ABSTRACT: Seismic Stratigraphy of Cape Sorell Basin, Tasmania

Timothy L. Bellow

Because large new exploration areas have become scarce, the Cape Sorell basin has become an increasingly attractive frontier area. Cape Sorell basin, located along the western passive continental margin of Tasmania, formed as a result of the breakup of eastern Gondwanaland 95±5 Ma. An extensional fault system trending west-northwest with dip-slip movement down to the south-southwest forms the northern boundary and a second fault system trending north-northwest with oblique slap down to the south-southwest creates the basin. Second-order extensional faults within the basin have created wrench-type flower structures, which are potential migration pathways for hydrocarbons.

Nine distinct depositional sequences identified within the Cape Sorell basin record the evolution of this passive continental margin. Late Cretaceous-early Paleocene sequences were deposited as the rifting ceased and clastic progradation over the rift terrain began. Relative lowering of sea level occurred during the Paleocene, resulting in extensive channeling of the Late Cretaceous-early Paleocene sequences. A subsequent rise in relative sea level resulted in canyon-fill deposition during the early Paleocene to early Eocene. During the Eocene, sedimentation sufficiently increased to produce a downlapping sediment progradation characterized by deltaic depositional environments. Although interrupted several times by changes in relative sea level and shifting sediment sources, deltaic d position continued until the late Oligocene. As the rate of clastic sedimentation slowed, carbonate shelf deposition began and has typified the basin since late the Oligocene.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990