Relations of Ouachita Fold-Thrust Belt to its Appalachian Counterpart and to Initial Late Triassic Opening of a "Closed" Gulf of Mexico

Dewitt C. Van Siclen

The southern Appalachian subduction system continued southwest off the North American craton into the Late Proterozic oceanic embayment that occupied the area of the present western Gulf Coastal Plain. These dissimilar crustal types (and altitudes) were separated by the convergent right-lateral Phillips basement-fault zone along the northern northeast side of the present Mississippi salt basin. On gravity and magnetic maps this faulting truncates the Appalachian structures and supports the continuation of the Phillips faulting into the eastern "core" of the Ouachita Mountains.

The narrow Wiggins arch along the southern side of this basin was part of the volcanic arc assigned to the oceanic embayment. Of four described wells drilled into Wiggins basement, two bottomed in granite and two in phyllite, all "age-dated between 275 and 300 million years (Early Permian-Late Pennsylvanian)", consistant with cooling ages for the mainly Pennsylvanian Ouachita deformation. Earlier, however, the eastern end of the Wiggins arc had collided with the craton near the present Wilcox embayment, where it slowly pivoted about 60° clockwise into its present orientation.

In Late Triassic, during the first stage in opening of the Gulf of Mexico, the Wiggins arch was left behind when the adjoining lithosphere north and east of it moved northward with the rest of North America. This rifting created the Mississippi basin and north-trending Jackson faults across the Wiggins' east end. The Monroe arch north of the west end of the Wiggins may be its former continuation that remained with North America, in which case these arches should be linked by a mirror image of the Jackson faulting.

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