Structural evolution of a gravitationally detached normal fault array: analysis of 3D seismic data from the Ceduna Sub‐Basin, Great Australian Bight

Abstract

The growth, interaction and controls on normal fault systems developed within stacked delta systems at extensional delta-top settings have not been extensively examined. We aim to analyse the kinematic, spatial and temporal growth of a Cretaceous aged, thin-skinned, listric fault system in order to further the understanding of how gravity-driven fault segments and fault systems develop and interact at an extensional delta-top setting. Furthermore, we aim to explore the influence of a pre-existing structural framework on the development of gravity-driven normal faults through the examination of two overlapping, spatially and temporally distinct delta systems. To do this, we use three-dimensional (3D) seismic reflection data from the central Ceduna Sub-basin, offshore southern Australia. The seismic reflection data images a Cenomanian-Santonian fault system, and a post- Santonian fault system, which are dip-linked through an intervening Turonian-early Campanian section. Both of these fault systems contain four hard-linked strike assemblages oriented NW–SE (127–307), each composed of 13 major fault segments. The Cenomanian-Santonian fault system detaches at the base of a shale interval of late Albian age, and is characterised by kilometre-scale growth faults in the Cenomanian-Sanontian interval. The post-Santonian fault system nucleated in vertical isolation from the Cenomanian-Santonian fault system. This is evident through displacement minima observed at Turonian-early Campanian levels, which is indicative of vertical segmentation and eventual hard dip-linkage. Our analysis constrains fault growth into four major evolutionary stages: (1) early Cenomanian nucleation and growth of fault segments, resulting from gravitational instability, and with faults detaching on the lower Albian interval; (2) Santonian cessation of growth for the majority of faults; (3) erosional truncation of fault upper tips coincident with the continental breakup of Australia and Antarctica (ca. 83 Ma); (4) Campanian-Maastrichtian reactivation of the underlying Cenomanian-Santonian fault system, inducing the nucleation, growth and consequential dip-linkage of the post-Santonian fault system with the underlying fault system. Our results highlight the along-strike linkage of fault segments and the interaction through dip-linkage and fault reactivation, between two overlapping, spatially and temporally independent delta systems of Cenomanian and late Santonian-Maastrichtian age in the frontier Ceduna Sub-Basin. This study has implications regarding the growth of normal fault assemblages, through vertical and lateral segment linkage, for other stacked delta systems (such as the Gulf of Mexico) where upper delta systems develop over a pre-existing structural framework.