Review of Stratigraphy, Structure, and Hydrocarbon Potential of Bass Basin, Australia

Abstract

The intracratonic Bass basin is the central basin of three that underlie Bass Strait in southeastern Australia. The basin was formed by extensional tectonics during the Late Jurassic to Early Cretaceous. It contains up to 7 km (23,000 ft) of nonmarine sediments of (?)Late Jurassic to late Eocene age and up to 3.5 km (11,500 ft) of upper Eocene to Holocene marine sediments. Volcanics occur in places. The sedimentary history of the basin is interpreted to have been dominated initially by Cretaceous flood-plain, alluvial-fan, and lacustrine deposition, then Late Cretaceous and early Tertiary flood-plain deposition, and finally, Cenozoic shallow marine deposition. Seismic reflection studies show that significant structural and stratigraphic prospects for petroleum exploration occur at Paleocene, Cretaceous, and (?)Jurassic levels. Source rock studies combined with depositional models for the Upper Cretaceous to Paleocene nonmarine fill suggest that suitable source and reservoir rocks occur at these levels. Present-day maturation levels of organic matter in sediments of the basin suggest that mature levels for petroleum generation occur at 3-5 km (10,000-16,000 ft) depth, which generally corresponds to Upper Cretaceous to Paleocene sediments. An analysis of the maturation history of the basin suggests that the lower levels of the Upper Cretaceous sediments had peak petroleum generation potential (Ro = 0.7%) by about 40 Ma, whereas the upper levels of the Paleocene sediments have attained this level of maturity only in the last 5 m.y. Furthermore, th relative lack of exploration success at shallower, immature levels of the basin argues against well-developed vertical migration paths, and suggests that petroleum may have been trapped mainly at mature levels. Considerable unexplored petroleum potential exists in the Bass basin. The best potential for petroleum exploration appears to be at mature levels within the Upper Cretaceous to Paleocene Eastern View Coal Measures.