Sedimentology of the New Hampshire Inner Continental Shelf Based on Subbottom Seismics, Side-Scan Sonar, Bathymetry, and Bottom Samples

Abstract

Typical of glaciated environments, the inner continental shelf of New Hampshire is composed of bedrock outcrops, remnants of glacial deposits (for example, drumlins), sand and gravel deposits, as well as muddier sediments farther offshore. A number of previous studies have defined the general trends of the New Hampshire inner shelf from the coarser deposits nearer the shore to the muddier outer basins. Most recently, a seismic survey (150 km of side-scan sonar and subbottom seismic profiles), as well as bottom sediment sampling (74 stations), has provided a detailed bottom map of the southern New Hampshire shelf area (landward of the 30-m contour). The surficial sediments within this area range from very fine sand to gravel. Bedrock outcrops are common. The seismic survey indicated several large sand deposits exceeding 6-8 m in thickness that occur relatively close to the coast. These sedimentary units, which are within 3 km of the shoreline, are composed of fine to medium sands. Examination of the general morphology and depositional setting indicates at least some of these features are probably relic ebb tidal delta shoals. However, a large eroding drumlin occurs between two of the sand bodies and may represent the source of these deposits. Additional work is needed to verify the origin of these sediment bodies.