The Bassian zone comprises the Early Cretaceous to Recent Otway, Bass and Gippsland Basins that occupy most of southern and offshore Victoria, Australia. It trends approximately east-west and cuts across the predominantly northerly trend of the Palaeozoic rocks. The three basins were formed by continental rifting, largely during the Early Cretaceous, followed by thermal subsidence through the Late Cretaceous and Cainozoic.

Two major groups of structures in the Bassian zone:
• Principally Early Cretaceous rotational normal faults and associated transfer faults. The normal faults trend between 290 degree and 310 degree in all three basins, and dip between 30 degree and 50 degree. They bound half grabens from a few km to a few tens of km wide and up to 6 km deep. The transfer faults are steeply dipping and approximately orthogonal to the normal faults, and accommodated variations in the position, spacing and dip direction of the normal faults during the Early Cretaceous extensional phase.
• Mainly reverse faults, with or without a strike-slip component, and associated anticlines that are predominantly mid to late Tertiary in age, and which are restricted to the northern part of the Bassian zone. The reverse faults and anticlines trend northeasterly, and are concentrated in an east-west prominent topographic lineament variously known as the Gambier-Gabo lineament, the Gippsland line, and at its eastern end, the Rosedale Fault system.