Oxygen and carbon isotopes from a continuous, 120-m-long, carbonate-rich core from Bear Lake, Utah-Idaho, document dramatic fluctuations in the hydrologic budget of the lake over the last 250,000 yr. Isotopic analyses of bulk sediment samples capture millennial-scale variability. Ostracode calcite was analyzed from 78 levels, mainly from the upper half of the core where valves are better preserved, to compare the isotopic value of purely endogenic carbonate with the bulk sediment, which comprises both endogenic and detrital components. The long core exhibits three relatively brief intervals with abundant endogenic aragonite (50±10%) and enriched δ18O and δ13C. These intervals are interpreted as warm/dry periods when the lake retracted into a topographically closed basin. We correlate these intervals with the interglacial periods of marine oxygen-isotope stages 1, 5e, and 7a, consistent with the presently available geochronological control. During most of the time represented by the core, the lake was fresher than the modern lake, as evidenced by depleted δ18O and δ13C in bulk-sediment carbonate.
Bibliographical noteFunding Information:
The GLAD800 coring at Bear Lake was sponsored jointly by the USGS, NSF, ICDP, and conducted by DOSECC. Funding for this work was provided by the US Geological Survey—Earth Surface Dynamics Program, and the Geological Society of America. We thank David Dettman and Chris Eastoe (University of Arizona) and Rebecca Clotts (University of Minnesota) for the isotopic analyses, and Doug Schurrenberger, Steve Colman, R. Scott Anderson, and Bruce Hungate for their input. Scott Tolentino and Bryce Nelson of the Utah Division of Natural Resources helped immensely to locate and sample the lake-marginal and sub-lacustrine springs. Gary Skipp (US Geological Survey, Denver) performed the X-ray diffraction analyses. We appreciate the reviews by Ulrich von Grafenstein and an anonymous reviewer which contributed to the improvement of this paper.
Copyright 2008 Elsevier B.V., All rights reserved.
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