Paper Number: 942
The Permian−Triassic succession in the southern Sydney Basin, southeastern Australia: a unique and complete stratigraphic record of global changes during the Palaeozoic−Mesozoic transition
Shi, Guang R.
School of Life and Environmental Sciences, Deakin University, Melbourne Campus, 221 Burwood Highway, Burwood, Victoria 3125, Australia [email: grshi@deakin.edu.au]
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The Permian−Triassic transition is widely regarded as representing an epic chapter in earth history. It is mostly notably characterized by a sequence of global-change events, including: the final collapse of the great Late Paleozoic Ice Age in the Middle Permian, the end-Permian mass extinction, and the rapid global warming at the dawn of the Triassic. Despite this rapidly emerging knowledge, well-preserved continuous stratigraphic sections that contain detailed records of these global changes are very rare in a global context. In this paper, I will report a nearly continuous stratigraphic succession in the southern Sydney Basin exposed along the south coast of New South Wales in southeastern Australia, spanning from the earliest Permian (Asselian-Sakmarian) to the Lower Triassic, with exceptionally preserved sedimentary and paleontological records that show profound changes in paleoclimate, depositional environment, biotas and ecosystems over this period.
The Permian−Triassic succession of the southern Sydney Basin in southeastern Australia comprises both marine and non-marine sedimentary sequences, as well as extensive outcrops of volcanic rocks. The marine component, of Early−Middle Permian age, is composed of a number of formations; they are, from the base to the top: the Wasp Head Formation, Snapper Point Formation, Pebbly Beach Formation, Wandrawandian Siltstone (Formation), Nowra Sandstone (Formation), Berry Siltstone (Formation), and Broughton Formation. This Lower−Middle Permian marine succession contains excellent field evidence in support of four stratigraphic intervals of glaciation, indicated by dropstones, glendonites, cold-water faunas, as well as evidence from oxygen stable isotopes. The Upper Permian (Lopingian) of the costal succession, locally known as the Illawarra Coal Measures, is predominantly a sequence of estuarine to alluvial plain facies, intercalated with multiple intervals of coal seams, unequivocally suggesting a climatic transition towards a benign climate state.
Although the precise Permian−Triassic boundary is still a matter of debate for eastern Australia, in the southern Sydney Basin, it is well constrained within a relatively narrow stratigraphic interval (20-50m) between the last Permian coal seam (the Bulli Coal) and the top of the Scarborough Sandstone. This interval also coincides with profound changes in depositional systems and terrestrial ecosystems and a drastic turnover (mass extinction) in plant species composition. The Lower Triassic in the study area is represented by the Narrabean Group, a succession of claystones, sandstones and conglomerates, believed to have been deposited in a variety of non-marine settings ranging from lacustrine, braided fluvial channel to inter-channel floodplain environments. Horizons of paleosols are common especially in the middle and upper parts of the Narrabean Group (e.g., Bald Hill Claystone), suggesting a strong degree of oxidation and chemical weathering under the influence of global warming.