The Pierre Shale Near Kremmling,"' Colorado, And Its Correlation to The East and the West
GEOLOGICAL SURVEY PROFESSIONAL PAPER 684-A
The Pierre Shale Near Kremmling, Colorado, And Its Correlation to The East and the West
By G. A. IZETI, W. A. COBBAN, and ]. R. GILL
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
GEOLOGICAL SURVEY PROFESSIONAL PAPER 684-A
Stratigraphy, faunal zonation, and correlation of the Pierre Shale
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971 UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY
William T. Pecora, Director
Library of Congress catalog-card No. 79-611461
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402- Price 70 cents (paper cover) CONTENTS
Pa&-e Page Abstract ______A 1 Pierre Shale-Continued Regional geologic setting ______2 Middle part-Continued Present work ______4 Unnamed shale member ______A14 Previous work ______7 Hygiene Sandstone Member_--_------__ 14 Acknowledgments ______7 Unnamed member-- ______-- __ _ 14 Pierre Shale ______7 Carter Sandstone Member ______14 Lower part ______7 Unnamed shale member ______15 Sharon Springs Member ______10 Gunsight Pass Member ______16 Middle part ______11 Upper part______16 Kremmling Sandstone Member______12 Correlation of the Pierre Shale to the east and to the west_ 17 Unnamed shale member ______12 References cited ______------_------19 Muddy Buttes Sandstone Member______12
ILLUSTRATIONS
Page PLATE 1. Columnar section of the Pierre Shale in the Kremmling area ______In pocket
FIGURE 1. Geologic sketch map of northern Colorado showing outcrop areas of Pierre Shale, Mancos Shale, and Iles and Williams Fork Formations______A2 2. Correlation chart of selected Upper Cretaceous rocks from Hamilton to Boulder, Colo ______------3 3. Geologic sketch map of the Kremmling 15-minute quadrangle showing distribution of the Pierre Shale __ ------6 4-11. Photographs of: 4. Septarian limestone concretion characteristic of the Sharon Springs Member______10 5. Buttress-weathering black shale characteristic of the upper part of the Sharon Springs Member______11 6. Calcareous sandstone concretions below the top of the Kremmling Sandstone Member______12 7. Type locality of the Kremmling Sandstone Member------'- 13 8. Type locality of the Muddy Buttes Sandstone Member ______----- 13 9. Hygiene Sandstone Member______15 10. Type locality of the Carter Sandstone Member______15 11. Upper sandstone and middle shale parts of the Gunsight Pass Member______17
TABLES
Page TABLE 1. Chart showing comparison of estimated thicknesses of range span of index ammonite zones in Pierre Shale in the Kremmling area with other sections of the Pierre Shale exposed along the eastern Front Range in Colorado and the southern Black Hills in Wyoming______A5 2. Fossils from the Pierre Shale______8
m
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
THE PIERRE SHALE NEAR KREMMLING, COLORADO, AND ITS CORRELATION TO THE EAST AND THE WEST
By G. A. IzETT, W. A. CoBBAN, and J. R. GILL
ABSTRACT The Pierre Shale of early Campanian to early Maestrichtian in the Range Zone of Didymoceras stevensoni. About 900 feet of age is well exposed near Kremmling, Grand County, Colo. It sandy shale that contains several levels of fossiliferous concre contains many levels of concretions that yield numerous fossil tions overlies the Carter and includes the Range Zones of B. marine mollusks useful for regional correlation. Much of the compres.Ytts, B. cuneatus, B. reesidei, and B. journal. The Gun Pierre was removed by erosion during Laramide deformation sight Pass Member is the upper 150-170 feet of the middle sandy prior to the deposition of the Middle Park Formation of Late part of the Pierre and consists of two standstone units separated Cretaceous(?) and Paleocene age, and the maximum remaining by about 100 feet of silty shale. The member possibly is in the thickness is about 5,000 feet. Regional correlation indicates that Range Zone of B. eliasi or B. jenseni. between 3,000 and 4,000 feet of the upper part of the Pierre was The upper part of the Pierre remaining in the Kremmling removed during Laramide time. area consists of about 200 feet of marine shale and lies within In the Kremmling area, the Pierre can be divided into three the Range Zone of B. eUasi. parts. A lower part, about 1,500 feet thick, consists chiefly of The excellent fossil record in the Pierre near Kremmling per dark-gray to black nonsandy ma!'ine shale. The distinctive mits correlation with the Pierre to the east near Boulder and Sharon Springs Member, about 45 feet thick, is about 1,100 feet with the Mesaverde Group to the west near Hamilton by way of above the base of the lower part and contains at least eight Fish Creek. The lower shale part of the Pierre (1,500 ft thick) bentonite beds. Ammonite zones in the lower part of the Pierre near Kremmling correlates with about the lower 1,000 feet of in ascending order include Baculites sp. (weak flank ribs), the shaly unit (1,650 ft thick) near Boulder. The middle sandy B. obtusus, B. mclearni, and B. asperiformis. part (3,300 ft thick) of the Pierre near Kremmling correlates The middle sandy part of the Pierre, about 3.300 feet thick, with about the upper 600 feet of the lower shale unit, the middle consists of alternating sandy shale and several newly named sandy unit (2,400 ft thick), and about the lower 100 feet of the sandstone members. In ascending stratigraphic order, the mem upper shaly unit near Boulder. The upper shale part of the bers and their thicknesses are as follows : The Kremmling Sand Pierre near Kremmling correlates with that part of the upper stone (new name), 20-70 feet thick; the Muddy Buttes Sand shaly unit from about 100 to 700 feet above the ba·se near stone (new name), 5-30 feet thick; the Hygiene Sandstone, 50- Boulder. 120 feet thick ; the Carter Sandstone (new name) , 30-65 feet The lower shale unit of the Pierre near Kremmling correlates thick; and the Gunsight Pass (new name), 150-170 feet thick. with the Mancos Shale from Fish Creek to near Hamilton ; this The lower 400 feet of the middle sandy part of the Pierre con correlation is with the units above the Niobrara Member and sists of silty shale with a few interbedded sandstone beds. Of below a prominent zone of large sandstone concretions about this 400 feet, the lower 200 feet is within the Range Zone of B. 2,500 feet above the Niobrara that yield B. asperiformis. The asperiformis, and the upper 200 feet is within the Range Zone of middle sandy part of the Pierre correlates with about the upper B. perplexus. The Kremmling Sandstone Member is about 400 1,000 feet of the Mancos and the Iles and Williams Fork Forma feet and the Muddy Buttes Sandstone Member is about 600 feet tions. The Kremmling Sandstone Member probably correlates above the base of the middle sandy part of the Pierre. Both with the upper sandstone in the Mancos near Fish Creek, and members are within the Range Zone of B. perplexus. An un the Muddy Buttes Sandstone Member is in the same strati named silty shale member about 1,000 to 1,200 feet thick over graphic position as the Loyd Sandstone Member of the Mancos lies the Muddy Buttes Sandstone Member; the lower 130 feet Shale near Hamilton. The Hygiene correlates with an un is in the Range Zone of B. perplexus, the middle 670 feet is in the Range Zone of B. gregoryensis, and the upper 200 feet is in the named sandstone above the Tow Creek Sandstone Member of the Range Zone of B. scotti. The Hygiene Sandstone Member is Iles Formation, and the Carter is equivalent to nonmarine shale, about 1,600 to 1,800 feet above the base of the middle sandy part sandstone, and coal beds in the upper part of the Iles. The Gun of the Pierre and is in the Range Zone of B. scotti. About 370 sight Pass ~!ember probably correlates with the Twentymile feet of sandy shale separates the Hygiene from the overlying Sandstone Member of the Williams Fork Formation. The upper Carter Sandstone Member. The upper 200 feet is probably in the shale in the Kremmling area correlates with the lowermost part Range Zone of Didymoceras nebrascense. The Carter is possibly of the Lewis Shale west of the Park Range. Al A2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
REGIONAL GEOLOGIC SETTING shale and sandstone assigned to the Pierre Shale ; on a The Pierre Shale, of Late Cretaceous age, in Middle regional scale it is characterized by western-pointing Park near Kremmling, Grand County, Colo., contains wedges of marine shale and eastern-pointing sandstone many levels of concretions that yield numerous marine tongues. A western facies, which lies west of Kremmling fossil mollusks useful for regional correlation. The for and west of the Park Range, consists of interbedded mation is locally well exposed near l(remmling, and units of marine and nonmarine shale, sandstone, and outcrops of the formation are the most complete of coal assigned to the Mancos Shale and to the Iles and those in Middle, North, and South Parks known to the Williams For!{ Formations of the Mesaverde Group writers. The purpose of this paper is to briefly describe (fig. 1). the Pierre Shale in the Kremmling area and to correlate Rocks of the Pierre Shale represent accumulations the formation to the east near Boulder, Colo., and to of mud, silt, and sand deposited in the deeper parts the west near Hamilton, Colo., by way of Fish Creek of the Late Cretaceous epicontinental sea that covered (fig. 1). much of the Western Interior region of North America. Much of the sediment delivered to this sea originated The Pierre in Middle Park is separated from the in a narrow unstable and constantly rising cordillera Pierre of the Great Plains and from Cretaceous rocks that bordered the sea on the west. Rocks deposited mar of western Colorado by the uplifted Precambrian crys ginal to the source consist of eastward-pointing wedges talline cores of the Front and Park Ranges. An under of shallow-water marine and nonmarine strata (lies and standing of the biostratigraphic relations of the Pierre Williams Fork Formations of the Mesaverde Group in in Middle Park is, therefore, especially important to northwestern Colorado) enclosed in westward-pointing reconstruct stratigraphic details of the regional east wedges of fine-grained marine· strata which are tongues west facies changes in Pierre age rocks. An eastern of the Pierre Shale but which have been designated the facies, which lies east of the Park Range and includes Mancos and Lewis Shales (fig. 2). Beyond the eastern the Kremmling area, consists of interbedded marine limit of intertonguing with coaly rocks, the entire se-
107" WYOMING 106° 105° COLORADO
-u lJ.J )::> ::u ~~ (!} ?' ~ ~ ~ "(' cr
1- 2 0 lt LL..
DENVER 0
Dillon~
0 25 MILES
FIGURE 1.-Geologic sketch map of northern Colorado showing large outcrop areas of Cretaceous marine shale and sandstone of the Pierre Shale (shaded) and Cretaceous marine shale and sandstone and nonmarine mudstone, siltstone, and 8andstone of the Mancos Shal·e and the lies and Willbms Fork Formations (diagonal ruling). Contacts modified from Burbank, Lov ering, Goddard, and Eckel (1935), Hail ( 1968), Izett ( 1968), and Barclay ( 1968) . Hamilton, Colo., area Fish Creek, Colo., area Kremmling, Colo., area Boulder, Colo., area (Konishi, 1959; Bass and (Bass and others, 1955) (this paper) (Scott and Cobban, 1965) others, 1955; this report) PARK RANGE FRONT RANGE
GROUPI r6Rri.A.r1ar:d · 26 Miles 58 Miles MEMBER I FORMATION Fox Hills 43~ Sandstone
c. ~ "' Upper t;oj Q)
t'1~ . --- ~ ~?--~0 -~---~-"·~"!''-""'"'"" z1-t -"' 0 ~0 lJ.. Larimer and Rocky Ridge Pierre (") Sandstones 0 j Shale Q) t'1 "0 ~ 0 Q) > ~ ))l > t:::l ~ ._:======~~=~=,~--~~ Baculites compressus. . ----:=;==j Sandstone,Terry Exiteloceras Jenney1 . ~ ·j ~0 · Didzrrnoceras stet•ensom DidyTrw'ceras nebrascense (") 0 ~ ~ • Anapachydiscus ~ t;oj Baculites scotti Hygiene
Sandstone I Baculites---. gregoryensis :::: -~--1-----...,.=1,·.. ,.:: s1-t Muddy Buttes Sandstone Member Baculites perplexus 0z Baculites perplexus Kremmling Sandstone Member • Bacu/ites perplexus _ 1-3 Baculites asperiformis 0
~ ._ ~!Lct:tnt-_t:~ ,~ncr,t::tHn,., 1 • Bncuiites mclea.rni ~ Bacul·ites m.clearn·i : 7 "' • ~ ~ ----- Sharon Springs Member Baculites obtusus Lower t;oj Q) llJ transition ~ Q) Niobrara t;oj (I) en Q) (part) 0 ii: [J1> FIGURE 2.-Correlation of selected Upper Cretaceous rocks from Hamilton to Boulder, Colo. ~ A4 ,SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY quence of marine shale and interbedded sandstone is Kremmling and made tentative correlations with sand referred to the Pierre Shale. stone beds in the Pierre east of the Front Range. Hail The eastern margin of the sea was bounded by the (1968) mapped the Pierre north of the Kremmling low-lying stable platform of the central part of the quadrangle, and Izett (1968) mapped the Pierre east United States. It seems that this area contributed little of Kremmling near Hot Sulphur Springs, Colo. sediment to the sea, and all evidence of the position of the eastern shore has been removed by post-Cretaceous ACKNOWLEDGMENTS erosion. Stratigraphic studies of the Pierre Shale in R. R. Trengove, N. T. Blake, and J. E. Peterson the northern part of the Western Interior region (Gill assisted in the field, measuring stratigraphic sections and Cobban, 1965, 1966) indicate that the Pierre grades and collecting fossils. Cobban identified most of the from marine shale in the central part of the sea way fossils. into shallow-water carbonate rocks in the eastern part PIERRE SHALE of the seaway. The Pierre Shale of figure 2 ranges in age from early The Pierre near Kremmling can be divided into sev Campanian to early Maestrichtian and represents a time eral mappable marine sandstone members, newly named span of about 12 million years. In 195·2, Cobban and herein, separated by unnamed members of marine shale Reeside recognized six ammonite zones in the Pierre and silty and sandy shale. The newly named sandstone Shale and equivalent rocks, whereas in the same rocks members of the Pierre are, in ascending order, the in 1966, Cobban (Gill and Cobban, 1966, p. A35) recog Kremmling, Muddy Buttes, Carter, and Gunsight Pass nized 28 ammonite zones, each occupying a time span ,Members. The names Sharon Springs Member and of about one-half million years (table 1). A comparison Hygiene Sandstone Member of the Pierre are extended of the thickness of beds that contain certain index from the Great Plains into the Kremmling area. A ammonites for selected areas is shown in table 1. Because columnar section of the Pierre in the Kremmling area these ammonites and their associated molluscan fauna (pl. 1) shows the general lithology and the position of have a limited vertical stratigraphic range but a broad selected fossil mollusk collections. Only a few of the geographic range and occur in a variety of marine rocks, many fossil mollusk collections made in the Kremmling they are an indispensable aid for correlation in the area are shown on plate 1 to establish the succession of Western Interior. index ammonites. In addition to the index ammonites of Gill and Cobban ( 1966) shown on plate 1 other fossils PRESENT WORK associated with the ammonites from the Pierre are given in table 2. Not all the fossils shown on plate 1 were This paper is a result of current detailed mapping of collected along the line of the measured sections; some the Kremmling 15-minute quadrangle, stratigraphic stratigraphically important collections from elsewhere studies of the Pierre by Izett, and regional stratigraphic in the area were projected into the generalized columnar studies of Upper Cretaceous rocks in Montana, Wyo section where stratigraphic control was good. ming, and Colorado by Gill and Cobban. A preliminary The Pierre Shale, which is about 5,000 feet thick, can sketch map (fig. 3) that shows the distribution of the be divided for purposes of discussion into three parts. Pierre Shale in the Kremmling quadrangle includes A lower part chiefly consists of dark-gray to black non the line of outcrop of several members and a zone of sandy marine shale about 1,500 feet thick. It is overlain concretions of the formation. by a middle part of interbedded marine silty shale and sandstone about 3,300 feet thick. An upper part, which PREVIOUS WORK originally could have been between 3,000 and 4,000 feet The Pierre near Kremmling was first mapped and thick, has largely been removed by erosion, and only studied by Marvine (1874) of the Hayden Survey, who about 200 feet of dark-gray shale is preserved in the recognized the formation's equivalence to the marine area. The top of the lower shale part of the Pierre occurs Cretaceous Pierre of the Great Plains. More recently, about 10-20 feet below fossil collection D5412 (pl. 1) ; the Pierre near Kremmling was studied as part of sev the top of the middle sandy part is at the top of the eral theses, including those by Richards ( 1941), Miles Gunsight Pass Member and below collection D6575 (1961), Holt (1961), Howard (1961), and Barclay (pl. 1). ( 1968). Griffitts ( 1949) made regional correlations of At some places in Middle Park, part of the Pierre was the Pierre of the Kremmling area with the Pierre east removed by erosion during Late Cretaceous deforma of the Front Range, Colo. In the late 1950,s, Scott and tion prior to the deposition of the Middle Park Forma Cobban ( 1959) collected fossils from the Pierre near tion of Late Cretaceous ( ?) and Paleocene age, and only PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST A5 TABLE 1.-0omparison of the estimated thicknesses (in feet) of the range span of index ammonite zones in the Pierre Shale in the Kremmling area with other sections of the Pierre Shale exposed along the eastern Front Range in Colorado and the southern Black Hills in Wyoming. Selected Esti- Boulder, Colo. Pueblo, Colo. Red Bird, Wyo. Upper Cretaceous Western Interior ammonite Kremmling, potassium- mated (Scott and (Scott, 1969, (Gill and Cobban, stages and substages sequence Colo. argon dates dates Cobban, 1965) p. 83, pl. 1) 1966, p. A28-A34) Middle Park 631 63 Erosion? Formation (part) 64±21 64 65 upper Lance 66±21 66 Laramie Formation Formation Maestrichtian 67 Erosion r--- 68 Discoscaphites nebrascensis I roanensis 69 Sphenodi.scus (Coahuilites) Fox Hills Fox Hills Sandstone lower 580± Baculites clinolobatus 855+ 175+ 701 70 grandis 740 225 baculus 770 215 71 eliasi 340+ 880 240 jenseni 210 130 65 --- 72 reesidei 260 500 135 cuneatus 50 120 5 (undated; possible 75±21 73 compressus 75 115 unconformity) Didymoceras cheyennense 115± 135 0 Top of exposure <:<1 0 00- 74 Exiteloceras jenneyi 110± 70 50± 115 Ill Oil +I Didymoceras stevensoni + 110 ..<:: 290 100+ 0 30 0 w. 0 Ill s upper 3 0> Cfi 75.5± 12 75 nebrascense ""1'- 220 380 100 100 '"' Ill Ill'"' ..., ?l:; Oil 690 525 ..<:: 190 Baculites scotti '"'ol 430 w. -5 + Ill 76 120 I:: 310 gregoryensis ~ 500 130 ~ ol ~ .:ll Campanian ..<:: ...... - p.., perplexus (late form) w. Ill t I:: ol 77 gilberti Ill 705 590 200 250 900 ?l:; -5 ~} Ill - perplexus (early form) Oil 525 ..<::w. 78 sp. (smooth) 0 0 ~ 0 100 .:ll asperiformis 560 420 p.., 40 155 r--- 79.5±22 79 ·mclearni 50 140 10? 55 obtusus 180 265 40 90 80 sp. (weak flank ribs) 510 ~~~~~t:d~ 290 sp. (smooth) 140 lower 425± ------30 (undated interval) 81±21 81 Scaphites hippocrepis III ------hippocrepis II Niobrara Niobrara Formation Niobrara 82 hippocrepis I Formation (part.) Formation Niobrara (part) (part) Formation Desmoscaphites bassleri (part) Santonian upper (part) 83 erdmanni 1 Potassmm-argon dates summarized by Gill and Cobban (1966, p. A35). 2 J.D. Obradovich (written commun., 1968). 3 Mean of age determinations on two separate bentonite samples. 418-228 0-71--2 A6 ,SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 106°30' R. 79 W. 106°15' 40° 15',------.--- --'-'-F-~'-'------,------,-----~---. R. 80 W. EXPLANATION T. Contact 3 Approximately located, dashed where indefinite N. D u Fault D, downthrown side; U, upthrown s·ide 0 2 3 MILES R 79Y2 W Wolford Mountain I \ T. 1 I N. • COLORADO Geology by G. A. lzett and C. S. V. Barclay, 1963-64 I FIGURE 3.-Distribution of the Pierre Shale (shaded) including outcrop traces of several members and a zone of concre tions of the formation, Kremmling 15-minute quadrangle, Grand County, Colo. Members and type localities (numbered) identified on facing page. PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST A7 about the lower two-thirds of the Pierre remains. At 2 inches thick occur in the uppermost part of the Ni other places in Middle Park, all the Pierre and older obrara and the lower 50 feet of the Pierre. Mesozoic formations are truncated beneath the uncon formity at the base of the Middle Park Formation. In TABLE 2.-Fossils from the Pierre Shale Middle Park where the Pierre is preserved the middle USGS Collector sandy part of the formation is only slightly thicker than Mesozoic Location and year Fossils the equivalent part of the Pierre near Boulder, Colo., locality described by Scott and Cobban ( 1965). If thicknesses D5995-NEUNWU sec. 16, G. A. Izett, Inoceramus sp. of the Pierre near Kremmling are comparable with T.3N., R.80W. 1967. Hoploscaphites sp. thicknesses near Boulder, then about 3,000 feet of the D6575-SEUSEU sec. 8, T. G. A.lzett, Inoceramus typicus (Whitfield). 3 N., R. 80 W. 1968. Pecten ( Chlamys) nebrascensis Meek and upper part of the formation was eroded during latest Hayden. Cretaceous time in Middle Park. Younger Cretaceous Baculites eliasi Cobban. Baculites sp. (baculus-grandis group). formations, the Fox Hills Sandstone and the Laramie Fish scale. Formation of the Great Plains, were probably present D7047-NEUSWU sec. 8, G. A. Izett, Lucina sp. T. 3 N., R. 80 W. 1969. Pseudobaculites sp. in Middle Park, but were removed during Laramide D6565-SEUSEU sec. 12, G. A. lzett, Baculites jenseni Cobban. time. T. 3 N., R. 81 W. 1968. D6564-_____ do ______do ______Inoceramus sp. LOWER PART Baculites sp. D5971-SWUSWU sec. 8, G. A. Izett, Lingula sp. The lower part of the Pierre Shale is intermittently T. 3 N., R. 80 W. 1967. Inoceramus sp. well exposed in roadcuts along Colorado State High Anisomyon centrale Meek. Baculites cf. B. reesidei Elias. way 9 south from Kremmling to near Dillon, Colo., and Hoploscaphites nodosus (Owen). north of Kremmling along and generally west of U.S. D6568-NEUNEU sec. 18, G. A. Izett, Pyriporoid bryozoan (on baculite). T. 3 N., R. 80 W. 1968. Inoceramus barabini Meek. Highway 40 to near Muddy Pass. Anomia sp. Near Kremmling, as elsewhere in Middle Park, the Astarte sp. Thetis circularis (Meek and Hayden). lower part of the Pierre is composed of about 1,500 feet Geltena? gracilis (Meek and Hayden). of dark-gray to black fissile nonsandy marine shale. The Drepanochilus sp. Baculites reesidei Elias. unit is easily distinguished on electric logs as a generally Hoploscaphites nodosus (Owen). uniform shale unit. It is generally clay shale that only D6563-SEUSEU sec. 12, _____ do ______Inoceramus sp. T. 3 N., R. 81 W. Baculites reesidei Elias. rarely contains a few thin silty and sandy zones less Hoploscaphites nodosus (Owen). than 2 feet thick. Several bentonite beds less than 3 Placenticeras sp. D6569-NEUNEU sec. 18, _____ do ______Inoceramus sp. inches thick crop out near the base of the unit, 350--400 T. 3 N ., R. 80 W. Baculites reesidei Elias. feet above the base, and in the Sharon Springs Member. Hoploscaphites nodosus (Owen). D1284-SWUSWU sec. 7, D. Arnold Bryozoan (on Inoceramus). At the base of the Pierre is a calcareous shale 10 feet T. 3 N ., R. 80 W. and W. A. Inocermnus cf. I. vanuxemi Meek and or less thick that is transitional into the underlying Gillespie, Hayden. 1956. Ostrea inornata Meek and Hayden. Niobrara Formation. The contact between the transi Baculites cuneatus Cobban. tional part of the Pierre and the Niobrara is well ex Hoploscaphites nodosus (Owen). D1351-NWUSWU sec. 17, G. R. Scott Inoceramussagensis Owen. posed at several places in the Kremmling area ; one of T. 3 N ., R. 80 W. and W. A. Inoceramus vanuxemi Meek and Hayden. the better exposures is in the SW~ sec. 33, T. 1 N., R. Cobban, Ostrea inornata Meek and Hayden. 1957. Pecten (Camptonectes) sp. 80 W., just east of State Highway 9. There, rocks as Anomiasp. signed to the Niobrara are calcareous speckled platy CymellabeUa Conrad. Baculites compressus Say. shale that weathers tan, overlain by a few feet of dark Anaklinoceras reflexum Stephenson. gray flaky calcareous shale assigned to the Pierre. Sev Axonoceras compressum Stephenson. Hoploscaphites nodosus (Owen). eral yellowish-weathering thin bentonite beds less than Placenticeras meeki Boehm. EXPLANATION OF FIGURE 3 Gu, Gunsight Pass Member, upper sand H, Hygiene Sandstone Member (Zone 1, Kremm~ing Sandstone Member; stone part (Zone of Baculites eliasi) ; of BacuUtes scotU) ; 2, Muddy Buttes Sandstone Member; Gl, Gunsight Pass Member, lower sand M, Muddy Buttes Sandstone Member 3, Carter Sandstone Member ; stone part; (Zone of Baculites perplewus) ; 4, Gunsight Pass Member, lower sand cz, concretion zone (Zones of Baculites K, Kremmling Sandstone Member (Zone stone and middle shale unit; compressus and B. cuneatus) ; of BacztlUes pcrplexus) ; 4a, Gunsight Pass Member, upper sand· C, Carter Sandstone Member ; stone unit. AS SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 2.-Fossils from the Pierre Shale-Continued TABLE 2.-Fossils from the Pierre Shale-Continued USGS Collector USGS Collector Mesozoic Location and year Fossils Mesozoic Location and year Fossils locality locality D6556-SE~SE~ G.A.lzett, Inoceramus sp. D5974-NW74NE~4 sec. 30, _____ do ______Pyriporoid bryozoan (attached to sec. 12, T. 1968. Ostrea sp. T. 3 N., R. 80 W. baculite). 3N., R.81W. Baculitescompressus Say. Nuculana sp. Hoploscaphites nodosus (Owen). Inoceramus sp. D6557-SE~SE~ _____ do ___ ----- Inoceramus vanuxemiMeek and Hay- Baculites scotti Cobban. sec. 12, T. 3 den. · Didymoceras u. sp. N.,R.81W. Hoploscaphites brevis (Meek). Anapachydiscus complexus (Meek and D5985-Center SW~ sec. 1, G. A. Izett, Perrisonota sp. Hayden). T.3,N., R.81 W. 1967. Nucula sp. D5966-NWUSW~ sec. 32, _____ do ______Pyriporoid bryozoan(on inoceram). Nuculana sp. T.3N.,R.80W. Inoceramus sp. Inoceramus sublaevis Hall and Meek. Pteria cf. P. linguaeformis (Evans and Pteria linguaeformis (Evans and Shu- Shumard). mard). Baculites gregoryensis Cobban. Ostrea sp. Didymoceras sp. Pecten (Syncyclonema) sp. Menuites n. sp. Laternula sp. D599Q-NEUNEU sec.ll, G. A. Izett Pyriporoid bryozoan (attached to Cuspidaria sp. T. 3 N., R. 81 W. and W. A. inoceram). Cardium sp. Cobban, Inoceramus sp. Dentalium pauperculum Meek and 1967. Lucina sp. Hayden. Baculites gregoryensis Cobban. Baculites crickmayi Williams. D6554-NWUNW~ sec. 13, G. A. Izett, Nucular&a sp. Hoploscaphites sp. T. 3 N., R. 81 W. 1968. Didymoceras stevensoni (Whitfield). D6007-SE~NE~ sec. 6, G. A. Izett, Inoceramus subcompressus Meek and Placenticeras sp. T.1N.,R.80W. 1967. Hayden. D5987-NWUNW~ sec., G. A. Izett Crinoid fragment. Baculites perplexus Cobban. 18, T. 3N., and W. A. Perrisonata sp. D6006-NEUNE~ sec. 6, W.A. Cobban, Calcareous worm tubes (attached to R.80W. Cobban, Nuculana sp. T.1N.,R.80W. 1967. baculite). 1967. Inoceramus sublaevis Hall and Meek. Pyriporoid bryozoan (attached to Ostrea sp. baculite). Cuspidaria sp. Cymbophora sp. Lucina sp. Baculites perplexus Cobban. Tenea circularis (Meek and Hayden). Hoploscaphites n. sp. Cymbophora sp. D6005-NWUNE~ sec. 6, G. A. Izett Inoceramus subcompressus Meek and Dentalium gracile Hall and Meek. T.1N.,R.80W. and W.A. Hayden. Cobban, Drepanochilus obesus Sohl (transitional BaLulites perplexus Cobban. 1967. form).l D5996-NE~NE~ sec. 1, _____ do ______Inoceramus subcompressus Meek and Ellipsoscapha subcylindrica (Meek and T. 2 N., R. 81 W. Hayden. Hayden).t Baculites perplexus Cobban. Oligoptycha sp.t D5997-_____ do______do ______Pyriporoid bryozoan (attached to Baculites crickmayi Williams. baculite). Hoploscaphites sp. Inoceramus subcompressus Meek and -----do______aff. Anderson. D6009-SWUNEU sec. 5, Inoceramus I. turgidus Hay· en. T.2N.,R.8QW. Pteria linguaeformis (Evans and Baculites perplex1ts Cobban. Shumard). D5401-NW~NE~ sec. 7, G. A. Izett, Pyriporoid bryozoan. Didymoceras sp. T.1 N., R. SOW. 1966. Cymbophora? sp. D5904-SW~ sec. 29, T. G. A. Izett, Calcareous worm tube (attached to Baculites gilberti Cobban. 4N., 1967. baculite). D5893-SEUNE~ sec. G. A. Izett, Inoceramus subcompressus Meek and &.sow. Oxytoma sp. 18, T. 2 N., 1967. Hayden. Cymella montanensis (Henderson). &.sow. Cymbophora sp. Tellina cf. T. scitula Meek and Hayden. Baculites perplexus Cobban. Cymbophora formosa (Meek and Hay- D6014-NW~SE~ sec. _____ do ______Baculites perplexus Cobban. den). 33, T.1 N., Oligoptycha sp. R.SOW. Eutrephoceras sp. D6546-SWUSEU G. A. Izett, Baculites perplexus Cobban. Baculites scotti Cobban. sec. 33, T. 1 N., 1968. Didymoceras n. sp. &.sow. sp. Placenticeras D655Q-SEUSEUNW~ _____ do ______Baculitiet perplexus Cobban. D5964-NW~ NW~ sec. _____ do ______Calcareous worm tube. sec. 7, T. 1 N., 12, T. 3 N., Dysnoetopora demissa (White). R.sow. R.81W. Pteria linguaeformis (Evans and Shu D6549-_____ do ______do ______Inoceramus subcompressus Meek and mard). Hayden. Oxytoma cf. 0. nebrascana (Evans and Cymbophora sp. Shumard). Baculites perplexus Cobban. Ostrea sp. D5916-SEUSE~ sec. 18, G. A. Izett, Inoceramus subcompressus Meek and Pecten (Camptonectes) sp. T.2N.,R.80W. 1967. Hayden. Crenella sp. Baculites asperiformis Meek. Baculites scotti Cobhan. D6548-SEUSEUNWU G. A.Izett, Inoceramus subcompressus Meek and Placenticeras sp. sec. 7, T. 1 N., 1968. Hayden. Crab fragments. &.sow. Baculites asperijormis or B. perplexus. See footnote at end of table. PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WES'D A9 TABLE 2.-Fossils from the Pierre Shale--Continued medium-gray dense limestone concretions as much as 2 feet in diameter that weather yellowish gray occur USGS Collector Mesozoic Location and year Fossils chiefly in the Sharon Springs Member. Yellowish-gray locality weathering septarian limestone concretions as much as D5400-_____ do ______G. A. Izett, Pyriporold bryozoan (on baculite). 4 feet in diameter occur: in the upper part of the Sharon 1966. Inoceramus sp. Springs and in the overlying black shales (pl. 1; fig. 4). Cymbophora sp. Baculites asperiformis Meek. Fossils are locally abundant in the lower part of the Hoploscaphites sp. Pierre, especially in the Sharon Springs Member. Fos D5409-NE~NE~ ..... do ______Inoceramus sp. sec. 1, T. 1 Pteria linguaeformis (Evans and Shu sil fish vertebrae were found about 50 feet above the N., R. 81 W. mard). base of the Pierre, and fish scales are common in many Cymbophora sp. Baculites asperiformis Meek. of the thin platy ironstone concretions. Poorly preserved Hoploscaphites sp. D5412-___ .. do .. ______do ______Inoceramus sp. impressions in shale of a smooth baculite were found Cymbophora sp. in the lower 200 feet of the Pierre. These may represent Baculites sp. (noded juveniles). the Zone of Baculites sp. (smooth). (See Gill and Cob Hoploscaphites sp. D601&--WY:;SE~ W. A. Cobban, Inoceramus subcompressus Meek and ban, 1966, p. A35, for Western Interior ammonite 33, T. 1 N., 1967. Hayden. sequence.) About 700 feet above the base of the Pierre, R.sow. Baculites sp. D7042-Center. sec. G. A. Izett Baculites asperiformis Meek. limestone concretions contain weakly ribbed baculites 18. T. 2N., and J. E. representing the Zone of B aculites sp. (weak flank R.8oW. Peterson, 1969. ribs). Poorly preserved specimens of Baculites obtusus D697l -NE~SW~ sec. G. A. Izett, Baculites asperiformis Meek. Meek (early form) occur in ironstone concretions about 18, T. 2 N., 1969. R.8oW. 130 feet below the base of the Sharon Springs, and well D7044- SW~SW~ sec. 2, G. A. Izett Baculites asperiformis Meek. preserved specimens of Baculites obtusus (late form) T. 2 N., R. 81 W. and J. E. Peterson, are found in limestone concretions in the Sharon 1969. Springs Member. The range of both forms of B. obtusus D6980-SW~SW~ sec. 2, _____ do ______Baculites mclearni Landes. T.2N.,R.81W. are shown together on plate 1. Crushed gypsiferous D697Q-NE~SW~ sec. 18, G. A. Jzett, Inoceramus tausiensis Aliev. limonite specimens of Baculites mclearni Landes are T.2N., R.SOW. 1969. BaculitesobtususLandes. restricted to a silty shale interval 5-10 feet thick above D6011-EY:!BW~ sec. 33, W. A. Cobban, Inoceramus of. I. barabini Morton. T. 1 N., R. 80 W. 1967. Baculites obtusus Meek. the top of the Sharon Springs Member. Limestone and D601Q-_____ do ______G. A. Izett Inoceramus sp. ironstone concretions from 60 to about 500 feet above and W. A. Ostrea sp. Cobban, Baculites sp. the Sharon Springs contain Baculites asperiformis 1967. Scaphites n. sp. Meek. D6543-SE~SW~ sec. 33, G. A. lzett, Baculites sp. T.1N.,R.80W. 1968. D6586--Center SW~ sec. 33, G. A. Izett, Cymbophora sp. T.1N.,R.80W. J.R.Glil, Baculites obtusus Meek (early form). and W.A. Fish scales. Cobban, 1968. D6992-SW~SW~ G. A. Izett, Baculites sp. sec. 2, T. 2 1969. N.,R.S1W. D7033-NW~SW~ G. A. Izett Baculites sp. (weak flank ribs). sec.10, T. and J, E. Scaphites n. sp. 3N.,R. Peterson, 81 w. 1969. 1 Identified by N. F. Sohl, U.S. Geol. Survey, 1967. Several distinctive types of concretions occur in the lower part of the Pierre. Some types of concretions are limited to the rocks of certain broad stratigraphic inter vals and can be used to determine the approximate stratigraphic position of isolated shale outcrops in FIGURE 4.-Yellowish-gray-weathering septarian limestone con structurally complex areas. Thin platy reddish-brown cretion characteristic of the Sharon Springs Member of the weathering ironstone layers and concretions generally Pierre Shale. Photograph taken in the SE1,4SE14 sec. 2, T. 2 N., R. 81 W., Grant County, Colo. Some specimens of Baculites less than 1 foot thick are found in much of the lower obtusus occur in the septarian limestone concretions, but black shale part of the Pierre, but they are especially specimens of this species are also in smooth gray dense prominent below the Sharon Springs Member. Smooth limestone concretions in the Sharon Springs. AlO ,SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY SHARON SPRINGS MEMBER and bentonite-bearing unit that can be traced through Extension o:f the name Sharon Springs Member o:f out much o:f the Kremmling area and elsewhere in the the Pierre Shale :from the Great Plains into Middle Western Interior region. It is useful in determining Park is based on lithology, stratigraphic position, and structure in a thick sage-covered shale sequence. The member crops out about 1,100 :feet above the base o:f the :fossil content. The member is generally about 45 :feet Pierre in this area. The member is easily recognized thick and is well exposed at several places in the and characterized by as many as eight thin bentonite Kremmling area. Good exposures occur south o:f beds in the lower part o:f the member and by a shale Kremmling in the Sljz sec. 33 and the SW1,4SW1!.&, sec. unit that is rich in organic material and more resistant 21, T. 1 N., R. 80 W. North o:f Kremmling, good out and buttress weathering than the adjacent shale (fig. 5). crops are along Muddy Creek in the NE1,4SE% sec. ~6, The bentonite beds are easily traced along outcrops by along Red Dirt Creek in the Sljz sec. 2, T. 2 N., R. 81 their :frothy surfaces and by scattered selenite and cal W., and in a roadcut along U.S. 40 in the center NW% cite crystals. The shale in the upper part o:f the member, sec. 14, T. 3 N., R. 81 '\V. Other good outcrops are along informally called the buttress shale, characterizes the Muddy Creek in the SW% sec. 18, T. 2 N., R. 80 W., Sharon Springs in its type locality (Elias, 1931, p. and the NE1,4NW% sec. 25, T. 3 N., R. 81 W. 58- 77) in western Kansas and in much of Wyoming The member is a distinctive buttress-weathering shale and South Dakota. This shale unit contains much jaro- FIGURE 5.- Buttress-weathering organic-rich black shale characteristic of the upper part of the Sharon Springs Member of the Pierre Shale in the SE%,SEJ,4 sec. 2, T. 2 N., R. 81 W., Grand County, Colo. Hammer shown for scale. PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST All site-stained carbonaceous debris and fish remains and, The lower 200 feet of the middle sandy part of the at one locality, a log of a fossil conifer about 15 feet Pierre contains many concretions that contain abundant long. The base of the member was chosen at the lowest specimens of Baculites asperiformis. Other anunonites bentonite bed, and the top of the member is at the top found in association with this baculite are H oplosca of the buttress shale. phites sp. and small fragments of a heteromorphic am monite. Baculites perplewus Cobban first occurs about MIDDLE PART 200 feet above the base of the middle part. The middle part of the Pierre Shale is exposed best A discontinuous interval of dark-gray shale about in the north-central part of the Kremmling quadrangle 50 feet thick crops out 300 feet above the base of the east of U.S. Highway 40. It is a diverse unit, about middle part of the Pierre and below the Kremmling 3,300 feet thick, consisting of alternating marine silty Sandstone Member. This shale unit contains several shale and sandstone beds roughly equivalent to the conspicuous reddish-brown limestone layers about 1 foot Mesaverde Group of northwestern Colorado (fig. 2). thick. These layers form small ledges that can be traced readily along outcrops, and they yield large well-pre The lower 300 feet of the middle unit of the Pierre served specimens of B aculites perplewus that show consists of slope-forming interbedded shaly siltstone strongly ribbed venters. This zone with its numerous and thin beds of ripple-marked very fine grained clayey fossils can be traced intermittently north from Kremm sandstone. The sandstone beds are discontinuous and ling for at least 15 miles. locally form small ledges. One of these calcareous sand stone beds, about 2 feet thick, contains many worm KREMMLING SANDSTONE MEMBER trails and occurs near the base of the middle unit. The lower 300 feet of the middle unit contains dis Thin-bedded ledge- to cliff-forming sandstone beds continuous rusty siltstone concretions and layers and that are about 1,900 feet above the base of the Pierre are large yellowish-brown-weathering calcareous sandstone here named the Kremmling Sandstone Member of the concretions that form an excellent marker zone about Pierre Shale. The member is well exposed at Muddy 25-75 feet above the base of the middle unit (fig. 6). Buttes about half a mile north of Kremmling, and it These concretions are ellipsoidal and locally as much as can be mapped for many miles north and south of 15 feet in diameter. They were traced through much of Kremmling. The type locality (fig. 7) is in the SE% the Kremmling area and were identified in the upper NW% sec. 7, T. 1 N., R. 80 W., Grand County, Colo.; the member is named after the town of Kremmling, part of the Mancos Shale along the Williams Fork Grand County, Colo. River from Hamilton to Fish Creek. The thickness of the member ranges from 20 to 70 feet, the variation due to a gradational lower contact. The lower contact is placed between the laminated shaly siltstone of the Kremmling Sandstone Member and the underlying silty shale. The upper contact is placed at the highest sandstone bed overlain by shale. The lower part of the member consists of shaly silt stone and sandstone, and the upper part is generally flaggy very fine grained sandstone. Ripple marks and worm trails and burrows are generally found along bed ding planes. The member is 'vithin the Range Zone of Baculites perplewus, and poorly preserved generally crushed specimens of Baculites perplexus \vere found at some outcrops. UNNAMED SHALE MEMBER FIGURE 6.-Large yellowish-brown-weathering calcareous sand Dark-gray slope-forming shale about 150-200 feet stone concretions about 350 feet below the top of the Kremm ling Sandstone Member near the center of sec. 7, T. 1 N., thick overlies the Kremmling Sandstone Member. Lo R. 80 W., 0.5 mile northwest of Kremmling, Colo. Specimens cally discontinuous sandstone beds less than 5 feet thick of Baculites asperitormis that have widely spaced prominent occur in the lowermost part of this unnamed shale mem flank nodes occur in the concretions, but are more common in yellowish-brown lenticular ferruginous siltstone con ber. This member is well exposed at Muddy Buttes in cretions. the NE% sec. 7, T. 1 N., R. 80 \V., and along the east A12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY side of Muddy Creek in the E1;2 sec. 1, T. 2 N., R. 81 W. 3 N., R. 80 \iV., but for the most part, the member is A zone of reddish-brown-weathering ledge-forming exposed only in isolated outcrops. limestone layers generally occurs in the upper third of The member is composed chiefly of gray hackly slope the unit below the Muddy Buttes Sandstone Member. forming silty shale that contains a few thin siltstone The shale member is within the Range Zone of Baculites and sandstone beds in the lower 200 feet. Layers of gray perplexus inasmuch as that species occurs in the overly silty limestone concretions less than 2 feet thick are ing Muddy Buttes Sandstone Member. Many well-pre scattered through the unit. The limestone concretion served baculites, many of which are inseparable from layers are unlike most others in the Pierre and charac Bamtlites gilberti Cobban, weather from the limestone terize only rocks above the Muddy Buttes Member and layers and litter the underlying slopes. In isolated ex below the Hygiene Sandstone Member. Smooth lime posures, these limestone layers resemble those in the stone concretions about 2 feet in diameter occur in the shale below the Kremmling Sandstone Member, but they upper 300 feet of the unit. differ in that the average baculite from limestone layers The lower 130 feet of the member lies in the upper below the Muddy Buttes is smaller and has more ventral part of the Range Zone of Baculites perplexus, and a I ribs per shell diameter (Baculites gilberti) than the few collections of this fossil were found in limestone average baculite ( B aculites perplexus) from below the concretions and sandy shale above the Muddy Buttes Kremmling. Other ammonites from the unnamed shale Sandstone Member in the NE~ sec. 6, T. 1 N., R. 80 W. unit are H oploscaphites sp. and Placenticeras n. sp. vVell-preserved ammonites are difficult to find in the middle part of this member, but enough were found to MUDDY BUTTES SANDSTONE MEMBER establish the presence of the Zone of Baculites gregory Thin-bedded ledge-forming sandstone beds about enis Cobban. The baculites occur in silty limestone 150- 200 feet above the Kremmling Sandstone Member layers from about 500 to 800 feet above the base of the are here named the Muddy Buttes Sandstone Member unit. Other ammonites found in this interval are of the Pierre Shale. The type locality is in the NW1,4 Didymoceras sp. and 111 emtites n. sp. The interval from sec. 8 and the NE~ sec. 7, T. 1 N., R. 80 W., at Muddy about 800 feet above the base to the top of the unit lies Buttes about 1 mile north of Kremmling, Grand within the Range Zone of Baculites scotti Cobban County, Colo. (fig. 8). The member can be traced from· (pl. 1). Several collections from limestone concretions near Kremmling for about 15 miles to the north and in this shale interval yield Bacnlites scotti, Didymoceras for several miles to the south. n. sp., Anapachydiscus complexus (Hall and Meek), The member ranges from 5 to 30 feet in thickness. and lJ/ enuites n. sp. The lower contact is gradational through several feet and is placed where silty shale grades upward into silty HYGIENE SANDSTONE MEMBER sandstone. The upper contact is generally sharp and is Cliff-forming sandstone as much as 120 feet thick placed at the point where silty shale overlies sandstone. about 3,200 feet above the base of the Pierre is assigned The member is composed of very fine grained sand to the Hygiene Sandstone Member of the Pierre. The stone and shaly siltstone that weather yellowish brown. name Hygiene is assigned to this thick sandstone near The sandstone is thin bedded to laminated, and bedding Kremmling because it occupies a stratigraphic position planes are covered by ripple marks and trails of un similar to the uppermost sandstone of the Hygiene of known organisms. Along Muddy Creek, in the NW~ the type locality near Boulder and it also lies within sec. 1, T. 2 N., R. 81 vV., the uppermost sandstone bed the Range Zone of Bacttlites scotti. The Hygiene in the is overlain by a layer of glauconitic sandstone and Boulder area is about 600- 800 feet thick, and its base associated ironstone. lies 2,400 feet above the base of the Pierre (Scott and The member is within the Range Zone of B amtlites Cobban, 1965). perplexus, as good collections of this fossil occur above The Hygiene in the Kremmling area generally forms and below the member (pl. 1). Fossils are sparse and a conspicuous cliff and is well exposed in the southwest not well preserved in the member, but a few specimens ern part of T. 3 N., R. 80 W., and in sec. 12, T. 3 N., R. of B aculites perplextts were found. 