STORM-WASHOVER FANS AS ICHNOLOGICALLY UNIQUE ENVIRONMENTS, WITH EXAMPLES FROM GEORGIA AND SOUTH CAROLINA

Storm-washover fans are the most visible signs of how barrier islands in the eastern U.S. migrate landward. These deposits, which are typically caused by tropical storms or nor’easters, are primarily composed of sand but also may include coarser sediments. Fans are the end result of storm surges that carry sediments from beach and offshore environments; waves breach primary dunes and dump sediment loads on back-dune meadows, maritime forests, or salt marshes. Washover fans are ichnologically unique because they represent rapid changes in substrates that permanently replace a previous set of tracemakers with an entirely new and different set of tracemakers. For example, sandy storm-washover fans deposited on top of salt marshes displace mud snails, mud fiddler crabs, polychaetes, wading birds, alligators, and other tracemakers. In the weeks following their deposition, fans are colonized or otherwise exploited by a diverse suite of tracemakers such as ghost crabs, sand fiddler crabs, hermit crabs, ants, solitary wasps, moles, shorebirds, and nesting sea turtles. If allowed enough time, this initial colonization may then give way to ecological succession, with new plant growth, fewer marginal-marine animals, and more terrestrial animals (e.g., insects, deer, raccoons). An ideal marsh-to-washover sequence would show low-energy strata with marsh traces overlain by initially high-energy deposits, then low-energy strata with mixtures of traces from marginal-marine and terrestrial animals, which in turn are crosscut by root traces and backfilled burrows of cicada nymphs and other insects. For our study, we will provide examples of modern ichnoassemblages from two Georgia barrier islands (Sapelo and St. Catherines) and one South Carolina Island (Edisto), and compare these to Pleistocene storm-washover deposits on St. Catherines Island.