Palaeozoic basins of southern South Australia: New insights into their structural history from regional seismic data

Publisher Website
Google Scholar
Abstract
Interpretation of three recently recorded offshore seismic lines provides a regional picture of the geology from the Gawler Craton across the Stansbury and Troubridge Basins to the Otway Basin in South Australia. The 300 km transect crosses most of the Cambrian Stansbury Basin, which consists of a marginal platform in the west and the Kanmantoo Trough in the east. The Kanmantoo Trough is filled by an eastward deepening sedimentary prism formed by the Kanmantoo Group. The little‐deformed platformal Cambrian sedimentary rocks onlap the Gawler Craton and underlie the Gulf St Vincent. The eastern margin of the platform is separated from the western Kanmantoo Trough by a northeast‐trending zone of intense deformation. This transition zone comprises numerous southeast‐dipping faults which are correlated to faults and shear zones with reverse displacement that are mapped in outcrop on Kangaroo Island and Fleurieu Peninsula. These faults constitute contractionally reactivated former extensional faults, which controlled the western margin of the Kanmantoo Trough. A southeast limit to the Kanmantoo Trough could be indicated immediately north of the Otway Basin by an opposing, northwest‐dipping structural grain within the presumed Cambrian succession. Faults, which were active only during the Cambro‐Ordovician Delamerian Orogeny, and the top of the Cambrian sedimentary rocks are truncated by a Permian glacial event during which the Permian Troubridge Basin sequence was deposited. This sequence is generally 200–400 m thick but this increases to 2000 m in a major trough east of Backstairs Passage. This feature may be of interest for petroleum exploration. A Tertiary sequence covers the region with a thickness of up to 600 m. Tertiary‐Holocene compression reactivates the western boundary faults of the Kanmantoo Trough and is attested by marked uplift that causes the present day topographic relief of Kangaroo Island, Fleurieu Peninsula and the southern Flinders Ranges. In this framework the depression of the Gulf St Vincent could be a shallow, contemporaneous foreland basin.