DEFINING THE ORIGIN OF AN ANOMALOUS SAND RIDGE FIELD IN PAMLICO SOUND, NC, USA

The Outer Banks of North Carolina have been shown to undergo geomorphic change, exhibiting varying degrees of barrier island continuity during the late Holocene. These changes affect the environmental conditions (salinity, tidal and wave energy, currents, etc.) in the Pamlico Sound, the estuarine system behind the Outer Banks. The modern estuarine system is characterized by minimal tidal energy (tidal range of 10 cm), and limited exchange with the marine environment through three inlets, resulting in the accumulation of organic-rich muds in the basin, and low- to mid-salinity estuarine foraminifera. However, an anomalous relict sand ridge field occurs in the eastern Pamlico Sound basin, suggesting different hydrodynamic conditions in the past. The field extends up to 10 km into the basin, and is oriented perpendicular to the barrier islands, and consists of a sand unit that is partially covered by mud. To understand the geologic history and origin of this sand ridge field, two vibracores that recovered the sand unit are being analyzed for sedimentology, foraminiferal assemblages, and age. Chirp seismic data are also being examined to understand the dimensions and stratigraphy of the unit. Additional cores and analyses are planned. Possible explanations for the ridges include: 1) tidal deposits during a phase of greater tidal influence; 2) major storm deposits; 3) tsunami deposits, possibly associated with failure of the nearby Cape Fear Slide. The sedimentology reveals a coarsening up trend which is unusual when compared to dominantly fining up sequences associated with overwash and flood-tide delta deposits. Previous paleoenvironmental work suggests the sand ridges were deposited under high salinity conditions. Defining the mechanism of formation of this sand ridge field will assist in the understanding of the geological evolution of the region.