The role of shale deformation and growth faulting in the Late Cretaceous evolution of the Bight Basin, offshore southern Australia

Abstract

Abstract The Jurassic-Cretaceous Bight Basin of offshore southern Australia is a large, under-explored basin with little stratigraphic control. Sequence stratigraphic and structural interpretation of regional-scale 2-D seismic data has revealed the presence of two large progradational delta systems of mid-Late Cretaceous age, which are vastly different in terms of geometry and stratal architecture. The Cenomanian White Pointer Delta is characterized by shale deformation and growth faulting. Growth fault-controlled depocentres occupy a wide band across the Ceduna Subbasin of the Bight Basin that records the progradation of the delta across the palaeo-shelf during the Cenomanian. The growth faults are generally listric and basinward dipping (regional). Counter-regional faults are uncommon. The updip extensional features are accompanied downdip by a zone of diapirs that coincides with an outer basin high and, in deeper water at the toe of slope, a region of contractional deformation and toe-thrusts. In comparison, the younger (Late Santonian-Maastrichtian) Hammerhead Delta exhibits strongly progradational stratal geometries with little evidence of shale tectonics except in the SW part of the Ceduna Sub-basin. There, sustained progradation under a high sediment supply regime caused gravitational instability and the formation of listric growth faults at the palaeo-shelf margin with associated down-dip contractional deformation.