THE POSSIBLE LINK BETWEEN EAST-WEST TRENDING FAULTS IN THE VALLEY AND RIDGE PROVINCE OF EASTERN TENNESSEE AND THE GRAY FOSSIL SITE

The Gray site, recently discovered near Johnson City, Tennessee, is a Miocene(?) age deposit. It consists of dark gray, organic-rich clay entombing abundant mammalian, amphibian, and plant fossils, overlain by medium gray varved clay with minor sand interbeds, overlain by late Pleistocene to Holocene alluvium. The site lies just beyond the mapped extent of one of several strike-slip faults exposed at the surface near Johnson City, Tennessee. These strike-slip faults do not follow the dominant trend (N 55 E) of thrust faults in this part of the Tennessee Valley and Ridge physiographic province. Instead, the faults cut nearly E-W across Cambrian through Ordovician sedimentary rocks with maximum displacement amounts of one mile, although displacements are generally less. The strike-slip faults may act as displacement transfer zones between Alleghanian thrust faults, and may also localize karst formation in near-surface carbonates. One possible explanation for the Gray site’s location may be greater carbonate solution in a zone of weakness at the tip of one of these E-W striking faults where it loses macroscopic displacement. Similar sites, if they exist, may be difficult to identify based on geomorphology (the Gray site had no surface expression and was not discovered until road excavation had begun), so searches concentrated along the trend of these faults may be most productive. Strike-slip faults of this orientation are not common in the Valley and Ridge and have not been mapped in large numbers further south. Earthquakes in the east Tennessee seismic zone have fault plane solutions with east-west orientations but occur at depths below the Alleghanian basal detachment fault. The relationship between surface faulting and the earthquake focal plane orientations is unclear, but the similarity in trend suggests basement structures influence not only the location of Alleghanian strike-slip faults but also the location of the Gray site.