Uppermost Cretaceous and Tertiary Stratigraphy of Fossil Basin, Southwestern Wyoming By STEVEN S. ORIEL and JOSHUA I. TRACEY, JR. GEOLOGICAL SURVEY PROFESSIONAL PAPER 635 New subdivisions of the J,ooo-Joot-thick continental Evanston, Wasatch, Green River, and Fowkes Formations facilitate understanding of sediment genesis and Jl7yoming thrust-belt tectonic events UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 70-604646 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 65 cents (paper cover) CONTENTS Page Wasatch Formation-Continued Abstract __________________________________________ _ 1 Fossils and age-Continued· Page Introduction ______________________________________ _ 2 Tunp Member______________________________ 28 Purpose ______________________________________ _ 2 Origin--------~-------------------------------- 28 Earlier work_ .. __ - __ - ___________________ - _-- _- __ 2 Tectonic implications ____________ -_-------------- 29 Acknowledgments __ . ___________________________ _ 2 Green River Formation ___ .. _______ ------------------ 30 General relations ___ -- _________________________ _ 5 Name and usage __________________ -------------- 30 Evanston Formation _______________________________ _ 5 Definition __________________ -_-------------- 30 N arne and usage _______________________________ _ 5 Lithologic heterogeneity. ______ --_----------- 30 Lower member _____ - ___________________ - ______ _ 6 Subdivisions used here_______________________ 30 Hams Fork Conglomerate Member ______________ _ 6 Fossil Butte Member ____________ -_-------------- 30 ~ain bodY------------------------------------- 9 Angelo ~ember_ .. ________________ -------------- 31 Lower con tact_ ________________________________ _ 10 Fossils and age ___________________ --_----------- 32 Fossils and age_--_--_-- __________ - _____ - ______ _ 11 Origin_________________________________________ 32 Lower member_. __________________________ _ 11 Tectonic implications ______________ -------------- 33 Hams Fork Conglomerate ~ember __________ _ 12 Fowkes Formation _____________________ -_--------,.-- 33 Main body _______________________________ _ 12 Name and usage________________________________ 33 Origin ________________________________________ _ 13 Definition _____________________ - _____ -_-_--- 33 Tectonic implications ________________________ ..: __ 14 Subsequent usage _____________ ------------.,.- 33 Wasatch Formation ________________________________ _ 14 Suggested usage____________________________ 33 N arne and usage _______________________________ _ 14 Subdivisions used here ________ --_----------- 34 Definition _________________________________ _ 14 Sillem ~ember ___________________ -------------- 34 Veatch's subdivisions _______________________ _ 16 Bulldog Hollow Member_________________________ 35 Subdivisions used here ______________________ _ 16 Gooseberry Member ______________ --------------- 35 Basal conglomerate member _____________________ _ 17 Fossils and age _________________ -_-------------- 36 Lower member ________________________________ _ 17 Origin_________________________________________ 37 ~ain body ____________________________________ _ 18 Tectonic implications____________________________ 37 Sandstone tongue ______________________________ _ 20 Some regional relations _____ ------------------------- 38 ~udstone tongue ______________________________ _ 20 Lower strata of the Wasatch_____________________ 39 Bullpen Member---- ___________________________ _ 21 Relations of Iower.units------------------------- 39 Tunp ~ember---- _____________________________ _ 22 Fossils and age ________________________________ _ Relations of tongues of the Wasatch and Green 27 River Formations_____________________________ 39 Basal conglomerate member _________________ _ 27 Fowkes-N orwood-Bridger relations ___________ -_--- 41 Lower member ____________________________ _ 27 ~ain Type sections for members defined in this report_ __ -_--_ 41 body ________________________________ _ 27 Sandstone and mudstone tongues ____________ _ 28 References cited ____________________________ -_------ 4 7 Bullpen Member ___________________________ _ 28 IndeX--------------------------------------------- 51 ILLUSTRATIONS FRONTISPIECE. Photograph of Fossil Butte, type locality for a new member of the Green River Formation, showing slumping near the contact with underlying varicol~red mudstones in the Wasatch Formation. Page FIGURE 1. Map showing the location of the Fossil basin in southwestern Wyoming and nearby geographic features ___ _ 3 2. Topographic map of the northern part of the Fossil basin showing location of geographic features ________ -_ 4 3-7. Photographs of the Evanston Formation: 3. Lower units, west side of Commissary Ridge _____________________________________ --_------------- 7 4. Ridges and flatirons formed by boulder beds in the Hams Fork Conglomerate Member __ ------------- 8 5. Type section of the Hams Fork Conglomerate Member _____ , _____________________ -·--------------- 9 v VI CONTENTS FIGURE 3-7. Photographs of the Evanston Formation-Continued Page 6. Quartzite pebbles and cobbles in the Hams Fork Conglomerate Member, south end of Commissary Ridge-------------------------------------------------------------------------~--------- 10 7. Main bodY---------------------------------------------------------------------------------- 11 8. Geologic map of part of the Kemmerer quadrangle showing the divergence of boulder conglomerate beds from the basal contact of the Evanston Formation __ ·____________________________________________ _ 15 9-15. Photographs of the Wasatch Formation: 9. Lower member, north side of Morgan Canyon ______________________________________________ _ 18 10. Color-banded mudstone and siltstone in the main body, southwest side of Fossil Butte ___________ _ 18 11. Lenses of moderately well sorted brown conglomerate in mudstones of the main body ____________ _ 19 12. "Algal log" in the mudstone tongue _______________________________________________________ _ 21 13. Diamictite in the Tunp Member __________________________________________________________ _ 23 14. Block of Ephraim Conglomerate in diamictite of the Tunp Member ___________________________ _ 24 .. 15. Geometric relations of the Tunp Member __________________________________________________ _ 25 16. Map showing locations of the Eocene lakes in which the Green River Formation was deposited ___________ _ 33 TABLES Page TABLE 1. Nomenclature of uppermost Cretaceous and Tertiary stratigraphic units in the Fossil basin ______________ _ 5 2. Fossils from the lower member of the Wasatch Formation in the Sage quadrangle, Lincoln County, Wyo __ _ 26 3. Dominant rock types and sequences of Upper Cretaceous and Tertiary stratigraphic units in the Fossil basin and adjoining areas ____________________________________________________________________ _ 38 4. Approximate ages of the stratigraphic units in the Fossil basin and adjoining areas ______________________ _ 40 UPPERl\:fOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, SOUTHWESTERN WYOMING BY STEVEN S. ·.ORIEL and JosHuA I. TRACEY, Jn. ABSTRACT into more abundant sandstone and conglomerate toward the More than 7,000 feet of uppermost Cretaceous and Tertiary basin margins. continental strata in the northern Fossil basin, along the 4. The sandstone tongue is 40-50 feet thick in the southern part southern part of the western Wyoming thrust belt, is here sub­ of the mapped area, where it divides the lower member of divided into newly defined formal and informal rock-strati­ the Green River Formation into two units, and it pinches graphic units. Recognition of these units makes possible the out northward. It consists of well-sorted medium- to coarse­ dating of some thrust-fault movement, of the development of grained brown crossbedded sandstone and green and gray the Fossil structural basin, and of some later block faulting, as mudstone. well as reinterpretations of the origins of the strata. 5. The mudstone tongue, as much as 50 feet thick, lies between The Evanston Formation, which is more than 2,000 feet thick the two members of the Green River Formation and consists and more extensive in the Fossil basin than formerly recognized, of dark- to brick-red mudstone which grade~ basinward into consists of an unnamed lower member, the Hams Fork Con­ pink and gray-green claystone. glomerate MemiJer, and the main body. The lower member con­ 6. The Bullpen Member, which overlies the Green River Fonila­ sists of as much as 500 feet of gray to dark-gray mudstone, tion and is 400 feet thick, consists of red, salmol}, green, siltstone, claystone, and carbonaceous fine-grained, but partly and gray mudstone, fine- to coarse-grained partly con­ gritty and conglomeratic, sandstone a11d is of latest Cretaceous, glomeratic sandstone, and thin but extensive beds of brown probably Lance, age. The Hams Fork Conglomerate Member, to white limestone similar to that in the Green River previously mapped erroneously as the Almy Formation along Formation. the east side of the l!"'ossil basin, consists mainly of 450-1,000 7. The Tunp Member is a 200- to 500-thick peripheral diamictite feet of latest Cretaceous (Lance) boulder conglomerate and facies of the Wasatch Formation. It consists of dark-red interstratitied partly conglomeratic brown and