Fact Sheet 2006–3042

A map of seafloor geology off the coast of Marblehead, Massachusetts.

Figure 7. Geologic map of seafloor for area 1. Five environments, or physiographic zones, are delineated on the basis of the data from seafloor–mapping systems and sampling presented in figures 2–5. These geologic environments are described in the table at right. [km2, square kilometers; mi2, square miles]

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  1. Nearshore Basin (light green)

    • smooth, flat-lying areas; thick muddy sediment
    • sheltered areas within embayments
    • cover 7.0 km2 (2.7 mi2, 5.3 percent) of map area

     

  2. Rocky Zone (light blue)

    • high-relief rock outcrops, boulders and gravel
    • exposed areas along open-ocean coast
    • cover 52.4 km2 (20.2 mi2, 39.2 percent) of map area

     

  3. Nearshore Ramp (lavendar)

    • smoothly seaward-sloping areas; generally sandy sediment
    • extend offshore from coast to depths greater than 40 meters
    • cover 57.3 km2 (22.1 mi2, 42.9 percent) of map area

     

  4. Shelf Valley (yellow)

    • elongated valleys and interconnected depressions partially filled with sediment
    • extend offshore, perpendicular to coast
    • cover 12.5 km2 (4.8 mi2, 9.3 percent) of map area

     

  5. Bay Mouth Shoal (light orange)

    • flat-topped banks of sand and gravel
    • reworked by waves and tides at mouths of embayments
    • cover 4.4 km2 (1.7 mi2, 3.2 percent) of map area

     

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Description of the figure

This color figure is a map that shows the seafloor geology offshore of the Massachusetts coast from Gloucester to Nahant. Green depicts Nearshore Basins, blue depicts Rocky Zones, purple depicts Nearshore Ramps, yellow depicts Shelf Valleys, and orange depicts Bay Mouth Shoals.

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