SPATIAL DISTRIBUTION OF SEDIMENTARY SUB-FACIES WITHIN RECENT WASHOVER DEPOSITS

Extensive overwash occurred along the Florida Gulf and Atlantic facing barrier islands during the passage of three strong hurricanes in 2004. Washover sediment deposits along the Gulf- facing Panhandle coast induced by Hurricane Ivan and along the east-central Atlantic-facing coast associated with the passages of Frances and Jeanne were examined through coring, trenching, time-series beach profile and ground penetrating radar (GPR) surveys, and aerial photography. The data reveal distinct and consistent spatial sedimentological patterns within the washover deposits across the barrier profile.

Five sedimentary sub-facies are recognized, which can be related to antecedent barrier morphology, depositional environments, as well as sediment transport processes. The near-shore sub-facies lies seaward of the foredune ridge and is characterized by thickening seaward, horizontal to seaward dipping layers and laminae, and a sharp planar basal contact. Landward, the foredune ridge marks a transition in barrier response from dominantly erosion seaward, to accretion landward. Washover deposition in this transitional zone (transitional sub-facies) exhibits converging upward, bi-directional dipping stratification. Sediment eroded from the dunes is in turn transported landward and deposited onto a wetted subaerial surface forming a broad flat layer (platform sub-facies), thickening landward, and dominated by horizontal to sub-horizontal stratification. Owing to increased accommodation space, the platform sub-facies thickens landward as the washover progrades into interior marsh wetlands, flooded back barrier lagoons, and the back-bay, were deposition is largely subaqueous. The subaqueous sub-facies is characterized by steeply inclined tabular foreset and sigmoid bedforms, a tangential basal contact, and washover thicknesses approaching 2 meters in places. Overwash or runoff channels commonly dissect the central and distal portions of the interior platform. Channelized features are spatially limited, typically asymmetrical, and yield distinct ripple bedforms, as well as converging downward, bi-directional dipping stratification (channel sub-facies).