QUATERNARY FAULTING AND DEFORMATION ALONG THE SOUTHEASTERN MARGIN OF THE REELFOOT RIFT AT FORT PILLOW RIDGE, LAUDERDALE AND TIPTON COUNTIES, WESTERN TENNESSEE

Geologic mapping along with borehole data and satellite imagery of Fort Pillow ridge in Lauderdale and Tipton counties in western Tennessee provide evidence for faulting and tilting of Quaternary deposits during middle to late Pleistocene time. Fort Pillow ridge lies ~5 km north of the structural intersection of the southeastern margin of the Reelfoot rift and the NE-trending Meeman-Shelby and associated faults in westernmost Tennessee. The ridge forms the northern topographic barrier for the Hatchie River, a western Tennessee tributary of the Mississippi River. Outcrop and borehole data indicate a maximum of ~30 m Quaternary uplift along the ridge during Pleistocene time, as evident by reworked Pliocene Upland gravel adjacent to the uplift along the contact between the Crowley’s Ridge (MIS 8?) and Loveland (MIS 6) loesses. Dissected Hatchie River terraces are uplifted and tilted as much as ~ 1 to 2° southeastward along the eastern part of the ridge. The highest terrace, likely the Humboldt or Henderson terrace, is ~30 m above the modern Hatchie River and crosses the ridge crest, indicating the probable middle Pleistocene Hatchie River course. The less dissected Hatchie terrace is ~18 m above the modern Hatchie River, and crosses the ridge in two narrow gaps, each ~300 m wide. Previous studies document Hatchie River paleovalley fill along the western ridge margin, near Fulton, Tennessee, during latter deposition of the Loveland loess. Uplift of Fort Pillow ridge is argued to have deflected the path of the Hatchie River to the west during deposition of Loveland loess. Continued uplift and southeastern tilting of the ridge led to abandonment of the Fulton paleovalley by ca. 21,500 calendar years before present and further deflection to the southwest. The modern course of the Hatchie River is deflected southwest along several N to NNE-trending structures, indicating that uplift and tilting continue today. This study argues that Fort Pillow ridge is an active tectonic structure along a complex bend in the southeastern Reelfoot-rift margin, strike-slip fault zone with releasing and restraining characteristics, and may pose significant seismic hazard.