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Abstract

Regional chronostratigraphic correlations were developed within the Barrow Subbasin, a rift-margin basin associated with the breakup of eastern Gondwanaland.

Three major Mesozoic-Cenozoic transgressive-regressive cycles were identified using excellent seismic control in an area of sparse well control. Each unit within these cycles could be seismically identified. Each cycle comprises a basal-transgressive sand unit, an overlying transgressive marine shale and a final regressive phase of fluvial-deltaic (or carbonate) progradation. Submarine channels and fans, associated with early and late stages of these cycles, have been recognized.

The initial Triassic cycle and part of the second Early to Middle Jurassic cycle, were deposited prior to the main, Middle Callovian breakup period. Considerable uplift, erosion and sediment transport took place following this period, from off the eastern margin of the subbasin.

In the Neocomian upper part of this second cycle, the sediment transport direction changed and extensive coarse clastic deposition infilled the basin from south to north.

The third cycle, from Early to Late Cretaceous to Tertiary time, reflects the final dispersal of eastern Gondwanaland and the opening of the Indian Ocean w ith the development of a thick prograding carbonate wedge. Examples of the seismic sequences w ithin each cycle are shown together with selected seismic facies maps. The methodology of developing these sequences and maps is given.

A variety of stratigraphic traps have now been recognized - these traps rely on sands enclosed in turbidite sequences related to prograding fronts as well as to submarine canyons incised into the eastern shelf. Shaling out and updip pinchout of basal-transgressive units also sets up attractive targets. Some of these traps have now been drilled and their geological results confirmed the seismic stratigraphic interpretation.

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