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ABSTRACT: Tectono-Stratigraphic Development of the Vulcan Sub-Basin, Timor Sea Region, North-West Australia.

Jonathon Pattillo, Peter J. Nicholls

The Vulcan Sub-basin underlies the Timor Sea region, offshore northwest Australia, and is currently the focus of much oil industry interest, both national and international. Seventy wells have been drilled in the sub-basin and two fields are currently producing oil. The Vulcan Sub-basin represents a failed Late Jurassic/Early Cretaceous intracratonic rift system, formed in response to the opening of the Argo Abyssal Plain and subsequent development of the Indian Ocean along what is now the northwest Australia continental margin.

The main extensional phase commenced in the late Callovian when pre-rift Jurassic, Triassic, and older sequences underwent regional uplift, block faulting, erosion, and synchronous graben collapse along northeast to southwest structural trends. Continuing instability and the resulting tectonism has intimately controlled the distribution of clastics and potential source rock facies within the graben regions. A second, more intense phase of tectonism in the Kimmeridgian rejuvenated existing structural trends and mobilized deeper Paleozoic salt. Intrabasinal highs were formed within the collapse graben areas and ENE-WSW structural grain was imprinted across the region. The resulting grabens were again rapidly filled with restricted marine sequences during the Tithonian to early Valangini n.

Post-rift Cretaceous sediments are typified by condensed, pelagic facies and local deep-water sands, overlain by a gradual northwest progradation of the passive margin. By the Tertiary a prograding carbonate shelf had been established. Active deformation of the region is currently occurring as a result of a collision of the northwest Australian margin with the southeast Asian plate commencing in the late Miocene to Pliocene.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990