Geological framework of the South Tasman Rise, south of Tasmania, and its sedimentary basins

Abstract

The South Tasman Rise is a continental fragment of 200 000 km2 lying south of Tasmania and surrounded on three sides by Late Cretaceous and Palaeogene oceanic crust, which assumed its present configuration in the Palaeogene. The western side of the rise is dominated by the Tasman Escarpment, the northernmost part of the Tasman Fracture Zone. The South Tasman Rise consists of three structural blocks, linked to Tasmania by thinned continental crust, that moved southward with Antarctica from Tasmania in the Late Cretaceous. All have been affected by northwest‐southeast strike‐slip motion in the Late Cretaceous and north‐south extension in the Tertiary. The western block moved from west of Tasmania, had the longest and most intense tectonism, and consists of large basement highs and the complex Ninene Basin. Basins on all three blocks are generally fault‐controlled and are believed to contain Late Cretaceous to Early Oligocene detrital non‐marine and shallow‐marine sedimentary rocks, and Late Oligocene and younger bathyal to pelagic chalk and ooze. The Ninene Basin is more extensive and generally somewhat thicker (up to 5 km) than basins on the other two blocks. Basins on all three blocks have long‐term petroleum potential but only the central block is in presently drillable water depths.