formation (Rich, 1962, p. 469-4 79). Abundant fossils section) , but, where traced north ward along the east from many localities are evidence that the Dad Sand flank of the Great Divide Basin, it thins owing to facies stone Member of the Lewis Shale, the regressive sand changes and nondeposition. Thirty miles north of stone tongue in the upper part of the Lewis of the Rawlins, near Bairoil, the lower part of the Lewis Shale Powder River Basin, and the Meeteetse Formation in is absent because of nondeposition; the upper part the W"ind River Basin were deposited during the range changes facies and is represented by beds assigned to of B aculites grandis. the Fox Hills and Lance Formations (M. W. Reynolds, oral commun., 1968). THICKNESS The thickness of the Lewis Shale is not easily deter RELATION TO ADJACENT FORMATIONS mined at most localities because the formation is poorly The Lewis Shale gradationally overlies the Almond exposed. Rocks of the Lewis Shale are nonresistant, and Formation in the area of this report, except in the the contract with the overlying Fox Hills Formation is Laramie Basin where it rests sharply on the Pine Ridge transitional and poorly exposed. Most previous workers Sandstone. Locally, as in the Lamont area (fig. 1), the .... have included the soft sandstones of the Fox Hills with Lewis Shale rests unconformably on beds as old as the the Lewis Shale (for example, Hyden, 1965; Davidson, Cody Shale (Reynolds, 1966). The Lewis also grades 1966), and this assignment causes the thickness of the into the overlying sandstone of the Fox Hills Forma Lewis to be excessive when compared to its thickness in tion. At this contact, sandy shale of the Lewis merges areas where the Fox Hills is recognized. Davidson gradually into the clayey sandstone of the Fox Hills. (1966, p. 26) reported tha.t the Lewis is 3,900 feet thick Northward and northwestward thinning of the Lewis in the northeastern part of the Hanna Basin. He in is associated with a facies change from marine shale to cluded the Fox Hills in the Lewis, and in this area the the south to nearshore marine sandstone and to fluviatile Fox Hills is more than 700 feet thick. Davidson (1966, deposits to the north. p. 26) also reported that the Lewis is 3,000 feet thick at FOSSILS Mill Creek in the southwestern part of the Laramie Basin, but he included an unknown thickness of the Fox The Lewis Sea sustained a large and varied inverte Hills with the Lewis. Hyden (1965) showed the Lewis brate marine fauna. Large collections of fossils from to be about 2,500 feet thick in the northern part of the many localities show that the Lewis Shale was deposited Laramie Basin, but he also included an unknown thick in the eastern part of the area during the range of six ness of the Fox Hills in the Lewis. successive ammonite zones. These ammonites are listed The maximum thicknesses of the Lewis that we have below, with the youngest species at the top: measured are 2,600 feet on the southeast flank of the BacuUtes clinolobatus Carbon Basin and 2,300 feet on the northwest side of grandis the Hanna Basin. These and other measurements are bacultts eliasi evidence that the Lewis thins from south-central jenseni Wyoming in a north and northwest direction. The Lewis reesidei LEWIS SHALE 39 .... Many other invertebrate fossils were found in asso Principal ?'eference section of the Dad Sandstone M mnbe1· of the ciation with these ammonites, and some of these are Lewis Shale-Continued listed in the reference section of the Lewis. Fox Hill Formation-Continued 14. Sandstone, pale-yellowish-gray, soft; con AGE AND CORRELATION tains local lenses 4 ft thick by 30 ft in di In comparison with the classic Cretaceous section of ameter of light-brQwn-weathering concre- tionary sandstone______40 central Montana, the Lewis Shale of the Laramie Basin .is equivalent to the uppermost Bearpaw Shale, the Fox Total Fox Hills Formation______150 I-Iills Sandstone, and the lower part of the IIell Creek = Formation. The Lewis Sea remained in south-central Lewis Shale : vVyoming after receding from centrall\{ontana; conse Upper pa.rt : 13. S·hale and sandstone interbedded; shale dom quently, the upper part of the Lewis Shale in the report inant; sandstone in thin beds 0.1-0.4 ft area is equivalent to nonmarine rocks of the Hell Creek thick; weathers yellowish gray------110 Formation in centrall\{ontana. 12. Shale, olive-gray, flaky, sandy near toP---- 220 The Lewis Shale correlates with the Meeteetse Formation of the western 'iVincl River and Big Horn Total upper part______330 .. Basins and with the upper unnamed shale member of Dad Sandstone Member : the Pierre Shale in the eastern Powder River Basin 11. ·sandstone, pale-yellowish-gray, very fine (Gill and Cobban, 1966a, pl. 4). The Lewis is equivalent grained, soft ; contains shale pebbles in to the Almond Formation and the Lewis Shale of the lower part and a 0.3-ft-thick bed of platy- Rock Springs uplift and approxim·ately equivalent to weathering siltstone at base______60 10. Shale, olive-gray, sandy; weathers yellowish- the Lewis Shale of northwestern Colorado. gray ------15 9. Sandstone, pale-yellowish-gray, very fine REFERENCE SECTIONS grained, soft ; contains at top light-brown weathering sandstone concretions 4. ft thick Two reference sections are described. One is the prin and 8 ft in diameter------25 cipal reference section for the newly adopted Dad Sand 8. Shale, olive-gray, sandy ; contains a few sand- stone Member of the Lewis, and the other is a reference stone laminae in middle part; weathers section of the Lewis Shale and Fox Hills Formation in yellowish graY------150 the western part of the report area. 7. Sandstone and shale, yellowish-gray, soft; contains local masses of concretionary sandstone 2-3 ft in diameter ______40 Principal ?'Gfcrcncc sect·ion of the DacZ Sandstone Member of the 6. Sandstone, pale-yellowish-gray, very fine Lewis Sha.le grained ; contains some tuberous-shaped [Measured with planetable and Jacob's staff by J. R. Gill and G. A. and cannonball-like concretions as much as Bergman, August 1067. Measured on the south side of Wild Cow 1.5 ft in diameter; forms low ridge______Ct·eek from the SW%,SW%NW% sec. 27 to the NW%,NE%,SW1Jl, 40 sec. 28, ~'. lu N., R. 01 w., Carbon County, Wyo. (Baggs 15-mlnute G. Shale, gray ; weathe.rs yellowish gray; con- ()tlll ·~· 40 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Reference section of the Fow Hills Formation and Lewis Shale Reference section of the Fow Hills Formation and Lewis Shale (including Dad Sandstone .Member) (including Dad Sandstone .Member)-Contlnued [l\Ieasured with planetable and Jacob's staff by J. R. Glll and G. A. Lewis Shale-Continued .Bergman. Fossils identified by W. A. Cobban. Measured. on the north Upper part--continued side of Indian Springs Creek starting in the SW~SW~ sec. 1,3 a.nd ending in the SE%,SE~ sec. 14, T. 22 N., R. 89 W., Carbon County 26. Shale and sandstone; weathers yellowish Wyo. (Rawlins Peak 15-minute quadrangle.)] gray; contains orange-brown-weathering Feet sandstone concretions 5 ft thick and 15 ft Lance Formation : in diameter------55 \- 40. Shale and sandstone interbedded; sand 25. Shale, medium-dark-gray; weathers dark stone beds are thin and lenticular; shale gray; contains sparse gray limestone con- cretions in middle ______beds are carbonaceous------ 30 33 USGS D6334, from 10 ft above base of 24. Sandstone, yellowish-gray to dusky-yellow, unit: fine-grained, soft; contains numerous Oorbiettla fracta (Meek) concretions and Ophiomorpha in upper 39. Shale, dark-brown to 'black, ca~bonaceous 3 part. Probably represents a northward 38. Coal, lignitic, black ______1.2 thickening tongue of the Fox Hills Sandstone ------85 Total Lance Formation measured __ 34.2 USGS D6248: Ora.ssostrea glabra (Meek and Fox Hills Formation: Hayden) 37. Sandstone, pale-yellowish-gray, very fine 23. Shale and s-andstone interbedded, soft; grained, massive; weathers yellowish weathers yellowish graY------55 gray ; contains some concretionary 22. Siltstone and shale interbedded; weathers yellowish gray ; contains local lenslike masses ------33 36. Shale and sandstone intef!bedded, ,soft ; concretionary masses of orange-brown- weathers yellowish gray; contains local weathering siltstone in upper part______81 concretionary ledges of lbrown ... weather- 21. Shale, dark-gray; forms dark band on out ·crop; contains a 0.1-ft-thick bentonite ing sandstone as much as 2 ft thick____ 32 •,A_. 