FORAMINIFERA AND SEDIMENT GRAIN-SIZE AS INDICATORS OF STORM-DRIVEN, ONSHORE SEDIMENT TRANSPORT IN ONSLOW BAY, NC.

The seabed of Onslow Bay, offshore of North Carolina, USA, is characterized by outcrops and subcrops of Miocene and Oligocene strata overlain by patchy Holocene sand sheets. Sediment transport can be identified through comparison of fossil foraminifera in foraminiferal assemblages from modern sediment taken from the inner shelf of Onslow Bay with those from the adjacent Bear Island. Three replicate samples were taken from modern sediments overlying five Miocene foraminiferal biofacies and one Oligocene biofacies using a Shipek grab sampler at an average water depth of 12 m. Subsamples were taken from 0–1 cm and 4–5 cm sediment depth from each grab sample. Sites were further characterized using a 450 kHz side-scan sonar and grain-size analysis. Coarser grained sediment (mean of 2.01 phi) was more abundant in the west near Bogue Inlet whereas slightly finer sediment (mean of 2.43 phi) was more abundant eastward. Sediments were moderately sorted (west), then poorly sorted (Bogue Inlet), before becoming moderately to well sorted (east). In Onslow Bay, modern foraminifera dominated assemblages (85%–97%), with the remainder being phosphatic or sugary fossil specimens. Rotaliids dominate modern assemblages (78% average), miliolids are less abundant (19%), and textulariids were rare (~2%). Phosphatic fossil foraminifera in modern shelf sediment were more abundant than sugary fossil foraminifera, which contrasts with Bear Island, where sugary fossil foraminifera were more common. Phosphatic fossil foraminifera were particularly abundant in foreshore and washover deposits on Bear Island after hurricanes. Further sediment (XRF) and foraminiferal analyses (strontium isotopes) are pending but will be presented.