INLET-ASSOCIATED MARSH ISLANDS: NORTH INLET, SOUTH CAROLINA

Inlet-associated marsh islands rise above the vegetated marsh surface and mark the location of active or former tidal inlets. They were first described along the North Carolina coast in the late 1970’s and since that time have been found in New England, Virginia, New Zealand, and Portugal. They appear to be common along mixed-energy barrier island coasts in which salt marsh and tidal creeks comprise the backbarrier. In planform they are sinuous to linear and have been often misidentified as beach ridges associated with barrier progradation. Depending upon their elevation, proximity to tidal inlets, and age, they may be covered by grasses, shrubbery, or climax vegetation. At North Inlet, South Carolina, historical marsh islands, now found landward of the former inlet channel, range in elevation from 0.5 to 2.5 m above the present marsh surface and occur in several 200-600 m segments, totaling over 1200 m in length. Vibracores taken along abandoned and active marsh islands reveal that the island lithosome consists of fining-upward sands overlying 0.3-0.5 m-thick muddy Spartina peat. The basal unit, which has a sharp contact with the peat, is a coarse to medium sand and represents flood-tidal delta and channel sediments that were transported onto the marsh by wave action and flood-tidal currents during storms. These deposits are overlain by beach and dune sand that are commonly capped by a soil horizon in protected regions. The stratigraphic sequence of the historical marsh islands is similar to that in the modern inlet-associated marsh ridges of the North Inlet. Continuing saltmarsh development and inlet migration may ultimately result in a new chain of abandoned marsh islands.