FORMATION AND CHRONOLOGY OF GEORGIA BACK-BARRIER ISLANDS

Holocene back-barrier islands, marsh-encircled islands between the ocean-fronting barrier islands and the mainland or Pleistocene barriers along the Georgia coast, comprise a record of sediment-supply and sea-level related shoreline dynamics over the past 4,000 years. Archaeological research along the Georgia coast has suggested a dynamic coastal zone during this time period as well. To better constrain the history of coastal geologic development and provide age constraints on coastal evolution, a chronology was developed for a small number of back-barrier islands using Optically Stimulated Luminescence (OSL) Dating. Modern beach ridges, because of their close regional proximity and morphological similarity to these Holocene islands, were examined as possible modern analogues. Holocene and Pleistocene island characteristics (upland slope, stratigraphy, grain size) have been compared. The Holocene islands are typically comprised of unconsolidated, sandy sediments with poor soil formation. Pleistocene barriers have more stratigraphic variability and soil development. Pleistocene barriers and Holocene back-barrier islands are younger in a seaward direction, suggesting that the coastline near the Savannah River has been prograding over at least the past few thousand years. Sedimentary deposits formed in coastal environments representing late MIS 3 have also been documented in this area. Grain size trends show good correspondence between back-barrier islands and modern beach ridges, suggesting similar mechanisms and environments of deposition. Quartz grains from both settings are subangular and lack significant frosting or abrasion, suggesting a similar origin.