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Mid-shelf ridges on the New Jersey mid-continental shelf, in water depths of 20 to 40 m (65 to 130 ft), were recently reinterpreted as degraded barriers. These barriers are believed to have developed at various intervals between 8,000 and 14,000 years B.P. The 30 km (16.2 nmi) width of this barrier complex suggests: (1) two or more prograding barriers with the younger barrier being landward of the older barrier; or (2) successive small barriers forming landward of preexisting, partly preserved barriers. During periods when sand supply was in excess of the amount needed for maintenance, the barriers prograded. During this time the sea level rose, causing the barriers to both aggrade and prograde. As the barrier grew, an increasing amount of sand was needed to maintain the arrier. When the sea level rise exceeded the amount of available sediment, the barriers became submerged.
Our model proposes that, during initial submergence, the dunes and upper shoreface of the barrier were removed by erosion, leaving only the lower portions of the shoreface. After isolation on the mid-shelf, the degraded barriers, which now constitute the mid-shelf ridges, continued to be modified by shelf currents. During winter northeasterlies, bottom currents deepened the preexisting topographic lows and carried the sediment upflank for deposition on the crest. During summer, mild storms and internal waves tended to degrade the upper portion of the ridges. The net result was slow aggradation of the ridges since isolation on the mid-shelf.
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