SHALLOW MARINE STRATIGRAPHY EAST-CENTRAL FLORIDA: SEA LEVEL OSCILLATIONS DURING THE LATE PLEISTOCENE

The research undertaken for this study focuses on stratigraphy preserved beneath the lower shoreface off Sebastian Inlet, Florida. The lower shoreface provides a detailed record of the sea level fluctuations during the Late Pleistocene. To achieve this objective two data sources were utilized. High frequency sub-bottom acoustic profiles were collected and interpreted. Vibracores were collected, logged, and analyzed for texture, fauna, and composition.

The stratigraphy found at the lower shoreface indicates a history of back barrier and lagoon sedimentation east of the modern barrier island. The deepest sediment reached by vibracores consists of partially lithified Late Pleistocene fine sand similar to a flood shoal or tidal flat environment. Previous studies interpreted this layer to be contemporaneous with the Anastasia Formation suggesting it was deposited as shoreline regressed <120,000 yrs BP. Located laterally are meandering channels filled with organic rich siliciclastic fines that date to >43,500 yrs BP. These fines are believed to have been deposited in response to rising sea level. The thickness of the interval of fines coupled with the preservation of organic matter and lack of fauna suggest rapid deposition of fines. Above these sediments are washover sands and thick layers of finely bedded organic rich fines, followed by another sequence of washover sands and organic rich fines. The deepest washover sequence dates to 41,310 yrs BP. These sequences are truncated at the top by a Holocene-aged ravinement surface. Modern sequences consist of lower shoreface fair/storm weather sedimentation below a coarsening upward sequence of siliciclastic fine sand interpreted to be ebb shoal in origin.

This research shows that during the Late Pleistocene, a barrier island complex may have existed east of the modern shoreline. The formation of this barrier island complex resulted in the deposition of washover sand and low energy lagoon fines beneath what would become the modern lower shoreface.