INVESTIGATION OF CLAY-RICH STRATA ON ST. CATHERINES ISLAND, GEORGIA

St. Catherines Island is one of a string of barrier islands along the Atlantic coast of Georgia, USA. The Pleistocene island core is bordered by Holocene accretional terrains and tidal marshes. St. Catherines Island (SCI) lacks major sediment input from proximal fluvial sources and is dependent upon adjacent tidal deltas and longshore transport from north to south for its sediment supply. Insufficient sediment supply and rising sea level are promoting rapid erosion that dynamically alters the morphology of the island and exposes relict marsh mud along beachfronts. Local deposits of wood rich sediment and peat suggest at least some of the muds accumulated in fresh water wetlands. Relatively little is known about the variation in clay mineral species and proportions in these sediments. The clay mineralogy of sedimentary strata can reveal information concerning sediment source, depositional environment, diagenetic processes and geologic history. The purpose of this project is to identify specific clay minerals and evaluate their proportions within muddy strata of SCI. Mud-rich samples have been collected from exposed relict marsh mud along the eastern shore and from the shallow subsurface via punch cores and vibracores. A representative suite of samples will be subjected to major and trace element analyses to provide a geochemical framework for the sediments. Samples selected for clay mineral analysis will be processed using sieve and centrifuge techniques to remove organics and particles larger than 2 microns. The fine fraction will be prepared and analyzed using X-ray diffraction to identify specific clay minerals. Grain mounts will be made of the sedimentary particles larger than 2 microns and analyzed using polarized light microscopy. Core samples containing discrete organic clasts may provide chronologic data by AMS radiocarbon dating. The mineralogical analyses will be examined with respect to variation with age and depositional environment. The resulting data may provide an additional tool for correlating muddy strata and depositional environments in cores and exposures of relict marsh mud. This study will contribute to our understanding of the erosional and depositional processes of SCI and how the clay mineralogy is reacting to dynamic coastal processes at this location.