Continuity of the Reelfoot Fault across the Cottonwood Grove and Ridgely Faults of the New Madrid Seismic Zone

Abstract

Previous investigators have argued that the northwest‐striking Reelfoot fault of northwest Tennessee and southeastern Missouri is segmented. One segment boundary is at the intersection of the northeast‐striking Cottonwood Grove and Ridgely strike‐slip faults with the Reelfoot fault. We use seismic reflection and geologic mapping to locate and determine the history of the Reelfoot South fault across this boundary zone. One reflection profile revealed a southwest‐dipping (81°) Reelfoot South reverse fault that displaces the top of the Paleozoic 65 m, Cretaceous 40 m, Paleocene 31 m, Eocene Wilcox Group 20 m, and Eocene Memphis Sand 16 m. A second reflection profile reveals a north‐dipping (84°) reverse fault 4.3 km south of the Reelfoot South fault, which defines the southwest margin of the Tiptonville dome. A geologic profile of the base of the ∼3.1 Ma Upland complex (Mississippi River terrace alluvium) within the Mississippi River bluffs reveals ∼6 m of displacement across the Reelfoot South fault. Similarly, Quaternary stream terrace distribution suggests ∼6 m of Reelfoot South hanging‐wall (Tiptonville dome) uplift that is probably Holocene. Fault strike trends show the Reelfoot fault and its hanging‐wall Tiptonville dome are not laterally offset across the Cottonwood Grove and Ridgely faults. The Reelfoot South fault northwest and southeast of the Cottonwood Grove and Ridgely faults has very similar vertical displacement on common stratigraphic marker horizons in the upper 900 m. These data indicate the Reelfoot fault/Tiptonville dome has acted as one continuous fault zone across the Cottonwood Grove and Ridgely faults since Late Cretaceous.