QUATERNARY FAULTING ASSOCIATED WITH THE EASTERN REELFOOT RIFT MARGIN IN TIPTON COUNTY, TENNESSEE

Recently discovered Quaternary faulting is exposed for 90 m along strike in a gravel quarry in western Tipton County, Tennessee, 30 km north of the Memphis metropolitan area along the eastern margin of the Reelfoot rift complex which contains the New Madrid seismic zone. The quarry exposes a 5 m-wide graben within the hinge zone of a 100^o-trending, asymmetric, south-verging anticline (N limb dip: 7^oN; S limb dip: 20^oS) in Eocene deltaic muds. Pliocene-Pleistocene fluvial terrace gravels and Pleistocene loess (pre-Wisconsin Loveland and Wisconsin Roxana) are dropped with up to 6 m of throw into the graben along the anticline axis. This graben and smaller peripheral grabens comprise a fault zone ~25 m wide. We interpret the graben as local extensional deformation due to anticlinal flexure. The amplitude of the anticline is >9 m, and the wavelength is >100 m. A zone of weathering at the top of the Eocene largely conforms to the anticlinal folding. This graben and anticline are 1 km south of an E/W-striking, N-dipping thrust fault exposed in the banks of Sugar Creek and its tributaries in the northwestern part of Tipton County. The asymmetric anticline fits the geometry of a fault propagation fold above a thrust with the same strike as the Sugar Creek thrust, and thus we speculate these structures may be en echelon subsidiary splays off a common master fault at depth. The Sugar Creek thrust displaces Eocene fluvial/deltaic sediments >6 m, but the Eocene/Pliocene-Pleistocene contact is not exposed, and post-Eocene thrusting is not documented. Some of the Sugar Creek thrust slip was Eocene because there is an angular unconformity showing that the hanging wall was eroded during Eocene, but before more fault movement. An Eocene sand marker bed on the north limb of the asymmetric anticline is absent on the south limb, suggesting there may be fault displacement across the fold hinge graben that pre-dates the graben faulting and the folding of the weathered zone on the Eocene. This early stage of deformation of the asymmetric anticline may have been coeval with the Eocene movement on the Sugar Creek thrust. Deformation of late Pleistocene loess within the asymmetric anticline and graben show that E/W-striking structures may pose a seismic hazard in the region.