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Book Chapter

Infaunal-Sediment Relationships at the Shelf-Slope Break

By
Norman J. Blake
Norman J. Blake
Department of Marine Science, University of South Florida
St. Petersburg, Florida 33701
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Larry J. Doyle
Larry J. Doyle
Department of Marine Science, University of South Florida
St. Petersburg, Florida 33701
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Published:
January 01, 1983

ABSTRACT

Infauna changes dramatically across the shelf-slope break, along with the physical and chemical parameters of the sediments and overlying water column. Grain size across the transition first increases slightly, then rapidly changes from sand to mud with concomitant increase in clay mineral and organic matter content. Light penetration decreases and there occurs a damping of seasonal temperature fluctuations. Infauna! assemblages change from those characterized by filter feeding organisms to those dominated by deposit feeders. Of the animals with hard parts likely to be preserved in the fossil record, the molluscan order nuculoida, composed of deposit feeders, is heavily represented seaward of the mudline. Biomass and density of organisms first decrease as grain size gets larger near the shclfedge, then increase as the mudline is crossed, then decrease again in the mud downslope. Winnowing recycles fecal material from the shelf infaunal assemblages back into the water column, this contributes to the generally high productivity of shelf waters. Much of the feces seaward of the mudline is incorporated as part of the sediment, contributing to the relatively high organic content. Deposit feeders downslope of the mudline are the primary source of sediment reworking, while physical winnowing processes are more important at and adjacent to the sheifedge.

In the sedimentary record, a sudden change in fossils from groups dominated by filter feeders to groups dominated by deposit feeders may indicate proximity to the shelf-slope break. Such a diagnostic change is associated with a decrease in fossil content of a sand layer and concurrent increase in grain size, followed by a facies change from sand to mud with rapid increase in fossil content, and finally followed by a decrease in fossil content in mud away from the zone of facies change.

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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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