The Townsville Basin is an east-west trending extensional basin located between the Queensland and Marion Plateaus offshore northeast Queensland, under water depths of 200 metres to 2000 metres. The basin is 450 km long and 20-120 km wide, underlies the bathymetric Townsville Trough and is subdivided into several sub-basins.
The basin fill occurs as two main megasequences that reflect the basin evolution from a rift basin with isolated depocentres to a sag basin with a more widespread distribution. The maximum sediment thickness is about 6.5 km. The oldest sediments are contained in a generally thin Late Jurassic to Early Cretaceous early synrift sequence with considerable variation in spatial distribution, and are likely to consist of terrigenous deposits derived from the adjacent plateaus and intra-basin highs. This is overlain by up to 2 km of a more widespread synrift megasequence, deposited in a variety of environments and inferred to be no younger than Palaeocene in age. A Cainozoic sag-phase megasequence up to 3.8 km thick consists of drape fill clastics overlain by mainly carbonates. The Townsville Basin formed through oblique northwest-southeast extension resulting in a half-graben morphology. This early rifting event was separate to and predated extension related to later Coral and Tasman Sea opening. However, a second rift phase in the Early to Late Cretaceous may be related to these regional extensional events. Multiple reactivation events occurred throughout the Cainozoic.
No wells have been drilled in the Townsville Basin and its petroleum prospectivity is speculative. The western part of the basin lies within the Great Barrier Reef Marine Park, in which petroleum exploration is prohibited.