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Open-File Report 2013–1003

Sea-Floor Geology in Northeastern Block Island Sound, Rhode Island

By K.Y. McMullen, L.J. Poppe, S.D. Ackerman, D.S. Blackwood, P.G. Lewit, and C.E. Parker

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Multibeam-echosounder and sidescan-sonar data collected by the National Oceanic and Atmospheric Administration in northeastern Block Island Sound, combined with sediment samples and bottom photography collected by the U.S. Geological Survey, are used to interpret sea-floor features and sedimentary environments in this 52-square-kilometer-area offshore Rhode Island. Boulders, which are often overgrown with sessile fauna and flora, are mostly in water depths shallower than 20 meters. They are probably part of the southern flank of the Harbor Hill-Roanoke Point-Charlestown-Buzzards Bay moraine, deposited about 18,000 years ago. Scour depressions, areas of the sea floor with a coarser grained, rippled surface lying about 0.5 meter below the finer grained, surrounding sea floor, along with erosional outliers within the depressions are in a band near shore and also offshore in deep parts of the study area. Textural and bathymetric differences between areas of scour depressions and the surrounding sea floor or erosional outliers stand out in the sidescan-sonar imagery with sharp tonal contrasts. Also visible in the sidescan-sonar imagery are broad, low-profile bedforms with coarser grained troughs and finer grained crests.

First posted September 5, 2013

For additional information contact:
Director, Woods Hole Coastal and Marine Science Center
U.S. Geological Survey
384 Woods Hole Road
Quissett Campus
Woods Hole, MA 02543

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Suggested citation:

McMullen, K.Y., Poppe, L.J., Ackerman, S.D., Blackwood, D.S., Lewit, P.G., and Parker, C.E., 2013, Sea-floor geology in northeastern Block Island Sound, Rhode Island: U.S. Geological Survey Open-File Report 2013–1003, 1 DVD-ROM,







Sidescan Sonar


Bottom Photography

GIS Data Catalog



References Cited


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