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Offshore of Sandbridge Beach, Virginia, the surface of the inner continental shelf is a generally featureless, gently sloping plain, broken by several isolated sand shoals. The westernmost shoal, commonly called the Sandbridge Shoal, is located approximately 5.5 km from the shoreline in 1 O - 12 m of water. An analogous feature is located approximately 15 km northeast of the Sandbridge Shoal at depths greater than 15 m. During a pretiminary study conducted in 1987, 534 km of trackline were surveyed with acoustic subbottom and side-scan sonar systems. Geophysical data were recorded for an additional 318 km of trackline between 1988 and 1990. Genetic similarities between the two shoal features were analyzed and conceptual models of development were proposed. In addition to the geophysical data, 11 vibracores with a maximum length of six meters and 18 surface grab samples were acquired. Shell materials in the cores were dated using amino acid racemization and radiocarbon methods. Correlation of seismic data with vibracores and surface grab samples indicate the Sandbridge Shoal is approximately 6 x 8 km in areal extent and has a horseshoe shape in plan view. The shoal contains at least 8 x 107 m3 of clean, well-sorted, medium to coarse sand, and tapers to the north and east. The offshore shoal has a larger areal extent, but its relief above the surrounding seabed is less than half that of the Sandbridge Shoal. Both shoals are associated with large paleochannel systems, and inferred lagoonal or estuarine sediments are located below and landward of the sand bodies. Sediments within the shoals fine downwards, have little evidence of an aeolian overprint, lack high concentrations of heavy minerals, and contain remains of only high-salinity organisms.
This report primarily serves to present minimally interpreted data from a tight spaced set of high-resolution, seismic-reflection, sub-bottom profiles obtained during the summer of 1992. The profiles were run in the inner continental shelf adjacent to Virginia Beach, Virginia as part of an investigation of offshore sounds potentially usable in beach nourishment and hurricane protection projects along Virginia's Atlantic shore south of the mouth of Chesapeake Bay. Figure 1 depicts the general study area. Berquist and Gomillion (1993) presented an interpretation of a small portion of the work. A larger, interpretive report (Hardaway et al., 1995) also utilizes information from this set of sub-bottom profiles. The full set of most recent studies builds upon, amplifies, and modifies the interpretations of a set of earlier works especially, Shideler et al. (1972), Swift et al. (1977), Williams (1987), Dame (1990), Kimball and Dame (1989), Kimball et al. (1991), Chen (1992), and Chen et al. (1995).
The Inner Continental Shelf of North Carolina between the South Carolina border and Cape Lookout was investigated to obtain information on bottom and subbottom sediment deposits and geologic structure. Primary survey coverage consists of 512 statute miles (824 kilometers) of high-resolution seismic reflection profiles and 124 cores ranging in length from 2 to 20 feet (0. 6 to 6. 1 meters). Sand suitable for restoration and nourishment of nearby beaches was located, described, and mapped for 27 potential offshore borrow sites. This sand occurs commonly in thin sheet deposits or as relict channel fill. However, extensive sand deposits exist in shoals off Cape Fear and Cape Lookout and in other low isolated shoals on the shelf floor and within the shoreface area. (Author).
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