Friday, 28 February 2020
OUT OF AFRICA
The geomorphology of South Africa consists of a high plateau rimmed to west, south and southeast by the Great Escarpment and rugged mountains beyond this there is a strip of narrow coastal plain. The basement of much of the northeastern part of South Africa is made up of the Kaapvaal Craton. To the south and east, the craton is bordered by the Namaqua-Natal belt.
In Neoproterozoic times, much of South Africa stabilized into the large Kalahari Craton that came to form part of the supercontinent Rodinia. The Kalahari Craton was near the center of Rodinia with paleogeographic reconstructions indicating it was surrounded by the cratons of Laurentia, Río de la Plata, Congo and Dronning Maud Land. Evidence of this is the continuation of the Namaqua-Natal belt in East Antarctica indicating that South Africa and East Antarctica formed a single continent when this belt formed about 1000 million years ago.
The uplift of these margins is tentatively related to far-field compressional stresses that have warped the region as a giant anticline-like lithosphere fold. These tectonics have had a profound effect in shaping the Great Escarpment and uplifting, creating and destroying plateaux including the African Surface, a key reference surface.
On average, 2.5 to 3.5 km rock was eroded in the Mid to Late Cretaceous. Further erosion in Cenozoic times amounts to less than one kilometre. Limited erosion means that many of the major relief features of South Africa have existed since the Late Cretaceous. Warping of Southern Africa has led to significant changes in drainage basins with the Orange River likely losing a drainage area in the Kalahari Basin, the Limpopo River losing interior drainage areas to the Zambezi River and the west-draining Karoo River ceasing to exist altogether. Overall, the boundaries of the drainage basins coincide with the axes of uplifted epeirogenic flexures.