Controls on shelf-margin architecture and sediment partitioning in the Hammerhead shelf margin (Bight Basin, southern Australia): Quantitative 3D seismic stratigraphy (QSS)

Understanding the stratigraphic architecture of shelf-margin clinoforms is key to determining how sediments are transported to deep-water settings and how the interplay of tectonics (subsidence/uplift) and eustasy, with variation in sediment supply, impacts deep-water sand delivery. Within this study clinothems are used to establish quantitative and statistical relationships between the shelf-margin architecture, paleoshoreline processes, and deep-water system types (i.e., using quantitative 3D seismic stratigraphy). In the Bight Basin on the southern margin of Australia, the Hammerhead shelf margin prograded during the Late Cretaceous following continental rifting from Antarctica. This understudied interval offers an opportunity to investigate controls on shelf-margin evolution during the early post-rift phase. All available data (2D seismic data, 3D seismic data and well data) from the Ceduna Sub-basin have been integrated to investigate the controls on shelf-margin architecture and factors affecting sediment delivery to deep water. Quantitative analyses of clinoform geometry are used to calculate several parameters at 3rd order and 4th-5th order scales. Sixteen 3rd order seismic sequences and 28 4th-5th order clinothems with an average duration of ~ 67 kyrs are recognised. Four phases of Hammerhead shelf-margin evolution are identified with lateral variations in sediment supply proposed to be the main driver of shelf-margin variability. We propose that after a major flooding event, the A/S ratio increased throughout the evolution of the Hammerhead with an increase in accommodation and a rapid decline in sediment supply in the Maastrichtian causing backstepping of the shelf edge. At higher resolution, results show shelfmargin architecture, shoreline processes, and deep-water system types are intimately linked. For example, wavedominated shorelines are related to no (or very little) deep-water deposition whereas fluvial-dominated shorelines are mostly linked with MTD's and/or long runout turbidite systems. Results of this research may be applied to other basins developed in similar tectonic and climatic settings.