Introduction

The search for hydrocarbons continues to be a major emphasis of the modern world. Whilst vast reserves are held within the OPEC nations, the strategic value of resources outside of the Middle East continues to bring exploration interests to higher risk and more marginal areas. The sector of the Pacific south of 45°S is no exception, although most parts of it have some of the severest climates which will test the ingenuity of any explorers or developers.

South of 45°S in the Pacific, there is at present no production of hydrocarbons, although the continental margins of the area have several large sedimentary basins. The sedimentary basins on the Antarctic shelf have now undergone quite detailed scientific scrutiny (Behrendt, 1983a,b; Davey, 1985; St. John, 1986; Hinz and Kristoffersen, 1987) and those around the New Zealand coast major oil exploration programmes (Anderton et al., 1982; Katz and Herzer, 1986). The traces and subcommercial finds of hydrocarbons have encouraged speculation about commercial prospects. Adding to this speculation is the presence of two productive basins with significant reserves of oil and gas immediately to the north of the region, namely the Gippsland Basin off the southeastern coast of Victoria, Australia, and the Taranaki Basin on the western margin of New Zealand (Fig. 6.1).

While the Taranaki and Gippsland basins fall outside the region, they were in much closer proximity to the basins of the Ross Sea and Campbell Plateau prior to the breakup of the supercontinent Gondwanaland (Fig. 6.2) (Davey and Houtz, 1977; Grindley and Davey, 1982; Katz, 1982). Their similar origins and early history during the breakup phase about 100 Ma B.P. offer a valuable comparison when evaluating the less explored basins of the region for the major factors required to generate and accumulate commercial hydrocarbons.

In addition to Gippsland and Taranaki, several basins of the region are worthy of exploration (Fig. 6.1). The Bellingshausen continental margin of Antarctica from the Amundsen Sea to the Antarctic Peninsula is distinctly different from that of the rest of Antarctica as it is the only margin of the continent which was not formed by the breakup of Gondwanaland. It has faced a deep ocean basin since the Palaeozoic or earlier (Craddock and Hollister, 1976; Davey, 1985). The shelf varies in width throughout this region reaching a maximum of 500 km in the Bellinghausen Sea where 2-3 km of Mesozoic and Tertiary sediment has built up (Davey, 1985; St. John, 1986). Further east and north, the Pacific margin along the South American coast consists of an active subduction zone backed by the Pata-gonian and Andean Cordillera which contain no sedimentary basins with potential for hydrocarbon generation. The petroleum producing basins of the

Argentina area are to the east of these cordillera and do not lie within the Pacific margin (Cameron, 1981).

Fig. 6.1. Present-day distribution of the sedimentary basins of the southwest Pacific. A = Gippsland Basin, B = Taranaki Basin, C = Solander and Waiau Basins, D = Great South Basin, E = Canterbury Basin, F = Campbell Basin, G = Pukaki Basin, H = Eastern Ross Basin, I = Central Ross Sea Basin, J = Victoria Land Basin.

Fig. 6.1. Present-day distribution of the sedimentary basins of the southwest Pacific. A = Gippsland Basin, B = Taranaki Basin, C = Solander and Waiau Basins, D = Great South Basin, E = Canterbury Basin, F = Campbell Basin, G = Pukaki Basin, H = Eastern Ross Basin, I = Central Ross Sea Basin, J = Victoria Land Basin.

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