Phytolith assemblages as indicators of coastal environmental changes and hurricane overwash deposition

Abstract

We demonstrate that phytolith assemblages are a useful proxy for reconstructing coastal environmental changes and for validating the overwash origin of sand layers in palaeotempestology studies. Phytolith analysis was conducted on 50 topsoil or surface sediment samples collected from a variety of coastal plant communities or depositional environments in the southeastern USA. The data suggest that different coastal subenvironments can be distinguished by their modern phytolith assemblages. For example, coastal marsh samples contain a diverse phytolith assemblage dominated by smooth-elongate and square morpho-types and maritime forest samples are dominated by phytoliths from palms and broadleaf dicotyledonous plants. Remarkably, the phytolith assemblages from sand dunes are characterized by high percentages of two-horned-tower, flat-tower, spool/horned-tower and short-saddle types. Phytolith analysis of three prehistoric sand layers in a sediment core from Western Lake, northwestern Florida, shows that they contain a phytolith assemblage similar to those characteristic of sand dunes and interdune meadows. These observations are confirmed by the results of principal components analysis and discriminant analysis on the modern and fossil phytolith data sets. Our study results support the interpretation that the sand layers in Western Lake were indeed formed by the erosion of sand dunes during overwash processes caused by landfalling catastrophic hurricanes.