--> Abstract: Foraminiferal Response to Downslope Sand Transport Processes and Seafloor Morphology Offshore Fraser Island, Australia; #90063 (2007)

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Foraminiferal Response to Downslope Sand Transport Processes and Seafloor Morphology Offshore Fraser Island, Australia

 

Schroder-Adams, Claudia J.1, Ron Boyd2, Kevin Ruming2, Marianne L. Sandstrom3 (1) Carleton University, Ottawa, ON (2) University of Newcastle, Callaghan, Australia (3) University of Adelaide, Adelaide, Australia

 

The extensive longshore sediment transport system along the SE margin of Australia transports 500,000 m3 /year of sand from New South Wales and southern Queensland north towards Fraser Island. However, Fraser Island, consisting of 203 km3 of Quaternary sand, is presently not increasing in size, and quartz sand gives away to carbonate sand north of the island. A recent multidisciplinary study using multibeam sonar imagery and sediment sampling has established that sand is being diverted over the shelf edge into the deep sea. The sand is channeled through a series of gullies that puncture the slope. Foraminiferal distribution patterns are intimately linked to the variable ocean floor morphology as unveiled in detailed sea floor images. Samples representing locations outside gullies, unaffected by downslope sediment transport, show a clear relationship between foraminiferal assemblages and bathymetric zones and their substrate types. On the shelf, assemblages differ in estuarine, sandy, temperate carbonate and tropical carbonate facies; the slope assemblages are variable with an increasing agglutinated component towards greater depth and those in turn differ from the continental rise fauna.

 

Within the same depth range, assemblages within gullies significantly vary from those outside gullies. Furthermore, subtle topographic features such as ridges and levees that allow protection from the main erosional sand transport routes support fragile, erect suspension feeders. Assemblages in gullies fed from the shelf edge have a different composition than those without connection to the shelf. Foraminiferal distribution patterns would have received an entirely different biofacies interpretation without linking them to ocean floor processes as revealed through multibeam sonar imagery.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California