31 Deserts Over the Last 100,000 Years

Saturday, 26 July 2003
8:00 AM - 12:00 PM

WETTING AND DRYING AT THE TSODILO HILLS, BOTSWANA OVER THE LAST 30 KA

Paper number: 31-5
Program: SYMPOSIA
Time: 9:10 AM – 9:30 AM

Authors

Abstract

Few sites of paleoenvironmental and archaeological significance in the Kalahari Desert have yielded composite direct proxies of both arid and humid conditions during phases of occupation. The Tsodilo Hills, inselbergs that rise from the sandy Kalahari plain, are an exception, possessing both a rich archaeological archive and contiguous sedimentary records of aeolian and lacustrine conditions. Cave and rock shelter horizons indicate occupation of the site back to about 100 ka. Fish and wetland mammal bones in LSA layers have led to suggestions of standing water in this currently arid location.

To the southwest of the hills, lacustrine carbonates, containing abundant mollusc and diatom remains and shorelines provide evidence of perennial lake conditions in the past. Stabilised linear dunes are indicative of past drier conditions, with the dune closest to the hills eroded by lake waters and lower dune sediments superimposed by a shoreline feature. The lacustrine surface possesses four sub-basins suggestive of the feature having variable extents depending on the volume of runoff and seepage generated from the hills themselves.

17 radiocarbon ages from lacustrine carbonates, 6 AMS dates from molluscs, 6 OSL ages from dunes and 4 from shoreline deposits have to date been determined from the Tsodilo complex. Diatom and mollusc species analysis provide data on water conditions. The evidence suggests that linear dune construction has not occurred since the Last Glacial Maximum, with particular development at 36-28 ka. Lake stands indicating wetter regional conditions than present occurred at 40-32 ka, with more seasonal conditions from 36ka, and at 27-12 ka with a possible drying out at 22-19 ka.

The relationship between the local Tsodilo and regional palaeoclimatic records are considered. Data are consistent with other independent studies from the region, and with recent evidence obtained from Atlantic cores off the coast of Namibia. The presence of fish bones in archaeological horizons, potentially sourced locally or from the perennial wet Okavango delta 40km to the east, may provide information on the relationship between site occupation and prolonged climatic extremes.