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Lacustrine lithofacies, depositional processes, and diagenesis of the Uteland Butte Member, Green River Formation, eastern Uinta Basin, Utah and Colorado
Logan, S. Katherine
Logan, S. Katherine
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2015
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2015-12-08
Abstract
The excellent basin margin outcrops and tie to the subsurface in this study has increased the understanding of the Uteland Butte depositional system of the Green River Formation of Lake Uinta in the Early Eocene. The purpose of this study was to correlate and map outcrop-to-subsurface, sequence-stratigraphic and geologic elements of the Uteland Butte Member across the eastern part of the Uinta basin from the Douglas Creek Arch marginal area to the Greater Natural Buttes Field sublittoral area. Eighteen facies and eight facies associations were established to represent the sediment types and their depositional environment. Facies were identified based on lithology, grain size, texture, and sedimentary structures, bed thickness, bed boundaries and geometries: (F1) Green-grey siltstone, (F2) calcareous to dolomitic mudstone, (F3) ostracod lime wackestone/mudstone, (F4) molluscan lime wackestone-mudstone, (F5) oolitic lime wackestone/mudstone, (F6) intraclastic-ostracod packstone-grainstone, (F7) ostracod packstone-grainstone, (F8) oncolite packstone- grainstone, (F9) oolitic packstone-grainstone, (F10) pisolite packstone-grainstone, (F11) bioclastic floatstone to rudstone, (F12) ostracod sandstone, (F12) structureless sandstone, (F13) structureless sandstone, (F14) cross-stratified sandstone, (F15) coal, (F14) illitic oil shale, (F16) illite oil shale, (F17) argillaceous mudstone, and (F18) laminated silty oil shale. Sedimentary facies were grouped into nine facies associations based on lateral and vertical association of facies environments or zones, based on energy level and relative water depth: (FA-A) shoreline mudstone, (FA-B) delta deposits, (FA-C) littoral to sublittoral claystone to sandstone, (FA-D) carbonate shoal, (FA-E) microbial carbonates, (FA-F) littoral to sublittoral wackestones to mudstones, (FA-G) littoral to sublittoral oil shale, and (FA-H) laminated oil shale. On the eastern edge of the lake basin where a ramp margin persists and deltaic and fluvial influences are minor, except in the Evacuation Creek area south, outcrops display marginal shoreline environments that underwent four major flooding events. These events raised water levels as much as 7.5 meters in marginal areas, and greater than 12 meters in sublittoral regions. Facies showed major changes over the 62 kilometers studied, but four persistent cycles were also identifiable in the deeper regions of the lake. Sublittoral successions are 30% thicker than the marginal Uteland Butte, and are lean in silt, richer in dolomite, with nearly every bed containing >25% dolomite. The Uteland Butte Member lacks stromatolites, evaporites and analcime, and is rich with abundant bivalves, gastropods and ostracods across the lake that indicates a fresh water lake environment. Mud occurred in three forms, calcite, dolomite and clay in this lake succession. Dolomite displays intercrystalline porosity, averaging between 7.2 to 17%. Dolomitic mud found in packstones and grainstones is primarily located within grain coatings, intraclasts, peloids or peloids within isolated ostracod shells. .
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