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Book Chapter

Modern Sediment Dynamics at the Shelf-Slope Boundary Off Nova Scotia

By
Philip R. Hill
Philip R. Hill
1
Present address: Atlantic Geoscience Centre, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2 Canada.
Departments of Geology and Oceanography, Dalhousie University
Halifax, Nova Scotia, B3H 3J5, Canada
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Anthony J. Bowen
Anthony J. Bowen
Departments of Geology and Oceanography, Dalhousie University
Halifax, Nova Scotia, B3H 3J5, Canada
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Published:
January 01, 1983

ABSTRACT

Long term current-meter data from outer shelf, shelfbreak and slope sites off Nova Scotia have been compared with sediment textures in the same area to assess whether they are in equilibrium. Currents on the shelf and shelfbreak are strong with maximum velocities exceeding 50 cm s−1. Sediment grain-size distributions were dissected into near-Gaussian medium sand subpopulations and non-Gaussian tails. These subpopulations were interpreted dynamically as representing bed-load (coarse tail), suspended load with “dynamic settling” (central subpopulation) and suspended load with “passive settling” (fine tail). Below 500 m water depth, only the fine-tail subpopulation is seen. The modal size of the central subpopulation corresponded well, in most cases, to u* estimates from Shields' criterion and to the observed maximum currents.

Sediment textures can be explained by modem dynamic conditions. Sand transport is dominantly in suspension and in an alongslope direction with a small downslope component. Medium sand is transported only during short periods of high flow, whereas fine sand transport is during more continuous weaker flow. Permanent deposition occurs at a point downslope where the currents rarely exceed the suspension criterion for the size of particle concerned. Slight differences between inferred u* gradients at two slope areas, separated by 150 km, are tentatively interpreted as reflecting the effects of topographic Rossby waves, formed by Gulf Stream eddies impinging on the slope.

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SEPM Special Publication

The Shelfbreak: Critical Interface on Continental Margins

Daniel Jean Stanley
Daniel Jean Stanley
Division of Sedimentology Smithsonian Institution
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George T. Moore
George T. Moore
Chevron Oil Field Research Company La Habra California
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SEPM Society for Sedimentary Geology
Volume
33
ISBN electronic:
9781565761636
Publication date:
January 01, 1983

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