The Red Bird Section of the Upper Cretaceous Pierre Shale in Wyoming GEOLOGICAL SURVEY PROFESSIONAL PAPER 393-A The Red Bird Section of the Upper Cretaceous Pierre Shale in Wyoming By JAMES R. GILL and WILLIAM A. COBBAN With a section on A New Echinoid from the Cretaceous Pierre Shale of Eastern Wyoming By PORTER M. KIER STRATIGRAPHY, PALEONTOLOGY, AND SEDIMENTATION OF A CLASSIC REFERENCE LOCALITY OF THE PIERRE SHALE GEOLOGICAL SURVEY PROFESSIONAL PAPER 393-A Description, environmental interpretation, and correlation of a 3,IOO-foot-thick sequence of marine shale UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract _______________________________________ Al Megafossils Continued Introduction. __________________________________ 2 Brachiopods_________________-___-----------__ A25 Earlier work.__________________________________ 4 Mollusks.-_---_______--_--_---_--_-_-------- 25 Geographic and geologic setting._________________ 4 Arthropods.________-------------_-----------_- 26 Regional setting.___________________________ 4 Vertebrates..___-----_---------------_--------- 26 Local setting.______________________________ 4 Trace fossils__________________-__---_-------_- 26 Contiguous formations._________________________ 5 Range zones of ammonites________________-_---_--___ 28 Resume of the Pierre reference locality at Red Bird. 5 Age span_______-__-__---_-----------_------------- 34 Gammon Ferruginous Member_______________ 7 Depositional environment ____________-_____---_.__ 37 Sharon Springs Member.____________________ 8 Proximity to strandlines._____________._-_-----__ 37 Mitten Black Shale Member.________________ 12 Depth of the Pierre sea_____-___-_-----------_- 37 Red Bird Silty Member, ____________________ 15 Effects of currents._______________----_-------__ 38 Lower unnamed shale member._______________ 16 Dissolution of molluscan shells. ___________----___ 39 Kara Bentonitic Member____________________ 17 Rate of deposition__-__-_---------------------_- 41 Upper unnamed shale member______________ 19 Correlation of section._--__-----_-----_-----------__ 43 Megafossils_ _ __________________________________ 19 Regional geologic history.____-__--_--------_-------- 43 Relative abundance of fossil forms.___________ 19 Localities at which fossils were collected.______________ 48 Mineralogy of mollusk shells.________________ 21 Detailed measured section________-/--------_--_------ 49 Chamber fillings____________________________ 22 A new echinoid from the Cretaceous Pierre Shale of eastern Corals. ____________________________________ 23 Wyoming, by Porter M. Kier._____________________ 62 Worms ____________________________________ 23 Systematic description____________--__-_-_--.--- 63 Echinoderms_ ______________________________ 23 References cited.__ __-____-__-_---_---_-------_----- 6 Bryozoans_ ________________________________ 24 Index__________-_-___-----_------_---------------- 75 ILLUSTRATIONS [Plates 1-4 are in pocket, plates 5-12 follow index] PLATE 1. Geologic map showing location of reference locality and distribution of ammonite zones within the Pierre Shale, Red Bird area, T. 38 N., R. 62 W., Niobrara County, Wyo. 2. Reference section at Red Bird, Niobrara County, Wyo., showing subdivisions of the Pierre Shale, range span of ammonite zones, and correlation with the electric log of a nearby oil and gas test hole. 3. Fence diagram showing facies relations, nomenclature, and selected ammonite zones, Upper Cretaceous rocks, northern Great Plains. 4. Chart showing correlation of Red Bird section, Niobrara County, Wyo., with equivalent rocks in the Western Interior, southern Alberta, and east-central Texas. 5-12. Photographs showing 5-7. Trace fossils. 8-10. Dissolution features and trace fossils. 11. Trace fossils and baculite accumulations. 12. Fossil fillings. Page FIGURE 1. Geologic map of the Red Bird area on an aerial photograph_______-_--_-__---_--__--------------------- A.3 2. Geologic map showing location of Red Bird area__________________-_____----------------------------- 6 3-7. Photographs showing 3. Gammon outcrop at Red Bird-_______________________-____--_---_---_-----.------------------ 8 4. Gammon concretions.___________________________________-_-_------------------------------- 9 5. Type Ardmore Bentonite Bed_ ______________-______________-----_--------------------------- 10 6. Basal Sharon Springs at Red Bird____________________-_____-------------------------------- H 7. Typical Sharon Springs outcrop-_______________________---_----_----------------------------- 12 8. Electric and gamma-ray log of Sharon Springs and Gammon__-___-___-_------------_------------------ 13 IV CONTENTS FIGURE 9-14. Photographs showing Page 9. Ironstone cone-in-cone concretion. ___________________________________________________________ A15 10. Hard shale of basal Mitten_________________---_-----_---------_-_--_------__________________ 16 11. Limestone concretion of lime-cemented shale __________________________________________________ 17 12. Dark shale of lower unnamed shale member.