81 W. Typical outcrops of the member are shown in figure 9. UNNAMED SHALE MEMBER The thickness of the member is variable because of At least 1,000 feet and perhaps as much as 1,200 feet the gradational lower contact, but generally ranges of shale overlies the Muddy Buttes Sandstone Member. from 50 to 120 feet. The lower contact is placed between A few good outcrops of this unit were seen in the NW~ silty sandy shale of the underlying shale unit and lami sec. 12, T. 3 N., R. 81 W., and in the SW~ sec. 31, T. nated to thin-bedded sandstone. The upper contact is PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST A13 FIGURE 7.-Type locality of the Kremmling Sandstone Member of the Pierre Shale in the SEY-J,NW1,4 sec. 7, T. 1 N., R. 80 W., 0.5 mile north of Kremmling, Grand C FIGURE 8.-Type locality of the Muddy Buttes Sandstone Member of the Pierre Shale in the NW1,4 sec. 8 and the NE% sec. 7, '1'. 1 N. , R. 80 W., about 1 mile north of Kremmling, Grand County, Colo. ·well-preserved specimens of Baculites perplexus, some of which approach the specific characteristics of Baculites gilbcrti, are present in reddish-brown-weathering limestone layers from about 10 to 100 feet below the sandstone. A14 ,SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY arbitrarily assigned to the topmost thin-bedded ledge CARTER SANDSTONE MEMBER forming calcareous sandstone. A ridge-forming sandstone unit about 350 feet above The lower part of the member consists of massive the Hygiene Sandstone Member is here named the very fine grained sandstone that contains brown Carter Sandstone Member of the Pierre Shale. The weathering sandy limestone concretions as much as member takes its name from Carter Creek in the north 8 feet in diameter. The upper part of the member is soft eastern part of T. 3 N., R. 81 W., in the Kremmling slope-forming thin-bedded sandstone. quadrangle, Grand County, Colo., and the type locality The member lies within the Range Zone of Bamtlites is a few miles south of Carter Creek in the NW~NW~ scotti. Most of the fossils occur either in the large cal sec. 20 and the SW~SW~ sec. 17, T. 3 N., R. 80 W. careous sandstone concretions or at the top of the (fig.10). massive sandstone. The thickness of the member ranges from 30 to 65 Ammonites from the lower part of the Hygiene in feet and varies because of the gradational lower bound clude Bacttlites scotti, Anapachydiscus complexus, ary. The lower contact is chosen at the horizon where Didymoceras n. sp., Placenticeras sp., and Oxybeloceras sandstone of the Carter predominates over silty shale of sp. Some of the same ammonites are found in the top the underlying unit. The upper contact is defined to most bed of the Hygiene. be at the top of a layer of ellipsoidal calcareous sand stone concretions. UNNAMED MEMBER The sandstone is very fine grained and thick bedded About 370 feet of soft shaly siltstone, sandy shale, to massive. Low-angle medium-scale cross-stratification and sandstone overlies the Hygiene Sandstone Member. is common in the member. Dark-brown-weathering The member is poorly exposed and at most places forms calcareous sandstone concretions as much as 4 feet in sage-covered slopes. A few outcrops of the lower part diameter are in the uppermost beds of the member. of the unit were seen along Antelope Creek in the NE~ Carbonaceous shale is present at the base near the center sec. 19, T. 3 N., R. 80 W. Good outcrops of the upper of sec. 12, T. 3 N., R. 81 W. 150 feet occur in the SE~ sec. 5, T. 2 N., R. 80 W. No fossils other than fragments of Inoceramus have Fragmentary fossil ammonites from the upper 100 feet as yet been found in the member, but it probably lies of the member suggest that the rocks are in the Range \vithin the Range Zone of Didymoceras stevensoni Zone of Didymoceras nebrascense (Meek and Hayden). (Whitfield) (pl. 1). FIGURE 9.-The Hygiene Sandstone l\fember of the Pierre ShalP in the SE1,4 sec. 30 ani! the NI<~1,4 sec. 31, T. 3 N., R. 80 W., about 9 miles north of Kremmling, Grand County, Colo. Specimens of Baculites scotti are in large brown-weathering calcareous sandstone concretions in the sandstone and in gray silty limestone concretions as much as 200 feet below the top of the sandstone. PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST A15 Axonoceras compressum Stephenson, Placenticeras meeki Boehm, Anaklinoceras reflexum Stephenson, and Solenoceras reesidei Stephenson. Limy sandstone concretions as much as 6 feet in diameter make an excellent marker zone about 420 feet above the top of the Carter. The lower limit of the Range Zone of Baculites cuneatus Cobban is at about this level in the SWl-4 sec. 7, T. 3 N., R. 80 W. Large ellipsoidal concretions contain specimens 2 or 3 feet in diameter of Placenticeras in addition to many other marine fossils, including the index ammonite Baculites cuneatus and the ammonites H oploscaphites nodosus and Eutrephoceras sp. FIGURE 10.-Type locality of the Carter Sandstone Member of From 420 to 925 feet above the Carter Sandstone the Pierre Shale in the NW1,4 NW% sec. 20 and the SW1,4SW% Member is silty and sandy slope-forming shale. Gray sec. 17, T. 3 N., R. 80 W., a bout 11 miles north of Kremmling, dense limestone concretions and silty limestone layers Grand County, Colo. about 490 and 660 feet above the Carter contain the in dex ammonite Baculites 1'eesidei Elias. Gray limestone UNNAMED SHALE MEMBER concretions less than 2 feet in diameter about 780 feet About 900 feet of shale overlies the Carter Sandstone above the Carter yield numerous well-preserved speci Member and is best exposed in the northwestern part mens of the index ammonite Baculites ienseni Cobban. of T. 3 N., R. 80 W., and in the northeastern corner of Black shale about 40 feet thick that contains thin iron T.3N.,R.81 W. stone concretions and bentonite beds occurs about 800 The lower 30 feet of the member is soft silty and feet above the top of the Carter Sandstone Member. sandy shale that contains near its base smooth gray The upper part of the unnamed shale unit consists of limestone concretions about 1 foot in diameter that 80 feet of silty to sandy shale that is transitional to the locally yield specimens of Baculites crickmayi Williams overlying Gunsight Pass Member. and H oploscaphites sp. Gray septarian limestone con GUNSIGHT PASS MEMBER cretions in this interval are generally barren. At the top of this 30-foot shale interval of rocks is a distinc The Gunsight Pass Member of the Pierre Shale is tive marker bed of ledge-forming dark-green glauconitic here named for about 150-170 feet of sandstone and sandstone about 3 feet thick capped by a thin reddish silty shale about 4,535 feet above the base of the Pierre. The member forms the topmost unit of the middle part ironstone layer. Two glauconite zones are present in of the Pierre. The member is named for Gunsight Pass theE% sec. 5, T. 2 N., R. 80 W. Phosphatic nodules in sec. 22, T. 3 N., R. 80 W., Grand County, Colo., and are common in this sandstone. Concretions from this the type locality is in the northwestern part of T. 3 N., level contain the index ammonite Didymoceras steven R. 80 W. The member can be divided into three parts. soni in addition to Placenticeras sp. and Baculites sp. The lower part of the member is a 10- to 20-foot-thick From 30 feet to about 350 feet above the top of the very fine grained sandstone bed that is typically ex Carter Sandstone Member is a poorly exposed soft posed in the SWl4NWl4 sec. 8, T. 3 N., R. 80 W. The sandy and silty shale interval. Two