The Permo-Triassic Sydney Basin straddles Australia's central eastern coast in New South Wales. The basin covers 64,000 km2, 36,000 km2onshore and 28,000 km2offshore under water depths of up to 4,500 metres. The Sydney Basin is part of a major basin system that extends over 1,500 km from the Bowen Basin in Queensland through to the Gunnedah Basin in NSW. Onshore, the basin contains 4,500 metres of Permo-Triassic clastic sediments, while the offshore basin contains 6,000 metres of sediments. The basin overlies the Lachlan Fold Belt and Late Carboniferous volcanoclastic sediments. The basin formed during extension in the Early Permian, with half-graben infilled with the Dalwood and Talaterang Groups. Foreland loading followed with the compression of the Currarong Orogen in the Early Permian. Late Permian uplift associated with the New England foreland loading phase resulted in the formation of depocentres with the northeast Sydney Basin. These depocentres filled with pyroclastic and alluvial-paludual sediments of the Newcastle Coal Measures. In the Triassic, uplift of the offshore basin resulted in reworking of Permian sediments in fluvial environments. The basin underwent a final phase of deformation (thrusting) in the Middle Triassic. Extension and breakup in the Tasman Sea beginning in the Late Cretaceous resulted in the current structural boundaries of the basin's eastern margin.
Over 100 wells have been drilled in the onshore Sydney Basin, although no wells have yet been drilled offshore. The onshore basin contains rich coal deposits with associated natural gas and minor oil shows. The geochemistry of oil shows indicate a terrestrial source from a clay-rich environment, although not associated with the coal facies. The main trap types are anticlinal and overthrust, with some structural reactivation during Tasman Sea rifting.