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Abstract: Geologic Framework, Processes, and Rates of Subsidence in the Mississippi River Delta Plain

P. Shea Penland, S. Jeffress Williams, Harry H. Roberts, Alan Bailey, Gerald J. Kuecher, Joseph N. Suhayda, Karen E. Ramsey

Since the 1930's, Louisiana has lost an estimated 3,950 km2 of coastal wetlands and barrier islands. The loss of these coastal lands resulted primarily from subsidence and erosion rather than the draining and filling of wetlands. More than 40% of the coastal wetlands in the U.S. are found in Louisiana and 80% of our nation's total wetland loss occurs here at alarming rates. Beach erosion rates exceed 10 m/yr and the rate of wetland loss is currently measured at 75 km2/yr. The causes of Louisiana's coastal land loss include delta switching, storm impacts, man's impacts on this deltaic system, and high rates of subsidence. Recent studies indicate that the highest subsidence and coastal land loss rates occur where the underlying Holocene sediments are the thickest. This relationship suggests that subsidence through the consolidation and settlement of these young deposits is of primary importance to the coastal land loss problem found in Louisiana. To understand the role of subsidence in Louisiana's coastal land loss problem requires a knowledge of the Late Quaternary history of the lower Mississippi River, of the infilling of its incised valley during the Holocene transgression, and of the processes of delta switching.

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