Foraminifera as an indicator of overwash deposits, Barrier Island sediment supply, and Barrier Island evolution: Folly Island, South Carolina

Micropaleontological analysis of four vibracores from back-barrier marshes of Folly Island, South Carolina, detected intervals of storm-deposited sediment. Individual washover intervals were not detectable from lithology alone, but only in conjunction with associated foraminifera. Washovers contained more modern offshore and Oligo-Miocene genera and total calcareous foraminifera than `backgroundʹ marsh samples. The presence of Tertiary foraminifera in the back-barrier cores from Folly Island supports the hypothesis that much of the sediment for barrier island migration is derived from offshore. Foraminiferal analyses of back-barrier cores were also used to calculate relative bioturbation rates by the method of Officer and Lynch [Officer, C.B., Lynch, D.R., 1983. Mixing, sedimentation rates and age dating for sediment cores. Mar. Geol. 46, 261–278, eqs. 10–14]. In all cores, the current depositional environment correlated well with the expected mixing parameter (G): the highest mixing parameter (greatest signal attenuation) was recorded in a core from a low-marsh/creek-side environment whereas the lowest mixing parameter (least smearing of signal) was recorded in a high-marsh core.