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Sidescan-Sonar Imagery and Surficial Geologic Interpretations of the Sea Floor in Central Rhode Island Sound


Historic Seismic-Reflection Data

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Historic Seismic-Reflection Data
Figure 2. Map showing the outline of the study area, locations of historic seismic-reflection data, the locations of detailed views, and the location of a sand sample.
Figure 2. Map showing the outline of the study area, locations of historic seismic-reflection data, the locations of detailed views, and the location of a sand sample. Click on figure for larger image.
Figure 7. Seismic-reflection profile across eastern end of study area from Needell and others (1983a) with interpretation and corresponding sidescan-sonar image.
Figure 7. Seismic-reflection profile across eastern end of study area from Needell and others (1983a) with interpretation and corresponding sidescan-sonar image. Click on figure for larger image.
Figure 8. Seismic-reflection profile across western end of study area from Needell and others (1983a) with interpretation and corresponding sidescan-sonar image.
Figure 8. Seismic-reflection profile across western end of study area from Needell and others (1983a) with interpretation and corresponding sidescan-sonar image. Click on figure for larger image.

Seismic-reflection data from a previous study in Rhode Island Sound cross the study area (fig. 2; Needell and others, 1983a). The bottom-most unit of the seismic-reflection data is delineated by a prominent reflector that denotes Paleozoic bedrock of mostly gneiss and schist (fig. 7; Needell and others, 1983b). A prominent reflector that forms a northward-facing escarpment in the southern part of the study area overlying the bedrock was interpreted to be Cretaceous coastal plain sediments (fig. 8; Needell and others, 1983b). Overlying the bedrock and coastal plain sediments is a unit with irregular and discontinuous reflectors, interpreted to be Wisconsin glacial till. Overlying the till across much of the northern and western parts of the study area are laminated sediments that are mostly horizontal, but conform to the underlying surface (figs. 7 and 8; Needell and others, 1983a). These rhythmically laminated deposits are interpreted to be composed of glaciolacustrine sediments that were deposited during recession of the Laurentide Ice Sheet as meltwater was impounded behind mounded glacial drift, much like the varved sediments in Block Island Sound described by Bertoni and others (1977). Holocene marine and transitional deposits fill fluvially eroded channels near the surface that cut into the glaciolacustrine and till deposits (figs. 7 and 8).

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This page last modified on Monday, 24-Nov-2014 12:30:07 EST