Lake Lewis basin, central Australia: Environmental evolution and OSL chronology

Lake Lewis is the furthest from the coast of Australia's salt lakes and lies at the southern edge of influence of the Australian monsoon regime. The MacDonnell Ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain. We describe lacustrine, fluvial and aeolian environments of the basin and report optically stimulated luminescence (OSL) dates from representative sediments. A long period of generally wetter conditions during most of the Pleistocene is represented by thick uniform lacustrine clay beneath and near Lake Lewis. This is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin, which indicate fluctuating climatic conditions. OSL results show that dune building in the basin commenced before 95 ka, when salinity at the depocentre was high. Dune building peaked around 23-21 ka. OSL ages of fluvial deposits show that floods occurred during the last 20 ka, following the last phase of maximum aridity in the region.