ABSTRACT: Tectonic Evolution of the Gippsland/Bass Petroleum Province, Southeastern Australia

WILLCOX, J. B., and J. B. COLWELL, Bureau of Mineral Resources, Canberra, Australian Capital Territory, Australia

The Gippsland/Bass depocenters lie within Bass Strait, to the east of a string of "Southern Margin" basins which are the products of Australia-Antarctica extension and breakup, and to the west of the Tasman Sea Basin which is related to the rifting of the Lord Howe Plate. The region shows the tectonic influence of all these events.

A grid of deep (14 second) reflection seismic data, and complementary refraction data, indicate that the Gippsland and Bass Basins were linked, and initiated by movements of the Paleozoic basement on a detachment complex at a depth of 10-15 km. The thick, largely Cretaceous basin-fill, appears to have entered the thermal sag phase of basin development in the Campanian. A major erosional event in the latest Cretaceous, led to peneplanation of the basin sediments and adjacent basement platforms. This event, which has also been recognized in other Southern Margin basins, attests to the continued interaction of the Australia and Antarctic Plates at the time. The seismic data show that oblique extension (both 'transtension' and 'transpression') appear to have played an important role in ba in development: however, it is the transpression in the Gippsland Basin which has led to formation of the major anticlines -- the traditional petroleum traps below the Eocene top Latrobe unconformity.

Theoretically, there may have been several phases of petroleum generation and migration. Potential non-traditional traps occur within the Late Cretaceous sequence -- some as older wrench-related anticlines with little or no expression at the top Latrobe, others as fans along the northern boundary of the basin associated with ?lacustrine deposits, and as compaction drape structures within an undrilled ?Late Cretaceous sequence in the center of the basin.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)