Simon Paul Holford, Paul Green, Ian Duddy, Richard Hillis, Steve Hill, Martyn Stoker

The antiquity of the Australian landscape has long been the subject of debate, with some studies inferring extraordinary longevity (>10^8 Myr) for some subaerial landforms dating back to the early Palaeozoic. A number of late Palaeozoic glacial erosion surfaces in the Fleurieu Peninsula, southeastern Australia, provide an opportunity to test the notion of long-term subaerial emergence, and thus tectonic and geomorphic stability, of parts of the Australian continent. Here we present results of apatite fission-track analysis (AFTA) applied to a suite of samples collected from localities where glacial erosion features of early Permian age are developed. Our results indicate that the Neoproterozoic-Lower Palaeozoic metasedimentary rocks and granitic intrusions upon which the glacial rock surfaces generally occur were exhumed to the surface by the latest Carboniferous-earliest Permian, possibly as a far-field response to the intraplate Alice Springs Orogeny. The resulting landscapes were sculpted by glacial erosive processes. AFTA results suggest that the erosion surfaces and overlying Permian sediments were subsequently heated to between ~60 and 80°C, which we interpret as recording burial by a Permian-Mesozoic sedimentary cover, roughly 1 kilometre in thickness. This interpretation is consistent with existing thermochronological datasets from this region, and also with palynological and geochronological datasets from sediments in offshore Mezozoic-Cenozoic-age basins along the southern Australian margin that indicate substantial recycling of Permian-Cretaceous sediments. AFTA suggests that the exhumation which led to the contemporary exposure of the glacial erosion features probably began during Paleogene, during the initial stages of intraplate deformation that has shaped the Mt Lofty and Flinders Ranges in South Australia. Our findings are consistent with several recent studies, which suggest that burial and exhumation has played a key role in the preservation of Gondwanan geomorphic features in the contemporary Australian landscape.