Submarine Slide and Slump Complexes, Exmouth Plateau, NW Shelf of Australia

Abstract

Analysis of 3D seismic data shows that the Neogene to near seabed section along the NW flank of the Exmouth Plateau Arch has been affected by numerous slope failures. Seabed collapses originated at water depths of ~1000 m and extend down dip to depths well in excess of 1500 m. A wide spectrum of slope failures have been identified, from coherent slides, incoherent slumps to mass flow deposits, the product of debris-flows and turbidity currents. The slides in the study area are characterized by proximal slide fault block systems that are expressed at the seafloor as extensional ridges up to 500 m wide and 1 km long. The up-dip extension is matched by down-dip toe thrusts. The downslope toe is characterized by imbricate thrusts with fault-related folds that form a prominent fold belt at the seabed. The over-thickened leading edge of the toe-thrust systems commonly has undergone gravitational collapse resulting in second-order toe slides detached at shallower stratigraphic levels. Slump systems are characterized by contorted seismic facies that rest on top of erosive basal shear surfaces that are typically strongly striated. These striations are commonly arranged in multiple crosscutting sets. Detailed analysis of the orientation and crosscutting relationships of these sets suggests a complex multi-stage evolution of slumps. Progressive down slope disaggregation at the leading edge of slumps promoted the development of mass flows. These are characterised by strongly erosive canyons that link slumps to down dip debris flow and turbidite fans. The results of this work broaden our knowledge of the distribution and characteristic of slope failure in the Exmouth Plateau and shows that multiple slope processes can develop and coexist within a single event and hence produce a final composite failure.