HR: 0800h
AN: OS41D-0518    [Abstracts]
TI: Surficial Geology of the Sea Floor in West-Central Long Island Sound as Shown by Sidescan Sonar Imagery
AU: * McMullen, K
AF: Coastal and Marine Geology Program, U.S. Geological Survey, Woods Hole, MA 02543 United States
AU: Poppe, L
AF: Coastal and Marine Geology Program, U.S. Geological Survey, Woods Hole, MA 02543 United States
AU: DiGiacomo-Cohen, M
AF: Long Island Sound Resource Center, Connecticut Department of Environmental Protection, Avery Point, Groton, CT 06340 United States
AU: Moser, M
AF: Atlantic Hydrographic Branch, National Oceanic and Atmospheric Administration, Norfolk, VA 23510 United States
AU: Christman, E
AF: Atlantic Hydrographic Branch, National Oceanic and Atmospheric Administration, Norfolk, VA 23510 United States
AB: The United States Geological Survey is working cooperatively with the National Oceanic and Atmospheric Administration (NOAA) and Connecticut Department of Environmental Protection to conduct detailed studies of the surficial geology in Long Island Sound (LIS). Sidescan sonar imagery, processed from data collected during NOAA survey H11044, details almost 300 km$^{2}$ of the sea floor in west-central LIS and is used in conjunction with bathymetry, sediment, bottom video, and seismic data to interpret the area's surficial geology. The distributions of sediments and sedimentary environments interpreted from these data sets are products of the Quaternary geology, regional bathymetry, and effects of modern tidal and wave-driven currents. Most of the study area sea floor slopes gently to the southeast or south, though more complex bathymetry consisting of shoals, lesser bathymetric highs, and troughs is also present. Four distinct sedimentary environments consisting of 1) erosion or nondeposition, 2) coarse-grained bedload transport, 3) sorting and reworking, and 4) fine-grained deposition were identified and mapped. High-energy conditions characterized by erosion or nondeposition occur on bathymetric highs where gravel and gravelly sediments are present. Sedimentary environments characterized by coarse-grained bedload transport, distinguished by sandy sediments with current-derived bedforms, are located on an unnamed shoal in the northwestern part of the study area and on the northern flanks of Stratford Shoal. Fine sand, silty sand, and sand-silt-clay are the dominant sediment types within sedimentary environments characterized by sorting and reworking. This environment, which marks the transition from relatively higher energy conditions to lower energy conditions, occurs on the sides of basins and flanks of bathymetric highs. Elongate sinuous features of low backscatter also occur within sorting and reworking environments and are interpreted to be down-slope density-flow pathways through which fine-grained sediments are remobilized and transported deeper into the basins. Relatively low-energy environments prevail where deposition of clayey silts occurs in deeper water throughout the central part of the study area and in the protected areas of the far northeastern corner. Thus, bathymetric highs tend to have high-energy environments with coarser grained sediments, bathymetric lows tend to have low-energy environments with finer grained sediments, and transitional environments and conditions occur between the two.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting