Pliocene – Pleistocene history of the Gippsland Basin outer shelf and canyon heads, southeast Australia

Abstract

The Gippsland Basin on Australia's southeastern continental margin is host to a number of large shelf-breaching canyons that form part of the Bass Canyon system. Analysis of high-resolution bathymetry data and biostratigraphically controlled shallow seismic data across the shelf and upper slope and associated canyon heads shows that widespread erosion at the canyon heads began in the earliest Pleistocene (CN13a, 1.95 – 1.72 Ma). Deep V-shaped channels were eroded into pre-existing U-shaped channels. Erosion was not necessarily a response to Pleistocene lowstands but followed a period where (carbonate) sedimentation rates on the shelf were greatly elevated. Both carbonate production and erosion were likely to be amplified, if not caused, by intensification of the Bass Cascade density current during Late Pliocene eustatic highstands. During the Middle Pleistocene (CN14a, 0.95 – 0.47 Ma) outer shelf canyon-head channels were rapidly infilled. Canyon-head channels migrated laterally across the shelf, predominantly in a northeast direction, influenced by the prevailing northeast moving Bass Cascade. Upper slope canyon heads have remained largely non-depositional exposing Pliocene strata at the seafloor. A minor episode of deformation occurred during the Middle Pliocene (CN12, 3.70 – 1.95 Ma) that produced low-amplitude open folds in Upper Pliocene and older sediments, beneath the northern inner shelf. Beneath the central inner shelf and middle shelf, similar open folds developed during the Late Pliocene to at least the Middle Pleistocene (CN13 – CN14a, 1.95 – 0.47 Ma).

Key words:

• Bass Cascade
• density currents
• cool-water carbonates
• Gippsland Basin
• sedimentation rate
• seismic stratigraphy
• submarine canyons
• swath-mapping

Acknowledgements

We wish to thank Geoscience Australia for providing the bathymetry data for the Gippsland Basin and southeast Australia, and the Department of Industry, Technology and Environment (Geological Survey of Victoria) for permission to use the airborne magnetic image of the Gippsland Basin. The University of Sydney's Ocean Drilling Program is thanked for providing and running the seismic-acquisition equipment (particular thanks to Jock Keene and Dave Mitchell). The RV Franklin cruise was partially funded by ARC Research Grant No. A39803024. Reviewers Neville Exon and Barry Bradshaw are thanked for their helpful comments and suggestions.