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TitleStratal architecture of an early Eocene fluvial-lacustrine depositional system, Little Muddy Creek area, southwestern Green River Basin, Wyoming
AuthorZonneveld, J -P; Bartels, W S; Clyde, W C
SourceCenozoic systems of the Rocky Mountain region; by Raynolds, R G (ed.); Flores, R M (ed.); 2003 p. 253-287
Alt SeriesGeological Survey of Canada, Contribution Series 2001003
PublisherRocky Mountain Section, SEPM (Society for Sedimentary Geology) (Denver, CO, USA)
AreaUnited States of America
Lat/Long WENS-111.0000 -107.0000 42.7500 40.5000
Subjectsmarine geology; sedimentology; stratigraphy; paleontology; Paleogene; basins; sedimentary basins; regressions; transgressions; lacustrine deposits; fluvial deposits; intermontane basins; sea level changes; sea level fluctuations; paleomagnetism; biostratigraphy; well level fluctuations; flood plains; alluvial deposits; alluvial plains; lacustrine environments; carbonates; Eocene; unconformities
Illustrationslocation maps; cross-sections, stratigraphic; geological sketch maps; stratigraphic columns; photographs; schematic diagrams
ProgramGeological Society of America, Funding Program
AbstractThe Paleogene sedimentary record of the Green River Basin, Wyoming was largely controlled by the regressions and transgressions of Paleolake Gosiute, a large shallow lake that occupied the center of this intermontane basin. Fluctuations in lake depth, occurring in response to both climatic and tectonic con-trols, resulted in extensive inundation or exposure of the lowlands adjacent to the lake. In the southwest-ern Green River Basin, lacustrine deposits of the Green River Formation intertongue extensively with the predominantly fluvial strata of the Wasatch and Bridger Formations. These fluvial units reflect periods of lacustrine lowstand during which the lake contracted to the center of the basin. In intermontane basins, stratigraphic base level is not directly affected by changing sea level. Fluctuations in lake level due to variations in climate and local tectonics therefore play a dominant role in the stratigraphic evolution of the basin. Paleomagnetic and biostratigraphic data obtained from the Little Muddy Creek area provide a chronostratigraphic framework to facilitate reconstruction of the sequence stratigraphic history in the study area and provide a means for assessing temporal equivalency between outcrop exposures in differ-ent parts of the Green River Basin. Early Eocene strata within the Little Muddy Creek area are character-ized by four fluvial-lacustrine sequences separated by erosional unconformities (lacustrine lowstand sur-faces of erosion). The first unconformity occurs in the latest Wasatchian (Lostcabinian, base of GPTS chron C23r). The medial unconformity occurs in the earliest Bridgerian (early Gardnerbuttean, middle chron C23r). The upper unconformity occurs in the medial early Bridgerian (late Gardnerbuttean, upper chron C23r). Three types of regionally significant stratal surfaces occur within the study interval. Sequence bound-ing unconformities are characterized by abrupt upward changes in lithology, from lacustrine carbonates to amalgamated fluvio-deltaic sandsheets. Initial transgressive surfaces are characterized by a shift from sandstone zones to heterolithic, mud-dominated, alluvial floodplain deposits. Maximum lacustrine flooding surfaces mark the point of maximum lake advance on the margins of the basin. Individual sequences have a predictable geometry, akin to that observed in marine successions, reflecting lake level variations and concomitant fluctuations in fluvial base level and available accommodation space.