A REVISED, LATE PALAEOZOIC GLACIAL TIME-SPACE FRAMEWORK FOR EASTERN AUSTRALIA, AND COMPARISONS WITH OTHER REGIONS AND EVENTS

A timeframe of glacial and nonglacial intervals in the Carboniferous and Permian systems of eastern Australia was published by Fielding et al. (2008). In this scheme, eight discrete intervals (four in the Carboniferous: C1-C4, and four in the Permian: P1-P4) in which indicators of glacial activity and cold climate are preserved alternate with intervals in which no such evidence is preserved. The timeframe has been widely used both to better understand the time-space distribution of glacial events in eastern Australia and as a basis for comparison with late Paleozoic glacial events in other regions of the world. In the period since publication of that paper, a large inventory of new, radiogenic isotope ages has become available for the late Paleozoic strata in eastern Australia, and the time ranges of the global stages of the Carboniferous and Permian have also been adjusted in the light of new age data. Accordingly, this paper presents a reappraisal of the Fielding et al. (2008) timeframe, based on the much-improved chronostratigraphic database. Of the Carboniferous glaciations, only C1 has changed significantly, expanding in time range downward. Of the Permian glaciations, P1 and P2 remain as in the previous evaluation, whereas P3 and P4 become significantly younger in absolute time. Indeed, the close of P4, supported by a large number of high-precision ages, is now estimated to have occurred at 254.5 Ma, only 2.6 m.y. before the end-Permian biotic crisis and extinction event. Carbon isotopic records from Permian marine strata reveal that alternating glacial and nonglacial conditions in eastern Australia corresponded to changes in the global carbon cycle. Paleoweathering proxies show that the intensity of chemical weathering during the late Paleozoic in eastern Australia changed in response to climate swings, with nonglacial intervals likely becoming warmer and more humid through the course of the Permian. There are broad coincidences between the timing of glaciations in eastern Australia and those recorded elsewhere on Gondwana, but sufficient differences to support the conclusion that glaciations were not synchronized across the ancient landmass. The eastern Australian record persists in being the best-constrained in time anywhere in the world.