Dep. Sci. and Ind. Res., New Zealand

The basins on Lord Howe Rise are 20-40 km wide; some contain up to 4000 m of sediment. Sediments are also relatively thick on the eastern flank of the Middleton and Lord Howe Basins. The seismic profiles indicate that wave-base erosion was taking place on Lord Howe Rise in the Late Cretaceous, and imply that a shallow marine environment was present prior to seafloor spreading in the Tasman Basin. Shallow marine silts and clays penetrated in DSDP Site 207, and paleogeographical reconstructions, which juxtapose central Lord Howe Rise and the Gippsland Basin, indicate that both marine and non-marine petroleum source rocks may be present. Petroleum traps appear to exist against the boundary faults of the grabens, as internal structures within basins, and in structures interpreted as reefs of Late Cretaceous and Paleocene age. A seal may be provided by pelagic oozes. The eastern flank of Lord Howe Rise was probably the ancient (pre-Maestrichtian) continental margin of the "Australian-Antarctic supercontinent". A wedge of Late Cretaceous or older sediment, up to 2000 m thick, which was deposited across the margin, may also be prospective. The presence of potential source rocks, suitable traps, and indications of higher than normal heat flow, suggest that this deep water area, which is now just within range of oil drilling technology, should be considered prospective for petroleum at least in the long term.