Eocene Rocks, Fossils, and Geologic History, Teton Range, Northwestern Wyoming
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Eocene Rocks, Fossils, and Geologic History, Teton Range, Northwestern Wyoming GEOLOGICAL SURVEY PROFESSIONAL PAPER 932 -B Prepared in cooperation with the National Park Service, the Geological Survey of Wyoming, and the Department of Geology of the University of Wyoming Eocene Rocks, Fossils, and Geologic History, Teton Range, Northwestern Wyoming By J. D. LOVE, ESTELLA B. LEOPOLD, and D. W. LOVE GEOLOGY OF THE TETON -JACKSON HOLE REGICN, NORTHWESTERN WYOMING GEOLOGICAL SURVEY PROFESSIONAL PAPER 932 -B Prepared in cooperation with the National Park Service, the Geological Survey of Wyoming, and the Department of Geology of the University of Wyoming Remnants of Eocene rocks along the modern Teton Range date the final uplift and subsidence of the ancestral Teton-Targhee arch, and determine direction of Eocene drainage UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1978 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Love, John David, 1913 Eocene rocks, fossils, and geologic history, Teton Range, northwestern Wyoming. (Geology of the Teton-Jackson Hole region, northwestern Wyoming) (Geological Survey Professional Paper 932-B) Bibliography: p. 37 Supt.ofDocs.no.: I 19.16:932-8 1. Geology, Stratigraphic Eocene. 2. Paleontology Eocene. 3. Geology Teton Range. I.Leopold, Estella B., joint author. II. Love, D. W., joint author. III. United States. National Park Service. IV. Wyoming. Geological Survey. V. Wyoming. University. Dept. of Geology. VI. Title. VII. Series. VIII. Series: United States Geological Survey Professional Paper 932-B QE692.2.L68 557.3'08s [551.7*8] 77-608133 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-03123-0 CONTENTS Page Page Abstract ..................................... 1 Eocene rocks Continued Introduction ................................. 1 Hominy Peak Formation Continued Purpose of report and summary of results and Stratigraphic and structural relations 21 conclusions ............................. Age and correlation ................. 23 History of investigation .................... Tectonic implications ............... 30 Acknowledgments ........................ Dacite porphyry intrusive of the Birch Hills 31 Eocene rocks ................................. Eocene geologic history ...................... 32 Hominy Peak Formation .................. Summary of post-Eocene geologic history ...... 34 Name and definition .................. Oil and gas and geothermal-energy potential .. 35 Distribution and thickness ............. References cited ............................ 37 Lithology ............................ Index ...................................... 39 ILLUSTRATIONS [Plates 1-4 follow "Index"; plate 5 is in pocket) PLATES 1 -4. Pollen characteristic of the Kisinger Lakes floral zone. 5. Correlation diagram showing geographic and stratigraphic relations of the Hominy Peak Formation to other Eocene rocks south of the Yellowstone-Absaroka volcanic field and the horizons of radiometric, mammal, and pollen age determinations. FIGURE 1. Map showing relation of Hominy Peak Formation to regional geographic features ................................. 4 2. Map showing outcrops of Hominy Peak Formation in the Teton region, Wyoming .................................. 5 3. Reliefmap ................................................................................................. 6 4. Geologic map of Hominy Peak Formation in the vicinity of the type section ....................................... 8 5 11. Photographs showing: 5. Regional air oblique view of type section of Hominy Peak Formation ....................................... 10 6. View northwest showing type section of Hominy Peak Formation and underlying Pinyon Conglomerate ........ 11 7. Detailed view of Hominy Peak Formation ............................................................... 12 8. Details of gold-bearing quartzite conglomerate ........................................................... 13 9. Igneous and sedimentary facies of Hominy Peak Formation ............................................... 18 10. Vent facies of Hominy Peak Formation .................................................................. 19 11. Detail of vent facies ................................................................................... 20 12. Geologic map of Grand Targhee Resort area ................................................................... 22 13-16. Photographs showing: 13. Air oblique view of Grand Targhee Resort area ........................................................... 25 14. Unconformity between Hominy Peak and Darby Formations .............................................. 