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U.S. Geological Survey Open-File Report 2009-1001

Geological Interpretation of the Sea Floor Offshore of Edgartown, Massachusetts
List of Figures Title             PageList of             FiguresConversion             FactorsAbstractIntroductionSettingMethodsBathymetrySidescan             Sonar Seismic             Profiles SedimentsBottom             Photography Data             CatalogSummaryAcknowledgmentsReferences             Cited ContactsFigure 1. Cape Cod and the             islands and the study area off Martha's Vineyard, Massachusetts (red             polygon). The areas of earlier studies (Poppe and others, 2006;             Poppe and others, 2007a; Poppe and others, 2007b; Poppe and others,             2008) completed as part of this series are shown as green polygons.           Figure 2. Edgartown Harbor, the             boundary of the study area (red line), and local physiographic             features. Figure 3. Regional             paleogeographic map showing the extent of the Laurentide ice sheet             over Cape Cod and the islands about 20–22 thousand years ago (ka).           Figure 4. Regional             paleogeographic map of Cape Cod and the islands just before 18             thousand years ago (ka). Map shows the extents of the Laurentide ice             sheet and Glacial Lake Nantucket Sound. Figure 5. Port-side             view of the National Oceanic and Atmospheric Administration Ship             Thomas Jefferson at sea. The 30-foot survey launch normally             stowed on this side of the ship has been deployed. Figure 6.             The National Oceanic and Atmospheric             Administration Launch 1014 being deployed from the NOAA Ship             Thomas Jefferson. Figure 7. A Klein 5000             sidescan-sonar system hull-mounted to a National Oceanic and             Atmospheric Administration launch. Figure 8. The RESON Seabat 8101             hull-mounted in the keel cut out of National Oceanic and Atmospheric             Administration Launch 1005. Figure 9. The RESON Seabat 8125             hull-mounted in the keel cut out of National Oceanic and Atmospheric             Administration Launch 1014. Figure 10.             Conductivity-temperature-depth (CTD) profiler. Data derived from             frequent deployments of this device were used to correct sound             velocities for the multibeam data. Figure 11. A port-side view of             the USGS research vessel Rafael that was used to collect             Chirp and Boomer seismic-reflection profiles, bottom photography,             and sediment samples in the vicinity of Edgartown Harbor,             Massachusetts. Figure 12. The locations of the             tracklines (blue lines) along which the 5 Boomer high-resolution             seismic-reflection profiles were collected during cruise 08034 of             research vessel Rafael. Also shown are the locations of             profile segments shown in figures 25 and 26 (red segments). Figure 13. The locations of the             tracklines (green lines) along which the 16 Chirp high-resolution             seismic-reflection profiles were collected during the August 2008             cruise 08034 of the research vessel Rafael. Also shown are             the locations of line segments shown in figures 27 and 28 (red segments). Because lines 1 and 2 were test             lines along which the survey did not produce useful data, they are             not shown on this map. Figure 14. The small Seabed             Observation and Sampling System (SEABOSS), a modified Van Veen grab             equipped with still and video photographic systems, mounted on the             aft starboard side of the research vessel Rafael. Note the             winch mounted on the davit (left) and the takeup reel for the             video-signal and power cable (right). Figure 15. Locations of stations             at which bottom samples and photographs were taken during cruise             08012 of research vessel Rafael to verify acoustic data.         Figure 16. Correlation chart             showing the relationships among phi sizes, millimeter diameters,             size classifications (Wentworth, 1922), and American Society for             Testing and Materials and Tyler sieve sizes. Chart also shows the             corresponding intermediate diameters, grains per milligram, settling             velocities, and threshold velocities for traction. Figure 17.             Sediment-classification scheme from Shepard (1954), as modified by             Schlee (1973). Figure 18. Reconnaissance             single-beam and multibeam bathymetry collected during National             Oceanic and Atmospheric Administration survey H11346. Hotter colors             are shallower areas; cooler colors are deeper areas. See key for             depth ranges. Figure 19. Digital terrain model             of the sea floor produced from the single-beam and multibeam             bathymetry collected during National Oceanic and Atmospheric             Administration survey H11346 and gridded to 25 m. Image is             sun-illuminated from 46° and vertically exaggerated 10X. Hotter             colors are shallower areas; cooler colors are deeper areas. See key             for depth ranges. Figure 20. Sidescan-sonar             imagery produced from data collected during National Oceanic and             Atmospheric Administration survey H11346. Light tones indicate hard             returns and generally coarser grained sediments; dark tones indicate             softer returns and generally finer grained sediments. Figure 