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 extensive Quaternary desert basins. On a regional scale, present-day aeolian activity is restricted to episodic dune crest reactivation in the most 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 optical dating of quartz sand grains to develop a chronology of arid intervals as recorded by phases of linear dune construction in the northeastern sector of the Mega Kalahari. We identify repeated phases of aeolian deposition during the last interglacial-glacial cycle, at ca. 95–115, 41–46, 20–26 and post-20 ka, which are separated by depositional hiatuses that we infer to correspond to more humid periods. These aeolian depositional events correlate with and are inferred to relate to millennial-scale cold sea surface temperature events in the southeast Atlantic which have been linked to sub-milankovitch climate changes recognised in northern hemisphere oceanic and cryospheric environmental archives 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 field) aeolian activity and subsequent erosion and reworking, much of the vertical expression of the larger dune forms corresponds to the earlier periods of activity. The linear ridges of the area are rich archives of late Quaternary terrestrial climate change.