Structural Geology of the Mississippi Fan Fold Belt, Atwater Valley Area, Northern Deep Gulf of Mexico

Peter L. Morris¹, Paul Weimer², Renaud Bououllec², and R. Jay Austin^2
1 ChevronTexaco, Bakersfield, CA
² University of Colorado, Boulder, Colorado

The Mississippi Fan fold belt is one of several Cenozoic deepwater fold belts in the Gulf of Mexico. This fold belt covers an area of approximately 110 by 40 miles south of the Sigsbee Escarpment in the northern Atwater Valley area. A thick layer of Middle Jurassic Louann salt is interpreted to have deformed during the Early Cretaceous, forming a regional salt canopy. This allochthonous layer was critical to the development of the Mississippi Fan fold belt. The folds are interpreted to be salt-cored and overlie the regional detachment of the Louann salt. The general trends of the fold axes are EW to ENE. The general fold geometry is southerly vergent folds with a north dipping thrust that offsets strata in the southern limb.

Two additional structural styles associated with the Mississippi Fan fold belt are present near shallow salt features. These features are only found in what is termed, in this study, the eastern Mississippi Fan fold belt. The fold geometry around these features tend to be either symmetric around a salt diapir, or they are folds with steeply dipping strata in the northern limb and gently dipping strata in the southern limb of the fold. The second fold model tends to be associated with salt features where the salt has evacuated and formed salt tongues on the paleo seafloor. The timing of deformation of the fold belt in this study is generally constrained between 15.5 and 5.5 Ma. However, minor folding may have begun as early as 30 Ma. Detailed study of the syn-growth strata is necessary to constrain the timing of deformation and sequential growth of the Mississippi fan fold belt.

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004