Post-glacial Permian stratigraphy and geography of southern and central Africa: boundary conditions for climatic modelling
Abstract The post-glacial stratigraphy of southern and central Africa comprises mudrocks with subordinate sandstones and coal measures belonging to the Ecca Group overlain by fossiliferous mudstones and sandstones of the Beaufort Group (Madumabisa Mudstone of south-central Africa), preserved in the Karoo, Congo and extreme western margin of the Paranabasins, the Kalahari-Zambezi and East Africa-Malagasy basin complexes, and the Nyasa basin and range complex. The palaeogeography of the region was controlled by the stable, elevated Kalahari and Congo cratons, a NE-trending weak zone between the cratons (site of the Kalahari-Zambezi-Malagasy basin complexes), a NNW-trending weak zone between the cratons and the Mozambique mobile belt (site of the Nyasa basin and range complex) and an E W mobile belt along the southern margin of the continent (site of the foreland Karoo Basin). The post-glacial Artinskian landscape which was inherited from the Permo-Carboniferous glaciation, consisted of a rugged interior plateau and shallow seas and seaways in the south and west. The Early-Late Permian landscape was still dominated by an uneven coastline in the south and freshwater lakes in the Congo Basin and along the Kalahari-Zambezi-Malagasy drainage systems. A marine incursion occurred in the Malagasy Basin. Relief on the interior plateau was steadily denuded. By Kazanian times large lakes covered the Karoo and Paranabasins whereas along the coastal region all shallow seas were destroyed by an orogen. Freshwater lakes in the interior had reached their maximum extent. The Permo-Triassic landscape shows an increase in the interior relief due to renewed graben formation with lakes becoming smaller and more desiccated. The surface area of southwestern Gondwana covered by water reached a maximum of 34% during the Early-Late Permian and decreased to about 6% at the Permo-Triassic boundary. Climatic zones shifted southeastwards as southwestern Gondwana drifted into lower latitudes during the Permian. The ice margin started to retreat in central Africa during the Sakmarian, but the marine ice sheet in the Karoo Basin collapsed only in the Artinskian. Deglaciation was followed by a cool wet climate suitable for the formation of peatlands. In central and south-central Africa this climate was followed by temperate to warm, seasonal conditions which became progressively wetter with less seasonal fluctuation towards the east (Malagasy Basin) and drier towards the west. These conditions lasted until the end of the Kazanian. In the Karoo Basin the cool wet climate of the Artinskian became more temperate and also lasted until the end of the Kazanian when warm, semi-arid conditions expanded over the entire southern and central Africa. The geographic controlling factors for Permian climatic change were the interplay of latitudinal setting and continental evolution (formation of orographic barriers and loss of coastal seas).