Building the Bight: quantitative insights on shelf-to-basin sediment transfer mechanisms from the Hammerhead Shelf Margin

Shelf margins represent a crucial area along source-to-sink systems where sediments are partitioned from the shelf to slope and basin-floor areas. Quantitatively reconstructing the evolution of these depositional systems is key for interpreting the interplay between past accommodation, sediment supply, and sediment dispersal mechanisms into deep-water areas. The Late Cretaceous Hammerhead shelf margin in the Bight Basin (southern Australia) prograded following continental break-up with Antarctica and represents an understudied post-rift system developed under greenhouse conditions and high sediment supply. Integration of multiple high-resolution 3D seismic datasets (Springboard, Ceduna, and Nerites) enables analysis of shelf-margin architecture and the seismic geomorphology of both shallow- and deep-water deposits at unprecedented scale. A dynamic stratigraphic approach is used to quantitatively characterize the architecture of 28 paleo-shelf margins developed over approximately 1.9 Myr, each with a duration of approximately 67 kyr. By applying a shallow-marine process-based classification to paleoshorelines alongside quantitative analysis of the architecture of their coeval deep-water deposits, statistical relationships and clear links between shallow-marine processes, stratigraphic architecture, and deep-water sand delivery are revealed. Fluvial-dominated shorelines are associated with steeper slope gradients than wave-dominated shorelines (4.48° and 3.50° respectively), increased mass transport deposit frequency, and turbidite systems with up to 98 km runout distance. Forward stratigraphic modelling using Badlands is employed to further interrogate these relationships. Results from modelling support conclusions based on the seismic data, demonstrating that shelf-margin lateral variability is significantly influenced by shoreline processes. This research has direct application to improving prediction of reservoir locations within the Bight Basin for resource exploration and/or carbon sequestration and may also be applied to improving deep-water sediment and shelf-margin architecture predictability in other basins worldwide that developed in similar tectonic and climatic settings.