Sedimentology and Depositional History of the Upper Triassic Chinle Formation in the Uinta, Piceance, and Eagle Basins, Northwestern Colorado and Northeastern Utah U.S. GEOLOGICAL SURVEY BULLETIN 1 787-W AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List" Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. 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Geological Survey, Map Sales Box 25286 Maps may be purchased over the counter at the U.S. Geolog­ Denver, CO 80225 ical Survey offices where books are sold (all addresses in above list) and at the following Geological Survey offices: Residents of Alaska may order maps from U.S. Geological Survey, Map Sales ROLLA, Missouri-1400 Independence Rd. 101 Twelfth Ave., Box 12 FAIRBANKS, Alaska-New Federal Building, 101 Twelfth Fairbanks, AK 99701 Ave. Chapter W Sedimentology and Depositional History of the Upper Triassic Chinle Formation in the Uinta, Piceance, and Eagle Basins, Northwestern Colorado and Northeastern Utah By RUSSELL F. DUBIEL A multidisciplinary approach to research studies of sedimentary rocks and their constituents and the evolution of sedimentary basins, both ancient and modern U.S. GEOLOGICAL SURVEY BULLETIN 1787 EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government UNITED STATES GOVERNMENT PRINTING OFFICE: 1992 For sale by the Books and Open-File Reports Section U.S. Geological Survey Federal Center Box 25425 Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Dubiel, Russell F. Sedimentology and depositional history of the Upper Triassic Chinle Formation in the Uinta, Piceance, and Eagle basins, northwestern Colorado and northeastern Utah / by RussellF. Dubiel. p. cm. (Evolution of sedimentary basins Uinta and Piceance basins ; ch. W) (U.S. Geological Survey bulletin ; 1787) "A multidisciplinary approach to research studies of sedimentary rocks and their constituents and the evolution of sedimentary basins, both ancient and modern." Supt. of Docs, no.: I 19.3:61787W 1. Geology, Stratigraphic Triassic. 2. Geology Colorado. 3. Geology Utah. 4. Chinle Formation. I. Title. II. Series. III. Series: U.S. Geological Survey bulletin ; 1787. QE75.B9 no. 1787-W [QE679] 557.3 s dc20 91-23188 [551.7'09788] CIP CONTENTS Abstract Wl Introduction Wl Previous work W2 Geologic setting W4 Stratigraphy W4 Sedimentology W6 Lithofacies and depositional environments W6 Valley-fill and active channel-fill deposits W6 Lateral-accretion deposits W7 Floodplain deposits W10 Lacustrine-delta and crevasse-splay deposits W16 Lacustrine deposits W17 Eolian deposits W19 Depositional systems and paleogeography W19 Paleoclimate W22 Conclusions W22 References cited W22 FIGURES 1, 2. Maps showing: 1. Schematic reconstruction of Late Triassic paleogeography on Colorado Plateau and adjacent regions W2 2. Study area in northwestern Colorado and northeastern Utah W3 3. Chart showing correlation of stratigraphic nomenclature of Upper Triassic strata W4 4. Measured stratigraphic sections of Upper Triassic Chinle Formation W8 5-14. Photographs showing: 5. Fluvial valley-fill conglomerate and sandstone of Gartra Member W13 6. Purple-mottled sandstones of Temple Mountain Member W13 7. Lower part of red siltstone member of Chinle Formation near Derby Junction W14 8. Upper part of red siltstone member of Chinle Formation near Derby Junction W14 9. Intersecting sandstone-filled mudcracks in lower part of red siltstone member of Chinle Formation near Derby Junction W15 10. Pseudoanticlines in paleosols of middle part of red siltstone member of the Chinle Formation near Derby Junction W15 11. Root alteration haloes in red siltstone member of Chinle Formation near East Brush Creek, Eagle basin W16 12. Lacustrine-deltaic strata in Moss Back Member of Chinle Formation, San Rafael Swell W17 13. Lacustrine deposits in Chinle Formation W18 14. Eolian deposits at top of Chinle Formation, East Brush Creek, Eagle basin W20 15. Map showing schematic reconstruction of Chinle depositional systems in Uinta, Piceance, and Eagle basins W21 Contents III TABLE 1. Locations of measured sections of the Chinle Formation in the Uinta, Piceance, and Eagle basins, northwestern Colorado and northeastern Utah W12 IV Contents EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS Sedimentology and Depositional History of the Upper Triassic Chinle Formation in the Uinta, Piceance, and Eagle Basins, Northwestern Colorado and Northeastern Utah By Russell F. Dubiel Abstract depositional basin, which encompassed a large part of the Colorado Plateau and the regions adjacent to it. The Chinle Lithofacies analysis was used to examine depositional systems of the Upper Triassic Chinle Formation in the Uinta, depositional basin can be subdivided in this area into a Piceance, and Eagle basins in northwestern Colorado and major and a minor depocenter. northeastern Utah. Lithofacies analysis identified deposits of The major part of the Chinle depositional basin was valley fills and active channel fills, point bars of moderate- to centered near the Four Corners area of Colorado, Utah, high-sinuosity fluvial systems, floodplains containing paleosols Arizona, and New Mexico and was north of the Mogollon and rhizoliths, lakes and lacustrine deltas, and eolian sand Highlands and south of the ancestral Rocky Mountains (fig. sheets. Lateral fades relations determined from field relations 1) (Stewart and others, 1972; Blakey and Gubitosa, 1983; and stratigraphic cross sections depict the paleogeography at Dubiel, 1983, 1989a, b; Busbey-Spera, 1988). Detritus was the time of Chinle deposition. The ancestral Uncompahgre and shed northward and westward into this part of the Chinle Front Range uplifts in Colorado supplied clastic detritus to the basin from the Mogollon Highlands, which lay to the south, depositional basin. Fluvial systems flowed west and northwest and southward and westward off the ancestral Rocky from the bounding highlands and deposited sediment within Mountains, which lay to the north. The ancestral Rocky paleovalleys and channels and on associated floodplains. Mountains consisted of the ancestral Uncompahgre Fluvial systems graded distally into lacustrine and lacustrine- Highlands and the ancestral Front Range and several minor deltaic systems in the southern and eastern Uinta and Piceance ranges. Fluvial and lacustrine-deltaic depositional systems basins. In the Eagle basin, the close of Chinle time is marked by eolian sand-sheet deposition, reflecting the change from a flowed north and west off of the Mogollon Highlands and tropical monsoonal climate earlier in the Late Triassic to drier south and west off of the ancestral Uncompahgre and Front conditions at the close of the Late Triassic. Range highlands into the southern part of the Chinle depositional basin. A second smaller part of the Chinle