35. Sandstone, pale-yellowish-gray, very fine overlain .by a thin layer of dark-gray grained; contains Ophiomorpha______1 limestone concretions______37 USGS D6333: USGS D6331, from limestone concre- Orassostrea sp. tion: Pholadomya n. · sp. "Inoceramus" fibrosus (Meek and Tancredia 'I sp. Hayden) Ethmocardium n. sp. Baculites sp. Legumen sp. USGS D558S, from this level in the Oymbophora sp. Slh.SWIA, sec. 6, T. 21 N., R. 88 W. : Baculites sp. "Inoceramus" fibrosus (Meek 34. Shale, gray, sandY------8 and Hayden) 33. Shale, dark-brown, carbonaceous------4 Lucina sp. USGS D6332: Baculites cf. B. clinoZobatus Orassostrea sp. Elias 32. Coal, lignitic, impure, black______1 Hoploscaphites sp. 31. Sandstone, pale-yellowish-gray, concretion- 20. Shale, yellowish-gray, very sandy; con- ary at base, soft at top; weathers light tains small limestone concretions at top__ 20 gray ; contains Ophiomorpha______51 USGS D6330: 30. Sandstone and shale, interbedded in equal Baculites sp. amounts, soft; weathers yellowish gray_ 31 19. Shale, medium-gray; weathers light .gray; 29. Sandstone, pale-yellowish-gray, very fine contains a 0.1-ft-thick -bentonite with grained, concretionary at top______11 fibrous calcite at 6 ft below top (this bentonite is about 2 ft thick a few miles Total Fox Hills Formation______172 to the south)------70 Total upper part______525 Lewis Shale : Upper part: Dad Sandstone Member : 28. Shale, gray, silty to sandy, sandier toward 18. Sandstone, yellowish-gray to pale-yellow ... top; weathers yellowish gray; contains ish-gray, very fine grained, soft, friable; three layers of siltstone concretions____ 67 contains randomly distributed 5-ft-thick 27. Sandstone, pale-yellowish-gray, very fine by 10 ft in diameter masses of concre- grained; weathers yellowish gray ; top tionary sandstone______56 locally cont·ains large masses of concre- 17. Shale, gray, sandy; contains thin ·laminae tionary sandstone______22 of sandstone------34 FOX IDLLS FORMATION 41 llefet·ence sect·lon of the li'orc Hills Fot·mation and Le'wis Shale Reference section of the Fore Hills Formation and Lewis Shale ( inchtcling Dad Sandstone 111 ember) -Continued (including Dad Sandstone 111 ember) -Continued Lewis Shale-Continued Lewis Shale-Continued Dad Sandstone Member-Continued Lower part---'Continued 16. Shale, gray ; weathers light gray ; contains 4. Sandstone, pale-yellowish-gray, very fine thin siltstone laminae cemented with grained, thin-bedded ; locally concretion- limonite ------89 ary ------15 15. Siltstone, gray ; weathers yellowish gra.y __ 50 3. Shale, gray, poorly exposed______405 14. Sandstone, lig·ht- to dusky-yellow, glauco- 2. Shale, dark-gray, flaky; contains several nitic, fine-grained, soft; contains sand- layers of dark-reddish.Jbrown-weathering stone concretions 8 ft thick and 15 ft in limestone concretions, some of which are d-iameter ------77 septarian ------340 USGS D6629: Ostrea sp. USGS D6326, from 50 ft a•bove base: Arctica? sp. BacuZites eliasi Cobban 13. 'Shale, light-gray, sandy in upper half; Total lower part______1, 060 weathers yellowish gray ______69 Total Lewis Shale______2, 310 12. Sandstone, yellowish-gray, fine-grained, soft; contains thin laminae of shale___ _ 10 11. Shale, gray, sandy; weathers pale yellowish Almond Formation (part): gray to light gray------70 1. Sandstone, yellowish-gray to grayish-yel 10. Sandstone, yellowish-gray to dark-yellow low, fine- to medium-grained, thin ish-orange, fine-grained, soft, friable ; bedded ; contains many oysters in lower contains abundant burrows and near top 10 ft and abundant Ophiomorpka in UP- fossiliferous sandstone concretions 1.5 ft per ·part------25 thick and 3 ft in diameter------ 45 USGS D6325: USGS D6328, from top of unit: Orassostrea glabra (Meek ·and 111 icmbacia sp. Hayden) .~ Calcareous worm tube Bryozoan FOX HILLS FORMATION "lnoceram1ts" fibt·osus (Meek and Hayden) TYPE LOCALITY AND DISTRIBUTION Pteria linguaeformis (Evans and Shumard) The Fox Hills Formation was named by Meek and Ostrea russelU Landes Hayden ( 1862, p. 419) ror exposures of siltstone and Pecten sp. sandstone on Fox Ridge between the Grand and Anomia sp. . Moreau Rivers in central South Dakota. The name has 111 Olliolus galpiniana (Evans and been used in South Dakota, North Dakota, Montana, Shumard) Pholadomya u. sp. Wyoming, and Colorado for rocks that are transitional Goniomya americana Meek and with the underlying marine shale of the Pierre and Hayden Lewis and with the overlying fluviatile beds of the Dt·epanochilus sp. Hell Creek, Lance, and Medicine Bow Formations. BacuUtcs gra.ndi.'l Hall and Meek .. ~ Early geologists (for example, Dobbin, Bowen, and Discosca.phitcs sp. 9. Poorly exposed. Appears to be sandy shale Hoots, 1929, p. 23) recognized rocks equivalent to the with numerous thin beds of sandstone___ 110 Fox Hills in south-central Wyoming but included them 8. Sandstone and sandy shale interbedded, in either the upper part of the Lewis Shale or the lower pale-yellowish-gray, thin-bedded, ripple part of the Medicine Bow Formation. Dorf ( 1938, p. 6) laminated; weathers in light-brown con assigned the name Fox Hills Formation to the marine cretionary and sl·abby ledges 2-5 ft thick 115 .. )... sandstone and 1narine to nonmarine shale that had pre Total Dad Sandstone Member------725 viously been included in the lower part of the Medicine Bow Formation. We accept Dorf's assignment for. the Lower part: ~· area of this report and have identified the Fox Hills in 7. Shale, poorly exposed, .sandy; 15 ft above the Hanna, Carbon, and Laramie Basins. .base is ·a layer of limestone concretions-- 250 USGS D6327: LITHOLOGIC CHARACTER 11lnocerwmus" fibrosus (Meek and Hayden) The Fox Hills Formation consists dominantly of BacuZites sp. thick units of friable sandstone but includes units of 6. Sandstone, pale-yellowish-gray, very fine grained; weathers concretionary locally 5 shale. Sandstone units are pale yellowish gray, very 5. Shale, gray, sandy, poorly exposed------45 fine to fine grained, weather yellowish gray to light 42 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. J' brown, .and commonly contain fossiliferous sandstone FOSSILS concretions. They are thin bedded to massive, crossbed The Fox Hills Formation contains a shallow-water ded and ripple bedded, ·and generally nonresistant, but loca.Ily they a.re well cemented and cliff forming. The marine fauna consisting of a la.rge variety of clams and shale units are olive gray to dark gray, ma.inly sandy, snails. In the area of this report it also contains three nonresistant, and generally poorly exposed. Thin units distinctive types of ammonites which are B aculites clin of carbonaceous shale containing brackish-water fossils olobatus, Sphenodiscus ( Ooahuilites) sp., .and Discos or thin impure beds of coal crop out in some areas. caphites sp. B ar:nr:lites clinolobatus is an index ammonite Ophiomorp.ha is common in the sandy rocks, and oysters found in the upper part of the Pierre Shale in eastern are loca1ly abundant in beds of sandstone or shale. Wyoming, South Da.kota., and eastern Colorado where the Fox Hills is younger than in south-centra.! 'Vyom THICKNESS ing. The following three collections of fossils, identified The Fox Hills l.'anges in thickness from less than by W. A. Cobban and N. F. Sohl, are representative of 200 feet along the east side of the Great Divide and the fauna of the Fox HHls in south-central Wyoming: vVashakie Basins to at least 700 feet along the east side USGS D5538. NE*SElA, sec. 16, T. 21 N., R. 79 ,V., Carbon of the Carbon Basin near Medicine Bow; ·at other lo County. calities it ma.y be thicker. 