Split-spoon core samples from 14 bore holes on Shackleford Banks, Carteret County, North Carolina, revealed three lithologically distinct units above an erosional surface on upper Tertiary fine-grained sands. Two Pleistocene units are recognized. The lower unit, consisting of silty, highly fossiliferous sand, was deposited in a nearshore open marine environment during a late Sangamon transgression of the sea that advanced at least 32 km inland from the present coastline. This unit was informally named the Core Creek sand by Mixon and Pilkey. Overlying the Core Creek sand is a silty, sandy gray clay herein named the Diamond City Clay. It contains a fauna indicative of a back-barrier environment. Shells and salt-marsh peat from the Diamond City Clay were radiometrically dated between 24,000 and 30,000 B.P., indicating that the unit was deposited during a mid-Wisconsin high stand of sea level. It is speculated that a barrier at that time stood just offshore of the present-day Shackleford Banks. The Pleistocene surface was subsequently subaerially exposed, and a freshwater peat was deposited in one local depression.
The Outer Banks sand of Holocene age is the uppermost unit of the island. In this sand body ten sedimentary environments, of which barrier inlets were dominant, were recognized. At least one inlet was formed in the recent past on the eastern end of the island and then migrated to the present location of Beaufort Inlet — all while Shackleford Banks remained in its same relative position. The migrating inlet eroded all previous Holocene sediments and truncated the underlying Diamond City Clay.