The interplay between massive volcanism and the local environment: Geochemistry of the Late Permian mass extinction across the Sydney Basin, Australia
The isotopic, geochemical, and physical characteristics of the Late Permian mass extinction have been identified and assessed from terrestrial sections across the Sydney Basin, eastern Australia. These new data are used to both correlate the extinction event across the basin and elucidate its cause. Two stratigraphically well-constrained cores were examined, one each from the northern and southern regions of the Sydney Basin. Both sections show uninterrupted transitions from the last Permian coal to a carbonaceous shale, overlain by siltstones, mudstones, sandstones and shales whose mineralogical and physical characteristics are consistent with non-marine origins. These non-marine origins are also broadly supported by elemental data. Carbon isotopic data were the primary means for identifying the stratigraphic position of the Late Permian mass extinction across the basin; the data show that the mass extinction occurred as an interval with the form of a closely-spaced, double-negative δ 13 C org excursion within 1 m of the top of the last Permian coal, a feature previously unrecognised in the basin. This result is supported by coincident excursions in δ 15 N and δ 34 S pyrite , the first measurements of their kind for the Late Permian mass extinction in the Sydney Basin. The interrelationships between the C, N and S isotopic data, concentrations and elemental ratios, together with major, trace and rare earth element concentrations, ratios, and statistical analyses show severe environmental disruption occurred at the time of the extinction event with die-off of terrestrial vegetation and the injection of sulphate into the water column, consistent with massive volcanism. Geochemical evidence also shows, however, that local conditions have the potential to disrupt the Late Permian mass extinction signature and hence the data need to be interpreted carefully.
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