Analogue Modelling of the Effect of Lobe Switching on the Gravity-Driven Deformation in Ceduna Deltas System (Bight Basin, Southern Australian Margin)

Abstract

The Bight basin is one of the Late Jurassic – Early Cretaceous extensional basins that formed the Southern Australian passive margin as a result of the break–up of Gondwana and the separation of Australia from Antarctica. During Late Cretaceous time, as a consequence of the uplift and the erosion of the Eastern margin of the Australian continent, the Ceduna sub-basin was the depocentre for the Ceduna delta system with up to 15 km of sediment supplied from the Australian landmass to the north. The Ceduna sub-basin infill is characterized by a Late Cretaceous stacked delta complex with two major overlapping lobes. The oldest Cenomanian delta (White Pointer super-sequence) was deposited in the eastern part of the sub-basin, and the younger Santonian - Maastrichtian lobe deposition (Hammerhead super-sequence) formed in the western part of the sub-basin as a result of lobe switching. Differential loading induced by the rapid deposition of the Late Cretaceous deltas in the Ceduna sub-basin resulted in the generation of overpressure in the underlying shale, and triggered development of a thin-skinned gravity-driven collapse of the passive margin shelf with an extensional growth fault system linked to a down-dip deepwater contractional fold and thrust belt. In order to constrain the kinematic and the evolution of this gravity driven system scaled 3D analogue models were constructed to simulate the gravity sliding of sand lobes above ductile silicone detachments. This paper presents the results of these experiments that demonstrate how syn-kinematic lobe switching and oblique delta progradation could generate the fault architectures and geometries of the shelf collapse listric fault systems in the Ceduna sub-basin. The results of the models are compared to extensional fault architectures determined from seismic interpretation of data from the Ceduna sub-basin.

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