LATE QUATERNARY EVOLUTION OF THE APALACHICOLA, FLORIDA, BARRIER ISLAND RIM AND ITS RELATIONSHIP TO SEA-LEVEL CHANGE

St. Vincent Island is an uninhabited barrier island located on the northeastern Gulf of Mexico coast of west Florida, near the mouth of the Apalachicola River. It is a link in a chain of barrier islands on the Gulf Coast that stretch from the Mississippi River delta to northwest Florida. St. Vincent forms the western part of the barrier island rim of the extensive Apalachicola Bay estuarine system. The island is 6 kilometres wide at its east end, 14 kilometres long and covers an area of 50 square kilometres, making it one of the largest Gulf Coast barriers. A well-developed beach-ridge plain covers its surface. As many as 180 ridges have been formed over the island’s approximately 4000-year history. These beach ridges record the location, orientation and elevation of the coastline and, therefore, sea-level position at the time of their formation. St. Vincent Island has one of the best-preserved such records in the Gulf of Mexico. Core samples have been collected from basal deposits of several of the island’s beach ridge sets. Quartz sand extracted from the cores has been optically dated. The results are being used to examine how rapid changes in sea-level have influenced the evolution of the barrier islands and their associated wetlands around the rim of the Apalachicola Bay estuarine system. They are also being employed to document the effect that abrupt sea-level changes have had on the estuary system.