Coastal erosion reveals a potentially unqiue Oligocene and possible periglacial sequence at present-day sea level in Port Davey, remote South-West Tasmania

Cut-back of a sea-cliff at Hannant Inlet in remote South-West Tasmania has exposed Oligocene clays buried under Late Pleistocene “colluvium” from which abundant wood fragments protrude. The two units are separated by a transitional interval defined by mixed Oligocene and Pleistocene microfloras. Microfloras preserved <i>in situ</i> in the clay provide a link between floras in Tasmania and other Southern Hemisphere landmasses following onset of major glaciation in East Antarctica during the Eocene-Oligocene transition (c. 34 Ma). The Late Pleistocene “colluvium” preserves abundant fossil pollen of the shrub conifer genus <i>Pherosphaera</i> (al. <i>Microstrobos</i>). Assuming the parent plants had the same upper subalpine-alpine ecology as living <i>Pherosphaera hookeriana</i>, the microflora provides evidence for cold, wet conditions in the Port Davey lowlands during a low sea-level stand. The same data highlight the failure of <i>Pherosphaera</i> to regain its Pleistocene distribution during the Postglacial period. Our data are inconclusive whether Late Pleistocene conditions in Hannant Inlet were periglacial, i.e., the Oligocene sediments were turbated by freeze-thaw processes, or have been reworked by fluvial processes into the Pleistocene “colluvium”. Nevertheless, the inferred cold-climate is consistent with the former hypothesis. The sequence is sealed under cross-bedded coarse quartzite gravels of presumed Last Glacial Stage age.