SEDIMENTARY RECORD OF LATE HOLOCENE LAKE-LEVEL FLUCTUATIONS AT WALKER LAKE, NEVADA, USA

Walker Lake is a terminal lake located at the end of the Walker River in western Nevada. Lake-level lowering of about 45 m during the last 100 years has led to deep incision by the Walker River into the former lakebed. This incision has exposed a sedimentary record of lake-level fluctuations spanning at least the last 4000 years. Fourteen new radiocarbon dates on plant material collected from diverse sedimentary environments including fluvial, deltaic, beach, and offshore settings has led to the refinement of the late Holocene lake-level curve for this basin. In many cases, a single outcrop records multiple transgressions and regressions while in other outcrops fluvial-deltaic units can be traced directly into deeper water lacustrine units, thereby allowing precise estimation of lake-surface elevation. This new curve documents at least three prehistoric highstands that occurred around 3500, 1500, and 700 cal yr B.P. and three low water periods that occurred around 2000-2500, 1000, and 300 cal yr B.P.

Comparison of this outcrop-based record to existing lake-level curves and a new oxygen isotope curve for the last 1200 years at Walker Lake yields many similarities but differences between the records exist.

The results of this study emphasize the utility of reconstructing paleolake histories using the exposed sedimentary record of fluctuating lake levels, but this approach does not provide as much temporal resolution as is typical for various proxies used on cored sediments. Therefore, the integration of outcrop studies, where absolute water depth and lake volume can be estimated, with isotopic and other types of proxies that typically have a higher temporal resolution promises to be a productive avenue of future research.