Revised lithostratigraphy of the Upper Permian Balfour and Teekloof formations of the main Karoo Basin, South Africa

Abstract

A new lithostratigraphic framework is introduced for the Permian Balfour and upper Teekloof formations (lower Beaufort Group) in the main Karoo Basin of South Africa. The Balfour Formation’s Barberskrans Member (BM) is identified as the Oudeberg Member at its current type location. Thus the BM requires renaming, and is here defined as the Ripplemead member (RM) after Ripplemead farm 20 km north of Nieu Bethesda. The upper Teekloof Formation is subdivided into the sandstone-poor Steenkampsvlakte Member and sandstone-rich Javanerskop member which occurs in the highest points of the western escarpment between Beaufort West and Fraserburg. The thickness of the Balfour Formation does not significantly change from east to west, but thins rapidly northwards to a point where the Oudeberg Member is not present, and other subdivisions are much attenuated. Recent biostratigraphic revisions of Lopingian tetrapod fauna show the Ripplemead and Javanerskop members are not contemporaneous. Therefore, no lithostratigraphic members in the Upper Permian Beaufort Group have basin wide distribution, and it is recommended that they be used as local markers only in conjunction with other proxies (e.g. biostratigraphic and chronostratigraphic markers). Patterns of biostratigraphic disappearance of tetrapods in the Balfour Formation at the same stratigraphic interval throughout the basin despite the thinning of strata northward, supports a temporally phased terrestrial Permo-Triassic mass extinction (PTME). The lack of basin wide lithostratigraphic markers highlights the variable aggradation rates during the deposition of the Beaufort Group caused by foreland tectonics and localised subsidence. A need for a full consideration of these complexities and their effects on the fossil records is therefore required in determining whether the terrestrial PTME is synchronous with the marine extinction.