DOUBLE-DIPPING: GEOCHEMICAL CHARACTERISTICS AND POTENTIAL CAUSE OF THE PERMIAN-TRIASSIC MASS EXTINCTION IN THE SYDNEY BASIN, AUSTRALIA

The importance of δ¹³C_org measurements for identifying the Permian‑Triassic mass extinction (PTME) in the stratigraphic record is well‑established but other isotopic and geochemical evidence is required in order to establish the cause of this event. New isotopic and other geochemical data have been obtained from four diamond-drill cores for the non‑marine Permian‑Triassic transition in the Sydney Basin, Australia, and the results provide important information regarding the manifestation of the PTME in this region, the causal mechanism, and the influence of local effects on intrabasin correlation. The PTME across the Sydney Basin occurs within ~1 m of the top of the last Permian coal and is identified by a closely‑spaced, double negative δ¹³C_org excursion, a feature previously unrecognised in the region. The magnitudes of the excursions are similar across the basin. New δ¹⁵N and δ³⁴S_pyrite data from the region also show distinct excursions coincident with the δ¹³C_org excursions. Evidence for the influence of sulfide injection at the boundary comes from the δ³⁴S_pyrite measurements. The interrelationships between C, N and S isotopic data, concentrations and elemental ratios indicate severe environmental disruption and increased weathering at the time of the PTME with die off of terrestrial vegetation, the massive injection of greenhouse gases into the atmosphere and sulphuric acid into the water column, probably from the Siberian Traps volcanic eruptions. Changes in trace element concentrations and interelement ratios in all cores generally support this conclusion, although the degree of support differs between cores with two showing evidence of increased weathering playing a proportionally larger role. Values of V/Cr, Ni/Co and Th/U from one core indicate increasing oxygenation throughout the PTME interval. In another core, these values (plus N) indicate periodic exposure with possible soil formation, and values from all cores indicate that oxygen levels were high throughout the PTME interval, although the relative level of oxygenation decreased within the interval itself. The data indicate that local conditions (i.e. differences in energy, fluctuating oxygen levels and diagenesis) can potentially mask the PTME signature across basins.