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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 53 (2003), Pages 422-433

Evolution and Stratigraphy of a Recent Previous HitFloodNext Hit Tidal Delta: Raccoon Pass, Timbalier Islands Louisiana

Mark A. Kulp, Duncan FitzGerald, Shea Penland, Jeffrey Motti


Raccoon Pass is a wave-dominated tidal inlet embedded in the transgressive Bayou Lafourche barrier shoreline. Raccoon Pass separates East Timbalier Island and the Bayou Lafourche erosional headland, which has retreated more than 2 km landward within the last 100 years. Changes in width, depth, and position of the tidal inlet reflect variations in sediment supply and storm activity. As the barrier island-tidal inlet system migrates landward, sand is transported into the bay by overwash and Previous HitfloodNext Hit-tidal currents, building a large Previous HitfloodNext Hit-tidal delta. Historical aerial photographs and vibracores have been used to document the evolution and stratigraphy of the Raccoon Pass Previous HitfloodNext Hit delta. Presently, the delta extends 1.5 km into the bay over an area of several square kilometers. The 1 to 2-m thick Previous HitfloodNext Hit delta facies consists of very fine to fine-grained, moderately well-sorted sand in sharp contact with subjacent bay muds. Locally, as much as 1.0 m of sandy mud within the coarsening upward Previous HitfloodNext Hit delta facies suggests an interruption of deposition in response to spit migration or episodic inlet closure. Unlike Previous HitfloodNext Hit deltas in hydrodynamic equilibrium, the Previous HitfloodNext Hit delta at Raccoon Pass is thickest proximal to the inlet and thins bayward. This geometry is the result of rapid transgression of the coast, which inhibits formation of an ebb shield before the sand is reworked and the inlet shoreline migrates landward. Thus, the Raccoon Pass Previous HitfloodNext Hit delta represents an amalgamation of washover, recurved spit, and Previous HitfloodTop-tidal current deposits.

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