bentonite beds occur base of this sandstone bed is chosen as the base of the about 50 feet above the top of the Carter. No ammonites Gunsight Pass Member. The contact is gradational other than poorly preserved Baculites have been found through several feet and occurs where sandstone pre in this interval, probably owing to poor exposures and dominates over underlying silty shale. A zone of brown lack of concretions, but it probably lies partly in the weathering calcareous sandstone concretions about 3 Range Zones of E xiteloceras jenneyi (Whitfield) and feet in diameter is found in the unit. The middle part Didynwceras cheyennense (Meek and Hayden). of the member, about 100 feet thick, is silty shale that A silty shale interval about 380 feet above the Carter contains gray calcareous siltstone concretions about 1 is the most fossiliferous part of the Pierre in the foot in diameter. The upper part is cliff-forming sand Kremmling area. This level contains smooth limestone stone as much as 50 feet thick that is typically exposed concretions in which are several kinds of ammonites in the SWl4NWl4 sec. 16, T. 3 N., R. 80 W. (fig. 11). including Baculites compressus Say, Baculites sp., The upper contact of the member with the overlying Hoploscaphites nodosus (Owen), Eutrephoceras sp., dark-gray shale is sharp. Al6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The Gunsight Pass Member is in the Range Zone of CORRELATION OF THE PIERRE SHALE TO THE either Baculites jenseni Cobban or Baculites eliasi Cob EAST AND TO THE WEST ban. The only ammonite found in the member is The Pierre Shale near Boulder, Colo., about 60 miles which occurs in the Range Zones of Pseudobaculites, east of the Kremmling area, totals 8,020 feet in thick B. jenseni or B. eliasi elsewhere in the Western Interior. ness in a section measured by G. R. Scott and R. F. Wilson (Scott and Cobban, 1965). It consists of a lower UPPER PART shale unit; a middle sandy unit containing the Hygiene, The upper part of the Pierre remammg in the Terry, Rocky Ridge, and Larimer Sandstone Members; Kremmling area consists of about 200 feet of uniformly and an upper shaly unit. The upper shaly unit contains dark marine shale that contains numerous gray dense an unnamed sandstone member and at the top a thick limestone concretions. Good exposures of the contact sandy upper transition member that grades into the between the top of the Gunsight Pass Member and the overlying Fox Hills Sandstone. The section is well upper part of the Pierre are shown in figure 11. The dated by numerous collections of molluscan fossils. original thickness of this unit is unknown owing to The lower shale unit, about 1,600 feet thick, is cal latest Cretaceous deformation and erosion, hue it likely careous in its basal 40 feet (lower transition member) was more than several thousand feet thick. The upper and gradational into the underlying Niobrara Forma part of the Pierre is overlain with erosional uncon tion. Diagnostic fossils have not been found in the formity by arkosic sandstone of the Middle Park. basal 320 feet of the lower shale unit, but the overlying Formation of Late Cretaceous(~) and Paleocene age. 820 feet has mollusks indicating the Zones of Baculites The only ammonites found in the upper part are in obtusus, B. mclearni, and B. asperiformis. The upper phosphatic sandstone nodules as much as 6 inches long part of the unit contains many levels of limestone and that contain poorly preserved fragments of Baculites ironstone concretions with B. perplemus. eliasi, Baculites sp., and Hoploscaphites sp. These nod The middle sandy unit, about 2,300 feet thick, con ules lie on the top surface of the Gunsight Pass Mem tains many fossiliferous concretions of sandstone and ber and in the lower 3 inches of the upper part. sandy, silty, or ferruginous limestone. Baculites gre- FIGURE 11.-Upper sandstone and middle shale parts of the Gunsight Pass Member of the Pierre Shale in the SW:J,iNW:J,i sec. 16, T. 3 N .. R. 80 W., about 11.5 miles north of Kremmling, Grand County, Colo. Specimens of Baculites eUasi are present in phosphatic nodules at the top of the sandstone. PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST A17 goryensis occurs in the lower part of the Hygiene Sand down to the Niobrara Member is from the electric log stone Member, and B. scotti is found in the middle and of the McCulloch Oil Corp.'s Skeeter No.1 in the SWl!.t, upper parts. The shale separating the Hygiene and SW:!4 sec. 8, T. 5 N., R. 89 W., which is about midway Terry Sandstone Members, about 800 feet thick, con between the Fish Creek and Hamilton sections. tains B. scotti in the lower 150 feet, Didymoceras Only the uppennost part of the Mancos Shale is ex nebraiscense in the next 380 feet, and D. stevensoni in posed in Fish Creek Canyon. Bass, Eby, and Campbell's the rest. E witeloceras jenneyi is found in the 60-foot plotted section shows two sandstones about 550 feet Terry Sandstone Member and in the basal few feet of apart of which the upper is 450-500 feet below the top the overlying shale. The shale separating the Terry and of the Mancos. We found B acuiites perplewus in lime Rocky Ridge Sandstone Members is about 750 feet thick stone concretions in the shale separatili.g the two sand and contains an unnamed sandstone bed in its lower part stones. The upper sandstone resembles the l{remmling with Didymoceras cheyennense (Meek and Hayden) Sandstone Member, and the lower sandstone, which con (not shown in fig. 2) . The middle third of the shale tains large yellowish-brown-weathering sandy concre contains ammonites indicative of the Zones of Baculites tions, is interpreted as the equivalent of the marker zone compressus and B. cuneatus. Baculites reesidei occurs of similar concretions at l{remmling (fig. 6). in the upper third and in the Rocky Ridge and Larimer The third sandstone at Fish Creek is the Tow Creek Sandstone Members. Sandstone Member of the Iles Forn1ation (Bass and The upper shaly unit of the Pierre is composed of two others, 1955, pl. 21). It is fossiliferous, but none of the thick sequences, a lower sandy to nonsandy shale about fossils collected are indices to a particular ammonite 2,800 feet thick and an upper very sandy shale 1,170 r.one. feet thick (upper transition member) that contains beds Nearly 400 feet of marine shale overlies the Tow of soft sandstone. Fossiliferous limestone and ironstone Creek Sandstone Member. A robust normally coiled concretions are common in most of the upper shaly unit. ammonite, Anapachydiscus sp., was found about 100 Baculites jenseni occurs in the basal 100 feet, and feet below the top. This genus is most common in the B. eliasi occurs in the next 700 feet. An unnamed sand Zone of B. scotti in the Western Interior region. stone bed 1,010 feet above the base contains Inoceramus Above the 1narine shale is a conspicuous cliff-forming typimtS (Whitfield) and scaphites of the Hoploscaph sandstone containing Inoceramus aff. I. pertenuis Meek ites plenus (Meek and Hayden) group suggestive of the and Hayden. We believe that this sandstone is equiv Zone of Baculites baculus Meek and Hayden. Baculites alent to the Hygiene Sandstone Member near Kremm baculus has been found with I. typicus as high as 1,750 ling inasmuch as both sandstones physically resemble feet above the base of the upper shaly unit. Baculites one another and each overlies marine shale containing grandis Hall and Meek occurs higher in the unit, and Anapachydiscus. B. clinolobatus still higher. The uppermost part of the Several hundred feet of coal-bearing nonmarine beds unit (upper transition member) contains B. clinolobatus overlie the Hygiene equivalent. The nonmarine unit is in the basal beds and ammonites of post-clinolobatus overlain by a very poorly exposed marine shale grading age in the rest. up into the Trout Creek Sandstone Member at the top The excellent fossil record in the Boulder area per of the Iles Formation. Outcrops of this marine shale mits a ready correlation with the Pierre Shale in the along the Oak Creek-Hamilton road about 9 miles south Kremmling area up through the Zone of B. eliasi east of Fish Creek in the Slh sec. 25, T. 4 N., R. 86 W., (fig. 2) . Rocks as young as the Zone of B. clinolobatus contain limestone concretions with Ewiteloceras jenneyi were probably present at one time in the Kremmling (Whitfield). This ammonite has not been found in the