DESERT WETLANDS IN DEATH VALLEY NATIONAL PARK AND THE REGIONAL HYDROLOGIC RESPONSE TO CLIMATE CHANGE DURING THE LATE QUATERNARY

The Lake Rogers basin, located in the northern part of Death Valley National Park, is occupied by extensive, light-colored, fine-grained, vertebrate-fossil-bearing deposits that were interpreted for decades as a Pleistocene lacustrine sequence. New investigations show that the sediments actually represent widespread, spring-derived desert wetlands, which are critical arid land ecosystems and are preserved in the geologic record as groundwater discharge (GWD) deposits. We are establishing both a detailed stratigraphy and a geochronologic framework for the “Rogers beds” using radiocarbon dating of charcoal and terrestrial gastropods, as well as luminescence dating for older deposits. Our results show that the beds document a long record of climatic and hydrologic conditions in the basin consisting of spring discharge events that are terminated by stable surfaces and/or erosion, followed by renewed spring activity. These wet-dry cycles indicate that wetland ecosystems in the Rogers basin waxed and waned in response to climate perturbations many times during last glacial period, including on submillenial-scale timescales within the Younger Dryas cold event. The timing and nature of changes recorded by the Rogers Beds is strikingly similar to the sequence of wetland deposits in the middle-late Pleistocene Las Vegas Formation, where we previously documented that desert wetlands in the Las Vegas Valley register dramatic hydrologic changes in response to abrupt climate oscillations during the late Quaternary, in temporal correlation with Greenland/North Atlantic climate proxy data. The timing of ecosystem response observed in the Las Vegas Formation, which serves as the linchpin sequence of our studies, and the Rogers beds are also found in GWD deposits at multiple sites throughout the Mojave Desert and southern Great Basin. The fact that widespread desert wetland ecosystems closely track one another show that they are not simply reflecting local hydrologic conditions; rather, they are responding to changes in synoptic-scale climate patterns that operated over a large geographic region during the late Quaternary.