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Meyer, Craig T.1, Antonio B. Rodriguez1, John B. Anderson2, Alexander R. Simms2 
(1) University of Alabama, Tuscaloosa, AL 
(2) Rice University, Houston, TX

ABSTRACT: Geomorphic Evolution of Morgan Peninsula, AL: Influence of Incised Valley Architecture on a Progradational Barrier

Morgan Peninsula, Alabama is an attached barrier system about 25 km long and 2 to 5 km wide separating Bon Secour Bay from the Gulf of Mexico. The peninsula is composed of four obliquely-aligned sets of beach ridges that are underlain by the Mobile-Tensaw incised valley system, providing an opportunity to examine the effects of valley topography on prograding barrier morphology. 
Approximately 10.7 km of 100 mHz Ground Penetrating Radar (GPR) data, 21 km of 2-15 kHz chirp data, 7 cores with an average penetration of 13 meters, 30 cm resolution digital elevation data, and aerial photography were collected to examine the internal facies architecture and evolution of the peninsula. 
The peninsula is connected to the mainland in the east by a Pleistocene Gulfport Fm. barrier complex, while the rest of the peninsula is composed of Holocene sediment. The oldest Holocene portion of the peninsula, located between two valleys, consists of NW-SE trending beach ridges. A recurved surface morphology and the presence of articulated inlet-influenced bivalves both suggest that this early barrier set was influenced by the western valley paleotopography. This older beach ridge set is truncated by concave beach ridges that extend over the eastern incised valley. GPR profiles reveal prograding clinoforms with slopes of 10 to 15 degrees immediately above the valley. The westernmost part of Morgan Peninsula consists of a relatively narrow set of beach ridges that indicate spit accretion in modern times.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.