30 Coastal and Marine Geology (Posters) (CC)

Monday, 23 March 2009
8:00 AM - 12:00 PM

SIDESCAN-SONAR IMAGERY AND SURFICIAL GEOLOGIC INTERPRETATIONS OF THE SEAFLOOR IN CENTRAL RHODE ISLAND SOUND

Paper number: 30-5
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

In 2004, the National Oceanic and Atmospheric Administration (NOAA) conducted Survey H11321 in central Rhode Island Sound. Sidescan-sonar and bathymetric data were acquired within a 93 km2 area of seafloor located 12 km southeast of Brenton Point, Rhode Island. These data were used in conjunction with historic seismic-reflection data (Needell and others, 1983) to interpret the seafloor geology and sedimentary environments, and provide a geologic framework for additional marine research and coastal resource management studies. Four sedimentary environments are observed in the study area, including those characterized by processes of: 1) erosion or nondeposition, 2) coarse-grained bedload transport, 3) sorting and reworking, and 4) fine-grained deposition. Sidescan-sonar and bathymetric data reveal two northeast-southwest oriented, broad, moderate- to high-backscatter, low-relief ridges in the northern and southeastern parts of the study area. The ridges are topped with fields of sand waves that reflect a sedimentary environment characterized by coarse-grained bedload transport. Sand-wave crestlines in the northwest are oriented north-south and have 10- to 20-m wavelengths, whereas those in the east and south are oriented east-west and have 20- to over 100-m wavelengths. The southern side of the northern ridge contains a series of curvilinear, northeast-southwest oriented benches that are interpreted here as indicators of paleoshorelines. Historic seismic-reflection profiles show that the northern ridge is underlain by glaciolacustrine sediments, assumed to be Wisconsin in age. A central channel, which is 8 to 9 m deep and floored by low-backscatter Holocene marine and transitional sediments, stretches southwestward across the study area. Trawl marks within the channel are clearly visible within sidescan-sonar imagery as lines of low backscatter or paired high and low backscatter. Sedimentary environments characterized by sorting and reworking and deposition are found in the channel.