Year

2012

Degree Name

Doctor of Philosophy

Department

School of Earth & Environmental Sciences

Abstract

The primary aim of the thesis was to investigate the Permian-Triassic mass extinction (PTME) across the Sydney Basin of Eastern Australia, and to gather new evidence for use in determining the nature and cause of the PTME. This was achieved by identifying and assessing the significance of the isotopic, geochemical and physical characteristics of the PTME in the region.

An examination of the available evidence for the nature and characteristics of the PTME, together with a review of the mechanisms most likely to have been the cause, was undertaken to establish the isotopic, geochemical and physical signatures that characterize each of the possible mechanisms. This also served to establish the most appropriate sampling regime and measurement techniques for the investigation.

Four cores were chosen, two from the southern Sydney Basin and two from the northern Sydney Basin. Carbon isotopic data were used as the primary means for identifying the stratigraphic position of the PTME across the basin. Subsidiary measurements used were δ15N, δ34Spyrite, major elements, trace elements, rare earth elements and petrographic examinations. The isotopic and geochemical data, particularly their changes throughout the stratigraphic sequence and their statistical correlations, provided the basis for identifying the extinction trigger mechanism. X-ray diffraction results, used to quantify the major minerals and determine their changes throughout the stratigraphic sequence, and petrographic examinations were used to complement the isotopic and geochemical information.

The new evidence gathered in this thesis shows that the PTME across the Sydney Basin occurs within ~ 1 m of the top of the last Permian coal and takes the form of a closely-spaced double negative δ13Corg excursion, a feature not observed before in the region. This result is complemented by coincident excursions in δ15N and δ34Spyrite, the first measurements of their kind for the PTME in the Sydney Basin. The interrelationships between C, N and S isotopic data indicate severe environmental disruption and increased weathering at the time of the extinction event with die off of terrestrial vegetation and the injection of sulphuric acid into the water column.

The majority of the evidence presented here, including the results of their statistical analyses, indicate that the causal mechanism of the PTME was a massive injection of volcanic gases, possibly in closely-spaced multiple stages, resulting in severe environmental destabilization, including fluctuating oxygen levels. Geochemical evidence also shows that local conditions have the potential to mask the PTME signature and the data need to be interpreted carefully. The applicability of statistical analyses for gaining additional insight into the causal mechanism and the prevailing environmental conditions, and used for the first time for the PTME in the Sydney Basin, was also demonstrated.

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