Holocene Evolution of the Ocracoke Inlet Flood-tide Delta Region, Outer Banks, North Carolina

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Caroline Faulkner Smith (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Numerous studies have been conducted along the Outer Banks (OBX) barrier islands of North Carolina to address Holocene climatic change using a combination of lithological, micropaleontological, stratigraphical, and geochronological data to reconstruct Holocene paleoenvironmental reconstructions. These data reveal the importance of inlet formation in the evolution of the modern barrier island chain. However, few studies have been conducted within the Ocracoke Inlet and its associated flood-tide delta (OFTD), which has been proposed to be the most stable inlet along the OBX. Detailed knowledge of the anatomy of the modern, active OFTD is necessary to further elucidate the origin and geologic evolution of Ocracoke Inlet and the OFTD region during the Holocene. Five vibracores, and ca. 100 km of seismic data (boomer and chirp) were collected from the Ocracoke Inlet flood-tide delta (OFTD). Twenty-six age estimates were obtained from the five vibracores (13 AMS radiocarbon age estimates, and 13 Optically Stimulated Luminescence-OSL age estimates). Sediments recovered are all Holocene, except a blue clay interpreted to be Pleistocene that is overlain by a basal peat (core VC1) interpreted to have formed in a freshwater riverine swamp forest (EF VI) environment at ca. 7200 cal yr BP. Sediments are predominantly fine-to-medium grained quartz sand, and contain foraminiferal assemblages composed of 41 taxa dominated by Elphidium excavatum and Ammonia parkinsoniana. Foraminiferal assemblages were used to define four biofacies. The geographical distribution of bio- and lithofacies is related to salinity and to distance from the inlet. Six environmental facies (EFs) were determined by correlating bio-, litho-, and seismic facies. Using the six EFs, three transects and five evolutionary time intervals were produced to reconstruct paleoenvironmental changes recorded in the OFTD region during the Holocene. From ca. 7200-6900 cal yr BP rising sea level caused the initial flooding of the paleo-Pamlico Creek drainage system that was characterized by a freshwater swamp environment (EF VI). Between ca. 6900-6600 cal yr BP EF VI transitioned to a high salinity estuarine environment (EF III). EF IV (undetermined, likely mid-to high salinity) estuarine environments characterized the OFTD region ca. 3400 cal yr BP. Flood-tide delta deposits (core VC3B) occurred in the study area ca. 1100 cal yr BP (during the Medieval Climate Anomaly-MCA) and Royal Shoal began to form ca. 500 cal yr BP (during the Little Ice Age-LIA), when Ocracoke Inlet was first documented in historical maps. EF V represents a sand flat/ shoal environment typical of surficial sediments, specifically near Royal Shoal (core VC2B). OFTD deposits (cores VC3B, VC5A, and VC8A) are characterized by two normal marine salinity FTD depositional environments (EF II-low energy and EF I-high energy). The OFTD region probably existed to the south of the study area when estuarine deposits characterized the study area and migrated northwards as sea-level rose.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

Geology;Barrier islands;Flood-tide deltas;Foraminifera;Optically stimulated luminescence;Paleo-environments

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