Lacustrine stratigraphy and strontium isotope geochemistry of the Laney Member, Green River Formation, southwestern Wyoming

The lacustrine sequence stratigraphic interpretation and Sr isotope composition of the Laney Member of the Green River Formation demonstrate a shift in the paleohydrology of Eocene Lake Gosiute. Four thinning upward sequences recognized by basinward shifts in facies, followed by one thick terminal basin fill sequence marked by a major desiccation event at its base, are interpreted to represent the shift from balanced fill to overfilled conditions caused by the slow decrease in basin subsidence, the expansion of hydrographic boundaries, and the subsequent increase in the amount of sediment and water that entered the basin. This lake type shift occurred within the uppermost sequence, represented by the change in sedimentation across a basin threshold.; The Sr isotope composition of the carbonate fraction of fine-grained micritic mudstone throughout the Laney Member, averaging 0.71231 in the lower LaClede bed and 0.71172 in the upper LaClede bed, trends toward the incorporation of less radiogenic Sr upsection and is interpreted to indicate changes in the size or geology within the drainage basin to Lake Gosiute. Strontium mass balance models indicate that the range in strontium isotope composition measured from lacustrine expansion-contraction cycles can best be explained by a combination of drainage from uplifts in the Green River Basin, groundwater from mudflat environments, and less radiogenic drainage from the Absaroka Range during lake highstand.; Lacustrine sequences in the Laney Member are composed of packages of stromatolite-micritic-dolomicritic mudstone cycles bound by exposure surfaces that individually represent the expansion-contraction the lake. The Sr isotope composition and carbonate mineralogy of samples from lacustrine cycles shows deceasing 87Sr/86Sr ratios and increasing relative calcite abundance during lake expansion and increasing 87Sr/ 86Sr ratio and dolomite during lake contraction. This is interpreted to represent shifting lakewater provenance to include less radiogenic surface water runoff during lake expansion, and an increasing component of groundwater derived waters during lake contraction.*; *This dissertation is a multimedia document (contains text and other applications not available in printed format). The CD requires the following system requirements: Image viewer.