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Abstract

The Ross Sea contains three major depocenters, each underlain by a sediment-filled rift graben and an overlying glacial sedimentary sequence. The sedimentary sections are up to 14 km thick with up to 8 km in the rift grabens and up to 6 km in the presumed-glacial sequences. The rift grabens were downfaulted and filled probably during the late Mesozoic to early Cenozoic continental breakup of Gondwana; their early history may be analogous to coeval rift basins of southeast Australia, Tasmania, and New Zealand. The rift-graben sediments are unconformably overlain by glacial-marine sequences deposited since middle Eocene(?) to early Oligocene time. Renewed down-faulting has occurred along the west and east margins of the Ross Sea probably since Eocene time.

The hydrocarbon potential of the Ross Sea is poorly known because only post-Eocene glacial rocks have been sampled offshore. The age and type of rocks filling the rift grabens, below the glacial sequence, is unknown. Source beds do not occur in the glacial sequence, but may exist in the rift grabens. Structural and stratigraphic traps are likely near basement structures and unconformities, which are common, and near large sedimentary structures found only in the Victoria Land Basin and along margins of the Eastern Basin. Reservoir rocks are unknown but sands could occur throughout the glacial and rift sequences. Lopatin-Waples models indicate that hydrocarbons could be generated presently at depths of 2.5 to 4.0 km, if source beds exist. Migration is likely in dipping strata along rift-graben flanks and in late-rift fault zones of the Terror Rift.

Hydrocarbon seeps and accumulations are unknown in the Ross Sea. The preglacial strata that are deeply buried within the early- rift grabens have the best hydrocarbon potential; however, a definitive assessment awaits sampling of these deep,rift deposits.

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