Eocene Fossil Lake, Green River Formation, Wyoming: A History of Fluctuating Salinity
Published:January 01, 1994
H. Paul Buchheim, 1994. "Eocene Fossil Lake, Green River Formation, Wyoming: A History of Fluctuating Salinity", Sedimentology and Geochemistry of Modern and Ancient Saline Lakes Models, Robin W. Renaut, William M. Last
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Stratigraphic analysis of the 70-m thick Green River Formation in Fossil Basin of southwestern Wyoming reveals fluctuations in the water-column chemistry ranging from fresh to hypersaline. Fresh water dominated the first two-thirds of the lake’s history while hypersalinity dominated the final stages.
Salinity changes are identified by variations in calcite-dolomite ratio, tuff bed mineralogy (authigenic analcime, K-feldspar, and clay minerals), and paleontology. The lower two-thirds of the sequence are dominated by finely laminated carbonates (primarily kerogen-rich micrite), interrupted by 0.3- to 1.0-meter thick beds of massive dolomicrite. Dolomicrites grade laterally into bioturbated calcimicrites. The sequence is not random, and is related to a lithofacies assemblage including (from the base up) kerogen-rich laminated micrite, kerogen-poor laminated micrite, partly burrowed laminated micrite, and dolomicrite. Tuff beds occur randomly in the sequence and are composed of authigenic analcime and K-feldspar. Laterally, they grade into clays.
These data are interpreted as representing a lake fluctuating from fresh to hypersaline, with stages controlled by sudden freshwater expansions of the lake followed by more gradual regressions. However, initiation of dolomite precipitation was relatively sudden al the end of regressive stages. Even then, the lake remained relatively fresh along its margins as indicated by accumulated synchronous shore–phase calcimicrite. Tuff bed mineralogies confirm this conclusion.
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Sedimentology and Geochemistry of Modern and Ancient Saline Lakes Models
Sedimentology and Geochemistry of Modern and Ancient Saline Lakes - This volume of papers grew out of a four-day symposium entitled ?Sedimentary and Paleolimnological Records of Saline Lakes? held at Saskatoon, Canada in August, 1991. The aim of this Special Publication is to bring together selected papers from this conference that deal specifically with the sedimentological, inorganic geochemical, and hydrological aspects of salt lakes and their stratigraphic records. This volume is divided into four sections. The first section contains papers that deal with modern saline lakes. The second section contains papers dealing with sedimentation and diagenesis of late Quaternary salt lakes. The third and fourth sections contain papers devoted to ancient (pre-Quaternary) Lacustrine sequences.