A palynological investigation of the Central Depression on St. Catherines Island, Georgia

St. Catherines Island, Georgia, is a barrier island characteristic of the Georgia Bight. It is composed of a late Pleistocene core, with younger Holocene age sediment surrounding it. A linear topographic low exists along the length of the island’s late Pleistocene core, and has an unknown origin. This Central Depression (CD), has not been addressed by any previous work, leaving its underlying geologic characteristics unknown. Historic accounts recall artesian springs on St. Catherines Island as recently as the 18th century, but whatever their source, they are now gone. The purpose of this study is to use standard palynological techniques to discern the paleoecology of the CD, in order to address whether or not it was the source of these recorded springs. Nine vibracores were taken from the CD to be analyzed stratigraphically, structurally, and palynologically. Understanding the geological and paleoecological changes in this area are significant for determining any possible reason for the existence of the Depression, and to understand the Quaternary changes this region has undergone. Palynological analysis of the samples collected provides evidence of historically significant freshwater wetlands. Genera including Lachnanthes, Sphagnum, Botryococcus, Nymphaea, and Utricularia were present in various samples, indicating prominent freshwater marsh environments. Wetland taxon diversity increased with depth in the sampled cores and wall samples located across the CD. Integration of palynological data from the cores into a stratigraphic and geophysical profile across the CD provides indirect information on island hydrology and helps to constrain the origin of the CD and the hydrologic system that supported ancient wetlands in the CD. Along with historic accounts, this is interpreted to suggest that the CD used to be the site of flowing artesian springs and wetlands, and also implies a subsurface hydrologic connection between the Depression and subsurface freshwater bodies