The Great Australian Bight: A Break-Up Story Told With Deep Seismic

Abstract

Evaluation of high quality deep, regional seismic reflection data provides the opportunity to not only investigate the petroleum systems aspects of the Great Australian Bight (GAB) margin but also to link them to underlying crustal architecture and deformation mechanisms. Here, using ION's BightSPANTM, we present observations for the crustal structure, rift elements, and structural mechanisms responsible for the development of this margin of the Southern Rift System. Lithospheric break-up and seafloor spreading between the GAB and its conjugate in the Australian Antarctic Territory occurred ca. 83Ma following a protracted phase of continental stretching and break-up that initiated in the mid – late Jurassic. The evolution of this rift system was magma-poor and likely followed a history of stretching, thinning, and exhumation phases, similar to those described for the Iberia-Newfoundland rift system. Evidence for the stretching phase is confined to half graben structures bounded by high-angle normal faults beneath the proximal Ceduna delta. The thinning phase is characterised by the sag basin overlying hyper-extended crust (< 10km thick) that is likely to have been thinned via overprinted generations of detachment faults accompanied by crustal embrittlement and mantle serpentinisation. Exhumed mantle (up to 60 km wide) is present at the COT, unroofed by multiple generations of detachment faults, evidence for which lies in multiple continental allochthons oceanward of the unroofed mantle. We demonstrate the impact the extensional architecture has on the overlying Ceduna delta system and its gravitational collapse during continental break-up and discuss the implications for the petroleum potential of the basin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015