area. l{remmling area as yet, but i~ may eventually be dis Rocks of Pierre age crop out in Fish Creek Canyon covered low in the shale eeparating the Carter Sand 40 miles west of the l{remmling section. Here the rocks stone Member frmn the Gunsight Pass l\fember. are divided into Mancos Shale, Mesaverde Group, and Several hundred feet of coal-bearing rocks overlying Lewis Shale. The generalized section shown in figure the Trout Creek Sandstone l\fember forms the lower 2 is based mainly on the graphic section of the upper part of the Williams Fork Formation. These nonmarine most part of the Mancos Shale and the overlying Mesa rocks are overlain by a thick marine shale that grades verde Group presented by Bass, Eby, and Campbell up into the Twentymile Sandstone Men1ber of the Wil ( 1955, pl. 21, sec. 3). The thickness of the Lewis Shale liams Fork. Exposures of this mari~e shale are very is from the same authors, and the interval of rocks poor on Fish Creek, but they are excellent in cuts along from the Loyd Sandstone :Member of the Mancos Shale the Oak Creek-Hmnilton road a few miles to the east A18 ,SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY reesidei.. This ammonite occurs also near the middle of about 500 feet above the base of the Sharon Springs at where the lower part of the unit contains Ba1oulites Kremmling. The Hunt Creek Sandstone Member of the shale separating the Carter Sandstone Member from the Mancos Shale of Kucera (1959, p. 41-42) consists the Gunsight Pass Mmnber in the l{remmling area. The of three beds of sandstone separated by thick beds of Twentymile Sandstone Member is marine, but none of shale having an aggregate thickness of 265 feet the fossils found can be assigned to a particular am (l{ucera, 1959, p. 42, fig. 6). The upper sandstone of Inonite zone. However, a correlation with the Gunsight the Hunt Creek probably correlates with the Muddy Pass Member seems logical (fig. 2). Buttes Sandstone Member, and the lower sandstone of The Lewis Shale, which overlies the Williams Fork Hunt Creek probably correlates with the Kremmling Formation, is poorly exposed along Fish Creek, and no Sandstone Member. The middle sandstone of the Hunt significant fossils were found. Collections of fossils Creek is represented by shale in the Kremmling area. from the Lewis Shale about 16 or 17 miles north of The Hunt Creek Sandstone Member of the Mancos Fish Creek include "Inoceramus" fibrosus (Meek and Shale of Kucera ( 1959) and the Muddy Buttes and Hayden), Baculites clinolobatus, and Ooahuilites, which l{remmling Sandstone Members of the Pierre all he indicate an age at least as young as the Zone of B aculites within the range span of Bac·ulites perplewus. clinolobatus Elias. REFERENCES CITED The Hamilton section (fig. 2) is based on graphic sections presented by Bass, Eby, and Campbell (1955, Barclay, C. S. V., 1968, Geology of the Gore Canyon-Kremmling pl. 21, sec. 1) and Konishi ( 1959, pl. 1, sec. 1). In this area, Grand County, Colorado : Arizona Univ. master's thesis. area, the lies and 'Villiams Fork Formations are largely Bass, N. W., Eby, .T. B., and Campbell, M. R., 1955, Geology and nonmarine. Five conspicuous sandstones are present in mineral fuels of parts of Routt and Moffat Counties, the upper part of the Mancos Shale. The lowest, Colorado: U.S. Geol. Survey Bull. 1027-D, p. 143-250. Morapos Sandstone Member, lies in the Zone of B acu Burbank, W. S., Lovering, T. S., Goddard, E. N., and Eckel, E. B., lites nwlearni (Dyni, 1966). The second sandstone, 350 1935, Geologic map of Colorado: U.S. Geol. Survey: Dyni, .T. R., 1966, Geologic map of the Thornburg oil and gas feet higher, contains the same kind of large yellowish field and vicinity, Moffat and Rio Blanco Counties, brown-weathering calcareous sandstone concretions Colorado : U.S. Geol. Survey Oil and Gas Inv. Map OM-216. (fig. 6) with B. asperiformis as in the Fish Creek sec Dyni, .T. R., and Cullins, H. L., 1965, Meeker and Loyd Sandstone tion. The third sandstone, about 350 feet higher, and Members of the Mancos Shale, Moffat and Rio Blanco a fourth sandstone, about 100-150 feet higher, lie in the Counties, Colorado: U.S. Geol. Survey Bull. 1194-.T, 7 p. Elias, M. K. 1931, The geology of Wallace County, Kansas: older part of the Range Zone of B. perplewus. The next Kansas Geol. Survey Bull. 18, 254 p. overlying sandstone, Loyd Sandstone Member, about Gill, .T. R., and Cobban, W. A., 1965. Stratigraphy of the Pierre 50-100 feet above the fourth, is highly fossiliferous Shale, Valley City and Pembina Mountain areas, North (Dyni and Cullins, 1965, p. J5) and contains B. gilberti, Dakota : U.S. Geol. Survey Prof. Paper 392-A, 20 p. which lies in the middle of the Range Zone of B. per --1966, '£he Red Bird section of the Upper Cretaceous Pierre Shale in Wyoming, with a section on A new echinoid plewus. Less than 100 feet of 1narine shale separates the from the Cretaceous Pierre Shale of eastern Wyoming by Loyd Sandstone Member from the Tow Creek Sand P. M. Kier: U.S. Geol. Survey Prof. Paper 393-A, 73 p. stone Member at the base of the lies Formation. Diag Griffitts, M. L. 0., 1949. Zones of Pierre formation of Colorado: nostic fossils have not been found in this shale or in the Am. Assoc. Petroleum Geologists Bull., v. 33, no. 12, p. 2011- Tow Creek Member. 2028. Geologic reconnaissance in the fall of 1970 in the Hail, W . .T., .Jr., 1968, Geology of southwestern North Park and vicinity : U.S. Geol. Survey Bull. 1257, 119 p. Yampa valley near Phippsburg and Oak Creek indi Holt, H. E., 1961, Geology of the lower Blue River area, Summit cates that the ~{ancos Shale is roughly equivalent to and Grand Counties, Colorado : Colorado Univ. Ph. D. thesis, that part of the Pierre Shale beneath the Hygiene Sand Ann Arbor, Mich., University Microfilms, Inc. stone Member of the l{remmling area. The Sharon Howard, .T. A., 1961, Structural development of the Williams Springs Member of the Pierre is present as a distinctive Range thrust, Colorado: Columbia Univ. Ph. D. thesis, Ann unit in the Yampa valley and extends to the west as far Arbor, Mich., University Microfilms, Inc. Izett, G. A., 1968. Geology of the Hot Sulphur Springs quad as Rangely, Colo. Kucera (1959, p. 41-42) applied the rangle, Grand County, Colorado: U.S. Geol. Survey Prof. names Devils Grave and Hunt Creek Sandstone Mem Paper 586, 79 p. bers of the Mancos Shale to sandstone units in the upper Konishi, Kenji, 1959, Upper Cretaceous surface stratigraphy, part of the Mancos in the Yampa valley. The lowermost Axial Basin and Williams Fork area, Moffat and ·Routt sandstone, the Devils Grave, contains B aculites asperi Counties, Colorado, in Rocky Mtn. Assoc. Geologists, Sym posium on Cretaceous rocks of Colorado and adjacent areas, formis and correlates approximately with the distinc 11th Field Conf., 'Vashakie, Sand Wash, and Piceance tive siltstone concretion layer (fig. 6) that crops out Basins, 1959 : p. 67-73. PIERRE SHALE, KREMMLING, COLORADO, CORRELATION TO THE EAST AND THE WEST A19 Kucera, R. E., 1959, Cretaceous stratigraphy of the Yampa dis Richards, Arthur, 1941, Geology of the Kremmling area, Grand trict, northwest Colorado in Rocky Mtn. Assoc. Geologists, County, Colorado: Michigan Univ. Ph. D. thesis, Ann Arbor, Symposium on Cretaceous rocks of Colorado and adjacent Mich., Unive~sity Microfilms, Inc. areas, 11th Field Conf., Washakie, Sand Wash, and Piceance Scott, G. R., 1969, General and engineering geology of the north Basins, 1959 : p. 37-45. ern part of Pueblo, Colorado : U.S. Geol. Survey Bull. 1262, Marvine, A. R., 1874, Report [on the Middle Park region, Colo.] 131 p. Scott, G. R., and Cobban, W. A., 1959, So-called Hygiene group in Hayden, F. V., Seventh Annual Report of the U.S. Geo of northeastern Colorado [and Wyo.] in Rocky Mtn. Assoc. logical and Geographical Survey of the Territories * * * Geologists, Symposium on Cretaceous rocks of Colorado and for the year 1873: Washington, U.S. Govt. Printing Office, adjacent areas, 11th Field Conf., Washakie, Sand Wash, and p. 83-192. Piceance Basins, 1959 : p. 124-131. Miles, C. H., 1961, The geology of the Pass Creek-Wolford Moun ---1965, Geologic and biostratigraphic map of the Pierre tain area, Grand County, Colorado : Golden, Colorado School Shale between Jarre Creek and Loveland, Colorado : U.S. of Mines master's thesis. Geol. Survey Misc. Geol. Inv. Map I-439. U.S. GOVERNMENT PRINTING OFFICE:t971 0-418-288