26 15. Corroded boulder of Madison Limestone ................................................................. 27 16. Gold flakes ........................................................................................... 28 17. Structure sections of Hominy Peak Formation ................................................................. 29 18. Structure sections in Grand Targhee Resort area ............................................................... 30 19. Section from Teton Range to Cities Service well ................................................................ 32 20, 21. Photographs showing flora and terrain, State of Nayarit, Mexico ................................................. 34,36 TABLE TABLE 1. Pollen collections from type section of Hominy Peak Formation 24 III GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING EOCENE ROCKS, FOSSILS, AND GEOLOGIC HISTORY, TETON RANGE, NORTHWESTERN WYOMING By J. D. LOVE, ESTELLA B. LEOPOLD, and D. W. LOVE ABSTRACT horsts isolated the Gros Ventre segment of the ancestral Targhee Teton Gros Ventre uplift. The modern Teton Rang? arose The Hominy Peak Formation (new name), a sequence of mafic in the last 9 million years; from part of a low northwest-trend;ng an volcaniclastic sedimentary and igneous rocks as much as 610 meters ticlinal uplift it became a north-trending, west-tilted, asymmetric (2,000 feet) thick, is exposed at the north end and on the west flank faultblock range with a precipitous east face. of the Teton Range, as well as along the south boundary of The timing, magnitude, and other details of the tectonic hiftory of Yellowstone National Park. This formation overlaps Cambrian to the region are relevant to the renewed search for oil and gas in the Paleocene strata in the core of the Teton Range, and the entire sec Wyoming-Idaho thrust belt and to geothermal-energy evaluation. tion was subsequently deformed by post-Eocene tectonic movements. Two large artesian flows of hot water, one in Cambrian and th? other The Hominy Peak contains a pollen flora that correlates with middle in Pennsylvanian rocks, in the Cities Service oil test at moderately Eocene floras associated with Bridger A B vertebrate faunas at shallow depths in Teton Basin indicate a geothermal potential in the several sites in northwestern and southwestern Wyoming. K-Ar ages areas of late Cenozoic subsidence west of the present Teton Pange. here and in adjacent areas are compatible with this age assignment. The Hominy Peak Formation and underlying Paleozoic rocks along INTRODUCTION the south boundary of Yellowstone National Park are intruded by the dacite porphyry of the Birch Hills, which has a late Eocene fission- PURPOSE OF REPORT AND SUMMARY OF track age of 40.5 ± 2.6 million years. RESULTS AND CONCLUSIONS The newly discovered relations of the Eocene rocks to older and younger strata provide a more complete insight into the tectonic The purpose of this report is (1) to present new data history of the Teton Range. The ancestral uplift trended northwest that help reconstruct the geologic history of the Teton and consisted of two parts the low, broad Gros Ventre Teton up- uplift in Eocene time, (2) to summarize Pliocene and warp, bounded on its southwest flank by a thrust fault, and the much higher, larger Targhee uplift, at the northwest end. The dominant Pleistocene crustal modifications that disguise the tectonic forces that created this uplift moved southwestward, Eocene events and that account for some of the unique directly opposite those in the thrust belt to the south. Yet to be deter and more conspicuous features of the uplift, and (3) to mined are the subsurface limit to the northeast margin of the thrust relate the timing, magnitude, and other details of the belt under Teton Basin and whether the belt was overridden by the tectonic history of the region to the search for new oil ancestral Teton block. and gas deposits and to evaluate the geothermal-energy The Targhee uplift was eroded to its Precambrian core by mid-Late Cretaceous time and, for 35 million years, was the source of gold- potential. After a lapse of 70 years (since Veatch's bearing Precambrian quartzite conglomeratic debris to Upper Cre report in 1907), 1975 discoveries of major amounts of taceous, Paleocene, and Eocene strata in the Jackson Hole region. oil and gas in the southern part of the thrust belt The Targhee uplift subsided into the Teton Basin Snake River brought a suddenly renewed interest in the entire belt. downwarp, probably shortly after middle Eocene time, and was never In addition, exploration of the geothermal potential in again a source of sediment. This subsidence, accompanied in places by normal faulting, also involved the ancestral Teton