Sediment Flux and Composition Changes in Canyons from a Carbonate-Siliciclastic Margin: Evidence from Turbidite Deposits Along the Great Barrier Reef Margin

Jody Webster¹, Deane Ludman¹, Raphael Wust¹, Robin Beaman¹, Willem Renema², and Patrick Moss^3
1Earth and Environmental Sciences, James Cook University, Townsville, QLD, Australia
²Natural History Museum, Leiden, Netherlands
³University of Queensland, Queensland, QLD, Australia

The shelf edge and slope of the Great Barrier Reef is heavily incised by submarine canyons which terminate in the Queensland Trough. Traditionally, sedimentation on the margin has been investigated within the framework of idealized siliciclastic or carbonate systems, depending on whether rivers or shallow marine carbonate producers dominate supply. The widely accepted paradigm (‘reciprocal’ sedimentation) states that sea-level strongly influences shelf, slope and basin sedimentation, with siliciclastics dominating lowstand periods and carbonates dominating transgressions/highstands. However, recent work (e.g., Dunbar and Dickens, 2003) on cores from the slope and basin has challenged this view. These workers argue that accumulation of both siliciclastic and carbonate sediments varies in phase, with the highest rates observed during transgressions, lowest rates during lowstands and moderate sedimentation during highstands. Irrespective of which model is correct, exactly how the sediment (carbonate or siliciclastic) moves from the shelf to the basin, and the role of submarine canyons in this process is not understood. We address this problem directly by investigating sedimentation in the canyons bordering the GBR. Combining new multibeam data with x-radiograph, magnetic susceptibility, insitu reflectance spectroscopy, grain size, CNS, petrologic, pollen and 14C AMS analyses of canyon cores off Cooktown and Cairns, we aim to establish the source, timing and frequency of turbidite events deposited in the canyons over the last glacial to interglacial cycle, thereby testing the competing models. Preliminary analyses confirm that the canyons: (1) record a distinct stratigraphic change from siliciclastic turbidites to calciturbidites and; (2) they have been active throughout the last transgression and into the late Holocene.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas