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Woods Hole Coastal and Marine Science Center > Geologic Mapping of the Massachusetts Sea Floor > Interpretive Reports

Geologic Mapping of the Massachusetts Sea Floor


shimInterpretative Reports

In this project interpretation of high-resolution geophysical data (including interferometric and multibeam swath bathymetry, lidar, acoustic backscatter, and seismic reflection), sediment samples, and bottom photographs are used to produce a series of maps that describe the distribution and texture of sea floor sediments, shallow geologic framework, and physiographic zones inside the 3-nautical-mile limit of Massachusetts waters  and in adjacent federal waters. Data and interpretations are intended to aid efforts to inventory and manage coastal and marine resources, and provide baseline information for research focused on coastal evolution and environmental change.

The Massachusetts Office of Coastal Zone Management (CZM) is incorporating these interpretive products into their ocean management plan. Scroll through the images on this page to see examples of interpretative data products derived from geophysical and sample interpretations.

To learn more about the data collected, please visit the Data Collection and Interpretation page. To learn more about the data products, please visit the Geophysical and Sample Data Products page.



Sediment Texture

 Image of the Barnhardt and others (1998) bottom-type classification, which is based on four basic sediment units: rock (R), gravel (G), sand (S), and mud (M). There are twelve additional two-part units that represent combinations of the four basic units, where the primary texture (more than 50 percent of the area) is given an upper case letter and the secondary texture (less than 50 percent of the area) is given a lower case letter.

Above: The Barnhardt and others (1998) classification was chosen to represent sea floor texture for this study due to the complex nature and heterogeneity of sea floor material and the scale at which these data are mapped. This classification works well for inner-shelf environments where one sediment unit is generally inadequate for representing sea floor texture, such as the New England coast, where reworked tills and rocky pavements are common. The Barnhardt and others (1998) bottom-type classification is based on four basic sediment units: rock (R), gravel (G), sand (S), and mud (M). There are twelve additional two-part units that represent combinations of the four basic units, where the primary texture (more than 50 percent of the area) is given an upper case letter and the secondary texture (less than 50 percent of the area) is given a lower case letter.

inner continental shelf sediment textures within western Massachusetts Bay.

Above: Inner continental shelf sediment textures within western Massachusetts Bay classified using Barnhardt and others (1998). Bottom photographs A-D show sediment texture in select locations (photograph locations are shown as white dots on the sediment texture map). Grain size statistics are plotted as pie charts showing the relative percentages of gravel, sand, and mud. A, A photograph of the sea floor within an area classified as rock (R). No sample was recovered in this area due to large particle size. B, A photograph of a section of sea floor classified as primarily mud with sand (Ms). C, A photograph from a section of sea floor classified as primarily gravel with rock (Gr). No sample was recovered in this area due to large particle size. D. A photograph from a section of the sea floor classified as primarily sand and gravel with some mud. The viewing frame for photographs A–D is approximately 50 centimeters.


Surficial and Stratigraphic Geologic Maps

A map of surficial geology on the inner continental shelf between Nahant and northern Cape Cod Bay as it was interpreted from shallow seismic reflection profiles.

Above: Surficial geologic map of the Massachusetts inner continental shelf between Nahant and northern Cape Cod Bay interpreted from seismic-reflection profiles and correlated with stratigraphic units described by Oldale and Bick (1987). Qmn, Holocene nearshore marine sediments; Qmd, Holocene deepwater marine sediments; Qfe, Holocene fluvial and estuarine sediments; Qd, undifferentiated Pleistocene glacial drift sediments; Pz(?)/Tcp(?)/Qt(?), undifferentiated Paleozoic bedrock, late Cretaceous to Tertiary coastal plain sediments, or Pleistocene glacial tills. Holocene sediment veneers too thin to be detected in the seismic-reflection data (less than about 0.5 meter) may overlie outcrops of pre-Holocene units (blue and gray areas) locally. The locations of geologic cross sections B-B' and C-C' are indicated by cyan lines.

Geologic cross sections (B–B′ and C–C′) illustrating the general distributions and thicknesses of seismic stratigraphic units and elevations of major unconformities beneath the Massachusetts inner continental shelf between Nahant and northern Cape Cod Bay.

Above: Geologic cross sections (B–B′ and C–C′) shown above are illustrating the general distribution and thickness of seismic stratigraphic units and the elevation of major unconformities beneath the Massachusetts inner continental shelf between Nahant and northern Cape Cod Bay. Geologic cross sections are interpreted from chirp seismic reflection profiles. Vertical scale is elevation in meters below the North American Vertical Datum of 1988. Solid vertical black line denotes bend in the cross section, and dashed vertical black lines indicate intersection where B-B’ and C-C’ cross.


Physiographic Zones

Right: Following methods used in the Gulf of Maine to produce geologic maps, the sea floor is divided into physiographic zones based on sea floor morphology and dominant sediment texture. Physiographic zones  allow efficient mapping of large areas and present geomorphic and textural data in a single classification scheme. This designation is especially useful in complex inner-shelf settings such as northeastern Massachusetts, New Hampshire, and Maine. An added advantage of physiographic zones is that they do not require full data coverage and can be defined from a variety of data sources. The image above identifies the physiographic zones of an area offshore of Massachusetts from Boston Harbor to Salisbury Beach.

A map of physiographic zone designations within an area of Massachusetts from Boston Harbor to Salisbury Beach.

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