Sediment flux and composition changes in canyons on a carbonate-siliciclastic margin: evidence from turbidite deposits along the Great Barrier Reef margin

Webster, J.M., Ludman, D., Wust, R., Beaman, R., Renema, W., Moss, P., and Jacobsen, G. (2008) Sediment flux and composition changes in canyons on a carbonate-siliciclastic margin: evidence from turbidite deposits along the Great Barrier Reef margin. In: Australian Earth Sciences Convention 2008. p. 251. From: Australian Earth Sciences Convention 2008, 20-24 July 2008, Perth, WA, Australia.

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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 bathymetry and seismic 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. Our preliminary data confirm that: (1) the canyons record a distinct sedimentary shift from siliciclastic turbidites to calciturbidites; (2) the siliciclastic turbidites were deposited before 28 ka - providing strong support for the "reciprocal" model of margin sedimentation; and (3) the canyons have been active throughout the last deglaciation and into the late Holocene.

Item ID: 27804
Item Type: Conference Item (Abstract / Summary)
ISSN: 0729-011X
Date Deposited: 30 Jul 2013 05:21
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040305 Marine Geoscience @ 50%
04 EARTH SCIENCES > 0403 Geology > 040310 Sedimentology @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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