Investigating relationships between shoreline process regime, shelf-margin architecture, and deep-water sand delivery: Insights from the early post-rift Hammerhead shelf margin (Bight Basin, southern Australia)

Abstract

Shelf margins represent a crucial area along source-to-sink systems where sediments are partitioned from the shelf to slope and basin-floor areas. Reconstructing the evolution of these depositional systems is key for interpreting the interplay between past accommodation and sediment supply, and sediment dispersal mechanisms into deep water. In the Bight Basin, on the southern margin of Australia, the Hammerhead shelf margin prograded during the Late Cretaceous following break-up between Australia and Antarctica. This understudied interval offers important insights into source-to-sink processes in a post-rift, greenhouse, high sediment supply setting. A dynamic stratigraphic approach using high-resolution 3D seismic data across the Hammerhead shelf margin has been used to quantitatively characterise 28 clinothems developed over ∼ 1.9 Myrs each with an average duration of ∼ 67,000 years. By applying a shallow-marine process-based classification to shorelines, alongside quantitative analysis of the architecture of their coeval deep-water deposits downdip, statistical relationships and clear links between shallow-marine processes, stratigraphic architecture, and deep-water sand delivery are revealed. A statistically significant relationship between fluvial dominated shorelines, high slope gradients, and mass-transport deposit development is demonstrated, as is a requirement for fluvial influence at the shoreline for the initiation of long run-out turbidite systems. These long run-out turbidite systems are interpreted to have been formed by repeated density flows which lead to greater sediment transfer efficiency and increased sediment supply. This research has direct application to improve prediction of reservoir locations within the Bight Basin for resource exploration and/or carbon sequestration and may also be applied to improve deep-water sediment predictability in other basins worldwide developed in similar tectonic and climatic settings.