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Seismic Stratigraphic Evaluation Of A Neocomian Submarine Fan System , Browse Basin, Northwest Shelf, Australia.

Miller, Lyndon R

Honours Degree, 1989

University of Adelaide

Abstract

The Browse Basin is considered a typical Atlantic type passive margin. Successive phases of basin development progress from an intracratonic sag (Triassic), through extra-arch basin (Jurassic), rim basin (Upper Jurassic-Turonian) and to an open margin basin (Upper Cretaceous to present). Sedimentation was relatively continuous from Mesozoic time onwards, except for five unconformities that have been recognized in the Mesozoic section. These unconformities are associated with continental break-up and sea floor spreading. Deposition of deltaic sequences, basinal claystones and submarine fans represent the dominant mode of deposition from Scythian to Turonian time. Following the Turonian unconformity, open margin carbonate deposition was widespread over the North West Shelf. In general, the basin has been tectonically stable since the Lower Cretaceous.

A submarine fan system of Valanginian age occurs in the south of the western half of Block WA-212-P in the Browse Basin. Seismic mapping and interpretation has allowed the recognition of five seismic facies that occur in the upper, lower and outer segments of a submarine fan.

The five seismic facies are the upper fan channel facies, the upper fan interchannel facies, the lower fan channel facies, the lower fan sheet facies, and the outer fan facies. The reflections of the upper fan channel facies are discontinuous, disrupted, concave up, low amplitude and high frequency. The interchannel facies has reflections that are concave up, continuous, low frequency and moderate to high amplitude. The lower fan channel facies are recognised by convex up, discontinuous, high frequency and low amplitude reflections. The lower fan sheet facies is noted by mounded configurations with continuous, moderate to high amplitude, moderate frequency reflections. The outer fan

facies reflections are flat, often shingled reflections with moderate discontinuity, moderate to high amplitude and low to moderate frequency.

Since no wells penetrate the submarine fan, the interpretation is based on these reflection configurations which are considered typical of submarine fan segments. The interpreted ancient submarine fan occurs on the basin floor adjacent to the lower palaeoslope and in a logical geometry and sequence consistent with known submarine fans, such as the Eocene Frigg Fan situated in the subsurface of the North Sea, and the Lower Cretaceous Barrow Group turbidites in the Carnarvon Basin.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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