The Kalahari is an ancient depositional environment with a complex history. The Mega Kalahari sand sea, at 2·5 million km2 the largest on earth, is more extensive than the ill-defined Kalahari Desert and can best be considered as the surface expression of the Cretaceous to recent sediments in the Kalahari-Congo structural basin. These Kalahari Group sediments have accumulated and evolved through fluvio-deltaic, aeolian and groundwater processes, with characteristics due to primary deposition and subsequent modification being difficult to distinguish.

Low fossil content, limited exposures and poor differentiation within the dominant and ubiquitous Kalahari Sand, together with the failure of scientists to comprehend the nature of the extensive duricrust suite, have delayed understanding the sedimentological and environmental history of the basin. However, despite the absence of a satisfactory stratigraphical framework, the post-Cretaceous tectonic history and drainage development provides a basis for subsequent evaluation of the palaeoenvironmental significance of the depositional landform suites found in the surface sediments of the Mega Kalahari.