Mark G. Rowan1,
(1) Rowan Structural Consulting, Boulder, CO
(2) Agip Petroleum, Houston, TX
Abstract: Evolution of autochthonous salt and primary diapirs, southeastern Mississippi Canyon: lessons for the subsalt environment of the northern Gulf of Mexico
2-D and 3-D seismic data over a 175-block area (4400 km2) in southeastern Mississippi Canyon provide a unique look at the deep, primary salt geometry and evolution. Much of the subsalt environment farther west is underlain only by the Louann salt, with no other allochthonous levels. Therefore, a better understanding of the autochthonous salt and associated deformation is critical to subsalt exploration because it impacts trap geometries, facies distribution, and the generation and migration of hydrocarbons.
Primary diapirs in southeastern Mississippi Canyon are rooted along remnant ridges of Louann salt that form a polygonal pattern dominated by north-northwest and east-northeast trends. The former trend is controlled by basement faults across which the Louann salt thickened and the base-Louann deepened to the west. The remnant ridges comprise contractional, strike-slip, and withdrawal/extensional structures, and diapirs have been affected by shortening and/or strike-slip movement.
The post-Louann evolutionary history of southeastern Mississippi Canyon is divided into three stages: (1) condensed Upper Jurassic to Paleogene sedimentation and associated salt withdrawal into ridges and inflated plateaus, possibly triggered by early gravity-driven deformation; (2) lower- to mid-Miocene collapse of the inflated highs and growth of associated diapirs during relatively rapid clastic sedimentation; and (3) mid-Miocene to Pliocene gravity spreading of the entire post-Louann sequence, accompanied by shortening and strike-slip deformation, diapir rejuvenation, and radial spreading or asymmetric lateral extrusion of salt tongues.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana