T148 Paleoenvironmental Records in and around the Bonneville Basin: From Glacial/Interglacial Cycles to Anthropogenic Impacts

Tuesday, 18 October 2005
8:00 AM - 12:00 PM

A ~280KA PALEOECOLOGIC AND PALEOCLIMATIC RECORD FOR THE BONNEVILLE BASIN DERIVED FROM THE GLAD800 DRILLING CAMPAIGN AT GREAT SALT LAKE, UTAH

Paper number: T148-10
Program: Technical Sessions
Time: 10:25 AM – 10:40 AM

Authors

Abstract

Scientific drilling at the Great Salt Lake (GSL) in August, 2000 yielded a series of sediment cores, the longest of which (GSL-00-4, 121mblf, with 96% recovery) spans approximately 280ka. The core site lies in the GSL's north structural basin, about 1km north of the Carrington Fault in a region shown by prior seismic data to record fairly continuous deposition. GSL-00-4 has been subject to split core logging, geochronologic analyses (14C, U/Th, tephochronology and biostratigraphy) and intermediate resolution sediment sampling (~2ka resolution) for a variety of sedimentologic, geochemical and paleoecologic (primarily using ostracodes) indicators of regional hydrologic and paleoclimate change.

Fossil and sedimentological data indicate an alternation between three major environments at the core site (1) shallow saline or hypersaline lakes; (2) salt or freshwater marshes; and (3) occasional deep freshwater lakes. This alternation is consistent with shoreline studies of regional lake level fluctuations, but the core provides considerable new detail on both the timing and environmental conditions associated with the various lake phases. The core records the last four glacial/interglacial cycles. Salt/freshwater marshes were common during interglacials and deep freshwater conditions correspond with maximum global ice volume in OIS 2, and precede the maximum in global ice during OIS 6. Extreme low lake stands are marked by the development of marginal freshwater marshes at the core site, with characteristic paleoecologic indicators and isotopic indications of short residence times, or by complete desiccation and the formation of paleosols. Crashes in lake level from rapid desiccation occurred following lake high stands, and resulted in the deposition of thick evaporite units. Our study suggests drier climates in the GSL catchment during OIS 6 than during OIS 2.The GSL record over this 280ka time span shows some broad similarities to other Great Basin records but also intriguing indications of regional climate variability at the millennial time scale.