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An analysis of the Permo-Carboniferous glaciation in the marine Kalahari Basin, Southern Africa

1983; Elsevier BV; Volume: 44; Issue: 3-4 Linguagem: Inglês

10.1016/0031-0182(83)90108-6

1872-616X

J. N. J. Visser,

Geological formations and processes

The Dwyka Formation, which forms the basal unit of the sedimentary fill in the Kalahari Basin, consists of local reddish basal tillite, an argillaceous sequence of shale, mudstone, siltstone, sandstone, diamictite and carbonate lenses and nodules containing marine fossils, and a well-developedmain tillite. In the Hotazel Valley along the southern margin of the basin an upper tillite is also present. The sequence represents two major ice advances separated by a well-defined interglacial and a minor ice advance confined to the area around the ice-spreading centre. Glacial erosion during maximum glaciation in the late Carboniferous formed a dissected landscape depressed isostatically to below sea level. Ice flow during deglaciation was controlled by the basement topography and upon disintegration of the ice sheet the sea followed the retreating ice inland (Hardap Interglacial). Deposition of lodgement till at the ice grounding line was followed by debris flows, turbidity currents, debris rain and suspension settling leaving sediments typical of an ice retreat sequence. The Tses Glaciation, probably of Early Permian age, followed on the interglacial. A marine ice sheet covered the area and predominantly logdement tills and bedded and laminated diamictons were deposited during grounding line retreat, underside melting of ice shelves and by icebergs respectively. After rapid collapse of the marine ice sheet, small ice caps remained in the mountainous areas and during a temporary ice advance another till horizon was deposited along the southern margin of the basin.