ROWAN, MARK G., Boulder, CO; BRUCE D.TRUDGILL and PAUL WEIMER, Department of Geological Sciences, University of Colorado, Boulder, CO; and J. CARL FIDUK, Boulder, CO

ABSTRACT: Comparison of the Mississippi Fan and Perdido Deepwater, Salt-cored Fold Belts, Northern Gulf of Mexico

The Mississippi Fan and Perdido foldbelts are Tertiary deepwater contractional provinces located at the basinward margin of the Jurassic Louann Salt in the northern Gulf of Mexico. Both formed at different times in response to updip sedimentary loading and extension during gravity spreading of the continental margin above the salt layer.The structural styles are characteristic of salt-cored foldbelts, consisting of linear, generally symmetric detachment folds with regular wavelengths and relatively minor, high-angle reverse faults. However, there are significant differences between the two foldbelts: (1) fold wavelengths, amplitudes, and segment lengths are all greater in the Perdido foldbelt; (2) the Mississippi Fan foldbelt is more asymmetric (basinward-vergent); (3) fold geometries are more rounded in the Mississippi Fan foldbelt and more angular in the Perdido foldbelt; (4) the fold envelope is tilted basinward in the Perdido foldbelt but is subhorizontal in the Mississippi Fan foldbelt; (5) domal structures are found in the Perdido foldbelt; and (6) antecedent folds, highly-rotated fault blocks, and deeplyrooted diapirs are present in the Mississippi Fan foldbelt but absent in the Perdido foldbelt.Variations in the thickness and mechanical stratigraphy of the folded multilayers explain some of the differences. Others are ascribed to the facies and original thickness distribution of the evaporite layer, which in turn was controlled by the underlying rift-basin geometry. Finally, preexisting salt structures from an early phase of deformation account for the short fold-segment lengths, the rotated fault blocks, and the diapirs in the Mississippi Fan foldbelt.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England