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Sidescan-Sonar Imagery, Multibeam Bathymetry, and Surficial Geologic Interpretations of the Sea Floor in Rhode Island Sound, off Sakonnet Point, Rhode Island

Sedimentary Environments

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Sedimentary Environments

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Figure 19. Map showing distribution of sedimentary environments.
Figure 19. Map showing distribution of sedimentary environments.

The present day sea floor in the study area is interpreted to contain three sedimentary environments characterized by the processes of erosion or nondeposition, coarse-grained bedload transport, and sorting and reworking (fig. 19). These environments are delineated using interpretations of the sidescan-sonar, bathymetric, and seismic-reflection data. The boundaries of the sedimentary environments are gradational and borders are inferred.

Erosion or Nondeposition

Environments characterized by erosion or nondeposition, which dominate the sea floor in the study area, are distinguished by the presence of rocks and gravel, tabular erosional outliers, or a hummocky surface. These processes are prevalent on the moraine and flanks of the ridges. These high-energy areas are exposed to currents that winnow away finer grained sediments and leave a coarser grained lag.

Coarse-Grained Bedload Transport

Environments characterized by coarse-grained bedload transport are located where sand waves are present, which occurs mostly in the northern parts of the study area. The orientations of sand wave crests are generally east-west and tend to parallel the bathymetric contours. In two sand-wave fields the slip faces are oriented northward, suggesting this is the direction of sediment transport. Currents are most likely flowing into and out of the central basin across the northern ridge.

Sorting and Reworking

Environments characterized by the processes of sorting or reworking are located in the central and western basins and on parts of the northern ridges. These areas have moderate backscatter and lack sand waves and gravelly sediment as indicated in the interpretations of the sidescan-sonar imagery. There does not seem to be any fine-grained deposition of sediment in the study area as McMaster (1960) interpreted the area to be sandy with some areas of gravel. Thus, sediments are interpreted to be undergoing processes of sorting and reworking in areas that lack characteristics of erosion and coarse-grained bedload transport.

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