Sedimentation rates and coal formation in the Permian basins of eastern Australia

Abstract

The main Permian coal-bearing basins of eastern Australia are the foreland Sydney and Bowen Basins in the east and the interconnected cratonic Cooper and Galilee Basins in the west. The morphotectonic domains of these basins are described in terms of sediment thicknesses, sediment accumulation rates, percentage of coal and coal accumulation rates. Early Permian deposition in the foreland basins was marine, with coal measures restricted to the orogenic and cratonic margins. Because of expansion of the eastern orogen, marine deposition was replaced in the Late Permian by deltaic then fluvial sediments and extensive coal measures. The cratonic basins were sites of coal measure deposition for most of the Permian. The foreland basins have asymmetrical depoaxes located in the ‘outer foreland’ near and parallel to the eastern orogen, and contain more than 6 km of Permian sediments. Towards the craton in the west in the ‘inner foreland’, the successions are thinner and are comparable with those in the cratonic basins. Maximum sediment thickness in the cratonic basins is 1.5 km in the Cooper Basin. In the foreland basins, maximum total sediment accumulation rates (400 m/Ma) and coal measure accumulation rates (500 m/Ma) were an order of magnitude greater than those in the cratonic basins, and overlap only in the inner foreland. The percentage of coal is significantly greater in the cratonic compared with the foreland basins. On average, coal makes up 5.5–8.5% of the foreland basins coal measures compared with 12–19% in the cratonic basins. Sediment accumulation rates and the distribution of coal in the Permian basins reflect the primary tectonic control of subsidence.