- GeoRef, Copyright 2004, American Geological Institute.
Boreholes drilled in the Tshabong area of southern Botswana have delineated two southwest-trending valleys infilled with Lower Karoo Supergroup strata. The valleys occur beneath a cover of Kalahari beds and are separated by positive topography related to pre-Karoo quartzites. The base of the Karoo strata comprises a thick glacial sequence (Dwyka Group) in which two lithostratigraphic formations can be recognized. These formations are tillites of a basal Malogong Formation overlain by the heterolithic Khuis Formation, with lithofacies indicative of a number of glacial environments, including glacial re-advances. Preserved palynomorphs in these rocks indicate a marine setting. The overlying Ecca Group strata are also divisible into two formations, again of regional extent. A thin sandstone sequence at the base of the lower Kobe Formation is interpreted as evidence for a basal Ecca marine transgression. Overlying rocks contain freshwater palynomorphs. The upper Otshe Formation is made up of deltaic sediments. Locally, the Ecca Group is overlain by a thin sequence of Beaufort Group argillites. Palynology indicates that the Dwyka Glaciation in the southeastern part of the Gemsbok Sub-basin lasted from about 303 Ma to about 280 Ma, that is from the Late Carboniferous to the Early Permian. The overlying Ecca Group ranges in age from the Early to Late Permian. The palynology has confirmed the presence of Beaufort Group strata in southern Botswana.