TECTONIC EVOLUTION OF THE GIPPSLAND BASIN AND HYDROCARBON POTENTIAL OF ITS LOWER CONTINENTAL SHELF

Abstract

Tectonic evolution of the Gippsland Basin, par­ticularly for the 120 to 66 Ma period, is reviewed based on the interpretation of BMR Continental Mar­gin Seismic data and industry seismic and well infor­mation over the continental shelf. It is revealed that the eastern limit of the Early Cretaceous (120-97 Ma) rift is the Gippsland Rise—a new tectonic element. The Rise is part of a regional deep-seated metamor­phosed Palaeozoic lineament belonging to the Tasman Fold Belt upon which the Strzelecki Group onlapped from the west. Two newly-identified transfer fault zones named here, the Eastern Gippsland Margin Transform and the Cape Everard Transfer Fault, bound the rise from the east and the west respectively.

In a second phase of rifting (97-80 Ma) the following tectonic events took place:

A narrower rift was incised at the onset of this phase parallel to the initial rift;

The Gippsland Rise became unstable;

A new NW-SE tensional regime commenced;

The Southern Platform collapsed (in the Cenomanian) and the Southern Ocean accessed the three Bass Strait basins;

Towards the end of this episode (in the Campanian) the Southern Platform and the Gippsland Rise emerged, and

The Northern and Southern Grabens (new names) were incised in the Gippsland Rise connecting the newly formed Tasman Sea to the basin.

Ingredients necessary for potential hydrocarbon exploration in the lower shelf and upper slope such as source, reservoirs, seal, trapping mechanism and re­charge do exist but require additional seismic and geological evaluation.