Stratigraphy of Washover Deposits in Florida: Implications for Recognition in the Stratigraphic Record

Peter E. Sedgwick, Richard A. Davis Jr.

Storm washover deposits comprise a substantial part of the stratigraphic record of barrier island systems and serve as potential hydrocarbon reservoirs when surrounded by fine-grained back-barrier deposits. Despite this importance, little has been done to distinguish such deposits from similar facies in the stratigraphic record.

Washover deposits on the coast of Florida were cored to identify a modern stratigraphic signature on the basis of sedimentary structures along with textural and compositional trends. To examine the loss of that signature over time, an artificial time series was established using modern deposits, historical deposits identified through air photographs, and ancient deposits as interpreted by barrier morphology. The data set consists of 31 cores collected from three Florida coastal areas, including the west central barrier coast, the panhandle, and the northeastern coast. Repository cores from the west central coast were also examined for washover content.

A modern washover deposit typically displays plane beds consisting of well-sorted quartz sand with distinct bands of shell material and heavy minerals. The upper deposit tends to be heavily bioturbated and may be capped by an algal mat representing a hiatus between events. In as little time as a decade, bioturbation begins eradication of small-scale shell, heavy mineral, and algal stratification, leading to difficulty in delineating individual washover events. Even after visual characteristics have been destroyed, however, washover deposits are still identifiable on the basis of textural and compositional framework in a larger stratigraphic context.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995