'Ve interpret the differences in thickness to be a result of different rates of subsidence From 215 ft below the top of the Fox Hills Formation. and sediment delivery. In areas of maximum thickness, Lingula sp. the rates of sedimentation and subsidence were probably Nttet(,la planirnarginata Meek and Hayden ·~ about equal; consequently, the strandline was nearly Oxytorna neb1·ascana (Evans and Shumard) stationary for a long period of time. Where the Fox Olarnys nebrascensis (Meek and Hayden) Hills is thin, the strandline probably retreated seaward CreneZla sp. at a relatively rapid rate. Astarte sp. Clisocolus sp. RELATION TO ADJACENT FORMATIONS Protocardia rara (Evans and Shumard) Legurnen sp. The sandstone of the Fox Hills Formation inter TeZlina sp. tongues with the m·arine shale of the Lewis and with the Dentaliurn sp. brackish-water ~and fluviatile shale and sandstone of Euspirasp. the Medicine Bow Formation. The Fox Hills represents Ellipsoscapha sp. a transitional depositional environment between a Cylichna volvaria (Meek and Hayden) deeper water marine environment ·and the lagoonal and Oligotycha concinna (Hall and Meek) continental environments. The formation resulted from Baculites sp. the deposition of sediments in shallow marine, barrier Aptychus bar, and beach environments as the Cretaceous sea with drew from the area of the northern Rocky Mountains. USGS D5539. SE*N\V* sec. 21, T. Z1 N., R. 79 ,V., Carbon The contact between the Lewis and Fox Hills is pro County. gressively lower in the section in ·a north and northwest From the middle and upper parts of the Fox Hills Formation. direction because the marine shale of the Lewis is re Dysnoetopora demissa (White) placed laterally by the shallow-water marine sandstone Lingt(,la nitida (Meek and Hayden) of the Fox Hills. The lower contact of the Fox Hills "Inoceranws" fibrosus (Meek and Hayden) Formation is placed a.t the horizon below which the Pseudoptera n. sp. rocks are predominantly marine shale. The upper con Oxytorna nebrasca1~a (Evans and Shumard) tact is located at the horizon above which the rocks are Ostrea sp. predominantly of fresh- and brackish-water origin, Ethrnocarditm,. sp. including coal and carbonaceous shale, a.nd below which P1·otocardia sttbquadrata (Ev·ans and Shumard) the rocks a.re predominately of marine origin. These Venerid pelecypod criteria are similar to those proposed by Lovering, Legumen ellipticum (Conrad) Aurand, Lavington, and Wilson (1932, p. 702) for the Gyro des? sp. recognition and delineation of the Fox Hills in north Baculites clinolobatus ,Elias eastern Colorado. Discoscaphites sp. MEDICINE BOW FORMATION 43 USGS 05540. SWI;.J,NWY.~ sec. 11, T. 21 N., R. 79 ,V,, Carbon stone, and shale with persistent beds of coal in the lower County. part. We have studied these rocks in detail only in the From 30 ft above the. bnse of the Fox Hills Formation. northwestern pa.rt of the Hanna Basin; consequently, Bryozoan our descriptions in this report are more limited than for Lingula nitilla Meek and Hayden am·vi.lUa sp. the underlying Cretaceous rocks. "Inooer(mws'~ fib1·osn.q (Meek and Hayden) Marine sandstone and shale included by early work P8C1HlOt>tem n. sp. ers in the upper part of the underlying Lewis Shale were Syncyclonema sp. placed by Dobbin, Bowen, and Hoots (1929, p. 22-24) PlloZnclomya n. sp. in .the Medicine Bow Formation. Dobbin and Reeside Jllthmocan1i·u.m n. sp. ProtOC(l1'd·in .mbqua(lrata, (I~ vans and Shumard) (1929, p. 21-23) recognized that these rocks represent Venerld pelecypod the transition from conditions of marine deposition to Legnme:;n cZli·1Jt-iowm Conrad continental deposition and determined them to be of ~J.lclUnn sp. Fox Hills age. Later, Dorf ( 1938, p. 4-6) redefined the Oym.b07>h01'(t 'lt:nrrcnctn(t (:Meek and Hayden) ~1edicine Bow Formation and restricted the several Gyrollcs? sp. JJaouUtcs sp. hundred feet of marine beds :at the base of the forma S1>hcnotUscus sp. tion to the Fox Hills Formation. We concur with Dorf's ~- redefinition. AGE AND CORRELATION We have not measured a complete section of the '!'he Fox I-Iills in south-central Wyoming is oldest in Medicine Bow, but are in general agreement with the the northern and northwestern pa1~t of the area and description given by Bowen ( 1918, p. 229-230) and by was probably deposited during the range span of Ba(Ytt Dobbin, Bowen, and Hoots (1929, p. 23-24). A brief lites gnundis or possibly during the time of B. bac'Uius. description by the laMer authors follows: In the central and southeastern part of the area, the Fox The Medicine Bow formation ranges from 4,000 to 6,200 feet H:ills was deposi,ted within the range span of B. clinolo in thickness and consists of yellow, gray, and carbonaceous batus. Nowhere in the area is it as young as at the type shale, 'beds of coal, .and gray and brown sandstone. * * • The locality in South Dakota (Gill and Cobban, 1966a, p. lower part of the formation is made up of massive to cross-bed ded brown sandstones, which usually ~orm a conspicuous group A35). of ledges and contain numerous beds of coal. These sandstones The Fox I-Iills Formation of this area is not neces are overlain ·by .an 'inter-mediate group of dark-colored shales sarily equivalent in age, but it correlates lithologically ·and thin-bedded fine-grained brown sandSJtones, with some beds with the Fox I-Iills of North and South Dakota, Mon of massive white sandstone. The sandstones at the top of the tana, ttnd eastern Colorado. It also correlates lithologi formation are coarse, massive, friable, and easily eroded and cally with the Fox IIills of the Rock Springs uplift and are interbedded with thick beds of dnrk-gray shale. with the Fox I-Iills of the Powder River Basin in Wyo The Medicine Bow Formation seems to be conform lning. It is equivalent to beds in the lower part of the ably overlain by coarse-grained to conglmneratic sand Lance Formation in northwestern Colorado, as mapped stone beds of the Ferris Formation. In the type locality by Bass, Eby, and Campbell ( 1955), and to the of the Ferris, in the central part of the Hanna Basin, Lion Canyon Sandstone Member of the Willimns Fork coarse-grained sandstone of the upper part of the Medi Formation, in the area of M:eeker, Colo., as mapped by cine Bow grades upward into pebble-bearing sandstone I-Iancock and Eby ( 1930). beds of the Ferris. Locally, along the east side of the Hanna and Carbon Basins, the Medicine Bow Forma MEDICINE BOW FORMATION tion is overlain in angular unconformity by the Hanna The Medicine Bow Formation is a thick unit of con Formation (fig. 14). .. ,).. tinental beds that were deposited during and after The Medicine Bow Formation is of Late Cretaceous withdrawal of the Cretaceous sea from south-central age, as was suggested by Bowen (1918, p. 230), Dob Wyoming. Bowen ( 1918) named and described the for bin and Reeside ( 1929, p. 22), Dorf ( 1938, p. 6), and mation from exposures ·along the North Platte River l(nowlton (1911, p. 369; 1914, p. 328). Dobbin, Bowen, near the n1outh of the ~1edicine Bow River in the west and Hoots ( 1929, p. 23) considered that most of the ern part of the I-Ianna Basin (fig. 1). The usage of the Medicine Bow Formation and the lmW-r 1,000 feet of the term "Medicine Bow Formation" is restricted to the Ferris Formation represented the Lance Formation of I-Ianna., Laramie, and Carbon Basins. At the type local eastern Wyoming. Dorf (1940, ·p. 223, 233) correlated ity and in adjacent areas, the ~1edicine Bow is about the Medicine Bow with the Lance, the Hell Creek For 6,200 feet thick and consists of fluviatile sandstone, silt- mation of Montana and the Dakotas, and the Laramie 44 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. •· FIGURE 14.-Rocks of the Hanna Formation resting unconformably on the lower part of the Medicine Bow Formation in the southeastern part of the Oarbon Basin, in the SEl\4SIDJ4 sec. 20, T. 21 N., R. 79 W., Carbon County, Wyo. Formation of Colorado. The Medicine Bow probably is USGS D6612. NElUNW% sec. 24, T. 24 N., R. 85 W. equivalent to only major parts of the previously named Anodonta aff. A. propatoris White units, as Dobbin, Bowen, and Hoots suggested, because Plesielliptio postbiplicata (Whitfield) Teredina laramiensis (Whitfield) the lower part of the Ferris Formation, which conform Tulotomops thom.psoni (White) ably overlies the Medicine Bow, is also of Late Creta Lioplacodes aff. L. temticarinata (Meek and Hayden) ceous age (Brown, 1943, p. 81-82; 1962, p. 21). aampelorna n.eb1·ascensis whitei Russell Numerous fossil collections from the Medicine Bow Physa reesidei Stanton Formation by earlier workers in the area include From lower part of Medicine Bow Formation: fresh- and brackish-water invertebrates, ceratopsian USGS D5618. Center of the N% sec. 1, T. 22 N., R. 80 W. dinosaur remains, and plants. The geographic and strat (eastern Hanna Basin). igraphic position of many of these earlier collections Plesielliptio postbiplicata (Whitfield) cannot be determined accurately. During the course of T1tlotomops thompsoni (White) Lioplacoaes sp. the present study, invertebrate fossils were collected aampeloma neb?·ascensis whitei Russell from the Medicine Bow Formation in the Carbon Basin aassiopella tttrricttla White and eastern part of the Hanna Basin, as well as from USGS D5544. SE%NEJ4 sec. 21, T. 21 N., R. 79 W. (Carbon the lower and middle parts of the formation near the Basin). west margin of the Hanna Basin (Seminoe Dam SW Sphaerittm sp. 7%-minute quad.). Representative fossil collections Tttlotomops th01npsoni (White) LioplacoiLes sp. from Carbon County, identified by W. A. Cobban, follow. From S%NE% sec. 1, T. 22 N., R. 80 W.: From middle part of Medicine Bow Formation: USGS D6241. (eastern Hanna Basin). Calcareous worm tube USGS D6607. SW%NWl4 sec. 26, T. 24 N., R. 85 W. (western arassostrea sp. Hanna Basin)· USGS D6242. 