Biostratigraphy of the lower Burgersdorp Formation (Beaufort Group; Karoo Supergroup) of South Africa – implications for the stratigraphic ranges of early Triassic tetrapods

摘要

The Beaufort Group (Karoo Supergroup) of South Africa comprises a thick sequence of fluvio-lacustrine sedimentary rocks thatudaccumulated in a landlocked, intracratonic foreland basin in southwestern Gondwana during the Middle Permian to Middle Triassic. Toudthe south this basin was bounded by the Cape Fold Belt, which acted as the major source of both sediment and discharge. Rocks of theudBeaufort Group are renowned for their rich fossil record and eight tetrapod-based biozones are currently recognized. The uppermostudtwo biozones of the Beaufort Group, the Lystrosaurus and Cynognathus assemblage zones, record terrestrial biotic recovery following theudPermo-Triassic mass extinction event. Stratigraphic overlap between these biozones occurs in the proximal sector, but their separationudby an unconformity in the distal sector reflects the incomplete preservation of the sequence in this part of the basin. Our results affordudchronostratographic control that impacts on current theories on the development of the Karoo Basin, and on the relative age of theudsequence.