Controls on shelf-margin architecture and sediment partitioning on the Hammerhead shelf margin (Bight Basin, southern Australia): Implications for Gondwanan break-up dynamics between Australia and Antarctica

Understanding the stratigraphic architecture of shelf-margin clinoforms is key to determining how sediments are transferred to deep-water settings and how the interplay of tectonics (subsidence/uplift), eustasy and variations in sediment supply rates and calibre, impacts deep-water sand delivery. Here, clinothems are used to establish quantitative relationships between shelf-margin architecture and shelf-to-basin sediment transfer. In the Bight Basin on the southern margin of Australia, the Hammerhead shelf margin prograded during the Late Cretaceous, following continental break-up from Antarctica. This understudied interval offers an opportunity to investigate controls on shelf-margin architecture during the early post-rift phase. Interpretation of integrated data (2D and 3D seismic reflection, and well data) has been completed using full-volume interpretation software (PaleoScan & COPY;), allowing for the first full high-resolution 3D interpretation of this interval. Quantitative analyses of clinoform geometry are used to calculate several parameters (e.g., shelf-edge trajectory angle, progradation rate, aggradation rate) within sixteen 3rd order seismic sequences mapped across the basin. This study increases our understanding of source-to-sink systems in extensional settings via this quantification of shelf-margin clinoforms. Overall, four discrete phases of Hammerhead shelf margin evolution are identified with lateral variations in sediment supply proposed to be the main driver of shelf-margin variability. Through time, the evolution of the accommodation and sediment supply rates (i.e., A/S ratio) suggests that after a major flooding event, the initial high sediment supply rates become progressively lower as shelf accommodation creation increases due to thermal subsidence, leading to an overall progradational to aggradational stacking pattern, with final backstepping of the shelf margin. Quantitative results show that a variety of factors influenced the delivery of sediments to deep-water areas (e.g., clinoform slope gradient, slope relief, faulting and lateral sediment transport) and that shelf-edge trajectory angle cannot be used solely to predict sediment partitioning. This research improves understanding of sediment partitioning and the development of shelf margins in post-rift tectonic settings and by investigating the Hammerhead shelf margin, the timing of tectonic events and dynamics of Gondwanan break-up have been refined.