240ft above D6241. Proparreysia sp. aorbicttla cf. a. planum.b01ta Meek Tttlotornops th01npsoni (White) USGS D6243. 30ft above D6242. aampeloma neb1·ascensis whitei Russell a01·bula cf. a. mactritormis Meek and Hayden Lioplacodes afl'. L. tenuicarinata (Meek and Hayden) USGS D6611. NE% SE% sec. 33, T. 24 N., R. 85 W. Unio sp. Proparreysia holmesiana (White) Gastropods cf. verntcositormis (Whitfield) USGS D6244. 60ft above D6243. Plethobasis aesopiformis (Whitfield) aorbula subtrigonalis Meek and Hayden j ... FOOTE CREEK AND DUTTON CREEK FORMATIONS 45 USGS 06245. 215ft above 06244. The Paleocene age of the Foote Creek was determined Oorbula cf. 0. mact?·ifO'I-tn-18 Meel{ and Hayden from plant microfossils in core samples of carbonaceous Gonio basis sp. shale and coal. The core was recovered from a hole 12 Vivipcvnts sp. USGS 06246.40 ft above 06245. miles southeast of the type section of the formation. .PlesieZUptio sp. The coal-bearing rocks ·penetrated by the drill are about T1tlOtO?nops thompson:i ( 'Vhite) 160 feet thick and were interpreted by Hyden, ·Mc Oam.peloma neb1·asoensis var. 1.vMte·i Russell Andrews, and Tschudy ( 1965, p. 1(8) as part of the USGS 06247. 45ft above 06246. Foote Creek Formation resting confonnably on the .PZesieZUptio cf. P. 1)0Stbi.plicata (Whitfield) T1tlot01nops thO?nl)SOn·i (White) Lewis Shale. 1V e believe these beds are a fine-grained Oant1)elom.a ncb1·ascensis var. 'I.Vhitei Russell facies of the Hanna Formation. Excellent and well Li01)lacolles cf. L. tenulicarinata (Meek nnd· Hayden) preserved pollen assemblages were obtained from five ... USGS 06080. NE:J,4NE1J.~ sec. 18, T. 24 N., R. 84 W. (western beds in the lower part of the Foote Creek and all are Hannn Basin). of late Paleocene age (R. H. Tschudy, oral commun., 01·assostrea glabra (Meek and Hayden) 1968). The lowest bed from which pollen was collected FOOTE CREEK AND DUTTON CREEK FORMATIONS and identified is 15 feet above the Lewis Shale. The basal part of the Foote Creek Formation (Medi The names Foote Creek and Dutton Creek were cine Bow of this report) at the type section contains recently introduced in the northern part of the Laramie 4 Late Cretaceous plant microfossils, but the basal part nnd southern part of the Carbon Bnsins by Hyden, of the Foote Creek (Hanna Formation of this report) McAndrews, and Tschudy ( 1965). The names were used at the locality of the drill hole contains plant micro on several geologic quadrangle maps. The Foote Creek fossils now considered to be late Paleocene instead of Formation was proposed for as much as 400 feet of Paleocene in age. interbedded fine-grained sandstone, carbonaceous shale In the center of the Hanna Basin, about 20 miles and siltstone, and coal. The Foote Creek (basal Medi northwest of the type section of the Foote Creek Forma cine Bow Formation of this report) was reported to be tion, rocks of Late Cretaceous age (the lower part of of Late Cretaceous and Paleocene age and to conform the Medicine Bow) are separated from rocks of late ably overlie the Lewis Shale (Hyden and others, 1965, Paleocene age (the lower part of the Hanna Forma p. 1(1). The Dutton Creek Formation (Hanna Forma tion) by as much as 13,000 feet of strata. This thick tion of this report) was proposed for 200-500 feet of ness contrasts with the reported maximum thickness of interstratified conglomerate, fine- to coarse-grained 400 feet between similar rocks of Late Cretaceous and sandstone, mudstone, carbonaceous shale, and coal. The late Paleocene (late Paleocene, R. H. Tschudy, oral Dutton Creek is of late Paleocene age and unconform commun., 1968) age in the Foote Creek Formation ably overlies the Foote Creek. These new formation (Hyden and others, 1965, p. 1(3). A major uncon names were used for rocks shown on the ·current Wyo formity at the base of the Hanna Formation has been ming State geologic map (Love and others, 1955) as described and mapped by Dobbin, Bowen, and Hoots the Medicine Bow and Hanna Formations. ( 1929, p. 25 and pl. 27). The Hanna Formation lies The Foote Creek Formation at the type section, about unconformably on the Ferris Formation and transgres 12 miles west of the town of Rock River, conformably ses across all underlying formations at least down to overlies the Fox llills Formation, which was included the Cloverly and possibly down to Precmnbrian granite by I-Iyden, ~1cAndrews, and Tschudy (1965, p. 1(7) in (Dobbin, Bowen, and Hoots, 1929, p. 25). 'Ve believe the Lewis Shale. At this locality the Foote Creek con that the Foote Creek Formation, reportedly of Late tains a thick unit of marine sandstone in its lower part Cretaceous .to late Paleocene age (Hyden and others, and is transitional with the underlying Fox Hills. The .'1-. 1965, p. 1(5), encompasses this unconformity . thickness of the Foote Creek at this locality is 228 feet, Rocks mapped as Foote Creek by Hyden and Mc and its lithology and fossil content are the same as those Andrews (1967) along the east margins of the Hanna of the Medicine Bow Formation in nearby areas. At the and Carbon Basins (T L Ranch 71h-minute and Saddle type section of the Foote Creek a coal bed, about 7 back Hills 15-minute quarangles) are at one place feet above the base, contains spores and pollen typical remnants of the basal Medicine Bow and at other places of the Hell Creek, Lance, and Medicine Bow Forma . ).• a fine-grained coal-:bearing facies of the Hanna For tions of Late Cretaceous age (Hyden .and others, 1965, mation. We have examined the local unconformity at p. 1(5). The beds a few feet above the co~l contain the base of the Foote Creek Formation, reported by 01•assostrea glabra (Meek and Hayden), a fossil oyster Hyden, McAndrews, and Tschudy (1965, p. K4), and typical of the transitional rocks in the upper part of the conclude that the unc~mformity is not local and that Fox Hills and lower part of the Medicine Bow. the rocks above it are a fine-grained facies of the Hanna 46 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Formation. Rocks as thick as 16,000 feet may be repre type locality. It consists of a thick sequence of conti sented by the unconformity at this locality. In most nental rocks that can be divided into two parts: a lower other quadrangles mapped by Hyden and others in the unit of Late Cretaceous age which is about 1,100 feet northern ·part of the Laramie Basin, the name Foote thick and composed of conglomeratic sandstone, sand Creek has been applied to remnants of the lower part stone, and shale, and an upper unit of Paleocene age of the Medicine Bow Formation. which is about 5,400 feet thick and composed of gray, We believe that the Dutton Creek Formation of late brown, and yellow sandstone and many thick beds of Paleocene age is a coarse-grained conglomeratic facies coal. The two units appear to be conformable, although of the Hanna Formation and that the name "Hanna" their lithologies are markedly different. should be reinstated for these rocks. Locally, the Dut The conglomerate of the lower unit ·is generally dark. ton Creek is the basal unit of the Hanna which grades It contains pebbles as much as 1 inch in diameter com laterally into a fine-grained facies, as can be demon posed of black, red, and yellow chert, red and gray strated in the northern part of the T L Ranch quad quartzite, and sparse rhyolite and quartz latite por rangle. Where the lower part of the Hanna is fine phyry (Bowen, 1918, p. 230). Some of the siliceous grained, the Dutton Creek crops out higher in the pebbles contain Paleozoic fossils. The pebbles appar Hanna Formation. ently do not consist of rocks exposed locally in moun Our reevaluation of the stratigraphic and paleon tains adjacent to the basin. Bone fragments are com tologic data from rocks of Late Cretaceous and early mon in the conglomerates, and some have been identified Tertiary age in the Hanna, Carbon, and Laramie Basins by C. W. Gilmore as T1·iceratops, which indicates a results in the conclusion that the F1oote Creek and Dut correlation between the basal part of the Ferris and the ton Creek Formations have been incorrectly inter Lance Formation (Bowen, 1918, p. 231). Plant micro preted. The stratigraphic sequence exposed