Seismic stratigraphic interpretation techniques were used to document the structural and stratigraphic evolution of the southwest Sumatran coast (Bengkulu shelf) between 4°00' and 5°00' S latitude. A Paleogene basinal area located under the Bengkulu shelf which, had previously been interpreted as a marine embayment is re-interpreted in this paper as a continuation of the south Sumatran graben system.

A large, northeast-trending, high basement Mock with an adjacent graben to the east are the prominent structural features. The western side of the graben has been down-dropped by a series of high-angle normal faults. Extension began during the Paleogene and was controlled by the same tectonic mechanisms that influenced the Eocene rift basins in the Sumatran back-arc area. Over 10,000 feet of Paleogene sediment, similar in composition to the Paleogene section of south Sumatra, accumulated in the rapidly-subsiding graben. The mid-Oligocene unconformity truncates the basement high and signifies a possible change in the tectonic configuration of the region. A key aspect of this change was the switch of rapid subsidence from the east side of the basement high to the west side with the formation of the present Sumatran forearc basin. Right-lateral slip along the Sumatran fault began during the middle Miocene with the onset of the collision of the Australian-Indian plate with the Asian plate. Restoring the approximately 100 kilometers of offset along the Sumatran fault causes this graben to line up with the Benekat Gully in the south Sumatra basin.

After the mid-Oligocene unconformity truncated the uppermost graben fill sequences, the first Neogene transgressive cycle began with the deposition of the Early Miocene Baturaja carbonates. The middle Miocene Parigi carbonate serves as a boundary between previously deposited fine-grained siliciclastic sediments and a younger regressive sequence of deltaic deposits. Erosion of the Barisan Mountains to the east, provided the sediment load necessary to build a series of Plio-Pleistocene deltaic/slope deposits which prograded onto the eastern flank of the Sumatran forearc basin.

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