New geochemical and palaeontological data from the Permian-Triassic boundary in the South African Karoo Basin test the synchronicity of terrestrial and marine extinctions

The end-Permian mass extinction (EPME) is widely recognised as the largest mass extinction in Phanerozoic history. In marine strata the main extinction event is well constrained, and has been radiometrically-dated to an interval of some 60 kyr, approximately 251.9 million years ago. However, the age and duration of the EPME in the terrestrial realm, as well as its possible synchronicity with that of the marine realm, is debated. Here, we shed light on issues pertaining to the identification and position of the terrestrial EPME in southern Africa. Using recently collected sedimentological (facies sequences), palaeontological (biostratigraphic ranges), geochemical (stable isotope analyses) and detrital zircon (ID-TIMS) data from a new site in the Xhariep District of the South African Karoo Basin, we demonstrate that the Permian-Triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction. We conclude that the terrestrial EPME recorded in the Karoo may be regarded as essentially synchronous with the EPME currently defined in the marine realm, and was likely the result of the same volcanically-induced atmospheric disturbances. This study describes the first single, vertical succession of vertebrate and plant fossils that span the terrestrial Permian-Triassic boundary that are also well-constrained both by relative (stable isotopes) and absolute (detrital zircon geochronology) dating methods.