Zurawski, L. (2019). A HIGH-RESOLUTION MICROPALEONTOLOGICAL AND SEDIMENTOLOGICAL ANALYSIS OF BURIED WASHOVER DEPOSITS FROM FOLLY ISLAND, SOUTH CAROLINA: IMPLICATIONS FOR PALEOTEMPESTOLOGY. Unc Charlotte Electronic Theses And Dissertations.
A 40-meter transect consisting of eight equally spaced 2.44-m vibracores was taken across a marginal-marine salt marsh behind North Folly Island, a barrier island located in Charleston County, South Carolina. Analysis of storm signatures from this transect was conducted for the purpose of attaining a better understanding of the characteristics that define a storm layer. Previous studies in paleotempestology have focused on either sediment layers or microfossil proxies, but rarely both. This study analyzes down-core changes in microfossil assemblages and sediment grain size. Spatio-lateral continuity and storm layer preservation are additional focal points in this examination as little investigation has occurred to expand scientific understanding of variables that affect how storm events are identified and conserved over time. Two buried storm layers were identified in the marsh strata along the transect. The upper storm layer is characterized by a thick sand lens of medium to fine grained sand. This sediment resembles the sand found at the beach front and dunes with respect to maturity, color and grain size. The lower sand lens is thin and appears in the middle of a 5-cm silt deposit. Both storm layers were laterally continuous and displayed a sharp contact between the bottom of the storm layer and marsh facies. Differences in grain size between the two storm layers suggest changes occurring over time caused by bioturbation, but also may be due to the differences in geomorphic environment or sediment source for the overwash. Microfossil assemblages from the sand lenses included multiple offshore-indicative calcareous Foraminifera genera. High-resolution analysis of these foraminiferal assemblages suggests that dissolution and abrasion result in a decrease in the correlation between sand content and marine taxa. Microfossil destruction is caused by the drying cycles and acidity typical of the high-marsh and intermediate-marsh environments. The lower storm layer contains a surprising diversity and richness of offshore genera, including many taxa not found within the larger, younger storm deposit. Variability in the storm signature, with respect to both sedimentary and micropaleontological proxies, exists for multiple cores in this study. While the fragility of the offshore-indicative and agglutinated microfossils may confuse paleoenvironmental interpretations and destroy the utility of the Foraminifera as a natural tracer, an increase in grain size accompanied with the presence of offshore foraminiferal assemblages is clearly the best indicator of the source of sediment in an overwash deposit and the method of deposition - (hurricane) - for the sand layer.