STRATIGRAPHIC RECORD OF THE LATE PALEOZOIC GONDWANAN ICE AGE IN EASTERN AUSTRALIA: A PROGRESS REPORT

We are undertaking a thorough review of the Carboniferous and Permian stratigraphy of eastern Australia, towards a more detailed understanding of the late Paleozoic ice age of Gondwanaland. Our research in Queensland (NE Australia) suggests that rather than being a single long epoch, glaciation occurred only during discrete, relatively short-lived periods in the mid-Carboniferous (c. 315 Ma), Late Carboniferous (c. 311 Ma) and Early Permian (289-293 Ma). The two earlier glacials are recorded in entirely non-marine, fluvial and lacustrine facies, whereas the Permian interval is preserved in both shallow marine and non-marine strata. Broad correlations can be made between the Carboniferous glacial periods recorded in Queensland and those recognized by previous workers in New South Wales (NSW: SE Australia), although we have not yet been able to confirm these correlations. The Permian section of southern NSW, however, preserves a shallow marine record of an Early Permian glacial in the Pebbley Beach Formation and equivalents that is apparently correlative with the youngest glacial preserved in Queensland. Furthermore, evidence is also growing for a mid-Permian glacial (c. 270 Ma) recorded in the Wandrawandian Siltstone of southern NSW and equivalents. Both this unit and the Pebbley Beach Formation are relatively fine-grained and record predominantly offshore transition to shelfal water depths, in contrast to the predominantly sandy, stacked shoreface facies of enclosing formations. We suggest that this apparent anomaly may be the consequence of isostatic loading during glacials resulting in deepening of the basin, followed by post-glacial isostatic rebound causing abrupt shallowing and leading to accumulation of the coarser-grained units. Testing of this hypothesis and correlation further afield of the glacial periods recognized thus far are in progress.