The Karoo basins of south-central Africa

Abstract

The Karoo basins of south-central Africa evolved during the first-order cycle of supercontinent assembly and breakup of Pangea, under the influence of two distinct tectonic regimes sourced from the southern and northern margins of Gondwana. The southern tectonic regime was related to processes of subduction and orogenesis along the Panthalassan (palaeo-Pacific) margin of Gondwana, which resulted in the formation of a retroarc foreland system known as the “main Karoo” Basin, with the primary subsidence mechanisms represented by flexural and dynamic loading. This basin preserves the reference stratigraphy of the Late Carboniferous–Middle Jurassic Karoo time, which includes the Dwyka, Ecca, Beaufort and Stormberg lithostratigraphic units. North of the main Karoo Basin, the tectonic regimes were dominated by extensional or transtensional stresses that propagated southwards into the supercontinent from the divergent Tethyan margin of Gondwana. Superimposed on the tectonic control on basin development, climatic fluctuations also left a mark on the stratigraphic record, providing a common thread that links the sedimentary fill of the Karoo basins formed under different tectonic regimes. As a general trend, the climate changed from cold and semi-arid during the Late Carboniferous–earliest Permian interval, to warmer and eventually hot with fluctuating precipitation during the rest of Karoo time. Due to the shifts in tectonic and climatic conditions from the southern to the northern margins of Africa during the Karoo interval, the lithostratigraphic character of the Karoo Supergroup also changes significantly across the African continent. For this reason, the Karoo basins sensu stricto, which show clear similarities with the main Karoo Basin of South Africa, are generally restricted to south-central Africa, whereas the Karoo-age successions preserved to the north of the equator are distinctly different. This paper focuses on the Karoo basins sensu stricto of south-central Africa, synthesizing their sedimentological and stratigraphic features in relation to the tectonic and climatic controls on accommodation and sedimentation.