2025 PESA WEBINAR SERIES: Cretaceous – Paleogene Evolution of Bottom Currents in the Northern Carnarvon Basin, Northwest Shelf of Australia

Bottom current deposits are common features along continental margins and are typically associated with slopes, either at the continental rise or adjacent to shallow shelves. In this study, we provide a detailed characterisation of Aptian to Rupelian deposits that developed in the centre of the Exmouth Plateau of the Northern Carnarvon Basin, Northwest Shelf of Australia, on c. 500 km wide ramp-type margin, characterised by gentle slope breaks between the coastline and the deep basin. Sediment mounds and moats initially developed during the Aptian to Turonian in clastic sediments in the southwest of the study area, whereas reduced sediment accumulation characterised the north-eastern sector. During the Turonian to Lutetian, a transition to carbonate sedimentation occurred. Interestingly, these features continued to develop, with the mounds gradually establishing themselves through aggradational growth, while the moats were infilled by sediments exhibiting complex structures, including small-scale mounds and incisions with a wide variety of different morphologies. From the Danian to Rupelian, there was a notable decrease in moat infilling and mound growth, leading to significant progradation of sediment toward the northeast. This final stage of sedimentation was characterised by stacked deep incisions, ridges, and conical depressions. Initial stages of deposition correspond to a period of time when a wide and open ocean was present to the north of Australia, but only narrow seaways and intracontinental rifts, associated with the breakup of Gondwana, were present to the west and south. The accelerated growth of mounds occurred during a period of accelerated separation of Greater Indian and Australia while cessation of bottom current activity corresponds to a period of rapid separation of Australia from Antarctica. The recognition and investigation of bottom current features provide new insights into the way in which oceanic circulation patterns may have evolved as the breakup of Gondwana progressed and can help our understanding of the processes that operate during the early stages of passive margin development and the formation of oceanic basins. In addition, more detailed knowledge of the sedimentary deposits that comprise the post-rift sequence in the Northen Carnarvon Basin can help improve understanding of velocity variations and drilling conditions in these sequences.