--> ABSTRACT: The Cretaceous Bathurst Island Group - Its Exploration Promise, by Virginia L. Passmore, Barry G. West; #91020 (1995).

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The Cretaceous Bathurst Island Group - Its Exploration Promise

Virginia L. Passmore, Barry G. West

The Bathurst Island Group is a hydrocarbon system in the Bonaparte Basin, offshore northwestern Australia, providing Cretaceous age reservoir, source and seal. Traditionally, the Cretaceous has been regarded primarily as an effective regional seal to Jurassic and Triassic oil and gas discoveries in the basin.

The 2000 km thick post-breakup sediments of the Bathurst Island Group represent a series of highstand parasequences laid down under prograding shelf and slope conditions. Tectonic movements that produced basin inversions and eustatic sea level changes resulted in the deposition of thick wedges of dominantly claystone and siltstone sediments containing carbonate zones in the lower part. A blanket of coarser marine siliciclastic sequences reflecting eustatic falls in sea level during the Campanian and Maastrichtian covered these wedges. Maastrichtian sands deposited as submarine fans in the grabens form excellent Cretaceous reservoirs. Gas shows in fractures within Albian limestones demonstrate fracture porosity exists in some of the Cretaceous carbonates.

Hydrocarbon generation in the lower Bathurst Island Group began in the mid Cretaceous, subsequent to most of the major structuring in the basin. These source rocks have the potential to charge large Cretaceous traps. Miocene reactivation of faults cutting the Bathurst Island Group sediments provided potential migration pathways for hydrocarbons into Maastrichtian reservoirs.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995