GEOPHYSICAL MODELING OF CRUSTAL STRUCTURES AND THEIR IMPACT ON THE FORMATION OF THE MIDDLE AND LOWER TENNESSEE RIVER VALLEY

The Tennessee River is the third largest river in the eastern US. It follows a circuitous course from the headwaters near Knoxville, Tennessee to its confluence with the Ohio River. The path completes two 90 degree turns, one near Guntersville, Alabama separating the upper and middle drainage systems, and a second near the border of Alabama, Tennessee, and Mississippi, between the middle and lower drainages. The upper Tennessee river exits the Valley and Ridge Province and enters the Black Warrior Basin, a Carboniferous foreland basin that formed during the Ouachita orogen. Mississippian strata within the basin are shallowly dipping to the southwest and gently folded. Near the western edge of the Black Warrior Basin, the river crosses Cretaceous sediments before returning to Paleozoic sedimentary bedrock as it turns north. The Cretaceous units unconformably overlies Paleozoic strata representing the formation of Mississippi Embayment following erosion and thermal uplift from the Permian to early Cretaceous.

To better understand the interaction between tectonics and drainage development, gravity and magnetic data were analyzed to determine the deeper crustal structure, including deep intrusions. Complete Bouguer gravity anomaly and magnetic maps reveal a large gravity maximum near the northwestern Alabama and Tennessee border, suggesting high-density regions implying some type of Proterozoic intrusion within Precambrian basement. Magnetic maxima follow the drainage divide between the Tennessee River and drainages to the west suggesting intrusions maybe related to Cretaceous rifting. 2D gravity and magnetic forward modeling indicates that intrusions are oriented parallel to the Mississippi Embayment or Ouachita orogenic front and basement faulting create a barrier for further progression of the Tennessee River into the Gulf Coastal Plain. We propose these subsurface features influenced the formation of the Tennessee River Valley and continue to affect the course of the river today.