EXTINCTION, EVOLUTION AND RECOVERY OF THE GONDWANAN FLORA THROUGH THE PERMIAN-TRIASSIC BIOTIC CRISIS IN SOUTHERN HIGH PALAEOLATITUDES, AUSTRALIA

The Permian–Triassic biotic crisis, c. 251.9 million years ago, was the largest of the ‘big five’ mass-extinction events in Earth’s history. Nearly 60% of families and 80% of genera were extinguished. Most previous studies of this crisis have focused on marine and Northern Hemisphere successions. We are undertaking the first detailed investigation of extinction and recovery patterns of the terrestrial flora at high (>65°) southern palaeolatitudes by extensive sampling of drill cores and outcrops in Sydney Basin, Australia. Quantitative palynology revealed the fine-scale floral changes across both the end-Permian mass extinction (EPME) and probable P–T boundary, which are separated by several metres of strata. Initial results indicate that cessation of coal accumulation marks the end-Permian extinction event shortly before the end of the Permian proper, and a gradual increase in red–green iron-rich mudrocks is represented through the Lower Triassic. Six spore-pollen biostratigraphic zones (one pre-EPME, and five post-EPME) have been identified across Sydney Basin, with no consistent evidence of a depositional hiatus across the extinction interval. The boundary between the Dulhuntyispora parthivola/ Playfordiaspora crenulata palynozones is concurrent with the EMPE in each succession. Forests of broad-leafed glossopterid gymnosperms dominated the late Permian peat-forming communities of the high southern latitudes. The collapse of peat-forming conditions is a key indicator of the end-Permian biotic collapse, and the glossopterids are typically considered the main land plant casualties of the extinction event. The stepwise recovery and replacement by new plant groups are reflected in both the macrofloral and palynological records. However, despite the abrupt cessation of the glossopterid flora, several common Permian pollen and spore types persist in low abundances until the upper Lower Triassic; these are replaced by a protracted, concomitant increase in abundance and diversity of Triassic forms over the same interval. Precise U-Pb zircon ages indicate a close temporal link between the end-Permian extinction on land and the primary extrusion phase of the largest known continental flood basalt eruptions: the Siberian Traps.