LATE PLIOCENE TO MIDDLE PLEISTOCENE PALEOCLIMATE AND TECTONIC RECONSTRUCTIONS OF DEATH VALLEY

Death Valley lakes are important because lakes accumulate in this hyper arid terminal basin only during periods of high effective precipitation. In the past, many studies of Death Valley lakes have focussed on the latest Pleistocene. We present here tephrochronologic and sedimentologic data from the Death Valley area between ~3.58 - 0.51 Ma that we use to reconstruct the late Neogene paleoclimate and tectonics of Death Valley. Our tentative conclusion is that many basins in Death Valley experienced increased sedimentation during the late Pliocene with extensive alluvial fan progradation (transport limited environment) on the basin margins. Deposits from the central parts of late Pliocene basins are limited, but where found, they show only playa or ephemeral lake facies. This is in contrast to the perennial lakes present in glacially fed Searles basin to the west. Alluvial fan and playa facies presently below sea level and uplifting (presently at maximum elevation), show that during the early Pleistocene (~1.9 - 1.7 Ma) was a time of relatively low effective precipitation (dry) with only short playa lake intervals. Deposits at Mormon Point show a shallow, small fetch perennial lake during Oxygen Isotope Stage 20 (~1 Ma) and playa lake during OIS 16. Tectonically, because lake deposits are deposited horizontally, thus we have used the lake sediments at Mormon Point to show that footwall tilting is <20 degrees in the Quaternary and to describe zones of folding and uplift at the fault intersections in the Death Valley fault system.