PESA WA Nov Evening talk: Controls on shelf-margin architecture and sediment partitioning in the Hammerhead shelf-margin

John Shepherd, Centre for Energy Geoscience, University of Western Australia

Understanding the stratigraphic architecture of shelf-margin clinoforms is key to determining both 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., quantitative 3D seismic stratigraphy). The Hammerhead shelf-margin prograded during the Late Cretaceous within the Great Australian Bight Basin, along the southern margin of Australia, following break-up with Antarctica. This understudied interval offers a unique opportunity to investigate the controls on the evolution of a shelf margin during the early stages of the post-rift phase.

All available data (i.e., 2D seismic data, 3D seismic data and well data) from the Ceduna Sub-basin has been integrated to investigate the controls on shelf-margin architecture and factors affecting sediment delivery to deep-water. Quantitative analyses involved the measurement of clinoform geometries (e.g., slope length, slope height, shelf-edge progradation and aggradation etc.), which were used to calculate several parameters (e.g., shelf-edge trajectory angle, progradation rate, aggradation rate). The extent of various deep-water systems (e.g. long run-out turbidites) was also measured. It is concluded that lateral variations in sediment supply were the main driver of shelf-margin variability at 3rd order scale.

The Hammerhead shelf-margin provides unique insights in the early stages of drifting between Australia and Antarctica, which has implications for better understanding of early post break-up dynamics. Quantitative results from the Hammerhead shelf-margin can also be used to improve predictability of offshore sediment deposits in other basins globally.