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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 27 (1977), Pages 259-271

Origin and Character of Washover Fans on the Georgia Coast, U.S.A. (1)

John R. Deery (2), James D. Howard (3)


Washover fans on the Georgia coast form initially in response to storms but continue to develop after the storm has passed. Most storm-induced fans flood only during spring tides, yet some are continuously active on a day-to-day basis. All washovers have essentially the same surface morphology and internal physical and biogenic sedimentary structures and, based on these features, the washover area can be subdivided into beach, fan, and marginal facies.

Our field studies, centered primarily on Ossabaw, St. Catherines, and Sapelo Islands, indicate that Georgia washover fans have an "active" and a "passive" phase of development and each leaves a characteristic record in fan stratigraphy and sedimentary structures. The "active" phase occurs when waves overtop the beach crest and water and sediments flow landward into the back barrier salt marsh. At such times subhorizontal stratification, ripple lamination, planar foreset crossbedding, and trough crossbedding form. The "passive" phase occurs when the fan is not undergoing overwash from the beach. During this time aeolian and biogenic processes and rain runoff are the principal agents in the formation of sedimentary structures. "Passive" phase structures include dunes, ripple-marks, blow-outs, wind-generated levees, bioturbation, and climbing ripples. Although less dynamic in origin, the "passive" phase structures represent the greatest period of time in washover fan development.

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