Evolution of Salt Structures and Cretaceous Uplift in Westernmost Mississippi Salt Basin, Madison Parish, Louisiana

A. H. M. Shah Alam, Rex H. Pilger, Jr.

Subsurface structures were interpreted from seismic images and well logs in the westernmost Mississippi Salt basin, Madison Parish, Louisiana. Structural and stratigraphic relations indicate that salt structures (Duckport, North Tallulah, South Coleman, Tallulah, and Walnut domes) have evolved through pillow, diapir, and postdiapir stages. Withdrawal synclines associated with each stage of growth occur adjacent to salt domes and are characterized by overthickening of sediments. Synclines associated with Walnut dome are particularly well recognized in the seismic data. Primary withdrawal synclines and present day "turtle" structure anticlines involve the deepest recorded reflections (possibly Jurassic carbonates) above seismically transparent Paleozoic basement and overlyi g remnant salt. Similar early (Late Jurassic) salt mobility has recently been documented in North Louisiana and East Texas Salt basins. Secondary withdrawal synclines (Cotton Valley) are exceptionally overthickened and their axes are closer to the dome than the axes of primary synclines. Tertiary synclines are broad and appear to be active at present.

North-south seismic sections that cross the approximate northwest boundary of the Mississippi Salt basin display post-middle Cretaceous upwarp (the Monroe Uplift) involving basement. Successively older Lower Cretaceous reflections are truncated to the north beneath an erosional surface. Upwarp apparently continued well into the Cenozoic.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.