___-_--___----------_-_--_-__-_____.______________ 18 13. Popcorn-weathering surface of Kara.__________--.__-_-----------_-_----_--____________________ 19 14. Outcrop of Kara and adjacent shales_________________________________________________________ 20 15. Outline map of Campanian seaway____________-__-__-_---_-_-_-------_____-_-_______-______________ 44 16. Strandline map of Wyoming.________.-________-_____----------------_-_-_-----_____._-.___________ 46 17. Sketch of Eurysalenia minima Kier, n. sp_____--_---------------------_----__-------------___________ 64 TABLES Page TABLE 1. X-ray determinations of aragonite and calcite in shells of fossil mollusks.______-______-___---_.----______ A21 2. Time relation of the Pierre Shale at Red Bird to the standard stages of the Upper Cretaceous, to potassium- argon dates, and to the Western Interior ammonite sequence______________________________________ 35 3. Thicknesses of ammonite range zones, and number of levels of fossil collections.__________________________ 41 STRATIGRAPHY, PALEONTOLOGY, AND SEDIMENTATION OF A CLASSIC REFERENCE LOCALITY OF THE PIERRE SHALE THE RED BIRD SECTION OF THE UPPER CRETACEOUS PIERRE SHALE IN WYOMING By JAMBS R. GILL and WILLIAM A. COBBAN ABSTRACT numerous fossiliferous yellowish-brown-weathering limestone The Pierre Shale of Late Cretaceous age (Campanian and concretions throughout. Maestriehtian) is well exposed and very fossiliferous in the The Red Bird Silty Member, 607 feet thick, is almost entirely a vicinity of Red Bird in Niobrara County, Wyo. A section meas­ soft silty shale that weathers a much lighter gray than the ured on the northwest flank of Old Woman anticline, a large adjoining dark-gray members. Yellow-, orange-, and tan-weath­ fold en echelon to structures of the Black Hills, is here presented ering fossiliferous limestone concretions are common. At the as a reference locality for the Pierre Shale of the northern top of the member and 284 feet below the top, limestone con­ Great Plains. The Pierre Shale is about 3,100 feet thick at cretions are so closely spaced that they are nearly continuous Red Bird and consists of dark- to light-gray-weathering non- in layers. calcareous clayey to silty shale that is entirely of marine origin. The lower unnamed shale member, 720 feet thick, consists of It rests on the chalky Niobrara Formation and is overlain by thick alternating units of dark-, medium-, and light-gray- the Fox Hills Sandstone; both contacts are conformable and weathering shale that give a banded appearance to the outcrop. gradational. Seven lithologic members compose the Pierre Fossiliferous limestone concretions are abundant throughout the Shale, from oldest to youngest: Gammon Ferruginous Member, member. Most weather gray, yellowish gray, or brown, but one Sharon Springs Member, Mitten Black Shale Member, Red conspicuous bed 306 feet below the top weathers bright orange Bird Silty Member, a lower unnamed shale member,' Kara brown. Dusky-red-weathering ferruginous concretions are pres­ Bentonitic Member, and an upper unnamed shale member. These ent at places and are especially noticeable at 140, 205, and 470 members are correlated with named and unnamed members of feet below the top. About 10 thin layers of bentonite are scat­ the Pierre Shale of eastern Colorado, western Kansas, central tered in the upper two-thirds of the member. South Dakota, eastern North Dakota, and southeastern Montana, The Kara Bentonitic Member, 36 feet thick, consists mostly of and with equivalent formations in southwestern Colorado, cen­ light-olive-gray-weathering silty bentonitic shale. It includes a tral Wyoming, Montana, southwestern Alberta, and east-central 6-foot-thick bed of bentonite at the base and thinner beds of Texas. bentonite near the top. The bentonite has a high swelling The Gammon Ferruginous Member, which is unusually thin capacity, and it weathers to gumbo soil bare of vegetation. (30 ft) at Red Bird, consists of hard platy-weathering gray Fossiliferous gray- and brown-weathering limestone concretions shale that contains a few layers of red-weathering siderite con­ are present; a bed of closely spaced concretions at the top of the cretions and several thin beds of nonswelling bentonite. member forms a ridge. The