Dune activity as a record of late Quaternary aridity in the Northern Kalahari: new evidence form Northern Namibia interpreted in the context of regional arid and humid chronologies

Sediments from presently vegetated linear dune ridges in the Caprivi Strip of northern Namibia are optically dated to assess the timing of dune building phases, and aridity, in the late Quaternary. The dunes have been constructed from sediments likely to have been initially transported into the area by fluvial processes. Dune sediments do not preserve obvious evidence of hiatuses in deposition in the dated period 48-121 ka, but continuous deposition (and therefore continuous aridity) is considered unlikely given differences in dated phases compared with chronologies from western Zimbabwe (to the southeast) and western Zambia (to the north) that include ages derived from the same equivalent sampling depths. Laboratory experiments provide evidence that dune sediments have not been bioturbated since deposition, such that sample palaeodoses determined from different sampling depths are a true reflection of the duration of sediment burial. Independent chronologies from cave sediments provide evidence that humid episodes have occurred in the region within the dated range of dune construction. It is concluded that dune construction in the late Quaternary has been punctuated, that the preserved record reflects the attributes of the aeolian processes that affect linear dune development, and that the late Quaternary record of dune building in the Middle and Northern Kalahari was spatially complex.