Authors / CoAuthors
Jones, A.T. | Kennard, J.M. | Logan, G.A. | Grosjean, E. | Marshall, J.
Abstract
Multibeam swath bathymetric data collected in 95-120 m water depth on Australia's North West Shelf revealed two distinct populations of sand waves: a laterally extensive low amplitude composite form comprising superimposed dunes and ripples, and a laterally restricted form that is anomalous in that the sand waves have unusually high height-slope-length relationships. These large subaqueous sand waves comprise bioclastic ooid/peloid sand. Significantly, evidence of seabed fluid flow was detected in association with the high amplitude sand waves. This evidence includes seabed pockmarks approximately 2-15 m in diameter imaged with side-scan sonar, tubular and massive carbonate concretions dredged from the seabed, and potential active venting of a fluid plume from the seabed observed during an underwater camera tow. Molecular and isotopic analysis of carbonate concretions collected from within pockmarks associated with the high amplitude sand waves indicate that the seeping fluids are modern seawater and not related to thermogenic fluids or microbial gases. The fluid flow is interpreted to be driven by currents flowing over seabed topography and leading to the expulsion of interstitial pore waters. Sites of fluid flow are thought to be preferentially focused due to the relatively steep slopes of the sand waves, the high permeabilities of the very well sorted, coarse oolitic sand, the relative stability of the bedforms, and the confining and focussing influence of subsurface mounds. This study represents the first time that this process has been inferred in a mid-shelf setting, and causally linked to seabed fluid expulsion features.
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nonGeographicDataset
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65579
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- External Publication
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2007-12-14T00:00:00
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