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ABSTRACT: Integrated Image-Processed Aeromagnetics and Seismic Study, Vulcan Graben, Timor Sea: New Ideas on Structural Evolution and Hydrocarbon Habitat

O'BRIEN, G. W., Bureau of Mineral Resources, Canberra City, Australia Capital Territory, Australia, M. A. ETHERIDGE, Etheridge and Henley, Geoscience Consultants, and D. J. NEEDHAM, Bureau of Mineral Resources, Canberra City, Australia Capital Territory, Australia

The Vulcan Graben in the Timor Sea has been one of Australia's most active oil exploration areas since the mid-1980s. However, following the early discoveries at Jabiru and Challis, success has been very elusive, principally because a well constrained model for the structural control on hydrocarbon entrapment has been lacking. To address this problem, the Australian Bureau of Mineral Resources has carried out a major study of the region in which an integrated suite of aeromagnetic, deep crustal seismic, high resolution seismic and water column geochemical data has been acquired and interpreted.

The deep crustal seismic data have revealed the presence of a strong, flat-lying event at approximately 8 sec two-way traveltime. The sequence above this event is relatively unstructured and appears to belong to the thermal subsidence phase, while below 8 sec, significant, rift-related, structuring is present. These data indicate that the principal rifting event occurred in the Permian-Carboniferous, rather than in the Triassic-Jurassic as previously believed. The Vulcan Graben itself is merely a reactivation of this much larger rift.

Image-processed aeromagnetic data have revealed two principal sets of structures that were not previously recognized. (1) A basin-wide set of northwest-trending faults and structural corridors. The northwest-trending features are believed to represent repeatedly reactivated, deep-seated transfer faults formed during the principal extension event in the Permian-Carboniferous. (2) Discrete northerly- and easterly-trending features that affect the Mesozoic and younger structuring.

Many of the hydrocarbon discoveries within the graben lie close to the intersection of north-, northwest-, and northeast-trending fault systems and thus their recognition has major implications for our understanding of the petroleum prospectivity of the region.


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