LATE QUATERNARY SEA-LEVEL HISTORY FOR THE NORTHERN GULF OF MEXICO AND ITS IMPACT ON BARRIER GROWTH AND DEVELOPMENT

All available sea-level data for the northern Gulf of Mexico coastline have been compiled and statistically filtered to produce a composite sea-level history for the past 20,000 years. The results compare well with global sea-level records. During the latter half of the Holocene several minor cycles of sea-level rise and fall have occurred in the northern Gulf. Their nature and timing have had a significant effect on the genesis and development of coastal sedimentary features. The large beach ridge plain on St. Vincent Island, off northwest Florida, records these events in an extensive and well-preserved set of ridges. As many as a dozen sets comprise the strandplain. We have analyzed this record in several ways in order to better understand the relationship between barrier growth and small-scale sea-level changes. We have trenched and cored a large number of the ridges to observe and record their structure. Basal ridge deposits have been dated using optically stimulated luminescence (OSL) dating. We have performed topographic surveys in order to determine the location of the ridge bases relative to sea-level. Additionally, we have carried out several ground-penetrating radar (GPR) transects of the island in order to examine the full extent of the ridge features and to understand the relationships between the strandplain and the pre-barrier surface. The results indicate that barrier growth has been strongly influenced by small-scale changes in sea level and local sources of sediment.