ABSTRACT: Deep Structure of the Gippsland Basin, Australia: Implications for Hydrocarbon Exploration

J. B. Willcox, J. B. Colwell, P. E. Williamson, C. D. N. Collins

The Gippsland basin is located offshore of southeast Australia. It is Australia's principal petroleum province: a region of mature exploration accounting for about 90% of the country's oil production. Traditionally, most exploration activity has been focussed on clearly defined anticlines at the Late Cretaceous-early Tertiary level. However, in recent years production from these structures has declined, leading industry and government agencies to look at deeper plays within the basin and the relationship between basin-forming structures and the overlying sedimentary section.

The basin's early history is thought to be related to the development in the Jurassic and Early Cretaceous of a complex rift system along the southern margin of Australia as a precursor to the late middle-Cretaceous sea-floor spreading between Australia and Antarctica. Late Cretaceous-Eocene spreading between Australia and the Lord Howe Rise/New Zealand has had an impact on the eastern part of the basin. A largely untested model for the basin's development invokes north-northeast-south-southwest lithospheric extension and suggests that many of the early Tertiary structures which contain oil and gas were developed by wrench-type reactivation of major early normal and transfer faults.

A research program was recently undertaken by the Bureau of Mineral Resources to investigate the deep structure of the basin. This program involved the collection of approximately 1600 km of regional, 96-channel, deep seismic reflection lines, together with ship-to-shore long-offset seismic refraction data. Initial results are elucidating a complex system of rotated fault blocks extending into the basin's center and their relationship to both the underlying deep-crustal structure and overlying hydrocarbon traps.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990