PRELIMINARY STRATIGRAPHIC ANALYSIS OF QUATERNARY LITHOFACIES ASSOCIATED WITH THE CAPE LOOKOUT HIGH, OUTER BANKS, NORTH CAROLINA

The North Carolina Geological Survey collected five cores from a northeast trending, 85-km long transect along the Outer Banks of North Carolina. The cores were taken from just west of Cape Hatteras, at both the ends and the middle of Ocracoke Island, and on the mainland at Cedar Island. Drill sites were chosen by proximity to features observed on seismic profiles from offshore and within the Pamlico Sound, and targeted major seismic reflection surfaces. Analysis of these cores is part of a cooperative coastal geology research program that is intended to provide a thorough study of the Quaternary geologic framework of northeastern North Carolina. Cooperating agencies and universities include the NCGS, the USGS, East Carolina University, the University of Delaware and the Virginia Institute of Marine Sciences.

A preliminary sedimentologic and stratigraphic analysis of the five cores indicates a Late Tertiary (Miocene?) “basement” to the south that consists of cream- to gray-colored, weakly indurated packstone dominated by bivalve and gastropod molds. This lithology occurs at the bottom of the cores taken from Cedar Island (-21 to -26 m below ground surface) and southernmost Ocracoke Island (-44 to -47 m). The packstone is overlain in these cores by either bioclastic gravelly muddy sand or muddy sandy gravel. The carbonate may also appear at the base of the hole drilled at mid-Ocracoke (-52 to -53 m); it is sharply overlain by black sand that quickly oxidizes to an orange-brown color when core tubes are split open. The northern two holes, from northern Ocracoke Island and Buxton on Hatteras Island, ended in gray, well-sorted, medium sand of uncertain age.

The limestone unit is interpreted to represent part of the Cape Lookout High and was deposited as part of a well-oxygenated carbonate shoal. The black sands found in the mid-island Ocracoke hole may be deposits from an adjacent restricted bay. The basal sands from the northern Ocracoke and Buxton holes may be part of a large shoal complex characterized by steeply dipping clinoforms observed in seismic profiles from Pamlico Sound. Integration of the lithologic analysis with biostratigraphic and seismic data, as well as ¹⁴C and AAR age data, will contribute significantly to the understanding of the Quaternary geologic framework of the area.