Dune activity as a record of late Quaternary aridity in the Northern Kalahari: new evidence from 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 buildi ng phases, and aridity, in the late Quaternary. The dunes have been constru cted from sediments likely to have been initially transported into the area by fluvial processes. Dune sediments do not preserve obvious evidence of h iatuses in deposition in the dated period 48-121 ka, but continuous deposit ion (and therefore continuous aridity) is considered unlikely given differe nces in dated phases compared with chronologies from western Zimbabwe (to t he southeast) and western Zambia (to the north) that include ages derived f rom the same equivalent sampling depths. Laboratory experiments provide evi dence that dune sediments have not been bioturbated since deposition, such that sample palaeodoses determined from different sampling depths are a tru e reflection of the duration of sediment burial. Independent chronologies f rom cave sediments provide evidence that humid episodes have occurred in th e region within the dated range of dune construction. It is concluded that dune construction in the late Quaternary has been punctuated, that the pres erved record reflects the attributes of the aeolian processes that affect l inear dune development, and that the late Quaternary record of dune buildin g in the Middle and Northern Kalahari was spatially complex. (C) 2000 Elsev ier Science B.V, All rights reserved.