ABSTRACT: Timor Sea, Northwestern Australia: New Ideas on Basin Development from Integrated Studies

O'BRIEN, GEOFFREY W., M. A. ETHERIDGE, D. J. NEEDHAM, A. E. STEPHENSON, and J. BLEVIN, Bureau of Mineral Resources, Canberra, Australia

The Australian Bureau of Mineral Resources has carried out a major study of one of Australia's most active exploration areas, the Timor Sea, in which an integrated suite of image-processed aeromagnetic data, deep crustal, conventional, and high-resolution seismic, well data, and water column geochemical data have been acquired and interpreted. These studies have shown that the rifting in this area actually began in the Late Carboniferous-Early Permian, rather than in the Triassic-Jurassic as previously believed. Reactivation of this Permian-Carboniferous rift system has resulted in the formation of the oil-rich Jurassic Vulcan graben, as well as other prospective Mesozoic features in the area. Moreover, the hydrocarbon accumulations in the Mesozoic depocenters directly relate to the r activation of deep-seated normal and transfer faults in the underlying Permian-Carboniferous rift system.

A significant strike-slip component, present during the Vulcan graben's development in the Triassic-Jurassic, resulted in the formation of a number of small, linear depocenters in the central and northern Vulcan graben. These troughs contain rich source rock sequences because a combination of very rapid subsidence and restricted circulation favored organic carbon accumulation and preservation. Similarly, image-processed aeromagnetic data have shown that the Vulcan graben is separated from the Browse basin to the south by a previously unknown ridge system (corresponding to a deep-seated transfer fault) and a series of basement highs. The ridge-basement high complex severely restricted oceanic circulation throughout the Triassic and Jurassic, resulting in rich source rock deposition in oth the northern Browse and the southern Vulcan graben. In the earliest Cretaceous, however, they were swamped by sediment and more open marine conditions were established, with a consequent loss of source rock quality.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)