HR: 0800h
AN: PP41A-0587    [Abstracts]
TI: Rare Earth Element Evidence for Paleolake Chemistry
AU: * Hemming, N G
EM: hemming@ldeo.columbia.edu
AF: Queens College, CUNY, School of Earth and Environmental Sciences, Flushing, NY 11367 United States
AU: Rasbury, E T
EM: troy.rasbury@sunysb.edu
AF: SUNY Stony Brook, Department of Geosciences, Stony Brook, NY 11794 United States
AB: The Eocene Green River Formation contains lacustrine deposits famous for their oil shales, fish fossils and cyclic nature. Although there are common trends in the facies and types of authigenic minerals seen in progressive lake phases and among the different lake basins, there are also distinct differences. These differences illustrate that the basins were not connected through at least part of their history. The common trends throughout the sequences and from all the basins include: 1) elevated alkalinity; 2) cycles that reflect contraction (elevated salinity) and expansion (freshening); and 3) sedimentary structures that allow us to place facies in a limno-geologic context. A key goal is to relate the facies to the paleo-lake chemistry. This requires comparison to modern lakes where similar facies are being created coupled with an integration of the chemistry of the fluids and the trace element patterns in the authigenic minerals. REE patterns from the Great Basin Lake waters are HREE enriched and show trends of increased REE concentrations that have been linked directly to alkalinity (Johannesson et al., 1994). Authigenic phases from facies that reflect lowstands, transgression and highstands in the Green River Formation have patterns that can be directly compared to those from the Great Basin Lake waters. This illustrates great potential for constraining the alkalinity of the precipitating fluids. Although the Kd of the authigenic minerals for the REE's has to be considered before conclusive models can be proposed, there are impressive similarities between REE patterns of authigenic phases from the Green River Formation and waters of modern alkaline lakes of the Great Basin.
DE: 1030 Geochemical cycles (0330)
DE: 1045 Low-temperature geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting