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Michael R. Power1, Daniel B. Palmowski1, Kevin C. Hill1, Martin Norvick1, Nick Hoffman1
(1) Latrobe University, Melbourne, Australia

Abstract: Tectonic evolution of the Gippsland and Otway Basins (Bass Strait, Australia); generation of new play fairways

The Jurassic to Early Cretaceous rift-geometries of the Gippsland and Otway basins are the key to understanding the later basin evolution, leading to new play concepts for petroleum exploration. 2-D balancing, decompaction and restoration of regional sections reveal the contrast in structural styles between the two basins. Restoration suggests that initial extension in the Gippsland Basin occurred above a south-dipping, low-angle, crustal scale regional detachment. Approximately 75% extension occurred in the Late Jurassic/Early Cretaceous, which led to approximately 10 km syn-rift subsidence and probably generating metamorphic core complexes and multiple intrusions. In the Late Cretaceous, with the opening of the Tasman Sea, the extension vector changed to a south easterly direction. Associated minor N-S compression obliquely reactivated the early structures generating hydrocarbon traps. Tertiary regional post-rift subsidence towards the east led to burial and hydrocarbon generation.

In the Otway Basin, major Jurassic to Cretaceous extension occurred along a north-dipping moho-detachment. The extension was initiated as slow initial rifting, but changed to fast seafloor spreading in the Eocene. Prior to the Eocene, sediments were deposited in an oblique rift environment with Antarctica as a buttress to the south. Within the main rift axis, approximately 150 km offshore, crustal thinning associated with the removal of the Antarctic buttress reached its maximum, leaving only 2-3 km of pre-Mesozoic crust above the moho-detachment. Initial oceanic crust formation occurred further offshore, leaving an inferred mantle core complex as an outer margin high. Main hydrocarbon plays developed during the period of syn-rift sedimentation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana