New insights on the gravity-driven deformation of late Albian – early Turonian stacked delta collapse systems in the Ceduna sub-basin, Bight Basin, southern margin of Australia

Abstract

Gravitational collapse of delta systems is thin-skinned deformation due to sedimentary loading that induces spreading or sliding above a very weak detachment layer and typically consists of up-dip listric extensional faults linked to down-dip a compressional system of toe-thrusts. Detailed mapping and analysis of a modern high-quality, 3D depth-migrated seismic data set from the offshore Ceduna sub-basin, southern Australian margin has shown that gravitational collapse in this sub-basin occurred by multiple failure episodes. We show that the late Albian – early Turonian succession consists of two stacked collapse features; a previously unrecognised Albian–early Cenomanian system 1 and the overlying system 2 of the Cenomanian–early Turonian White Pointer delta of the Ceduna sub-basin.Collapse system 1 is located beneath the extensional domain of the Cenomanian – early Turonian White Pointer collapse system 2, which itself consists of three structural sub-domains that are classified based on fault architectures and geometries, and are named after their relative location as proximal, central, and distal sub-domain. Individual sub-domain consists of scoop-shaped listric normal faults linked downwards to thrust faults. The main faults of these sub-domains detach on multiple decollement surfaces of shales, presumably overpressured. This study proposes an investigation into the development of stacked and complex basinwards sequential formation of gravity collapse features in delta systems on passive margins. The research documents the complex structural styles and evolution of the late Albian – early Turonian stacked delta collapse systems and proposes a revised structural and stratigraphic framework of the Ceduna sub-basin. A four-dimensional (4D) tectonostratigraphic models for the evolution of the late Albian – early Turonian succession within the Ceduna sub-basin is also proposed.