Refined stratigraphy of the Middle Permian Abrahamskraal Formation (Beaufort Group) in the southern Karoo Basin

Lithostratigraphic subdivision of South African lower Beaufort Group. Recognition of refined stratigraphic ranges of Middle Permian tatrapod taxa. Stratigraphic logging revealed that the Abrahamskraal Formation is 2565m thick in this part of the Karoo Basin. Last occurrence of dinocephalians is seen to be higher than previously envisaged. Fluvially deposited rocks of the Abrahamskraal Formation of the lower Beaufort Group in the South African Karoo record sediment deposition during the Middle Permian, the earliest terrestrial environment of Gondwana. A rich diversity of fossil tetrapods from this Formation provides a unique opportunity for understanding Middle Permian biodiversity changes in Gondwanan terrestrial ecosystems, but this is dependent on the existence of a robust stratigraphic framework that has been hampered by lack of lateral continuity of lithological markers combined with structural complexities relating to formation of the Cape Fold Belt. Because the Abrahamskraal Formation covers a large geographic area of the main Karoo Basin previous stratigraphic studies have been undertaken over large areas. This study combines geology and palaeontology to refine the stratigraphy of the Abrahamskraal Formation in a part of the southwestern Karoo Basin and revealed mappable lithological units with lateral continuity throughout the study area. The measured stratigraphic section manifests a total thickness of 2565m for the Formation (the thickest occurrence of the Abrahamskraal Formation in the Beaufort Group). For the first time stratigraphic ranges of biostratigraphically important Middle Permian index taxa which have restricted stratigraphic ranges have been determined and, apart from dicynodonts, include the parareptile Eunotosaurus and the biarmosuchid therapsid Hipposaurus. The Abrahamskraal Formation comprises a 1104m thick basal Eodicynodon Assemblage Zone, overlain by a 1441m thick Tapinocephalus Assemblage Zone whose upper limit is 20m below the Poortjie Member of the Teekloof Formation.