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U.S. Geological Survey Open-File Report 2012-1157

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


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Chirp seismic reflection profile (a) A-A’ with seismic stratigraphic interpretation (b). This profile illustrates the sub-surface stratigraphy of the study area. Qmn = Holocene nearshore marine, Qfe = Holocene fluvial and estuarine, Qd = undifferentiated Pleistocene glacial drift, and Pz(?)/Tcp(?)/Qt(?) = undifferentiated Paleozoic bedrock, late-Cretaceous to Tertiary coastal plain sediments, or Pleistocene glacial tills. Ul = fluvial unconformity marking the upper surface of Pz(?)/Tcp(?)/Qt(?), Ur = late Wisconsinan regressive unconformity, and Ut = transgressive unconformity over Qfe and Qd.

Figure 5. Chirp seismic reflection profiles A, A-A’ with seismic stratigraphic interpretation and B, illustrating the subsurface stratigraphy of the study area. Qmn, Holocene nearshore 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; Ul, fluvial unconformity marking the upper surface of Pz(?)/Tcp(?)/Qt(?); Ur, late Wisconsinan regressive unconformity; Ut, transgressive unconformity over Qfe and Qd. See figure 6 for detailed 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.

 

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