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Geochemical evidence for modern sediment accumulation on the continental shelf off southern New England

Journal of Sedimentary Petrology

By:
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DOI: 10.1306/212F7C70-2B24-11D7-8648000102C1865D

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Abstract

An area of fine-grained sediment approximately 170 km x 74 km in size, located in water depths between 60 m and 150 m, south of Martha's Vineyard, Mass., is a site of modern sediment deposition. The 14C ages systematically increase with sediment depth from about 1,300 years B.P. at the surface to 8,000-10,000 years B.P. at the depth of maximum core penetration. The old age for the surface sediments probably results from a combination of deposition of old carbon and faunal mixing. In the finest sediments, the sedimentation rates were approximately 130 cm/1,000 yrs when deposition began and have decreased to about 25 cm/1,000 yrs. The decreasing sedimentation rate reflects a diminishing source of fine sediments, which presumably came from the Georges Bank and Nantucket Shoals area. Inventories of excess 210Pb in undisturbed cores average 70 dpm/cm2 (disintegrations per minute per square centimeter), more than two times higher than the flux of 210Pb from the atmosphere and from 226Ra decay in the overlying water. This additional influx of 210Pb either must be with new fine-grained sediment material or from solutions that are stripped of their 210Pb by particulates in the bottom nepheloid layer. Stable Pb concentrations in surface sediments are about 28 ppm, as much as two times higher than concentrations at depth. The high accumulation rates, 210Pb inventories, and trace-metal profiles imply that this area is a modern sink for fine-grained sediments and for pollutants associated with particulate matter in the water column. To our knowledge, this is the only site of present-day natural deposition on the Continental Shelf off the eastern United States, exclusive of the Gulf of Maine. Because the net currents on the outer half of this Continental Shelf flow from northeast to southwest, this fine-grained deposit may receive its sediments and possible contaminants from the Nantucket Shoals and Georges Bank regions.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Geochemical evidence for modern sediment accumulation on the continental shelf off southern New England
Series title:
Journal of Sedimentary Petrology
DOI:
10.1306/212F7C70-2B24-11D7-8648000102C1865D
Volume
51
Issue:
1
Year Published:
1981
Language:
English
Publisher:
Society for Sedimentary Geology (SEPM)
Contributing office(s):
Coastal and Marine Geology Program
Description:
12 p.
First page:
281
Last page:
292
Number of Pages:
12
Country:
United States
State:
Massachusetts
Other Geospatial:
New England
Online Only (Y/N):
N
Additional Online Files(Y/N):
N