The Late Jurassic-Cainozoic Otway Basin is a large, northwest trending basin on the southern Australian passive margin. Exploration is mature onshore and immature offshore, with >200 wells in South Australia, Victoria and Tasmania. Commercial gas discoveries include the offshore Thylacine, Geographe, Minerva and Casino fields, numerous smaller onshore gas fields and industrial grade CO2. No commercial oil discoveries have been identified.
The basin formed by multi-stage rift-sag, and inversion phases. Late Jurassic to Early Cretaceous rifting resulted in the east-west trending Inner Otway Basin. Late Cretaceous rifting, culminating in continental breakup in the Maastrichtian, produced northwest-southeast trending depocentres beneath the outer shelf and slope. Multiple phases of compression in the Cretaceous-Recent resulted in inversion and wrenching of pre-existing structures.
The basin contains five major depocentres, the mainly onshore Inner Otway Basin, the offshore Morum, Nelson and Hunter sub-basins, and eastern Torquay Sub-basin. A complex series of Early Cretaceous half-graben depocentres and intervening basement highs occurs along the northern margin of the basin whereas Late Cretaceous depocentres occur farther to the south, basinward of the major structural hinges of the Tartwaup and Mussel fault zones. The Otway Basin has a maximum total sediment thickness of about 13000 m.