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Sea-Floor Texture and Physiographic Zones of the Inner Continental Shelf From Salisbury to Nahant, Massachusetts, Including the Merrimack Embayment and Western Massachusetts Bay

Figure 6.Seismic stratigraphic units interpreted by Oldale and Bick (1987), Oldale and Wommack (1987), and Hein and others (2013). Barnhardt and others (2006) published a depth to sediment thickness map, which was used to identify areas of outcropping bedrock on the inner continental shelf between Nahant and Gloucester, Massachusetts. Transgressive (thick red line) and regressive unconformities (dashed red line) were also identified in several of these studies. The stratigraphic unit names and resolution of these studies differed, but the origin and texture of the deposits can be readily combined into a generalized geologic map (fig. 5) to correlate with sediment textures and physiographic zones presented in this study. Qb^B and Qhb^C, Holocene beach and bar deposits; Qss^D, late Pleistocene to Holocene transgressive sand sheet deposits; Qsrt^D, late Pleistocene to Holocene regressive-transgressive shoreline deposits; Qed^D, Holocene ebb tidal delta deposits, Qoc^D, late Pleistocene to Holocene offshore coarse deposits; Qm^B, Qhm^C, Qmm^E, and Qmsc^D, late Pleistocene to Holocene offshore marine deposits; Qfe^B and Qhf^C, Holocene fluvial and estuarine deposits; Qhd^C, Holocene deltaic deposits; Qdl^D, late Pleistocene lowstand delta deposits; Qd^B and Qmd^C, Pleistocene glacial-marine deposits; Qdo^B and Qdt^C, Pleistocene coarse drift deposits; Qtd^D and Qt^E, Pleistocene drumlin till deposits; Tcp^B,C, Tertiary and late Cretaceous coastal plain deposits; Pz ^B,C, Triassic and older bedrock.