Permian Deglaciations and Sub-Polar Carbonate Depostion along the Southern Margin of Gondwana

Despite potential for providing insight into climate evolution, carbonate rocks deposited in high-latitude, glacially influenced regions have not received extensive study. Exceptional, yet to date poorly constrained examples are limestone units within the Permian System of eastern Australia. The succession consists largely of marine siliciclastics, which accumulated along the southern margin of Gondwana in a series of basins that stretched from polar to temperate latitudes. Previous work has shown that the Permian System records four discrete glacial epochs, P1 (Asselian - early Sakmarian), P2 (latest Sakmarian - early Artinskian), P3 (late Kungurian – Roadian), and P4 (mid Wordian – Capitanian), which are separated by non-glacial intervals of similar duration. Carbonate deposits mantled structural highs during the initial stages of each non-glacial period. Facies disposition suggests carbonate accumulation in ramp settings inhabited by a low-diversity, heterozoan fauna of locally high abundance. Inner ramp rudstones and grainstones contain large eurydesmid bivalves, spiriferid and productid brachiopods, bryozoans, benthic foraminifers, calcareous sponge spicules, and crinoids. Muddy mid-ramp facies are dominated by bryozoans, crinoids, and productids. Outer ramp and basinal facies are argillaceous floatstones or shales with siliceous sponge spicules, productids, and fenestrate bryozoans. The predominant depositional motif is deepening upward, suggesting that carbonates formed during marine transgression. Limestone sequences are typically overlain by offshore siltstones deposited during highstands, suggesting that terrigenous clastic deposition was impeded during the initial stages of deglaciation and eustatic sea level rise. Stable isotopic records will provide a further test of relationships between deglaciation, sea level rise, and limestone accumulation as deduced from stratigraphic relationships. Because they record an interval of time not otherwise represented, the Permian sub-polar carbonates examined here have the potential to provide unique insight into environmental changes that accompanied transitions between glacial and non-glacial epochs of the late Paleozoic ice age.