Quaternary Geologic Evolution of the Croatan Beach Ridge Complex, Bogue Sound, and Bogue Banks, Carteret County, NC

Abstract

Foraminiferal, lithologic, chronostratigraphic, and geophysical data were utilized to describe the Quaternary geologic evolution of the Croatan Beach Ridge Complex, Bogue Sound, and Bogue Banks. The Croatan Beach Ridge Complex is a beach ridge feature located on the mainland of Carteret County, NC. It is separated from the adjacent barrier island, Bogue Banks, by Bogue Sound. Seventeen geoprobe and vibracores were collected along four shore-normal and shore-parallel transects from within the beach ridge complex, on the sound side of Bogue Banks, and in Bogue Sound. Seven depositional facies representing various coastal paleoenvironments were identified using sedimentological data and a cluster analysis of foraminiferal samples taken from core material. Three of these depositional facies were determined to be of normal marine salinity (high energy normal marine salinity, low energy normal marine salinity, and shallow inner shelf) and comprise the basal units of the Croatan Beach Ridge Complex, Bogue Banks, and Bogue Sound. The high energy normal marine salinity depositional facies is characterized by Buccella inusitata, Cibicides lobatulus, Elphidium galvestonense, Eponides repandus, Hanzawaia strattoni, Nonionella atlantica, Quinqueloculina spp., and Textularia cf. T. gramen. The low energy normal marine salinity depositional facies is characterized by Bolivina lowmani, Bolivina paula, Eponides repandus, Gavelinopsis praegeri, Quinqueloculina seminula, and Rosalina floridana. The shallow inner shelf depositional facies is characterized by Bolivina lowmani, Buliminella elegantissima, and Quinqueloculina bosciana. The flood tide delta depositional facies contains a diverse foraminiferal assemblage with abundant Elphidium excavatum, Ammonia parkinsoniana, and Elphidium mexicanum and is found in the older sediments underlying Bogue Sound. The high salinity estuary depositional facies, restricted to basal units of Bogue Sound and Bogue Banks, is characterized by Ammonia tepida, Elphidium poeyanum, Haynesina germanica, and Trochammina sp. The high energy back-barrier lagoon depositional facies comprises the modern sediment of Bogue Sound and contains the shelf taxa typical of assemblages South of Cape Hatteras (such as Ammonia cf. A. beccarii and Elphidium gunteri) as well as agglutinated species (Ammotium salsum). Chronostratigraphic data combined with foraminiferal, sedimentological, and geophysical data suggest that the Croatan Beach Ridge Complex formed and prograded south during MIS 5a (~80-95 ka), producing a cape structure at the southern end of the Suffolk Scarp. Similar data suggest aeolian reactivation of the upper segments of the Croatan Beach Ridge Complex during MIS 2 (~18 ka). OSL and radiocarbon age estimates and the occurrence of flood tide delta deposits indicate the formation of Bogue Banks approximately 6 ka. Seaward and westward spit progradation of Bogue Banks began in the Pine Knoll Shores area ca. 1.7 ka and continued to the eastern tip of Salter Path until ca. 1.3 ka. This corresponds to a spit progradation rate of ~16 m/yr, a rate similar to those found at Oregon Inlet. Normal marine salinity conditions were present in Bogue Sound ca. 1.1 ka, suggesting removal of at least the narrowest parts of Bogue Banks, coincident with the collapse of segments of the barrier islands along the Outer Banks.