along the fossils collected by us from the dark-brown shales in southeast margin of the Carbon Basin was reexamined the lower unit of the Ferris were examined by R. H. in the company of H. J. Hyden, and it was concluded Tschudy, who said (written commun., 1967): "Sample that the rocks assigned to the Foote Creek Formation D4085 yielded a characteristic late Cretaceous assem belong in the lower coal-hearing part of the Medicine blage including the genera P1·oteacidites and A-qu,ilapol Bow Formation and in the coal-bearing fine-grained lenites. There 'is no doubt concerning the age of this parts of the Hanna Formation. sa.mple." The Foote Creek Formation as a formal stratigraphic The upper unit of the Ferris differs from the lower name is abandoned in accordance with the wishes of Mr. unit in being much thicker, in containing numerous per Hyden before his untimely death. This action is taken sistent beds of coal, and in its lack of conglomerate or because the lower part of the Medicine Bow Formation conglomeratic sandstone. Plant microfossils coHected and the fine-grained facies of the Hanna Formation, · from about the 1niddle of the upper unit were examined although similar in appearance, can now be recognized. by R. H. Tschudy, who stated (written commun., 1967) : The two formations can be identified on the basis of "The few fossils identified indicate a Paleocene age for lithology and are separated by a large unconformity. the samples. The absence of 11/ onipites ten1tipol!us 'Sug The two units are, in addition, of different ages-Late gests early rather than late Pa.leocene." Cretaceous and late Paleocene. Inasmuch as most of the The Ferris Formation conformably overlies coarse rocks mapped as Foote Creek are now recognized as grained sandstones of the Medicine Bow Formation and remnants of the lower part of the Medicine Bow For unconform·ably underlies locally derived conglomerate mation, we recommend that the name ~1edicine Bow be or conglomeratic sandstone of the Hanna Formation. In reinstated for formal usage in this a.rea. The Dutton ·the type locality of the Ferris, in the west-central part Creek Formation represents one of the many coarse of the Ha.nna Basin, an angular relation between the grained tongues of the Hanna Formation; conse two formations is not apparent. Possibly in the centra.! ~.- quently, to avoid a duplication of names, the Dutton part of the Hanna Basin, the Ferris and Hanna Forma Creek is abandoned and the Hanna is reinstated. tions are virtually conformable, as suggested by !{night (1961, p. 162). A marked angular unconformity sepa FERRIS FORMATION rates the two formations along the east side of the Hanna The Ferris Formation was named by Bowen ( 1918, and Carbon Basins. The unconformity is well exposed p. 230-231) from exposures between the old Ferris in sec. 14, T. 22 N., R. 80 W., 2 miles north of the old Ranch on the North Platte River (sec. 33, T. 23 N., R. town of Carbon. 84 W.) and a hilltop to the east (sec. 28, T. 23 N., R. In the northern part of the Hanna Basin, Dabbin, 83 V\T.). The formation is about 6,500 feet thick in the Bowen, and Hoots (1929, pl. 27) mapped the Hanna un- 47 conformably overlying the Ferris. !(night ( 1961, p. 155- tributed throughout the formation, but is most abun 164) measured two sections in the area and found no dant in the lower half. The pebbles in the conglomerate evidence of an angular unconformity, and he did not are, in general, light colored and consist of chert, gran differentiate the Ferris and the I-Ianna. vVe have ex ite, quartzite, sandstone, Mowry Shale, oa.nd cong.lomer amined the 11rea and conclude thrut the ma.p of Dobbin, a.te frmn the Cloverly For1nation. The pebbles of Bowen, and I-Ioots is incorrect. The Hanna Formation granite, quartzite, Mowry Shale, and conglomerate are '"" overlies a p11rt of the :Medicine Bow For1nation; the in believed to represent nearby exposures of these rocks. tcrvening upper part of the :Medicine Bow and the Fer The conglomerates of the Hanna differ from those of the ris have been removed by pre-IIanna erosion. This ac Ferris in color and in the size ·and composition of the counts for the thinness of the l\1edicine Bow ( 3,950 ft clasts. Apparently, the conglomerates of the Ferris were .instead of 6,500 ft a few miles to the west) . We, like derived from a distant source and those of the Hanna .~ !(night, did not see a measurable angular unconformity from n. nearby source. The basal unit of the Hanna is at the base of the conglomeratic sequence, but it may generally composed of coarse conglomerate but may have been overlooked in exposures on the edges of ver locally be finer grained. tical beds. The I-Ia.nna Formation unconfol'lnably overlies the '!'he Ferris crops out in the I-Ianna and Carbon Basins, Ferris Formation in much of the area, but locally along but the original areal extent of the for1na.tion is not the margins of the basins it rests on rocks us old as Pre known. Bowen ( 1918, pl. 66) showed ~that the Ferris is cambrian .age (fig. 15). Bowen ( 1918, p. 232) estimated nt lenst 4,600 feet thick in places along the east flank that the unconformity at some localities represented the of the llannn. Basin. Probably the formation was also removal of rocks more than 20,000 feet thick. On the deposited in the Laramie Basin. The presence of loc;ally south flank of the Hanna Basin the I-Ianna and older derived conglomm~a.te in the basal part of the overlying formations are unconfol'lnably overlain by beds na.med l:In.nna Formation and a marked angular unconform the North Park Formation of Miocene age by Dobbin, ity at the base of this unit indicate that the Hanna and Bowen, and Hoots (1929, p. 26) and undivided Pliocene Carbon B11sins started to form during the early or Inid and Miocene rocks by 'Veitz and Love ( 1952). dle Paleocene. }(night (1953, p. 67) rep01.ted a loca.lly }(night (1961, p. 160) mapped unnamed continental derived conglomerate in the lower part of the l\1edicine rocks of Eocene age in the northern part of the I-I·anna Bow Fornm.tion, in the southwesten1 part of the Lara Basin and demonstrated that this unit was in angular mie Basin, and he concluded that the IV[edicine Bow unconfor1nity with the unded.ying Ha.m1a and older Mountains were elevated sufficiently in Cretaceous time formations at the basin margin. He further reported to expose roclrs of Precambrian age. that the rocks of Eocene -age became conformable with the underlying rocks as they were traced basinward. HANNA FORMATION Plant microfossils collected by H. J. Hyden in the lower The I-I anna Formation was named by Bowen ( 1918, part of }(night's Eocene sequence in the SE% sec. 16, T. p. 231) from exposures. north and west of the town of 22 N., R. 81 ,V., Carbon County, were examined by I-Ianna (fig. 1). Neither Bowen (1918, p. 231), who pro R. H. Tschudy, who stated (written commun., 1963) posed the for1nation, nor DolYbin, Bowen, and Hoots "USGS D3232A. Assemblage includes specimens of (1929), who first mapped it, designated a specific type Tiliae]Jollenites and is of late Paleocene or early Eocene locality and described a type section. We have studied age." Pl·ant microfossi1ls collected by us fron1 higher in the formation only in the Hanna and Carbon Basins, the m1it in the center of the SWl!t, sec. 34, T. 24 N., R. and our descriptions are limited to general lithology, 81 ,V., were described by Tschudy as follows (written fossil content, and the relation with adjacent fonnations. commun., 1967) : "USGS D4088. Assen1bla.ge includes the genera Oarya, Jruglans? Tiliapollenites, and Platy --~· The I-Ianna Formation of continental origin consists of conglomerate, sandstone, shale, and coal. Bowen ca'rya, and is of Eocene age." }(night's Eocene unit (1918, p. 231) reported that the formation was about was originally m·apped -as part of the Hanna by Dobbin, 7,000 feet thick, but sections measured subsequently by Bowen, and Hoots (1929, pl. 27), but the demonst.ra.ted !(night (1961, p. 159-161) on the north flank of the 1nappability of the unit (1\:night, 1961, p. 160) and the I-Ianna Basin and our field observations lead us to believe unconformity at its base lead us to conclude that it that the Hanna may be a-s much as 13,500 feet thick. should be excluded from the Hanna and perhaps in Bowen reported (1918, p. 231) that the H·anna For cluded in the Wind River Form-ation ·as }(night mation was "highly feldspathic" and composed of con suggested. .,.... gl01nerate, conglomeratic sandstone, sandstone, shale, The fossils in the Hanna Formation consist of well and many thick beds of coal. The conglomerate is dis- preserved leaves, spores and pollen, invertebrates, and 48 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. FIGURE 15.