NEOGENE TECTONICS IN SE AUSTRALIA: IMPLICATIONS FOR PETROLEUM SYSTEMS

Abstract

The influence of Neogene tectonics in the SE Australian basins has generally been underestimated in the petroleum exploration literature. However, onshore stratigraphic and offshore seismic data indicates that significant deformation and exhumation (up to one km or more) has occurred during the late Tertiary-Quaternary. This tectonism coincides with a change in the dynamics of the Australian plate, beginning at around 12 Ma, resulting in a WNW–ESE compressional regime which has continued to the present day.

Significant late Miocene tectonism is indicated by a regional angular unconformity at around the Mio-Pliocene boundary in the onshore and nearshore successions of the SE Australian basins.

Evidence of on going Pliocene- Quaternary tectonism is widespread in all of the SE Australian basins. Late Tertiary tectonism has produced structures in the offshore SE Australian basins which have been favourable targets for petroleum accumulation (e.g. Nerita structure, Torquay Sub-basin; Cormorant structure, Bass Basin). In the offshore Gippsland Basin, most of the oil- and gas-bearing structures have grown during Oligocene-Recent time. Some Gippsland Basin structures were largely produced prior to the mid- Miocene, while others have a younger structural history. In areas of intense late Tertiary exhumation and uplift (e.g. proximal to the Otway and Strzelecki Ranges), burial/maturation models of petroleum generation may be significantly affected by Neogene uplift.

Many structures produced by late Miocene-Pliocene deformation are dry. These relatively young structures may post-date the major maturation episodes, with the post-structure history of the basins dominated by exhumation and cooling.