δ18Op geographical variability within the South African Karoo Basin during Permo-Triassic based on tetrapod apatite.

The Beaufort Group of the Main Karoo Basin of South Africa covers approximately 200000 km², making up about 20% of the country surface. It represents an uninterrupted accumulation of fluvio-lacustrine sediments from the Middle Permian to the Middle Triassic. A diverse vertebrate fauna that includes therapsids, amphibians, archosauromorphs and parareptiles, has been recovered from this rock succession and allows geochemical studies on a large temporal and geographical range.
However, while questions about temporal and biological variations of oxygen stable isotope ratio (δ18Op) were investigated, no geographical variations of the bioapatite-recorded δ18Op have been studied on the Permo-Triassic of South Africa.
This work aims to highlights the possible variations in δ18Op recorded on a large-scale basin during the Permo-Triassic.
Several tetrapods, mainly therapsids, were sampled from four different biozones, two Permian (Cistecephalus AZ and Dicynodon-Theriognathus AZ) and two Triassic (Lystrosaurus declivis AZ and Trirachodon-Kannemeyeria AZ). For each of those biozones, fossils were sampled from several localities to compare their recorded δ18Op values.
While the results showed no variation for both Permian AZ, restricted to the South-western part of the Basin, a decrease of the δ18Op values from North to South can be noted for both Triassic AZ. Also, a ‘high’ set of values can be separated from a ‘low’ set for each AZ.
Permian absence of variation might be the result of the sampled localities being close as well as a unique source for the δ18Op.
Triassic latitudinal variation of the δ18Op values results from either a latitudinal gradient of temperature, the continental effect or even the distance from the sources of the watershed or a combination of those. The two set of values suggest two different sources of water, one from the North-East and the other from the South.