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Abstract
This paper attempts to reconstruct the regional history of uplift and climate since the Cretaceous from the terrace deposits and equivalent features in the Middle Ugab Valley, and from their relationship to adjacent erosion surfaces.
Pre-Karroo planation was not advanced, but by earliest Tertiary times the “African” Surface, with characteristic inselberge, had been formed. This surface is preserved on the divide to the south and as a summit plane north of the Ugab, although modified by Tertiary warping along the Otavi axis. The pre-Middle Eocene Ugab occupied a broad valley on this surface.
Within the valley three levels are recognised. The Main Terrace surface lies 500 feet above the present river and contains up to 300 feet of sands and conglomerates capped by calcareous sandstones and resting on a weathered Eocene (“Pedestal”) surface. These deposits indicate aridity during the Tertiary period. Their dissection followed upon end-Tertiary uplift with a semi-arid climate and produced the Lower Terrace, 100 feet above river-level. This is mainly erosional, but equivalent deposits downstream have been dated from artefacts as Lower and Middle Pleistocene. An Upper Pleistocene wet phase caused erosion below the present floodplain followed by the deposition of a sandy alluvium with Middle Stone Age tools. This is now undergoing dissection into a lowermost terrace.