A NETWORK-BASED BIOSTRATIGRAPHIC FRAMEWORK FOR THE BEAUFORT GROUP (KAROO SUPERGROUP), SOUTH AFRICA

The biostratigraphic assemblage zone (AZ) framework of South Africa’s Karoo Basin has become a standard for local and global correlations of Permo-Triassic synapsid, parareptile, temnospondyl amphibian, and archosaur-dominated assemblages. However, few studies have moved beyond a qualitative assessment of these tetrapod communities. We analyzed a dataset representative of the vertebrate fossil record (1402 occurrences of 115 species) from the Cistecephalus (CiAZ), Daptocephalus (DAZ), Lystrosaurus declivis (LAZ), and Cynognathus (CAZ) AZs using network analysis to compare alternative assemblage zone frameworks and develop a data-derived biostratigraphic model that facilitates geological and paleontological research. Our results show that older frameworks and those based on lithostratigraphic units obscure the communities. The CiAZ is not well supported in any framework, most likely because it relies more heavily on lower-resolution historical occurrences and older biostratigraphic schemes. The LAZ is well supported across all network-derived frameworks, and is likely a reflection of significant shifts in community structure during the end-Permian mass extinction event. Our data also identify possible new communities within the uppermost LAZ and lowermost CAZ. A "mega-community" shift at the base of the CAZ could represent a time-hiatus at this stratigraphic interval, and supporting possible Landinian-Carnian biostratigraphic links with South American and eastern African assemblages. In addition, new meter-level occurrence data from the DAZ show that sampling stratigraphic intervals of 20 to 50 m thickness are sufficient to capture the network-derived Karoo AZs. Consequently, the first and last appearance datums used to delineate AZ boundaries could be defined at 20-50 m accuracy. Our network-based biostratigraphic framework has the potential to clarify correlations and can be used to design future field campaigns in the Karoo Basin and across southern and eastern Africa.