Salt and Slope Tectonics-Offshore Louisiana

Shengyu Wu, A. W. Bally

Various stages of the mid-Jurassic salt deformation resulted in post salt extensional and contractual systems of the continental slope offshore Louisiana.

The pre-mid Cretaceous salt deformation resulted in salt massifs, small allochthonous salt bodies, pseudo-clinoforms and turtle structures.

During a significant period of sediment starvation between mid-Cretaceous and mid-Oligocene, previously formed salt and related structure remained stable.

Following the mid-Oligocene to Early-Miocene re-activating of the pre-existing salt structures, the rapid sedimentation during the Middle Miocene resulted in the development of large diapiric salt walls and stocks fed from the pre-mid Cretaceous salt massifs. The rising diapiric salt structures displaced the downslope section of the rapidly deposited overburden seaward. As a result of the downdip displacement, the Mississippi Fan Fold Belt was formed and focused near the frictional boundary along the basinward limit of the mid-Jurassic salt. The shorting in the fold belt ceased when the allochthonous salt began to spread near sea floor during the Late Miocene.

Since late Miocene, up-dip from the fold belt, large scale primary allochthonous salt sheets continued to form and spread downslope. As the massive salt withdrew from the mother salt, large primary withdrawal basins, regional, counter-regional growth fault systems, tension faults, primary and secondary welds and turtle structures formed. With supra-allochthonous salt, secondary and tertiary withdrawal basins, tertiary, quaternary and welds and large extensional growth faults and occasionally contractional faults. The allochthonous salt on the shelf is mostly second generation.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995