A balanced 2D structural model of the Hammerhead Delta–Deepwater Fold-Thrust Belt, Bight Basin, Australia

Abstract

The Hammerhead Delta–Deepwater Fold-Thrust Belt is located in the Ceduna Sub-Basin of the Bight Basin, offshore southern Australia. It is synonymous with the Hammerhead Supersequence and consists of three, Campanian to Maastrichtian, deltaic sediment packages. The Hammerhead Delta–Deepwater Fold-Thrust Belt is a short-lived gravity-gliding system that exhibits a distinctive spoon-shape in cross-section. The system detaches on a master horizon at the top of the Tiger Formation. Finite Element Method based two-dimensional restorations show that the Hammerhead Delta–Deepwater Fold-Thrust Belt is a near-balanced system with near equal amounts of up-dip extension and down-dip compression. Overall, there is only 2.4% additional extension in the Hammerhead Delta–Deepwater Fold-Thrust Belt. This near-balanced system is unusual in comparison with other passive margin Delta–Deepwater fold-thrust belts, which generally demonstrate large amounts of extension compared with shortening, due to the regional-scale progradational nature of the systems. The results suggest that sediment input to the Hammerhead Delta–Deepwater Fold-Thrust Belt was not sufficient to result in the regional-scale progradation of fault activity and that the sediment supply shutdown before the system could develop in an extensive passive margin Delta–Deepwater fold-thrust belt, hence demonstrating that it is sediment supply that drives ongoing gravitational deformation in Delta–Deepwater fold-thrust belts and not slope gradient.