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U.S. Geological Survey Open-File Report 2013–1003

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


Methods

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Click on figures for larger images
Thumbnail image of figure 3 and link to larger figure. Photograph of the NOAA Ship Thomas Jefferson.
Figure 3. Starboard-side view of National Oceanic and Atmospheric Administration ship Thomas Jefferson, which was used to collect bathymetric data in the study area.
Thumbnail image of figure 4 and link to larger figure. A photograph of one of the launches used in the survey.
Figure 4. National Oceanic and Atmospheric Administration launch 3102, one of two aluminum survey launches used to collect bathymetric and sidescan-sonar data in the study area.
Thumbnail image of figure 5 and link to larger figure. Photograph of a bathymetric instrument used in the survey.
Figure 5. A RESON SeaBat 7125 multibeam echosounder, which is hull-mounted to National Oceanic and Atmospheric Administration ship Thomas Jefferson and was used to collect bathymetric data.
Thumbnail image of figure 6 and link to larger figure. Photograph of a bathymetric instrument used in the survey.
Figure 6. A RESON SeaBat 8125 multibeam echosounder, which is hull-mounted to National Oceanic and Atmospheric Administration launch 3101 and was used to collect bathymetric data.
Thumbnail image of figure 7 and link to larger figure. Photograph of a sidescan-sonar instrument used in the survey.
Figure 7. A Klein 5000 hull-mounted on National Oceanic and Atmospheric Administration launch 3101 used to collect sidescan-sonar data.
Thumbnail image of figure 8 and link to larger figure. Photograph of the USGS RV Rafael.
Figure 8. Port-side view of the U.S. Geological Survey research vessel Rafael, which was used to collect sediment and photographic data.
Thumbnail image of figure 9 and link to larger figure. Photograph of the sampling device used to collect sediment and photographic data.
Figure 9. The small Seabed Observation and Sampling System, a modified Van Veen grab sampler with attached still and video cameras, on the aft starboard side of the U.S. Geological Survey research vessel Rafael.
Thumbnail image of figure 10 and link to larger figure. Chart showing sediment size classification.
Figure 10. Chart showing the relations among phi sizes, millimeter diameters, size classifications, and American Society for Testing and Materials and Tyler sieve sizes.
Thumbnail image of figure 11 and link to larger figure. A chart showing size classification.
Figure 11. Sediment-classification scheme from Shepard, as modified by Schlee and Poppe and others.

MBES and sidescan-sonar data were collected aboard the NOAA ship Thomas Jefferson (fig. 3) and its launches 3101 and 3102 (fig. 4) between August and October 2009 and in October 2011. A RESON SeaBat 7125 MBES (400-kilohertz (kHz); fig. 5) was used aboard the Thomas Jefferson and launch 3102, and a RESON SeaBat 8125 (455-kHz; fig. 6) was used aboard launch 3101. Sidescan-sonar data were collected with Klein 5000 (455-kHz) systems (fig. 7) that were hull-mounted aboard launch 3101 and towed behind launch 3102. Sounding data are to mean lower low water datum and are corrected for tides using stations in New London, Connecticut, Newport, R.I., and Montauk, N.Y. Horizontal positioning was determined using differential global positioning system (DGPS) equipment with corrections obtained from U.S. Coast Guard beacons at Acushnet, Massachusetts, and Moriches, N.Y.

MBES data were acquired and line navigation was performed using Hypack 2009. The data were processed using CARIS HIPS software to produce and combine the bathymetry adjusted for statistical error (BASE) surfaces. The combined BASE surfaces were converted to Esri grids with 2-meter (m) horizontal resolution by the USGS. Sidescan-sonar data were acquired using Klein SonarPro software and processed with CARIS SIPS software to produce a mosaic with 1-m resolution. Neither MBES nor sidescan-sonar data completely cover the sea floor in the study area. Some areas have large gaps between lines, and in other areas there was no data collection. More detailed information on the data acquisition and processing for this survey are in National Oceanic and Atmospheric Administration (2009a, b).

Sediment samples and bottom photography were collected in the study area during USGS cruise 2012-002-FA aboard the research vessel (RV) Rafael (fig. 8) in June 2012. Samples and photography were collected with a small Seabed Observation and Sampling System (SEABOSS; fig. 9), which is a Van Veen grab sampler that has still and video cameras attached. Sediment samples were taken from the top 2 centimeters (cm) of the sea floor; the grain sizes of the samples were analyzed at the USGS Woods Hole Coastal and Marine Science Center's Sediment Lab following the procedures outlined in Poppe and others (2005). The coarse fractions (diameters equal to or greater than 0.0625 millimeters (mm)) of the samples were analyzed by using sieves, and the fine fractions (diameters less than 0.0625 mm) were analyzed by using a Coulter counter. Gravel-sized shells have been removed from the samples, because they can be deposited in situ and are often not representative of the sedimentary environment. Sediment descriptions are based on Wentworth's (1922) modified nomenclature (fig. 10) and Shepard's (1954) modified size classifications (fig. 11).

Bottom video and still photographs of a transect of the sea floor were obtained at each station as the SEABOSS drifted over the sea floor. Still photographs were taken at the discretion of the operator with a Canon G12 digital camera from a height of about 60 cm above the sea floor, resulting in images with widths covering from 30 cm to 1 m of the sea floor. Low-resolution images of the still photographs are available for viewing in the Bottom Photography section of this report. High resolution images along with photograph location information are available in the Geographic Information System Data Catalog section.

 


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