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Stratigraphy of Mid-Cretaceous Formations at GEOLOGICAL SURVEY P RO F E S S I ON A t P A P E R 1180-A Stratigraphy of Mid-Cretaceous Formations at Drilling Sites in Weston and Johnson Counties, Northeastern Wyoming By E. A. MEREWETHER PALEONTOLOGY AND STRATIGRAPHY OF MID-CRETACEOUS ROCKS- NORTHEASTERN WYOMING GEOLOGICAL SURVEY PROFESSIONAL PAPER 1186-A A description and comparison of the dissimilar formations of early Late Cretaceous age in core holes and outcrops on the eastern and western flanks of the Powder River Basin UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON:1980 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Merewether, Edward Alien, 1930- Stratigraphy of mid-Cretaceous formations at drilling sites in Weston and Johnson Counties, northeastern Wyoming. (Paleontology and stratigraphy of mid-Cretaceous rocks, northeastern Wyoming) (Geological Survey Professional Paper 1186-A) Bibliography: p. 25 Supt. of Docs, no.: I 19.16:1186-A 1. Geology, Stratigraphic Cretaceous. 2. Geology Wyoming Weston Co. 3. Geology Wyoming Johnson County. I. Title II. Series. III. Series: United States Geological Survey Professional Paper 1186-A QE687.M47 551.7'7'0978714 80-607109 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page ./\DS tract ----- — — ----.--.-—-——.., — ...... — ... — ...........—— .......... — .......... — .................. — ......................... j^ j.ntr Ouiiction ™-™™««— — ««-•——. — ............... — ................. — ._....«..................».._.......__..-...........»........ j^ o^Itmf wi «. uigi lornnVixr ct^iijf — _ « _ .......... _ —.........— . ......... .....—.....— . ......... .... ...... ........... .......... ... ......... .. ^9 Belle Fourche Shale _______________________________________ 5 Greenhorn Formation -------------------»-----—— ——-«-——-———— -—--—— —-—«-»— -—»«—— 6 lplt _ ____________ — — — — _........ .. - — . — .......... —— ..... ............ —....... __.......... - .... 7j Pool Creek Member ——————————————————————————————————————— 10 Turner Sandy Member —————————————————————————————————— 10 od£>e Jzsreaj£s iviemoer ••—•———— —————— ....-.-. — ..... — . — ......... — ......._................._....... — ... j^ ^ UlrkTTYin'l'irkTi Hid L1U11 ................. " ....... ' ....*._...—— . - .......... ........... .......... ............. ...... .... 1J^Q Q Belle Fourche Member ««—«——«———-————-———«-———«««««»—-——"—-——» 15 ______ __ _• --———— —— - - ........ _........ ___..... ____..... ____ ...»- 1j_ Q^y Sage Breaks Member —————————————————————————————————— 19 Depositional environments and geologic history .————————————-——-—————— 20 ILLUSTRATIONS Page FIGURE 1. Index map showing the Powder River Basin and locations of outcrop sections, boreholes and selected oil and gas fields - 2 2. Correlation chart of the lower Upper Cretaceous formations at selected localities in northeastern Wyoming ——————— 3 3. Outcrop section of the lower Upper Cretaceous formations near Osage ———-————————-———————————————— 4 4. Lithologic and geophysical logs of lower Upper Cretaceous formations near Osage ————————————————............. g 5. Drawing showing crossbedding in the Turner Sandy Member near Osage —————————————————————————— 10 6. Photomicrograph showing authigenic crystal of feldspar on a corroded crystal of quartz, from sandstone in the Turner oanciy iviemoer ----------«-«—««...———.........................—..—.......—........-..........-...................................._.._......_.._..*.•............. j^^ 7. Photomicrograph showing corroded grains of quartz, chert, and feldspar in a thin section of sandstone from the Turner oanoy iviemoer -----—-•—....———...................—.........—.............—.......—...................—.......—._.._........................_..............._....*. j^^ 8. Stratigraphic sections of the lower Upper Cretaceous Frontier Formation near Kaycee ————————————————---'— 14 9. Photomicrograph showing corroded grains of quartz, chert, and feldspar in a thin section of sandstone of the Belle i7 ourcne iviemoer -----—...——.—.........._...._........_..........._....._.........—........._......_....._..........................._...........................*...... j^ ^ 10. Photomicrograph showing angular to subrounded grains of quartz, chert, and feldspar in a thin section of sandstone of fhdullC WallVV All V^/lProolr CCXV 1V1C111L/C21Momhor————————— ——„————„—.•-—— ____—— - ___ ... _________________________________________. _L1Q ^ 11. Map showing approximate thickness of a representative unit of sandstone in the Belle Fourche Member of the Frontier s. ormacion --------—---—-.—-———-«.-————--—--———-.-——-————.._...._...._..__........................__.—....._.._.......