A STRATIGRAPHIC INVESTIGATION OF PALEOSHORELINE POSITION ON SKIDAWAY ISLAND, GEORGIA

Skidaway Island is a Pleistocene barrier island in Chatham County, Georgia, protected from the active shoreline by Wassaw Island, a Holocene barrier. This area of the Georgia coast has been inhabited for the last 10,000 years, and is host to the oldest pottery in North America. The goal of this project is to delineate the detailed location of the Late Holocene paleoshoreface from 4,500 years ago to the present, using geological, paleontological, and archaeological tools. Five shell middens (ancient Native American refuse mounds) exist in the intertidal zone along the eastern edge of Skidaway Island. Previous work has used these middens to approximate a late Holocene paleoshoreface, assuming that these middens were originally deposited on the paleoshoreface and that sea level has since risen. The validity of using these middens to locate a paleoshoreface for Skidaway Island has been questioned by previous work. In order to support or refute the suggested paleoshoreline location, six cores have been taken perpendicular to Skidaway’s current shoreline and across the midden study area. These cores have been used to show (1) if the middens exist on a sandy paleoshoreface, and (2) the subsurface depth to that paleoshoreface. Cores are being analyzed for grain size, organic content, and the presence of Atrotorquata Lineata, a fungal spore specific to Juncus Roemerianus, a high marsh indicator species. These analyses are being used to describe the Pleistocene and Holocene deposits and the interface between them. Grain size measurements show that the ratio of sand to mud increases with depth in each core, consistent with the idea that the sandy paleoshoreface exists beneath the existing marsh surface. The morphologies of important surfaces have been determined using probing and RTK-GPS. The existing marsh surface, which is flat-lying and dips gently seaward, overlies a morphologically complex pre-existing surface, representing the Holocene island fringe. These field and laboratory observations are being combined into a model of paleoshoreface character and geologic development.