Publication: PESA's Eastern Australasian Basin Symposium II
Authors: D. Palmowski, K.C. Hill and N. Hoffman
Date Published: December 2004
Number of Pages: 39
Reference Type: Book Section
Abstract:A regional structural analysis of the offshore Otway Basin, largely based on the GA137 2D seismic survey, revealed substantial differences in structural styles between the eastern and western part. 15 km of sediments are underlain by southward-thinning laminated lower continental crust. In the west the depocentre is saucer-shaped and underlain by an Early Cretaceous growth section, but it exhibits only limited Late Cretaceous growth. The eastern basin has little underlying Early Cretaceous sediments and is characterized by pervasive faulting during the Turonian and strong Coniacian to Maastrichtian growth, as well as a change in structural style at the end of the Turonian.
Structural restoration and balancing of key profiles across both areas indicate differences in extension and
sedimentation rates. Turonian to Santonian extension rates were 2-l.5mm/a in the east compared to 0.8-0.7mm/a in the west. Coniacian to Maastrichtian extension rates were 0.5mm/a and 0.35mm/a, respectively. While the break-up unconformity is associated with local inversion and compression in the eastern part of the basin, coeval closely spaced domino-faults are associated with at least 8.5 km of extension along the western section. Extension rates decline exponentially along both sections, although extension was substantially faster throughout the Turonian in the eastern Otway Basin. The observed differences are consistent with an early phase of high extension rates in the west with a rapid decline prior to 89.5 Ma.
New deepwater hydrocarbon plays will rely on restricted marine conditions for good source rock potential since the late Albian in the west and during the Coniacian in the east. Known asphaltite strandings can be explained by an AlbianCenomanian marine source in the western basin with current migration.