THE INFLUENCE OF SUBTLE OUACHITA STRUCTURES ON THE MIDDLE TENNESSEE RIVER SYSTEM

The Tennessee River is the third largest river in the United States east of the Mississippi and flows 652 miles from Knoxville, TN to its confluence with the Ohio River in Paducah, KY. The river includes two major direction changes, one near Guntersville, AL, where the upper Tennessee River changes from a southeastward to northwestward flowing system, and a second bend near the Alabama-Tennessee-Mississippi state border, where the middle Tennessee River shifts from a northwestward to northward flowing system. The upper Tennessee River is confined to Appalachian structures in the Valley and Ridge province, and its main channel system and drainage divide are controlled by bedrock orientations. We present geologic mapping, structural orientations of bedding within Mississippian-age strata, paleotopographic modeling, and geophysical models to suggest that the middle Tennessee River is controlled by Ouachita structures in the northern Black Warrior foreland basin. Field observations reveal NW-SE trending gentle (>120° interlimb angle) folds within Mississippian strata in northwestern Alabama that are parallel to the course of the Tennessee River. Folding appears to be located above deep basement structures, which are defined by regional gravity and magnetic models. Reconstruction of paleotopography based on a basal Cretaceous unconformity surface shows a similar NW-SE structural trend was present during the Cretaceous, suggesting a similar structural influence on paleodrainage systems. The cause of the second bend is currently unknown. It may be the result of glacio-eustasic changes, dynamic topography, or a structural control similar to the upper and middle portions of the Tennessee River.