STRAIN ACCUMULATION IN THE EASTERN REELFOOT RIFT MARGIN: SURFICIAL EVIDENCE NEAR FORT PILLOW, TENNESSEE

TThe Eastern Reelfoot Rift Margin (ERRM) is a significant seismic hazard to large population centers in the Mid-south, United States. Limited field-work has been performed in the ERRM to constrain paleo-seismic events, as well, quantitative assessment of strain rates is limited. To improve this gap in understanding, we performed a detailed geological field study near Fort Pillow State Park, Tennessee. In this, we identified five lines of evidence for Eocene through Pleistocene/Holocene surfical faulting and strain accumulation. 1) Repeated up-valley migration of a Mississippi River meander bend. Sediments in the region consist of unlithified sands, silts, and clays which all dip shallowly to the west. Therefore, lithology and dip of the sediments should have minimal to no influence on the river’s behavior. Because of this, we suggest tectonic uplift in the region causing the repeated up-valley meander migration. 2) The discovery of the surfical Fort Pillow thrust fault (FPTF). The FPTF is an N45E striking up-to-the-northwest transpressional fault that is exposed at five locations over 280 m. The FPTF juxtaposes Eocene clay and Pleistocene gravels against Holocene colluvial silts. Based on the number of exposures, and the linear trend of the FPTF, we argue that it is structural as opposed to a mass wasting feature, and has been seismically active in the Holocene. 3) Northeast of the FPTF is a series of northwest-plunging anticlines and synclines, which warp Eocene sediments. 4) Throughout the study region, Eocene sands display a planar fabric, which we interpret as a deformation feature in the damage zone of a fault, indicating Eocene seismicity. 5) Eocene outcrops are exceptionally high in elevation, as compared to other locations in the ERRM, which we argue is a result of tectonic uplift. Due to these lines of evidence, we argue this region is actively accumulating strain and has been seismically active since the Eocene, with seismic events occurring as late as the Holocene. Our research indicates this region is a significant seismic hazard along the ERRM and warrants future study.