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Shallow Geology, Seafloor Texture, and Physiographic Zones of the Inner Continental Shelf from Nahant to Northern Cape Cod Bay, Massachusetts

Figure 23. Chirp seismic-reflection profile F–F′ with seismic stratigraphic interpretation. This profile illustrates the stratigraphy beneath northern Cape Cod Bay offshore of Duxbury Beach and Plymouth Bay, Massachusetts, seaward of profile E–E′ in figure 22. Deep fluvial channels incised into the surface of thick glaciolacustrine (Qdl) sediments are filled with Holocene fluvial and estuarine (Qfe) deposits. The truncated Qd and Qfe units are broadly exposed at the seafloor to the northwest, but buried beneath increasingly thick Holocene deepwater marine (Qmd) sediments to the southeast. See figure 6 for descriptions of stratigraphic units and major unconformities (indicated by red lines). See figure 8 for profile location. A constant sound velocity of 1,500 meters per second was used to convert two-way travel time to depth in meters.