-Hauna Farmation (Th) unconformably overlying the Lewis Sha,le (Kie) in the northeastern part of the Hanna Basin, in the NEJA:\fW14 sec. 10, T. 23 N., R. 80 W., Carbon County, Wyo. Sandstones of the Almond Formation (Ko) crop out in the area shown in the lower left corner of the photograph, and the soft shales of the Lewis form the valley in the foreground. vertebrates. The vertebrate remains described by The age of the Hanna remains in some doubt. The Bowen ( 1918, p. 231) "include fish scales, fragments of upper part of the underlying Ferris Formation is of turtle shells, and a fra.gmentary mammalian jaw identi early Paleocene age and the overlying unnamed se fied by J. W. Gidley as a creodont, probably 07-aeono quence mapped by Knight (1961) is of possibly latest clon, which may belong to either the Fort Union or Paleocene and early Eocene age. Fossils from the Wasatch." Bowen also reported that invertebrates from Hanna indicate a late Paleocene age, but the formation the Hanna were identified by T. W. Stanton 'and cor may be as old as late early Paleocene or middle Paleo cene in the center of the Hanna Basin. related with those of the Fort Union and Wasatch Formations. The plant fossils found by Bowen were re REFERENCES CITED ferred to the Fort Union by F. H. Knowlton. Barwin, J. R., 1959, Facies of the Mesaverde formation, east '\iV e collected plant microfossils frorn two localities central Wyoming, in Am. Assoc. Petroleum Geologists Rocky in the lower part of the formation in the eastern part of Mtn. Sec., Geol. record, Feb. 1959: p. 139-142. the Carbon and Hanna Basins. 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R., 1966, ~stratigraphy and depositional history of formations in the north part of the Laramie Basin, upper "Mesaverde" formation of southeastern ·wyoming: Wyoming: U.S. Geol. Survey Bull. 1194-K, p. Kl-Kl2. 'Vyomlng Univ., unpub. Ph. D. dissert., 122 p. Knight, S. H., 1953, Summary of the Cenozoic history of the Dickinson, R. G., 1965, Geologic map of the Gerro Summit Medicine Bow. Mountains, 'Vyoming, in Wyoming Geol. qun.drangle, Montrose County, Colorado: U.S. Geol. Survey Assoc. Guidebook 8th Ann. Field Conf., Laramie Basin, Geol. Quad. Map GQ-486 [1966]. Wyoming, and North Park, Colorado, 1953: p. 65-76. Dobbin, C. E., Bowen, C. F., and Hoots, H. W., 1929, Geology and ---1961, The Late Cretaceous-Tertiary history of the north coal and oil resources of the Hanna and Gnrbon Basins, ern portion of the Hanna Basin, CaJ:ibon County, Wyoming, ·Carbon County, Wyoming: U.S. Geol. .survey Bull. 804, 88p. in Symposium on Late Gretaceous rocks, ·wyoming and Dobbin, C. E., Hoots, H. ,V., Dune, ·C. H., and Hnncocl\:, E. T., adjacent areas, ·wyoming Geol. Assoc. Guidebook 16th Ann. 1929, Geology of the Rock Creel\: oil field and adjacent Field Conf., Green River, ·washakie, Wind River and Pow areas, Carbon and Albany Counties, \Vyoming: U.S. Geol. der River Basins, 1961: Casper, 'Vyo., Petroleum Inf., Survey Bull. 806-D, p. 131-153. p. '155-164. Dobbin, C. JD., and Reeside, J. B., .Jr., 1929, The contact of the Knowlton, F. H., 1911, Further data on the stratigraphic posi Fox Hills and r.~ance formations: U.S. Geol. Survey Prof. tion of the Lance formation ("Oemtops beds") : Jour. _,).. Paper 158-B, p. 9-25. Geology, v. 19, p. 358-376. Dorf, Erling, 1938, Upper Cretaceous floras of the Rocky ---1914, Cretaceous-Tertiary boundary in the Rocky Moun Mountain region; 1, Stratigraphy nnd paleontology of the tain region: Geol. Soc. America Bull., v. 25, p. 325-340. Fox Hills and Lower Medicine Bow formations of southern Love, J. D., Weitz, J. L., and Hose, R. K., 1955, Geologic ma.p of Wyoming and northwestern Colorado: Carnegie Inst. 'Vnsh Wyoming: U.S. Geol. Survey. ington Pub. 508, p. 1-78. Lovering, T. S., Aurand, H. A., Lavington, C. S., and Wilson, ---1940, Relationship between floras of the type Lance and J. H., 1932, Fox Hills formation, northeastern Colorado: l!..,ort Union formations: Geol. Soc. America Bull., v. 51, no. 2, p. 213-235. Am. Assoc. Petroleum Geologists Bull, v. 16, no. 7, p. 702- Fenneman, N. l\:1., and Gale, H. S., 1906, The Yampa coal field, 703. Routt County, Colorado, 'With a chapte1· on The character McAndrews, Harry, 1965, Geologic map of the Cooper Lake and use of the Yampa coals, by l\:1. R. Campbell: U.S. Geol. North quadrangle, Al'bany County, ·wyoming: U.S. Geol. Survey Bull. 297, 96 p. 1Survey Geol. Quoad. Map GQ-430. -. 50 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. Meek, F. B., and Hayden, F. V., 1862, Description of new Lower Smith, J. H., 1961, A summary of stratigraphy and paleontology, ·Silurian (Primordial), Jurassic, Cretaceous, and Tertiary Upper Colorado and Montanan Groups, southcentral 'Vyo fossils, collected in Xebraska Territory * ''' ':', with some re ming, northeastern Utah, and northwestern Colorado in marks on the rocks from which they were obtained : Acad. ·symposium on Late Cretaceous rocks, 'Vyoming and Nat. Sci. Philadelphia Proc. 1861, p. 41:}--447. adjacent areas-,Vyoming Geol. Assoc., 16th Ann. Field Reeside, J. B., Jr., 1924, Upper Cretaceous and Tertiary forma Conf., 1961: Casper, ·wyo., Petroleum Information, p. tions of the western part of the ·San .Juan Basin, Colorado 101-112. and New Mexico, and Flora of the Animas formation, by Smith, .J. H., 1965, A summary of stratigraphy and paleontology, F. H. KnowLton: U.S. Geol. Sm·yey Prof. Paper 134, 117 p. upper Colorado and Montanan Groups, southcentral 'Vyo Reynolds, M. ,V., 1966, Stratigraphic relations of Upper Creta ming, northeastern Utah, and northwestern Colorado, in ceous rocks, Lamont-Bairoil .area, south-central 'Vyoming, Sedimentation of Late Cretaceous and Tertiary outcrops, in Geological Survey r·2search 1966: U.S. Geol. Survey Prof. Rock Springs uplift-Wyoming Geol. Assoc. Guidebook 19th Paper 550-B, p. B69-B76. Ann. Field Conf., 1965: Oa·sper, 'Vyo., Petroleum Inf., p. ---1967, Phy.sical evidence for Late Cretaceous unconform 13-26, 4 pis. ity, south-central 'Vyoming, 'in Geological Survey researC'l1 Spieker, E. M., and Rees'ide, J. B., Jr., 1925, Cretaceous ·and 1967: U.·S. Geol. Survey Prof. P.aPer 575-D, p. D24-D28. Tertiary formations of the 'V·asatch Plateau,· Utah: Geol. Rich, E. I., 1962, Reconnaissance geology of HHand-Cla.rkson Soc. America Bull., v. 36, no. 3, p. 43:}--454. Hill area, Natrona County, 'Vyoming: U.S. Geol. Survey Stanton, T. '\V., and Knowlton, F. H, 1897, Stratigraphy and Bull. 1107-G, p. 447-540. paleontology of the Lar·arnie and related formations in 'Vyo Schultz, A. R., 1907, The northern part of the Rock Springs ming: Geol Soc. America Bull., v. 8, p. 127-156. coal field, Sweetwater County, 'Vyoming: U.S. Geol. Sur Veatch, A. C., 1907, Ooal fields of east-central Carbon County, vey Bull. 341-B, p. 256-282. 'Vyoming: U.S. Geol. Survey Bull. 316-D, p. 244-260. 'Veimer, R. J., 1959, Upper Cretaceous stra:tigraphy, Colorado, Scott, G. R., and Cobban, ,V. A., 1959, So-called Hygiene Group in Symposium on Cretaceous rocks o·f Colorado nnd ad of northeastern Colorado, in Symposium on ·Cretaceous Jacent area·s--Rocky l\ftn. Assoc. Geologists [Guidebook] rocks .of Colorado and adjacent a.reas_;Rocky Mtn. Assoc. 11th Ann. Field Conf., 'Vashakie, Sand '\Vash, and Piceance -- Geologists [Guidebook] 11th Ann. Field Conf., ·washakie, Basins, 1959: p. 9-16. 1Sand Wash, and Piceance Basins, 1959: p. 124-131. Weitz, J. L., and Love, J. D., 1952, Geologic map of Carbon Sears, J. D., 1926, Geology of the Baxter Basin gas field, Sweet County, 'Vyoming: U.S. Geol. Survey, prepared in coopera water County, 'Vyoming: U.S. Geol. Survey Bull. 781-B, tion with 'Vyoming Geol. Survey and Wyoming Univ. Dept. p. 13-27. Geology. ~. ·.... INDEX [Italic page numbers indicate major references] Page A Page Page Fossils-Continued Acknowledgments .. ______.... ---- ___ ...... 1 Distribution, Allen Ridge Formation______24 Belli/usus sp _____ ...... _____ .. 27 Ago, :nanna Formation .... ------48 Almond ~,ormation...... 31 Breviarca sp ___ ------...... --- ____ . 33 Ago and cotTCiatlon, Allen JUdge Formation 26 Fox Hills Formation. ___ ...... 41 bryozoan ...... __ .....•... 16 Almond Formation...... 88 Haystack Mountains Formation._...... 12 Calcareous .•....•...... 20 Fox .liiiis Formation...... 48 Lewis Shale...... 36 Campeloma nebrascensis ....•...... ------. 