__......................».............. ^ j^ 12. Map showing approximate thickness of a representative unit of sandstone in the Wall Creek Member of the Frontier Formation and the Turner Sandy Member of the Carlile Shale ——————————————————————————— 23 13. Outcrop sections and depositional environments of lower Upper Cretaceous formations in Johnson and Weston v~/oun vies -------——«—«»«—-.—-—...........—.—.....................—....................—..........—.............................—.........—.....__.*...._......... ^4 TABLES TABLE 1. Organic composition of lower Upper Cretaceous shale at boreholes 1 and 2, Powder River Basin, as determined by thermal-evolution analysis, combustion, and reflectance —————————————————————————— in PALEONTOLOGY AND STRATIGRAPHY OF MID-CRETACEOUS ROCKS- NORTHEASTERN WYOMING STRATIGRAPHY OF MID-CRETACEOUS FORMATIONS AT DRILLING SITES IN WESTON AND JOHNSON COUNTIES, NORTHEASTERN WYOMING By E. A. MEREWETHER ABSTRACT Fourche Member is disconformably overlain by the Wall Creek Member, which is about 30 m thick and grades from interlaminated The sedimentary rocks of early Late Cretaceous age in Weston shale and siltstone at the base of the member to sandstone at the County, Wyo., on the east flank of the Powder River Basin, are top. The Wall Creek accumulated during Turonian time in shallow- assigned, in ascending order, to the Belle Fourche Shale, Greenhorn marine environments. These beds are overlain by the Sage Breaks Formation, and Carlile Shale. In Johnson County, on the west flank Member of the Cody. Near Kaycee, the Sage Breaks is about 65 m of the basin, the lower Upper Cretaceous strata are included in the thick and consists mainly of shale which was deposited in offshore- Frontier Formation and the overlying Cody Shale. The Frontier marine environments during Turonian and Coniacian time. Formation and some of the laterally equivalent strata in the Rocky Lower Upper Cretaceous formations on the east side of the Mountain region contain major resources of oil and gas. These rocks Powder River Basin can be compared with strata of the same age on also include commercial deposits of bentonite. the west side of the basin. The Belle Fourche Shale at Osage is Outcrop sections, borehole logs, and core studies of the lower represented near Kaycee by most of the Belle Fourche Member of Upper Cretaceous rocks near Osage, in Weston County, and the Frontier. The Greenhorn at Osage contrasts with beds of similar Kaycee, in Johnson County, supplement comparative studies of the age in the Belle Fourche at Kaycee. An upper part of the Greenhorn fossils in the formations. Fossils of Cenomanian, Turonian, and Formation, the Pool Creek Member of the Carlile Shale, and the Coniacian Age are abundant at these localities and form sequences basal beds of the Turner Sandy Member of the Carlile, in Weston of species which can be used for the zonation and correlation of County, are represented by a disconformity at the base of the Wall strata throughout the region. Creek Member of the Frontier in southern Johnson County. A The Belle Fourche Shale near Osage is about 115 m (meters) thick middle part of the Turner in the vicinity of Osage is the same age as and consists mainly of noncalcareous shale, which was deposited in the Wall Creek Member near Kaycee. A sequence of beds in the up­ offshore-marine environments during Cenomanian time. These per part of the Turner and in the overlying Sage Breaks in Weston strata are overlain by calcareous shale and limestone of the County is the same age as most of the Sage Breaks Member of the Greenhorn Formation. In this area, the Greenhorn is about 85 m Cody in southern Johnson County. thick and accumulated in offshore, open-marine environments during the Cenomanian and early Turonian. The Carlile Shale overlies the Greenhorn and is composed of, from oldest to youngest, INTRODUCTION the Pool Creek Member, Turner Sandy Member, and Sage Breaks Member. In boreholes, the Pool Creek Member is about 23 m thick This report describes the lower Upper Cretaceous and consists largely of shale. The member was deposited in offshore- marine environments in Turonian time. These rocks are discon- strata at boreholes and nearby outcrops in Johnson formably overlain by the Turner Sandy Member, a sequence about and Weston Counties, Wyo. (fig. 1) and will supple­ 50 m thick of interstratified shale, siltstone, and sandstone. The ment the paleontologic studies of W. A. Cobban (mol- Turner accumulated during the Turonian in several shallow-marine lusca), W. G. E. Caldwell and B. R. North (foramini- environments. Conformably overlying the Turner is the slightly fera), F. E. May and B. L. Whitney (dinoflagellates), calcareous

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