Late Paleozoic Glaciation: II, Africa Exclusive of the Karroo Basin

Abstract

Africa, between about 4°N. and 32°S. latitude, was glaciated during the late Paleozoic as shown by glacial strata in several major basins and fault blocks—Karroo, Botswana, Orange River, Zambezi, and Congo—and in smaller areas of the Kaokoveld in South West Africa, in southern Madagascar, and in the Kafue Flats, Zambia. Age of the glaciation ranges from Late Carboniferous to Early Permian but may have begun in the Early Carboniferous. Striated floors beneath the glacial rocks indicate that extensive lobes of ice flowed radially outward from the African interior in Rhodesia and Zambia, suggesting that a continental ice sheet occupied this region. This is supported by environmentally significant facies relationships and paleocurrent flow directions. Major ice lobes occupied the Botswana fault block (flowing southwest), the subglacial valleys of the Kaokoveld region (flowing westwardly) and probably the coastal region of Tanzania, where ice flowed onto Madagascar toward the northeast prior to fragmentation of Gondwanaland. The major lobe of the Karroo basin, the Transvaal ice sheet, also flowed southward from the central African region. Smaller centers gave rise to the Namaland lobe, which flowed to the south from an elevated region on the western extremity of the Precambrian Damara belt, and to a piedmont glacier positioned at the foot of a mountainous region on the eastern side of the Congo basin. The Kaokoveld lobe overrode a mountain barrier in South West Africa, perhaps more than 1500 m high, and thence may have extended to the Brazilian shield and the Parana basin. This lobe probably was the only one to contribute to the glacial deposits of South America before the continents separated and drifted apart. Development of a continental ice sheet in southern Africa probably was enhanced by position of the continent in relatively high latitudes, as deduced from studies of rock paleomagnetism. As many as six glacial advances arc locally recorded, but many more may have occurred, in view of the abundant evidence of reworking of glacial deposits.