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Sediment transport in the Murray Canyons offshore South Australia

S. Schmidt1,2, P. De Deckker3, H. Etcheber1,2 and S. Caradec2

1 CNRS, UMR5805 EPOC, Avenue des Facultés, F-33405 Talence Cedex, France
2 Université de Bordeaux, UMR5805 EPOC, F-33405 Talence Cedex, France
3 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

We have examined some of the most spectacular canyons that are located offshore Kangaroo Island, and these are linked to ancient courses of the River Murray which would have flowed across the very wide Lacepede Shelf during periods of low sea level. During the AUSCAN-1 project held in 2003, modern sedimentation was assessed using a multi-tracer approach on interface sediments from 350 to 2,500 m water depth.

The presence of freshly deposited particles, tagged by 234Th in excess, 210Pb-based sediment accumulation (0.03 - 0.13 cm y-1) and 230Th-based focusing ratios support the occurrence of significant advection of marine sediments within these canyons. In the absence of direct riverine inputs, the shelf, being the site of intensive carbonate production, is the main supplier of material.

The presence of incised channels in the eastern portion of the Murray Canyons Group [MCG] [see figure 1] indicates recent to sub-recent activity along the courses. The presence of underwater slides in the western side of the MCG confirms that sediment transport to the abyssal plain does occur.

Based on our preliminary investigation and by synthesizing previous work on other canyons, we provide a conceptual model for sediment focusing and transfer within the canyons offshore Australia.