Title

Physical Properties and Age of Mid-slope Sediments Dredged from the Eastern Australian Continental Margin and the Implications for Continental Margin Erosion Processes

Abstract

A large number of submarine landslides were identified on the continental slope on the Eastern Australian margin during voyages aboard the RV Southern Surveyor in 2008. Preliminary sedimentological analysis as well as geotechnical and biostratigraphic data determined for mid-slope dredge samples are reported. The dredge samples are normally-consolidated, calcareous sandy-muds of Neogene age and were recovered from submarine scarps located on the mid-continental slope. These scarps probably represent submarine landslide failure surfaces. Slope stability modelling using classical soil mechanics techniques and measured sediment shear-strengths indicates that the slopes should be stable; however, the ubiquity of mid-slope slides on this margin indicates that their occurrence is relatively common and that submarine-sliding should probably be considered to be a normal characteristic of the margin as suggested by Boyd et al (2010). While this presents something of an interpretational paradox, it nevertheless indicates that an, as yet, unidentified mechanism acts to reduce the shear resistance of these sediments to very low values which enables the slope failures to occur. It is suspected that the expansion of the Antarctic Icesheet in Mid-Miocene time and the consequent large-scale production of cold, equator-ward migrating, bottom water has caused significant erosion and removal of material from mid-slope and lower slope of the Australian continental margin in the Tasman Sea since the Mid-Miocene. Such a process would help to explain the exposure of hard Palaeozoic basement rocks along much of the southern part of the Eastern Australian continental margin. It is also suspected that erosion due to equator-ward moving bottom water effectively and progressively removed material from the toe of the continental slope sediment wedge. This rendered the slope sediments that were deposited throughout the Tertiary more susceptible to mass failure than would have otherwise been the case. Reference: Boyd, R., Keene, J., Hubble, T., et al. (2010). Southeast Australia: A Cenozoic Continental Margin Dominated by Mass Transport. Submarine Mass Movements and Their Consequences, Advances in Natural and Technological Hazards Research. D. C. Mosher, et al. 28: 491-502.

Publication Date

12-2010

Journal or Conference Title

Fall Meeting, American Geophysical Union (AGU)

Conference Date

Dec 13 - Dec 17, 2010

Publisher Place

San Francisco, CA, USA

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding