2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 340-4
Presentation Time: 2:00 PM

SHACKLEFORD BANKS BACK-BARRIER COASTAL SYSTEM, CAPE LOOKOUT NATIONAL SEASHORE, NORTH CAROLINA: A RE-EVALUATION OF THE EVOLUTIONARY HISTORY


RIGGS, Stanley R.1, AMES, Dorothea V.1, MALLINSON, David J.1, PRENTICE, Guy2 and HELLMANN, Robert2, (1)Department of Geological Sciences, East Carolina University, Greenville, NC 27858, (2)Southeast Archeological Center, 2035 E Paul Dirac Drive, Johnson Building, Suite 120, Tallahasee, FL 32312, riggss@ecu.edu

Shackleford Banks (SB), a 14 km-long barrier island is situated west of Core Banks and Cape Lookout and south of Back Sound, a broad and shallow estuarine system. Geologic studies carried out over the past decades interpreted the geomorphic and geologic evolution of the back-barrier features as flood-tide deltas of former inlets. The present study of SB (based on field mapping, LiDAR and aerial photo time slice data, and ground-penetrating radar surveys) is in cooperation with NPS archeological surveys with radiocarbon age data, and incorporates the data from previous studies. Native American middens that occur on the sound-side of the sub-aerial barrier island and date from ca. 2500 cal y BP (Early Woodland Period) to ca. 600 cal y BP (Late Woodland Period).

SB formed as 3 discreet island segments through time as large-scale spits that prograded westward into Shackleford Bay (a wide and open marine embayment) all dominated by shore-oblique ridge and swale features. The eastern half of SB formed when sea level was ~2.5 m below present. This older depositional surface was in place by ca. 2500 cal y BP and is preserved along the sound side and extends into Back Sound as a vast area of paleo-ridge and swale features that occur today as intertidal to sub-tidal flats, shoals, and oyster reefs. All known Native American middens occur on this older topographic surface and beneath modern estuarine sediments and barrier island sediment sheet of overwash fans and dune fields. Deposition of spit segment 2 occurred as sea-level was less than 1 m below present and formed between the 14th and 17th centuries as evidenced by the burial of a soil horizon and associated European midden. As segment 2 formed it filled the deep drainage channels, diverting the estuarine discharge to the NW and maintaining a deep-water, back-barrier estuarine system behind this island segment. By the 1883 survey, most of the segment 2 morphologic sequence had developed a mature maritime forest, about half of which was subsequently buried by a massive influx of sand that formed the modern interior dune field by the late 19th to early 20th century. The most recent spit (segment 3) grew westward filling the last portion of Shackleford Bay, formed and eroded several times during the past few centuries, and now constrains the present position of Beaufort Inlet.