The Otway Basin is a northwest-striking passive margin rift basin that extends from southeastern South Australia to the northwestern coast of Tasmania (Figure 1 [PDF, 446KB] and Figure 2 [PDF, 79KB]). It belongs to a series of basins, including the Bight (comprising the Ceduna, Duntroon, Eyre, Bremer, Recherche and Denmark sub-basins), Polda, Otway, Sorell, Bass and Gippsland basins, that were formed during Gondwana break-up and the Antarctic-Australian separation (Willcox and Stagg, 1990). The Otway Basin is filled with Late Jurassic to Recent sediments and covers an area of 150,000 km2, 80% of which lies offshore. The basin's western, northern and eastern boundaries are defined by the preserved limits of the latest Jurassic-Early Cretaceous Otway Group sediments, whilst its southern boundary is delimited by the southernmost extent of Cenozoic sediments in the Hunter Sub-basin.
According to Norvick and Smith (2001), rifting along the southern Australian margin was initiated during the Oxfordian (about 158 Ma) and, progressing from west to east, had affected the Otway, Bass and Gippsland provinces by Tithonian times (about 150 Ma). However, when underlying basement rocks are considered, the southern Australian break-up rift system may have an older history that is recorded in the Polda Basin which hosts Neoproterozoic rift basalts in the Kilroo Formation (Rankin, 1993). In Western Australia, the break-up can be correlated with the northernmost extent of Neoproterozoic terrigenous clastic sediments of the Stirling and Mount Barren groups that are exposed north of the 1200 Ma Albany Fold Belt (Nelson et al, 1995).
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