Abstract

The U.S. Geological Survey research vessel S.P. Lee is investigating the area of continental breakup (90 m.y.B.P.) during which the Great Australian Bight separated from Wilkes Land, and Tasmania detached itself from the Ross Sea. Transform faults that formed along the Southeast Indian ridge are not perpendicular to the coast of Antarctica, but lie at an acute angle to it. This orientation indicates that the breakup followed a preexisting line of continental weakness. As new oceanic crust began to form after the breakup, the rift divided into a stairstep pattern of spreading axes and transform faults in harmony with the direction of separation. In places, the stairstep rifting created local basins of the continental-borderland type. Sediment flooded into the rifts from the two separated continents and lapped across stretched continental crust at the margins and onto newly formed and hot oceanic crust farther out. An optimistic scenario for petroleum formation in this area might be: (1) rapid sedimentation entrained organic petroleum precursors before they could decay at the sea floor, and (2) heat from the young oceanic crust below matured them. The favorable characteristics of rifted margins—silled grabens to reduce sea-floor oxidation, little reservoir-plugging volcanic ash, and rollover anticlines against curved growth faults—all make the area promising for exploration. Although petroleum is not known from the margin of Antarctica, analogous oil fields on the continental shelf near Tasmania suggest that the area has a resource potential.

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