Late Quaternary landscape evolution in the Keep River region, northwestern Australia

This paper evaluates the Late Quaternary chronostratigraphic context of archaeological sites in the Keep River region, Northern Territory, Australia. Cosmogenic dating, luminescence dating and sediment characterisation reveal sedimentary processes commencing from erosion of the escarpment and plateaux source through temporary storage in sand sheets, to final deposition in alluvial floodplains. Erosion of the sandstone plateaux (∼5 mm ka−1) and escarpment faces (probably ∼50-100 mm ka−1) provide the main sediment source for the adjacent sand sheets which have evolved over the past 100,000 years as the product of ongoing cycles of accumulation and denudation. The rate of sediment accumulation is lowest near the escarpments on the low-energy sediment-limited sand sheets (<100 mm ka−1) and greatest near the main streams (>400 mm ka−1) that have more numerous sediment sources. Collectively, luminescence ages indicate an apparent increase in sediment accumulation rate in the sand sheets from ∼100 mm ka−1 in the late Pleistocene to over 200 mm ka−1 in the Holocene. This most likely reflects enhanced monsoonal activity following postglacial marine transgression. Palaeosol horizons in the creek profile distinguished by sediment mottling mark potentially significant palaeoenvironmental and palaeoclimatic changes during the Quaternary.