Post-rift marine transgression of the southern Browse Basin margin: controls on hydrocarbon reservoir development and exploration potential

Abstract

The formation of the Precipice Fold Belt (560 Ma) marked the last significant modification of the basement drainage pattern and catchment area supplying sediment to the southern Browse Basin. Seismic mapping of the Proterozoic basement and the results of exploration drilling confirm the extension of both the geological formations and structural features exposed on the Proterozoic Kimberley Plateau into the offshore study area.

As with the present-day shelf, sedimentation during the Late Jurassic to Early Cretaceous marine transgression directly onlapped the basement in the study area and showed the influence of basement topography on stratigraphy. A marked increase in net-to-gross and reservoir sand thickness is observed moving northeast from the Leveque to the Yampi shelves.

This broad change in stratigraphy can be related to specific basement-controlled morphologies. A >250 m-high escarpment formed by the Proterozoic Kimberley Plateau basement terrane bounds the Yampi Shelf to the southeast of the Palaeozoic zero-edge line. This escarpment fixed the location of shelf sediment input points forming a barrier to marine transgression, which ensured that the Yampi Shelf was relatively immune from sediment starvation during highstand systems tracts. In contrast, the broad low angle Leveque Shelf experienced large lateral shifts in shelf sediment input points during eustatic changes in sea level with sedimentation dominated by transgressive systems tracts.

In addition to shelf morphology, the larger basement-controlled drainage area (80,000 km2) supplying sediment to the Yampi Shelf tended to increase sedimentation rates, leading to shelf delta progradation during highstand systems tracts. The quality and thickness of mass flow deposits seen in the Caswell Sub-basin and along the Prudhoe Terrace are the direct result of the concentration of high net-to-gross sand close to the offlap break on the Yampi Shelf.

Given the extreme long term stability of the southern Browse Basin margin, recognition of the influence of basement structure on shelf sedimentation has refined the geological model for the post-rift marine transgression. This model could be used to reduce the risk on reservoir and seal distributions in the Late Jurassic to Early Cretaceous study interval. In a broader context, observations on basement-controlled reservoir and seal distribution from the Browse Basin might be usefully applied to other basins where sediment is supplied from long-lived Proterozoic margins.