We report the results of a detailed paleoecological study of the Bonneville basin covering the last 280,000 yr. Our study used fossil ostracodes and a sedimentological record obtained from the August 2000 GLAD800 drilling operation at Great Salt Lake. We analyzed 125 samples, taken at 1 m intervals from Site 4 (GSL00-4), for ostracodes and other paleoecologic and sedimentologic indicators of environmental change. Multivariate analyses applied to the ostracode data and qualitative analyses of fossil and sedimentological data indicate an alternation between three major environments at the core site over the cored interval: (1) shallow saline or hypersaline lakes; (2) salt or freshwater marshes; and (3) occasional deep freshwater lakes. These environmental changes are consistent with shoreline studies of regional lake level fluctuations, but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases. Our age model (using 14C, U-series, tephra and biostratigraphic chronologies) allowed us to associate the core's record of regional paleohydrology with the marine oxygen isotope stages of global climate change. The core contains continuous records for the last four glacial/interglacial sequences. Salt/freshwater marshes were common during the interglacials and deep freshwater conditions correspond with maximum global ice volume in OIS 2, and before a maximum in global ice during OIS 6. Immediately following deep lake phases, crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units. Our study suggests that the climate of the Great Salt Lake catchment appears to have been drier during OIS 6 than during OIS 2.We compare our record of environmental change during OIS 6 glaciation with other records from the western United States and find that the overall pattern of climate was similar throughout the West, but differences in the timing of climate change (i.e. when a region became drier or moister) are common.

This research was generously supported by NSF grant ESH-9905168 to A.C., NSF grant MRI-0116395 to R.L.E., NSF grant EAR- 0001120 to DOSECC for drilling operations and a Summer 2002 internship to D.B. provided by DOSECC.

24 páginas, 6 figuras, 3 tablas.-- et al.

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