Carboniferous–Permian palynostratigraphy of west Australian marine rift basins: resolving tectonic and eustatic controls during Gondwanan glaciations

The longest interval of cold climate in Earth’s Phanerozoic history spanned some 55 million years from the Namurian (late Carboniferous) to the Kungurian (early Permian) when glaciation affected much of high-latitude Gondwana. Uncertainty surrounds the timing of glaciation(s) and the frequency of interglacial episodes, ice volumes and the location of ice centres. This is because the ‘glacial’ record is preserved predominantly within marine strata deposited in intracontinental rift basins marginal to onshore ice centres on uplifted basement highs. The direct stratigraphic record of glaciation is meagre on adjoining basement highs, and extremely difficult to date. Many basins contain broadly similar threefold lithostratigraphic successions of lowermost glaciomarine diamictite facies, middle shales and uppermost carbonate and sandstone-rich, commonly coal-bearing, deltaic strata. In the absence of absolute age control and infrequent presence of macrofossils, such ‘deglaciation sequences’ are widely assumed to be correlative from basin to basin recording Gondwanan deglaciation(s) and a world-wide glacioeustatic sea level rise. A newly compiled biostratigraphic database for west Australia, using first appearance datums of spore-pollen types, allows correlation of Late Palaeozoic siliciclastic successions between seven basins (Bonaparte, Canning, Carnarvon, Collie, Gunbarrel, northern and southern Perth basins). These extend some 3800 km along Australia’s western continental margin adjacent to the west Australian shield. All but the Gunbarrel Basin contain tripartite glacially influenced successions (diamictite/shale/sandstone). Biostratigraphic data reveal sharp differences in ages and stratigraphic distributions, and marked variations in the thickness of coeval units. Diamictite/shale/sandstone successions accumulated diachronously from basin to basin recording a dominant tectonic control on subsidence and relative sea level. Middle shale units are not exact correlatives between basins and thus are unlikely to simply represent widespread climatically controlled glacioeustatic events. Instead, they are argued to record high relative sea levels during times of maximum synrift subsidence. This tectonostratigraphic model can be applied to other intracontinental rift-basin successions across Gondwana.