Abstract: Sediment Texture and Composition Changes Along the Southwest Louisiana Coast: Implications to Sediment Supply

Matthew J. Taylor, Mark R. Byrnes, Randolph A. McBride

The chenier plain of southwestern Louisiana is over 200 km in length and up to 30 km wide. Models explaining chenier plain origin around the world have evolved from extensive studies conducted on the Louisiana chenier plain. The episodic supply of sediment from the shifting position of the Mississippi River is widely believed to be responsible for the evolution of this region, however, local sources of coarse clastic sediment may be important contributors during chenier formation.

Southwestern Louisiana chenier plain sediment sources and transport dynamics are examined through analysis of modern beach and ancient beach/chenier sediment samples. Sediment samples collected on the active berm, from approximately 90 km of beach between Big Constance Lake and the Sabine River, were analyzed to observe along-shore trends in texture and composition. Correlation of results from the Grand Chenier/Oak Grove Ridge/Front Ridge chenier complex and the modern beach has important implications regarding local late Holocene sediment sources to the chenier plain. Textural and compositional analyses of the samples collected range from sandy shell (1.53 mm) to very fine quartz sand (0.10 mm) and reveal highly dynamic, cellular sections of numerous fining and coarsening trends. A s ngle sediment source and/or unidirectional longshore sediment transport along this 90 km stretch of beach appears improbable given observed trends in grain size and composition. Instead, local sources of coarse clastics appear significant relative to chenier formation.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana