Harebell Formation (Upper Cretaceous) and Pinyon Conglomerate (Uppermost Cretaceous and Paleocene), Northwestern Wyoming GEOLOGICAL SURVEY PROFESSIONAL PAPER 734-A Prepared in cooperation with the Geological Survey of Wyoming and the Department of Geology of the University of Wyoming Harebell Formation (Upper Cretaceous) and Pinyon Conglomerate (Uppermost Cretaceous and Paleocene), Northwestern Wyoming By J. D. LOVE GEOLOGY OF GOLD-BEARING CONGLOMERATES IN NORTHWESTERN WYOMING GEOLOGICAL SURVEY PROFESSIONAL PAPER 734-A Prepared in cooperation with the Geological Survey of Wyoming and the Department of Geology of the University of Wyoming The gold-bearing Harebell Formation and Pinyon Conglomerate contain many cubic miles of quartzite conglomerate from the now-buried Targhee uplift UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600308 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price: paper cover ?1 domestic postpaid, or 75 cents GPO Bookstore Stock Number 2401-00316 CONTENTS Page Page Abstract _________________________________________ Al Harebell Formation Continued Introduction _____________________________________ 1 Interpretation of depositional environment _____ A32 Purpose of report _____________________________ 1 Pinyon Conglomerate _____________________ 33 History of investigation _______________________ 3 Name and definition ____________________ 33 Acknowledgments _____________________________ 4 Harebell Formation _______________________________ 7 Distribution and thickness ________________ 33 Name and definition ________________ _ 7 Lithology ___________________________ 33 Distribution and thickness _____________________ 7 Stratigraphic and structural relations _______ 41 Lithology ____________________________________ 7 Age and correlation ___________________ 45 Bobcat Member __________________________ 17 Gold occurrences _____________________ 48 Stratigraphic and structural relations __________ 24 Influence of Targhee, Washakie, and Basin Creek Age and correlation ___________________________ 27 Gold occurrences ______________________ 27 uplifts on Pinyon sedimentation __________ 48 Targhee uplift source of quartzite conglomerate Interpretation of depositional environment_____ 52 and gold ____________________________ 27 References cited _________________________ 52 ILLUSTRATIONS FIGURE 1. Geologic map showing outcrops of Pinyon Conglomerate and Harebell Formation, Jackson Hole and page vicinity, Wyoming __________________________________________________ A3 2. Index map showing mountains, basins, and other features surrounding Jackson Hole __________ 4 3. Relief map showing outline of geologic map area and relation of sections of Pinyon Conglomerate and Harebell Formation to regional features _______________________________________ 5 4. Map showing location of sections of Pinyon Conglomerate and Harebell Formation ____________ 7 5. Photograph showing type section of Harebell Formation ______________________________ 8 6. Map showing location of type section of Bobcat Member of Harebell Formation ________________ 9 7. Sections of Pinyon Conglomerate and Harebell Formation ______________________________ 10 8-12. Photographs: 8. Harebell Formation near Whetstone Falls ___________________________________ 16 9. Harebell Formation, East Fork of Pilgrim Creek ______________________________ 20 10. Closeup of conglomerate and sandstone in Harebell Formation _ __________________ 22 11. Conglomerate and sandstone in the Harebell Formation near Mytilus Zone ____________ 23 12. Dinosaur-bearing sandstone overlying conglomerate of the Harebell Formation __________ 24 13. Restored section D-D', southeastern Jackson Hole ___________________________________ 25 14. Block diagram of northwestern Wyoming showing geology at beginning of deposition of Harebell Formation ____________________________________________________ 26 15. Block diagram of northwestern Wyoming during deposition of Harebell Formation _____________ 28 16. Restored section F-F' ______________________________________________________ 30 17. Restored section, northern Yellowstone Park to Jackson Hole______________________-_____ 32 18. Oblique aerial photograph of Pinyon Peak area ________________ ___________________ 34 19. Section E-E' showing relation of Pinyon Conglomerate to type Harebell Formation ___________ 37 20. Photograph showing coal member of Pinyon Conglomerate_____________________________ 38 21. Cross section C-C' north of Mount Leidy _____________________________________ 38 22-32. Photographs: 22. Closeup of Pinyon Conglomerate _________________________________________ 39 23. Big quartzite boulder in Pinyon Conglomerate ________________________________ 40 24. Pinyon Conglomerate on Madison Limestone _________________________________ 41 25. Pinyon Conglomerate on northwest side of Teton Range________________________ 42 26. Contact between Pinyon Conglomerate and Cleverly and Morrison(?) Formations at Mount Sheridan _____________________________________________________ 43 III IV CONTENTS FIGURES 22-32. Photographs Continued Page 27. Pinyon Conglomerate and Harebell Formation on southwest face of Gravel Mountain A 43 28. Angular unconformity between Pinyon Conglomerate and Harebell Formation 45 29. Intertongued sandstone and conglomerate on Purdy Creek 45 30. Pinyon Conglomerate in "Narrows" of South Fork of Fish Creek 46 31. South Fork of Fish Creek 47 32. Pinyon Conglomerate and younger rocks, mouth of Devils Basin Creek 48 33. Cross sections A-A' and B-B', Gravel Ridge and Gravel Peak 49 34. Restored section from the Targhee uplift to Washakie Range __ - ___ - 49 35. Block diagram of northwestern Wyoming and adjacent areas showing geology at beginning of 50 36. Block diagram of northwestern Wyoming and adjacent areas during deposition of Pinyon Conglomerate- 51 52 TABLES Page TABLE 1. Comparison of data for Harebell Formation and Pinyon Conglomerate A14 2. Estimated volumes of unnermost Cretaceous and Paleocene sediments 29 GEOLOGY OF GOLD-BEARING CONGLOMERATES IN NORTHWESTERN WYOMING HAREBELL FORMATION (UPPER CRETACEOUS) AND PINYON CONGLOMERATE (UPPERMOST CRETACEOUS AND PALEOCENE), NORTHWESTERN WYOMING ByJ. D. LOVE ABSTRACT west and northwest of the Teton Range, beneath what is now the Snake River downwarp. The quartzite terrane of Pre- The Harebell Formation of Late Cretaceous age crops out cambrian and possibly Ordovician age in this uplift had an in an area of 265 sq mi (square miles) in Jackson Hole, north­ areal extent of 1,000 sq mi and provided a volume of quart­ western Wyoming, and has a maximum thickness of about zite conglomerate of 135 cu mi (cubic miles) to the Harebell 11,000 feet. The Pinyon Conglomerate of latest Cretaceous Formation and 425 cu mi to the Pinyon Conglomerate. Of and Pal eocene age crops out in an area of 150 sq mi and has this, 40 cu mi of conglomerate in the Harebell Formation and a maximum thickness of about 3,775 feet. Both formations 35 cu mi in the Pinyon are preserved in Jackson Hole. contain thick zones of quartzite conglomerate from the same The climate during deposition of both the Harebell and source; for this reason they are so similar that they have the Pinyon was humid and warm. Large swift rivers flowed frequently been misidentified. No type section or reference east and southeast from the Targhee uplift into Jackson section has previously been designated for either formation. Hole. Deposition was rapid in most places. Marine- or This report summarizes a comparison of differences and brackish-water incursions from the southeast were common similarities of both formations and designates and presents while the Harebell Formation was being deposited but ceased a type section for the Harebell Formation and its con­ prior to deposition of the Pinyon Conglomerate. Volcanism glomeratic Bobcat Member (a new name) and a principal north and possibly northwest of Jackson Hole contributed reference section for the Pinyon Conglomerate. The chief much tuffaceous debris to the Harebell but little or none to differences between the two formations are in color, indura­ the Pinyon. tion, and amount of volcanic debris. The Harebell is olive drab, has the greater induration, and contains abundant volcanic debris, especially in the northern sections. The Pinyon INTRODUCTION is light gray to light brown, has the lesser induration, and contains inconspicuous volcanic debris. A coal member, 50- PURPOSE OF REPORT 140 feet thick, of early Paleocene age, is at the base of the Pinyon in the southeastern part of Jackson Hole. There is no The purpose of this report is to summarize new such coal in the Harebell Formation. data, as well as old but previously unpublished data, Structural relations between the Pinyon and Harebell range on the Harebell Formation and Pinyon Conglomerate from an angular unconformity of nearly 90° west of the Buffalo Fork thrust fault to near parallelism in the Box Creek in northwestern Wyoming as an aid in distinguish­ downwarp. During deposition of the Harebell Formation, even ing them in field mapping. The Harebell Formation in its uppermost part, brackish water repeatedly invaded crops out in an area of about 265 sq mi (square the area. When the youngest strata were deposited, the oldest miles), and the Pinyon Conglomerate crops out in were 11,000 feet below sea level in the Box Creek