Submarine Landslide Morphology of Box Slides Present on the Continental Slope Offshore Fraser Island, Queensland, Australia

The Fraser Island slide complex is located on eastern Australia's continental slope. Two potentially tsunamigenic submarine landslides identified here as the 'North Fraser Island Upper Slope Slide' (25km2 in area, 100m thick) and the 'Middle Fraser Island Middle Slope Slide' (12km2 in area, 50m thick) are described. Morphologic, sedimentologic and geomechanical properties for these slides are compared to data reported for existing submarine landslides located to the south in New South Wales (NSW). The two Fraser Island slides are translational, box-shaped, slab slides. We suspect that the slabs remained intact during downslope transport. The upper slope slide is situated at a water depth of approximately 750m at the northern end of the Fraser Canyon complex. The head of this slide has apparently detached from a structural surface comprised of a Miocene reef complex located beneath the continental shelf edge. The middle slope slide is situated on a large plateau to the south of the Fraser Canyon complex in 1500m of water. Cores taken in the continental slope within both slides are long and present hemipelagic muds. Cores taken adjacent to both slides are short and terminate in stiff muds of suspected Miocene or Pliocene age. Additionally, the core adjacent to the upper slope slide presents a near surface layer of upper-fining of coarse to fine shelly sand which we interpret to be a turbidite deposit. This layer was deposited above hemipelagic muds which are ubiquitously present on the upper eastern Australian continental slope in NSW and Southern Queensland.