44,45 Haystack Mountains Formation...... 14 Pine H.idgc Sandstone...... 29 whitei...... __ ...... 44,45 J,owls Shale ••...... ---- .... --·----·... 89 Rock H.ivcr Formation...... 20 sp _____ ...... 26 Pine Jtldgo Formation...... 80 Dobbin, C. E., cited ...... 5,43 Cassiopella turricula .• ____ ...... 44 Rock Hlvor Formation...... Sf Dorf, Erling, cited...... 5,41 Cerithioderma sp. _...... 27 Steele Slmlo...... 11 Dutton Crock Formation ...... 5,7,45 Chlamys nebrascensis ____ ...... 22 Allen H.ldgo Formation ______5,11,14,24 Claeonollon. __ ...... -...... -. 48 Almond coal group or Mesaverde Formation._ 31 Clamys nebrascensis .• _...... 42 E Almond Formation. _____ ------·-.... 5, 11,90,81, 30 Clisocolus sp ___ ------.... __ ...... -- ..... 15,42 Eagle Formation...... 11 Amrnonlto zonation Uppct· Cretaceous Corbiculafracta •...... ------..... 40 ot Ericson Sandstone ____ ...... 5, 31 rocks In Western Interior...... 1 planumbona. ------____ ...... •. 44 Ammon ito zones •• ___ ..... ·------...... 38 sp. _...... _...... 34 Ardmore l3cntonlto Dod In Sharon Springs F Corbula mactriformis. _...... -...... -..... 44, 45 Member or PIOI'l'O Shale______10 subtrigonalis. _...... •. ---.. 44 Fales Member of Mesaverde Formation ...... 11, 15 undifera. __ ---- ...... 34 B Fcnneman, N. M., cited...... 2,3 sp _...... _...... _...... 23, 27 Crassostrea glabra ...... ••.... 34, 35, 40, 41,45 ._ Barwln, J. H.. , cltocl...... 11 Ferris Formation ...... 5, 7, 43, 40 .... Bentonite bods, Steele Shale...... 10 Fleisher, R. L., sections measured by _____ ... 15,27 sp ____ ...... 40,44 Borgman, 0. A., rofcronco section measured Foote Crllek Formation. ___ .... __ ...... 5, 7,45 Crenella sp. __ ...... 42 by------1(), 34, 35, 30,40 Fossils: Cryptorhytis cheyennensis. __ -...... 22 Borgstrom, J. H.., cltccL...... 24 Acmaea occillentalis. __ ...... 22,27 Cuspidaria moreauensis. _...... 22 Bighorn Basin. ______...... ____ .. -----_. 11 parva...... 27 variabilis ... __ ...... 22 Black)H\Wk Formation...... 5 Acteon sp ...... 22,27 Cylichna volvaria. _...... 42 Blackwelder, Eliot, cited...... 3, 7 Allen H.ldgc Formation .. _. __ ... __ ...... 26 Cymbophora .• ____ ..... __ . _ 10, 15, 10, 20, 23, 34,40 Blair Formation _____ ...... 5, 11 Almond Formation...... 32 holmesi ___ ...... -..... 20, 29 Bowen, C. F., cited •...... 5,43,40,47,48 ammonites .. _...... 15 warrenana...... 43 Buck 'l'onguo or M!lncos Slmlo ... -- .. ----.- -·- 15 Anapachydiscus sp...... 23 Cymella montanensis ...... 15, 10, 22, 23, 27 A.natimya dodllsi. _...... 23 Dentalium pauperculum ....•..... ---- ..... 22 .,. c sp. ___ ...... _. 22 sp_ .... _...... _..... _...... 22, 23, 42 Carbon Basin.------.. __ ...... 5, 7, 37, 4•1 Anisomyon borealis. _____ ...... __ ... 22 Desmoscaphites bassleri...... 11 Castlcgato Sandstone .... _. ___ .... _... _...... 15 centrale •...... _. __ ._...... 33 Didymoceras cheyennense...... 30 Claggett Formation. ___ ... _.. _...... 11 sp ___ ...... __ ..... ___ ...... ___ ...... 17 nebrasense. _...... 26, 27 CIIIY House Sandstone .•..... ------...... _ Anollonta propatoris. ____ .•...... ------. 27,44 stevensoni.. ------...... •..... ------22,26,30 Coal bod, Foote Crock Formation...... •15 Anomia sp ______·------...... 41 sp. ____ .... _...... 23 Fon·is Formation...... 40 Aporrhais biangulata ...... ____ . 27 Discoscaphites sp _____ .__ ...... 41,42 Cobban, W. A., cited...... 30 A1ltychus. -·---.•...... ______..... 42 Drepanochilus. ___ ...... 11 fossils ldontlfiod by ...... _...... _... 10, Aquilapollenites...... 40 nebrascensis ______. ------...... 22 sp __ -·------..... ______...... __ . 23,41 15, 17, 1(), 21, 20, 27, 3<1, 35, 40, •12, •14 Arctica SP------41 typo section measured by ______. ___ . 21 Arrhogeslobata...... 23 Dysnoetopora demissa. ___ ...... 22, 23, 42 Cody Shale ______7,11 Astarte sp. ____ ...... 23, 42 Ellipsoscapha sp ...... _...... 23, 42 Wallace Crook 'l'onguc ...... 11,15 Atira nebrascensis ...... _...... 22 Ethmocardium ursaniense. __ ...... •...... 20 Collier, A. J., cited...... 2 Baculites ...... 10,11,14 sp. _.. ___ .. _. _.... __ ... 15, 17, 23, 33, 40, 42, 43 Contact relations, Allen H.ldgo Formation.... 26 aquilaensis .... ___ ...... 11, 19 Euspira obliguata ..... __ ...... 22, 27 0. Almond Formation .•• ___ ...... 3S asperiformis ...... 14, 10, 18, 20,28 sp ...... 22,23,42 Fox Hills Formation______42 baculus ___ ...... 33, 38, 43 Eutrephoceras sp __ ...... 22 J [annn For.tnatlon ...... --- .. ------. __ 47 cli~olobatus. _...... •.. •10, 42,43 Exiteloceras jenneyi. . _ ...... 30 - ~- Haystack Mountnlns Formation...... 14 compressus. __ . _...... 30 F'usconaia sp. _____ ...... 27 Lewis Shale •.. ------...... ------. 38 crickmayi. ___ ...... •...... 22 Fox Hills Formation. __ . __ ...... 42 Plno Hldgo Sandstone...... 30 cuneatus __ ..... _...... 30 Gervillia recta ...... •...... 22 Hock H.lvor Formation...... 21 eliasi. ____ ...... _.. 32, 33, 34, 35, 38, 41 SP------43 Steele Shale...... 10 granllis. ___ ...... 38,41,43 Glyptoxoceras ...... 11 Cross, C. W., cltocL ...... 2,30 gregoryensis ...... _... 24, 26 Goniobasis sp. _...... ---.---.-- 45 jensenL ...... •...... 32,33, 38 Goniochasma sp ...... -- .. -- .. - 22 I) mclearni...... ___ 14, 10,29 Goniomya americana __ ...... 27,41 obtusus. _...... 10, 15, 10, 18, 20,29 Graphidula alleni. __ ...... -... - 23, 27 Dad Sandstone Moml>or or Lewis Shale ..... 7,36,37 11erplexus ...... 14, 15, 10, 17, 21, 24, 20, 27 Gyrolles sp ...... 27, 42, 43 Dakota Sandstone, coal-bearing units. _____ .. 2 reesillei. .. _...... _..... 30, 31, 32, 33, 38 Hanna Formation...... 47 or No.!...... 2 scotti. .. __ ...... 20 Haresiceras montanaense. _...... --... 11 Darton, N.H., cited...... 3,7 thomi. ------· 11 natronense . .. _... _.... _...... 17 Dlllymoceras stevensoni zone ...... ____ . 21 sp __ .... 14, 15, 17, 18, 19, 22, 23, 27, 29, 40, 42, 43 Haystack Mountains Formation .... -..... 14 51 52 INDEX Page ... Fossils---'Continued Page Fossils-Continued Page PropaJreusia hoiineaiana______44 :Hell Creek: Formatioh:..--'~-'------C-- 43 · Hoploscaphites sp __ ... __ .. _ 15, 18, 22, 23, 28, 34, 40 ..., Inoceramus ___ .. __ .. __ ...... ______10, 11,22 verrucosiformis. ______. ___ .. ______44 Historical background ••...... _------.______2 Holmes, W. H., cited ______balticus. _-----· ______------11,18 SP------44. convexus _. ___ .. _. _. _. __ . _... -_. _.... -- 22, 23 Proteacidites. ______4.6 Hoots, H. W., cited______5, 43 fibrosus __ .. ___ .. __ . ______..... _ 40, 41, 42, 43 Protocardia rara •.• ______42 Hyden, H. J., cited ______------____ ------5, 36,45 oblongus __ . _. _.. __ ..... _... --...... _. . 35 subquadrata ______• ______42 fossils collected by ______. 47 r. sp. ______.______27 pertenuis. _•• _.. __ ..... _. ---- .. -- .. __ - 27 proximus ______10, 11,19 Protodonox sp •. ___ • ______.. ___ . ______23 shikotanensis .. ____ . ____ . __ . --. _____ ... 22 Pseudoptera sp. ______. ___ . ___ . ______42, 43 Iles Formation •• ----- ______---- _____ 3, 5, 26 10, 11 Introduction ..•• ______.. _.. ____ . __ . 1 subcompressus ______.. ___ . _ 16, 17, 23, 24, 28 Pteria. ______. ______turgid us. ______------· 27 linguaeform·is ___ - ___ . _____ 10, 11, 22, 23, 27, 41 sp ___ . ______15, 16, 18, 20, 21, 24, 28, 33, 35 Pycnodonte mutabilis ..... ------______23 K Juglans tiliapollenites. _.. ______. __ . __ _ _ _ 47 Rock River Formation ______21,30 Legumen ellipticum. ____ . ______..... _. 23, 42,43 Scaphites hippocrepis ______11, 17 Kara Bentonitic Member of Pierre Shale..... _ 33 sp ______. __ . ______.. _. _. _. __ _ _ 40, 42 Senis sp. __ ------______------23 Knight, S. H., cited •... ------46,47 Leptosolen sp ______.. ____ . ______23 Serpula sp ______------_. _ 27 Lewis Shale._ ... ------__ .. ______30,38 Serrifusus dakotensis. ______. __ . _... ______22 L sp ______---- _____ 22,23 Limatula sp. _------· _____ . ______23 Lance Formation... ------43 Limo psis sp______22 Solemya sp. ___ ------______------22,33 Laramie Basin. __ ------_____ 5, 10, 20, 25, 26, 37,43 Lingula nitida. ______------______42,43 Solenceras sp. ______22, 23 Laramie Formation, coal-bearing rocks •.. __ ._ 2 subspatulata. ______.... _. ______15 Sphaerium sp ______------______27,44 Lewis Sea ••.. ______------. 30, 32, 37, 38,39 Sphenodiscus sp. ______------__ 43 SP------··----- 42 Lewis Shale •. _____ ------2, 3, 5, 30, 33,36; 45 Lioplacodes tenuicarinata ... ____ . ______44, 45 Steele Shale______10 Dad Sandstone Member. ______7,36,37 sp __ .. ____ .. ___ . ______.. ____ .. _____ . _ 44 Syncydonema hallii. ______22 tongues. ______---- ______------32 -~ Lucina subundata ... ______10, 11 simplicius ______. ______. ______23 Lion Canyon Sandstone Member of Williams sp •.. ___ ... __ .. ______22, 27, 40 sp .. -- _____ . ______.. __ . ______.. _. _. 