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Zhong Qiang Chen, The University of Western Australia (Australia)
David Haig, The University of Western Australia (Australia)
Arthur Mory, Geological Survey of Western Australia (Australia)
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The Permian-Triassic (P-Tr) mass extinction redirected dramatically the course of biotic evolution during the Mesozoic and Cenozoic. This event and its consequence have been globally studied. However, few data about this eologic crisis and subsequent recovery are known from Gondwana. Here, we report the restoration of marine ecosystems following the P-Tr extinction in the Perth Basin, which was part of the interior sea of the Gondwana during the P-Tr transition. The P-Tr boundary and Early Triassic successions are seen in borehole cores as well as outcrop sections in the northern Perth Basin (NPB). A complete P-Tr boundary sequence is revealed in the Well Hovea-3 of the basin. The early Induan succession seen in the Well Hovea-3 indicates a harsh (probably poorly oxygenated) environment. The Lower Triassic (mainly Dinerian-Smithian) is also exposed in the north Geraldton areas, where the stromatolites, resting on either pebbles or sandstone of the Silurian age, characterize the base of the section. Both pustular and smooth stromatolites and their growth patterns, including laminated mats and columns, as well as the associated microbial assemblages are well analogous to modern stromatolites in the Shark Bay. Following the stromatolites sequence, the reddish muddy limestone contains conspicuous wrinkle structures, shell beds and trace fossils. Abundant trace fossils (eight ichnogenera) are present in the above reddish mudstone and siltstone sandstone. Briefly, the ecosystem in Gondwana has been destroyed by the P-Tr extinction and became unfavorable to most biota expect few disaster taxa within >one modillion years after the event. The ecosystems were slightly ameliorated during the late Induan when stromatolites grew widely in the NPB. The amelioration is indicated by increase in diversity and complexity of trace-fossil assemblages recorded in the Kockatea Shale in the basin.
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