Characterizing paleoenvironmental/paleoclimatic change across the Permian-Triassic boundary in the terrestrial, high southern paleolatitudes: a multiproxy approach from the Bowen Basin, Queensland, Australia

Research shows that severe climatic perturbations, especially in the case of the worst ecosystem collapse of the Phanerozoic, the end-Permian extinction (EPE), have different spatial expressions across the globe. Using an integrated sedimentological and geochemical approach, this study from the Bowen Basin in Queensland, Australia provides a southern, high paleolatitude, stratigraphically-complete, terrestrial perspective across the Permian-Triassic boundary (PTB) that challenges previous interpretations. Analysis from this investigation allow for paleoclimatic and paleoenvironmental assessments to be made to (1) better understand the depositional environments at this time through drillcore analysis, (2) characterize the elemental signatures of mudrocks, and (3) identify the globally correlated negative carbon isotope excursion (CIE) commonly associated with the marine extinction horizon. A change in the elemental signature of mudrocks across the EPE, is highlighted through X-Ray Fluorescence (XRF) analysis, and most likely forced by increased rates of chemical weathering intensities, demonstrated by Chemical Index of Alteration (CIA) calculations. These changes are interpreted to reflect a change in climate towards warmer and/or wetter conditions and increased seasonality beginning around 253.32 ± 0.03 Ma (Metcalfe et al., 2015) and continuing post-EPE. Temporally, depositional environments change throughout the basin history, however, there is no significant change in depositional environment at the EPE/PTB. The latter finding contradicts previous interpretations, although a ponding event, represented by a dark gray, organic-rich “Marker Mudstone,” was identified just above the EPE horizon and can be traced across large parts of eastern Australia. A gradual shift towards better drained alluvial conditions into the Triassic is more probable than abrupt aridification as suggested for other localities. Lastly, the globally-recognized negative carbon isotope excursion (CIE) signature, is recorded just after the demise of the Glossopteris flora or the top of the uppermost Permian coal (EPE horizon). The offset between the EPE and the negative CIE reflect an asynchronous nature between marine and terrestrial extinctions. Climate changes and uniform depositional environments across the PTB in the Bowen Basin align with more recent interpretations from the more southerly, Sydney Basin, providing further evidence that Permo-Triassic paleoenvironmental perturbations have different expressions in high southern paleolatitudes relative to other areas. Advisors: Christopher R. Fielding & Tracy D. Fran