21. Interpretation of the             sea floor surveyed in National Oceanic and Atmospheric             Administration survey H11346. Interpretation includes the locations             of buried fluvially cut channels; areas characterized by boulders,             sand waves, and shell beds; and the locations of the detailed clips             of the sidescan-sonar mosaic shown in figures 22, 23, and 24.Figure 22. Detailed planar view             of the seaward extension of Middle Flats from the sidescan-sonar             mosaic produced during National Oceanic and Atmospheric             Administration survey H11346. View shows high backscatter targets             interpreted to be boulders. Location of view is shown in figure 21. Figure 23. Detailed planar view             of the sidescan-sonar mosaic produced during National Oceanic and             Atmospheric Administration survey H11346. View shows relatively             straight to sinuous alternating bands of high and low backscatter             (tiger-stripe pattern) indicative of transverse sand waves. Location             of view is shown in figure 21. Figure 24. Detailed planar view             of the sidescan-sonar mosaic produced during National Oceanic and             Atmospheric Administration survey H11346. View shows the contact             between areas characterized by high backscatter (shell deposits) and             low backscatter (fine-grained sand). Location of view is shown in figure 21. Figure 25. Segment of Boomer             high-resolution seismic-reflection profile and interpretation from             research vessel Rafael cruise 08034 line 4 across the             elongate bathymetric high that extends seaward from Middle Flats.             Coastal-plain deposits underlie the glacial drift. Location of             profile is shown in figure 12. Figure 26. Segment of Boomer             high-resolution seismic-reflection profile and interpretation from             RV Rafael cruise 08034 line 4 across the buried channel             that extends seaward beneath Edgartown Harbor. Estuarine and             transitional deposits fill the buried channel, and some of these             deposits contain gas-charged sediment. Location of profile is shown             in figure             12.Figure 27. Segment of Chirp             high-resolution seismic-reflection profile and interpretation from             research vessel Rafael cruise 08034 line 3 offshore of             Edgartown Beach. The surface of the glacial drift has been fluvially             eroded, and topographic lows have been filled by estuarine and             transitional deposits. Location of profile is shown in figure 13. Figure 28. Segment of Chirp             high-resolution seismic-reflection profile and interpretation from             research vessel Rafael cruise 08034 line 18 across the             buried channel that extends seaward beneath Edgartown Harbor. Some             estuarine and transitional deposits consist of gas-charged sediment.             Location of profile is shown in figure 13. Figure 29. Locations of stations             at which sediment samples were collected during cruise 08034 of             research vessel Rafael to verify acoustic data. Hotter             colors are coarser grained sediment; cooler colors are finer grained             sediments. See key for sediment classifications. Figure 30. Sessile fauna and             flora on the bottom at station 18. These organisms commonly cover             boulders in high-energy environments. Station location is shown in             figures 15 and 29. Figure 31. The flat, sandy             bottom at station E9. This flat, sandy sea floor is typical of the             deeper offshore waters in the western part of the study area. Note             the presence of animal tracks and burrows. Station location is shown             in figures 15 and 29. Figure 32. The bottom at station             E31. This undulating to faintly rippled sandy sea floor is typical             of the deeper offshore waters in the eastern part of the study area.             Note the presence of burrows. Station location is shown in figures 15 and 29. Figure 33. The bottom at station             E26. This flat, muddy sea floor is typical of the inner part of             Edgartown Harbor. Note the presence of animal tracks, a spider crab,             and dead eelgrass. Station location is shown in figures 15 and 29. Figure 34. The dense             slippersnail (Crepidula) shell bed on the bottom at station             E16 off the tip of the seaward extension of Middle Flats. Note             growth on the shells. Station location is shown in figures 15 and 29. Figure 35. The slippersnail             (Crepidula) shell bed on the bottom at station E22             northeast of the tip of the seaward extension of Middle Flats.             Station location is shown in figures 15 and 29. Figure 36. The slippersnail             (Crepidula) shell bed on the bottom at station E10             northwest of the tip of the seaward extension of Middle Flats. Note             the veneer of sediment on the shells. Station location is shown in             figures 15 and 29. Figure 37. The dense stands of             seaweed that grow on the flanks and crest of the seaward extension             of Middle Flats at station E17. Station location is shown in figures 15 and 29. Figure 38. The dense stands of             seaweed that grow on the flanks and crest of the seaward extension             of Middle Flats at station E13. Station location is shown in figures 15 and 29. 
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