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U.S. Geological Survey Open-File Report 2007-1373

High-Resolution Geologic Mapping of the Inner Continental Shelf: Cape Ann to Salisbury Beach, Massachusetts

Skip past contents informationTitle Page / Table of Contents / List of Figures / Introduction / Maps / Data Collection/Processing / Interpretation / Summary / Acknowledgments / References Cited / Appendix 1 / Appendix 2 / Appendix 3 / Appendix 4 / Appendix 5

Figure 3.7. Map showing the elevation of the transgressive unconformity, a gently sloping erosional surface that is etched into Pleistocene sediment. Although locally buried by Holocene marine sediment up to 9 m thick, the unconformity is exposed at the seafloor in many locations. Elevations of the transgressive unconformity were calculated by subtracting measured values of Holocene sediment thickness (fig. 3.6) from the combined bathymetric grid (fig. 3.3). In the nearshore area, elevations were used to generate an interpolated grid, but in the offshore area, they are only displayed as discrete points along the widely spaced seismic-reflection tracklines. Depths are relative to the local mean lower low water datum.


Figure 3.7.  Map showing the elevation of the transgressive unconformity, a gently sloping erosional surface that is etched into Pleistocene sediment.  Although locally buried by Holocene marine sediment up to 9 m thick, the unconformity is exposed at the seafloor in many locations.  Elevations of the transgressive unconformity were calculated by subtracting measured values of Holocene sediment thickness (fig. 3.6) from the combined bathymetric grid (fig. 3.3).  In the nearshore area, elevations were used to generate an interpolated grid, but in the offshore area, they are only displayed as discrete points along the widely spaced seismic-reflection tracklines.  Depths are relative to the local mean lower low water datum.  

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