HIGHSTAND CHANNEL-FILLS IN BARRIER ISLAND DEPOSITS: DATA FROM GPR AND SEISMIC PROFILING NEAR CAPE LOOKOUT, NORTH CAROLINA, USA

Barrier island deposits are diagnostic of sea-level rise culminating in highstands that inundate the continental shelf. During highstands, smaller sea-level variations, and changes in climate, estuarine/lagoon circulation and sedimentation affect barrier island morphology. Inlet incision and filling manifests changes in barrier morphology, and the geometry and stratigraphy of filled inlets may preserve a wealth of information. However, stability, retrogradation or progradation of the shoreline ultimately governs the preservation of channel-fill deposits. Thus local variations in wave energy, sediment supply and antecedent geology can affect channel-fill preservation along shoreline reaches that experience the same sea level and climate forcing. This study compares channel fills mapped on two barrier beaches, Bogue and Shackleford Banks, both on the south-facing limb of the Cape Lookout cuspate foreland, North Carolina, USA. We discuss the expression of buried inlet channels mapped onshore and offshore by ground-penetrating radar (GPR) and seismic profiling, respectively, and we interpret differences in channel preservation in terms of the Late Holocene histories of these two barrier islands.

Thirty-one km of GPR and 58 km of seismic profiles were gathered and analyzed. Seismic profiles reveal several paleochannels buried beneath the shoreface and inner shelf of both barrier islands. Based on published stratigraphies for nearby cores, many of the stacked paleochannels off central Bogue Banks are Pleistocene lowstand-incised features. Although the morphology of central Bogue Banks indicates the presence of at least one Late Holocene inlet channel bisecting the island, shoreface progradation has obscured most evidence of young paleochannels in the seismic and GPR records. A relict flood tidal delta in the backbarrier of Shackleford Banks suggests that a relatively recent Holocene inlet channel bisected the island. We observed a distinct paleochannel with a NW-SE trending axis in shoreface seismic profiles off central Shackleford. Onshore GPR profiles also imaged buried channels in this part of the island.