PUNCTUATED ARIDITY IN SOUTHERN AFRICA DURING THE LAST GLACIAL CYCLE -THE CHRONOLOGY OF LINEAR DUNE CONSTRUCTION IN THE NORTHEASTERN KALAHARI

The Mega Kalahari of central southern Africa is one of the most extens ive Quaternary desert basins. On a regional scale, present-day aeolian activity is restricted to episodic dune crest reactivation in the mos t arid southwestern desert core. There is, however, abundant evidence of former periods of both more arid and more humid conditions, many of which have little or no chronological control. We have employed optic al dating of quartz sand grains to develop a chronology of arid interv als as recorded by phases of linear dune construction in the northeast ern sector of the Mega Kalahari. We identify repeated phases of aeolia n deposition during the last interglacial-glacial cycle, at ca. 95-115 , 41-46, 20-26 and post-20 ka, which are separated by depositional hia tuses that we infer to correspond to more humid periods. These aeolian depositional events correlate with and are inferred to relate to mill ennial-scale cold sea surface temperature events in the southeast Atla ntic which have been linked to sub-milankovitch climate changes recogn ised in northern hemisphere oceanic and cryospheric environmental arch ives covering the same time period. While the present landscape is the product of either post-20 ka (Hwange National Park dune field) or 20- 30 ka (Victoria Falls dune held) aeolian activity and subsequent erosi on and reworking, much of the vertical expression of the larger dune f orms corresponds to the earlier periods of activity. The linear ridges of the area are rich archives of late Quaternary terrestrial climate change. (C) 1998 Elsevier Science B.V.