LATE QUATERNARY SURFACE FAULTING IN WESTERN TENNESSEE ALONG THE SOUTHEASTERN MARGIN OF THE REELFOOT RIFT

Faults of the southeastern margin of the Reelfoot Rift are expressed as a pronounced topographic lineament in western Tennessee referred to by previous authors as the “Big Creek lineament” and the “Rives lineament.” From its southwestern end in Shelby County, TN (20 km from Memphis) to Dyersburg, TN (100 km), the lineament is the NW-facing Mississippi River bluff line. From Dyersburg to its northeastern end near Union City, TN (58 km), the lineament is a series of collinear scarps that face primarily northwest. We acquired five shallow seismic reflection profiles, drilled three push-core transects, and excavated two trenches that reveal late Quaternary surface faulting along this lineament.

We previously reported results from Union City and Porter Gap (16 km SW of Dyersburg). At Union City, the lineament is a 9 m-high NW-facing scarp, and our seismic profile and push-core transect suggest >1.5 m of Wisconsin or Holocene down-to-the-west faulting. Our seismic profiles, push-core transect, and trench at Porter Gap show >3 m of late Wisconsin or early Holocene up-to-the-west reverse faulting and mid to late Holocene liquefaction at the base of the west-facing river bluffs. However, our seismic profile shows this fault displaces monoclinally folded strata with 25 m of down-to-the-west structural relief.

In our new work in Shelby County, we acquired two shallow seismic profiles, drilled a push-core transect, and excavated a 45 m trench across the west-facing river bluff lineament that show down-to-the-west faulting. The trench, cut down the slope of a small alluvial fan, revealed a near-vertical fault plane with ~1 m of late Quaternary displacement. Fissuring and subsidence adjacent to the fault in the down-dropped block suggest an extensional component but may be due to co-seismic sliding.

We conclude that a near-vertical late Quaternary fault with a down-to-the-west component follows the southeastern rift margin topographic lineament along most of its length. However, at Porter Gap this fault is a lateral boundary of the hanging wall block of the NW-striking Reelfoot thrust fault. Here, the rift margin fault has experienced late Quaternary up-to-the-west movement in the vicinity of the thrust ramp, although the longer-term movement has been down-to-the-west.