PLAYA SEDIMENTS AS PROXIES FOR LATE CENOZOIC PALEOCLIMATE IN THE WESTERN UNITED STATES: A POSSIBLE WAY FORWARD

Playa (dry lake) sedimentology (e.g. lithology, grain size, color and sedimentary structures) and geochemistry (e.g. stable isotopes, mineralogy, and fluid inclusions) have been used as proxies for paleoclimate in the Western United States since the 1970's. The most detailed use of these proxies has been in Death Valley, Panamint Valley, Searles Lake, and Bristol Dry Lake in California. All of these playas (and others in between) at one time were thought to be hydrologically connected during the Pleistocene. More recent work has called into question the hydrologic link between Bristol Dry Lake and the Death Valley area, but these studies provide a basis for showing the amount of information that can be gained from playa sediments. Chronologies in these lakes are greatly enhanced by the presence of multiple volcanic ash layers (tuffs) of known age within the sedimentary sequence. However, outside of California, analysis of paleoclimate histories of sediments from large playas (>50 km²) in the Western US have not been completed, even though large playas exist throughout the western US. A widespread effort to provide a coherent picture of paleoclimate throughout the west is needed by correlating the stratigraphies of playas that are spatially distributed throughout the Western U.S. This would provide information on potential changes in the direction of precipitation (monsoonal versus Gulf of Alaska and North Pacific or continental land mass precipitation) and would demonstrate whether climate records are synchronous throughout the west. Obstacles that need to be overcome include accurate chronologies between lakes, potential interferences from tectonics in each basin, and possible missing sections due to erosion when the playas were dry. However, using advanced techniques such as paleomagnetic properties and stable and radiogenic isotopes as well as understanding the tectonic and hydrological characteristics of each basin will greatly improve the chances for success. The advantage of this approach would be that multidisciplinary teams would collaborate, and paleoclimate information could be based on multiple proxies. In addition, multiple basins can be assessed on a national scale, and knowledge gained could be used for both paleoclimate histories as well as to constrain predictive climate models.