GEOMORPHIC AND STRATIGRAPHIC DEVELOPMENT OF PEA ISLAND NATIONAL WILDLIFE REFUGE: THE ROLE OF FLOOD-TIDE DELTAS

An integrated study, using sedimentological, foraminiferal, geochemical, geophysical, and geospatial (e.g., surveys, charts, maps, and aerial photographs) data sets, was conducted on Pea Island National Wildlife Refuge to address tidal inlet formation and the role of flood-tidal deltas (FTD) in maintaining barrier island width.

Based on an 1852 survey, the southern portion of Pea Island was relatively narrow (200-450 m). The formation and migration of New Inlet (1755-1922) and Loggerhead Inlet (1843-1870) initiated a period of barrier-island widening (1000-1500 m) as determined by time-slices derived from historic surveys (1852, 1870, 1909, and 1917) and georeferenced aerial photographs (1932, 1940, 1949, 1962, 1998). Sediment was transported soundward via flood channels and deposited on shoals. As supported by geospatial, geophysical, and sedimentological data sets, reworked FTD, overwash, and eolian sediments accumulated on the shoals to produce the present-day geomorphic highs (e.g., Lagerhead Hills and New Inlet FTD).

The stratigraphy of five shore-normal transects defines a system controlled by the opening, migration, and closing of tidal inlets. Repetitive fining-upward packages of sediment dominate the shallow stratigraphy (<6 m). The base of each package is a sharp, erosional contact overlain by a shelly, gravelly sand lithofacies containing a normal marine calcareous foraminiferal assemblage (e.g., Elphidium excavatum and Buccella inusitata). Overlying this unit is a variable sand lithofacies which can be subdivided into five subfacies based on sedimentology and foraminiferal assemblage: shelly sand, laminated sand, rooted sand, massive sand, or slightly muddy sand. The various sand subfacies are overlain by sandy mud and/or peat lithofacies, both of which contain agglutinated salt marsh foraminifera (e.g., Arenoparrella mexicana, Trochammina inflata, Jadammina macrescens, and Tiphotrocha comprimata).

The southern portion of Pea Island contains three temporally distinct stages of FTD evolution within the past 400 years, each associated with different inlets. The inlets were at least three meters deep and reworked sections of the barrier island stratigraphy.