Post-Gondwana geomorphic evolution of southwestern Africa: implications for the controls on landscape development from observations and numerical experiments

Abstract

The relationship between morphology and surficial geology is used to quantify the denudation that has occurred across southwestern Africa since the fragmentation of Gondwana during the Early Mesozoic. Two main points emerge. Significant denudation, of the order of kilometers, is widespread except in the Kalahari region of the continental interior. The denudation is systematically distributed so that the continental exterior catchment, draining directly to the Cape basin, is denuded to a greater depth than the interior catchment inland of the Great Escarpment. Existing models of landscape development are reviewed, and implications of the denudation chronology are incorporated into a revised conceptual model. Four numerical experiments are presented in which the roles of antecedent topography, resistant substrate, climate change, and lowering the baselevel of the interior catchment are investigated for an initially high elevation margin bordered by an escarpment. The model results suggest several styles of landscape evolution that are compatible with the observations. Escarpments may retreat in a regular manner, but they also degrade and are destroyed, only to reform at the drainage divide between exterior and interior catchments. -from Authors