NEOICHNOLOGY OF STORM-WASHOVER FANS ON THE GEORGIA COAST AND ITS USES IN PALEOECOLOGY

Storm-washover fans on barrier islands of the Georgia coast have long been recognized as fascinating sites for sedimentological and neoichnological studies. Part of this appeal has stemmed from their easy recognition as laterally restricted, thin, fan-like deposits that extend from beaches across dunes, and into back-dune meadows and salt marshes. Moreover, their ichnocoenoses include a wide variety of ecotone-crossing tracemakers and traces, providing neoichnologists with much material to study. For example, tracemakers of Georgia storm-washover fans include marginal-marine plants (Spartina alterniflora, Salicornia virginica) terrestrial plants (Juniperus virginiana, Myrica cerifera), marginal-marine invertebrates (Uca pugilator, Ocypode quadrata), terrestrial invertebrates (Scapteriscus spp., Cicindela spp., Tibicen auletes), terrestrial vertebrates (Procyon lotor, Odocoileus virginianus, Grus canadensis), and marginal-marine vertebrates (Caretta caretta, Dermochelys coriacea). Plant-root traces are definable on the basis of root morphology and are readily distinguished from invertebrate burrows. Fiddler and ghost crab traces include burrows, tracks, scrapings, and pellets; burrows are distinct and densely spaced, defining the ichnoassemblage. Mole-cricket, tiger-beetle, and cicada-nymph burrows are frequent components of sandy areas above the influence of tides. Vertebrate trackways are exceedingly common throughout fan surfaces; mole burrows are less common but present in some fans. Sea-turtle nests are present in more shoreward parts of fans, but are large and distinctive structures. Preservation potentials are highest for deeply emplaced traces, which include vertebrate tracks penetrating to greater depths than some insect burrows. Once deposited, washover fans make for natural laboratories conducive to the study of post-storm ecological successions, and cross-cutting relations of traces accordingly reflect such successions. We will provide an example of how this basic neoichnological model of Georgia washover fans was applied to the Yellow Banks Bluff Formation of St. Catherines Island (Pleistocene, Georgia), from which we interpreted storm-washover deposition and post-storm colonization events on the basis of trace fossil content.