15, 27,43 Fork Formation______43 Menuites sp ______. ______23 Tancredia sp ______------______40 Lithologic character, Almond Formation .••. _ 31 •• Micrabacia americana______22 Tellina munda ______------______23,27 Allen Ridge Formation______25 sp- _- __ ...... __ . ______. _ 41 sp. __ . ______. ______15, 22, 42,43 Fox Hills Formation ______41 Modiolus galpiniana ____ ------·----- __ _ 41 Tenea circularis ______. ______22 Haystack Mountains Formation ... _...... 13 sp ••. --.... --. _. ______. ___ 15, 18, 20,23 parilis. ______. ______. ______23 Lewis Shale •• ------______. ______36 mollusks. ____ .______21 sp.-.---- ______. __ .... _____ . ______27 Pine Ridge Sandstone _____ .. ------. ___ _ 29 Momipites tenuipolus ______46,48 Teredina laramiensis .. _------______44 Rock River Formation ______21 - Morea cancellaria______27 Thyasira______10 10 Steele Shale------__ ------. .. .J:_ marvlandica______27 Tilaepollenites. ______·47 Lower Laramie Cretaceous nonmarine rocks .. 3, 5 ' sp. __ .. ____ .. ______. ______.. ______27 Trachyscaphites praespiniger ____ . ____ . ____ 10, 11 Nemodon sulcatinus ______------_____ 22 Triceratops______46 M '-', McAndrews, Harry ______. ______5, 36,45 SP------·--·----- 23 Trigonia ... ---- ______. 21 Nonactaeonina attenuata.______22 Mancos Shale ... ------____ ------.. ------2, 3, 11 eufaulensis gabbi. ______23 Nucula pectincula sp______22 Buck Tongue.. ------15 planimarginata ______22,42 Tulotomops thompsoni. ..• ____ . ______44,45 Marine shale members of Haystack Mountains sp ••. -- .. __ . ______15, 16, 20,27 Tuba sp _____ ------______27 Formation ______. ____ ------. 14 Nuculana SP---·------33 Tulotomopslaevibasalis______26 Marine strata______------. 25 Oligotvcha concinna. ______42 thompson;______-~ 44,45 Allen Ridge Formation______25 sp •• --- .. __ . ______.. _____ 22, 23,27 Uintacrinus socialis. ______11 Medicine Bow Formation....•... 5, 7, 42, 43, 45, 46, 47 Ophiomorpha ••• ______13, Unio sp. ______44 Meek, F. B., cited.------41 15, 16, 17, 18, 19, 20, 21, 23, 25, 27, 28, Vetericardia sp______22 Meeteetse Formation •• ------33, 38,39 32, 34, 35, 36, 37, 40, 41 Menefee Formation•.... ___ ._. __ .. _.. _...... _ 2 sp ••. -- ...... _. ______. ______22 Viviparus sp ______------27,45 Mesa Verde Group______2 Westeria. ______. ______22 Ostrea •• ---. ______10, 11 Mesaverde Formation •• ------. 9, 5, 11,29 albertensis .•••• ______20 Yoldia evansL ______22,27,33 Almond coal group.------31 congesta. __ • ______. ______11 Fox Hills Formation. ______7, 36, 38,41 Fales Member. __ ------_____ 11, 15 plumosa. _------______22 Fox Hills Sandstone... ______5 Parkman Sandstone Member •. -.-.-...... 26 russelli. •• _.. __ . ______20, 21, 22, 23,41 Teapot Sandstone Member __ .. _..... _.. _. 29, 31 subtrigonalis. ______23 G Mesaverde Group ____ .------S, 3, 5, 11, 14,29 sp ______16, 18,22, 27, 41,42 Gale, H. S., cited______2,3 Missouri River region, stratigraphic classifica- Oxybeloceras sp. ______23 Geology of Sim Juan district.. .. ______2 cation of Cretaceous rocks .... ___ . I Oxytoma nebrascana ______18, 22, 23,42 Gill, J. R., cited______30 Montana Group .... ------···-·-----· 3 sp. ------. __ 15, 23, 27,33 sections measured by ___ 15, 19, 27, 31, 34, 35, 39, 40 Panopea sp ______------34 Gilmore, C. W.,fossilidentified by______46 N,O Pecten SP------__ ------______41 Perrisonota sp______22 H North Park Formation.------·-·-·-· 47 Pholadomya sp ______27, 40, 41,43 Hale, L.A., cited ______12,37 Northwestern Colorado, stratigraphic classifl· Physa reesidei______44 · Hancock, E. T., cited ______------· 3 cation •• _. ______. ______..... ____ 2 Pinna lakesi. ______------______23 sp •• -- ..... -- .. -- ___ . _____ . _. ______15 Hanna Basin ... 3, 5, 7, 10, 24, 25, 26, 33, 37, 43, 44, 45,46 Pistillipollenites .•.. ______48 lianna Formation .. ______5, 7, 45, 46,47 O'Brien Spring.. ____ .. ---- __ ------.---.. ---. 12 O'Brien Spring Sandstone Member of Hay- Placenticeras intercalare ______. 10, 17, 22, 23, 27 Hatfield dome .. ______10, 12, 13 stack Mou,ntains Formation .. 5,12, 19,15 meekL. ______10 Hatfield dome area, fossil collections ______. ___ 10,11 Hatfield Sandstone Member of Haystack sp-.----...... -.. __ .. ___ . 15, 18, 22, 23, 24, 28 p plant microfossils .... ______47,48 Mountains Formation .. _____ 5, 12, 13,15 Ferris Formation______46 Hayden, F. V., cited. __ ------41 Parkman Sandstone Member of Mesaverde Haystack Mountains. ______12,26 Foote Creek Formation.______45 Formation...•... ------_____ 11,26 Platycarya______.!7 Haystack Mountains Formation ______5, 10,11, 12,25 Phayles Member of Mesaverde Formation.___ 11 Plesielloptio postbiplicata. ______44, 45 Hatfield Sandstone Member ______5, 12, 13,15 Phayles Reef Member of Mesaverde Forma- Marine shale members ______. 14 tion. ___ . ____ ._. ______. __ . __ .__ 11 sp ______------_____ 27,45 Plethobasis aesopiformis. ______. ______44 O'Brien Spring Sandstone Member .. 5, 12, 13,15 Pictured Cliffs GroUP------·------! Tapers Ranch Sandstone Member ___ 5, 12, 13,14 Pictured Cliffs Sandstone. ___ ------. 3 INDEX 53 Page Page Page Pierro Shale •••...... ------...... ------39 Siebenthal, C. E., cited...... 3, 7 Type locality, Almond Formation ...... _._ 31 Ardmore Bon ton ito Bod In Sharon Springs Sohl, N .F., fossils identified by...... _.... 2I, 27,42 Lewis Shale ••...... 36 Mombor...... IO South-central Wyoming, !ltratigraphic classifi- Fox Hills Formation. ____ ...... _...... 41 Kara Bon tonltic Mom bcr _...... 33 cation...... S Pine Ridge Sandstone __ .. _._ ...... 29 Plno Rldgo ...... :...... 29 Southwestern Colorado, stratigraphic classifi- Type locality and distribution, Steele Shale._ 7 PI no R ldgo Sandstone •...... 5, 11, £9 cation •...... ______f Type section, Haystack Mountains Forma- Point Lookout Sandstone ..• _...... 2 Smith,J.H.,Cossils collected by______IO tion. _____ ... _...... _...... I2 Powder Rlvor Basin .••.•...... 7, IO, n; I4 Spencer, A. C., cited ••• --·····-· .... __ ...... 2, 36 Haystack Mountains Formation and its Price River Formation...... 5 Stanton, T. W., cited______2I O'Brien Spring and Tapers Creek fossils identified by------______: ...... _ 48 Sandstone Members __ . _...... 15 R Star Point Sandstone______5 Rock River Formation•... __ ..... _._ ... _. £0, £1 ·Steele Shale ______S, 7,14 Wallace Creek Tongue of Cody Shale..... 11 Roosldo, J. B., cited...... 3, 5 Shannon Sandstone Member.______14 Roforonco section, Allen Ridge Formation_ £4, £6. 27 Sussex Sandstone Member______I5 u,v Almond Formation...... SS Stratigraphic nomenclature, revision...... 5 Dad Sandstone Member of Lewis Shale... 39 Summary of stratigraphic nomenclature...... 5 Unconformity, at base-or Foote Creek Forma- Hatfield Sandstone Mombor or Haystack Sussex Sandstone Member or Steele Shale_---- IS tion. ___ . __ .. __ .. _.. _.. _...... __ .. 45 Mountains Formation...... 19 between Ferris and Hanna Formation_.__ 46 •• Haystack Mountains Formation...... I7 T Plno Ridge Sandstone...... 31 Tapers Ranch.. ------····-··-·······- I2 Lewis Shale, Dad Sandstone Member..... 39 Tapers Ranch Sandstone Member of Haystack Veatch, A. C., cited._ ...... __ ...... -- .. _.. 3, 5 Reynolds, M. W., cited._ ...... 25, 30, 32, 37,38 Mountains Formation .•..... 5, 1£, 13,14 Rock River aroa of Laramie Basin, Steele Teapot Sandstone Member of Mesaverde For- w Shale...... IO mation._ ...... ___ ...... _ ·II, £9, 31 Rock River Formation ...... 5, 11, £0, 25, £6 Telegraph Creek Formation .... _.. _...... II Wallace Creek Tongue of Cody Shale. ___ ._ ... 11, IS Rock Springs upl!Ct. ___ ...... _ 26, 3I, 39 Thickness, Allen Ridge Formation._ ... ______£6 Williams Fork Formation ______3, 5, 3I, 33 Almond Formation______Sf Lion Canyon Sandstone Member_ .. -_ ... _ 43 s Fox Hills Formation______4£ Wind River Basin ...... 11,26 Haystack Mountains Formation...... JS Wyoming, uplift in centraL.------.-- 37 38 San Juan district, geology ____ ...... £ Lewis Shale______Pine Ridge Sandstone______£9 Schultz, A. R., cited ••••...... 5,3I Y,Z Rock River Formation...... £1 Scott, G.R., typosoctionmoasured by ______2I Steele Shale..• ----···-·-······-···-······- 10 Yampacoalfield...... f 4.- Separation Rim •...... I4 Tschudy, R. H., cited ...... 5,45,46,47 Shannon Sandstone Mombor or Steele Shale._ I4 fossil collections described by_...... 48 Zapp, A. D., reference section measured bv.. I7 ~.... 0 r'