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Book Chapter

Diatoms in Sediments as Indicators of the Shelf-Slope Break

By
Constance A. Sancetta
Constance A. Sancetta
Lamont-Doherty Geological Observatory of Columbia University
Palisades, New York 10964
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Published:
January 01, 1983

ABSTRACT

Diatoms, a group of unicellular algae, are limited to the upper 100 m of the water column, due to their light requirement. Benthic diatoms, consequently, are restricted to the continental shelf, and primarily the inner shelf, coasts, and estuaries. Planktonic diatoms occur on the shelf (neritic) and in deeper waters (pelagic)—certain genera are restricted to one region while others occur in both. Salinity appears to exercise an important control on these distributions, so that a salinity front frequently produces a sharp boundary between populations. The shelf-slope break is usually associated with a sharp salinity gradient, where low-salinity shelf waters encounter a high-salinity oceanic current. The result is that benthic and low-salinity planktonic diatoms characterize shelf sediments, while higher-salinity planktonics and an absence of benthics characterize the slope and ocean basin sediments.

Two techniques for identifying the shelf-slope break are proposed, and examples given from the Bering Sea. The first involves use of the ratio of % benthic specimens to % pelagic-planktonic specimens in a series of sediment samples. The correlation of this ratio with depth is r = .85. A second technique uses quantitative population counts along a shelf-to-basin transect. In this case the shelf-slope break and its associated transition zone are seen to exert an ecologic control on species abundance. Other work in the literature, while not directly addressed to this question, suggests that similar results would be obtained in the Miocene diatomaceous sections of the U.S. East Coast and Japan.

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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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