POLLOCK, ROSALIE M., National Centre for Petroleum Geology and Geophysics, University of Adelaide, South Australia

ABSTRACT: Sequence Stratigraphy, Biostratigraphy and Depositional Systems in the Cainozoic Gambier Basin, Southern Australia

The Gambier Basin represents one of the frontier basins in southern Australia and forms part of a passive continental margin developed during the Jurassic to Tertiary resulting from the separation of Australia and Antarctica. The basin comprises Palaeocene-Eocene clastic sediments, but since the later part of the Middle Eocene, plate reconfiguration, marine transgression and introduction of a warm current into southern Australia, deposition of cool-water carbonate platforms and mounds has dominated. Sequence stratigraphy based on regional seismic interpretation, detailed biostratigraphy and depositional systems analysis is undertaken to aid exploration in the basin.

The Palaeocene-Eocene clastic succession has been recognised as a series of stacked, coarsening-upward deltaic parasequences, while several high-resolution sequences have been recognised in the Middle Eocene to Middle Miocene, carbonate section, as part of an overall regressive-transgressive-regressive cycle. The carbonate sequence shows clinoform geometries on the outer shelf, punctuated by many incision events. Large submarine canyons are evident on the seismic, probably produced by relative falls in sea level. Mounded structures, similar to those biogenic carbonate buildups observed, on the Eucla Platform over 1000km to the west, are thought to have developed during transgressive events.

Regional depositional environments, different rates of subsidence and sea level fluctuations, are the prime factors controlling the sediment buildup and consequently the development of the whole basin. The depositional model generated from this study will assist with development of play concepts for exploration in the Gambier and other southern Australian basins.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid