SEDIMENTOLOGICAL CHARACTERISTICS AND 3-D INTERNAL ARCHITECTURE OF RECENT WASHOVER DEPOSITS

Extensive overwash occurred along Florida's northern Gulf facing barrier islands during the passage of Hurricane Ivan in 2004. This high-energy storm event provided a unique opportunity to study depositional patterns and the 3-D internal sedimentary architecture of fresh washover deposits over a range of spatial scales. The cross-shore extent of washover deposition is controlled by sediment supply, accommodation space, and the extent of cross-shore penetration of overwash flow. Antecedent morphology of the beach or barrier island is the primary factor governing sediment supply and accommodation space, while antecedent morphology coupled with spatio-temporal factors including storm position, intensity, and duration govern the extent of landward excursion of overwash flow.

Four sedimentary sub-facies are recognized, the distribution of which are largely controlled by antecedent morphology of the barrier. Berm facies, characterized by a basal erosional surface and seaward dipping planar stratification dominates the beach and seaward side of the foredune. Back-berm facies extends landward from the dune crest down the backside of the foredune, exhibits little evidence of erosion along the basal contact, and is dominated by landward inclined stratification. Platform facies, largely confined to the interior platform, exhibits little evidence of erosion along the pre-storm surface, and horizontal to gently landward dipping parallel stratification which merges landward with, and often overlie steeply landward dipping foreset stratification. Antecedent hummocky dunes are commonly preserved within platform facies. Back bay facies, the landward most facies is dominated by subaqueous deposition within the back bay, and is characterized by steeply landward dipping tabular foreset and sigmoidal stratification, overlain by horizontally stratified washover. Back bay facies exhibit distinct ridge and trough morphologies oriented parallel to the primary flow direction. Vertical facies transitions can be attributed to temporal variations in storm forcing while architectural heterogeneity in both cross-shore and longshore directions illustrate the highly 3-dimesional nature of the washover deposits.