Deformation Bands In the Raccoon Mountain Formation at the Pinnacles, Southern Cumberland Plateau, Sewanee, TN

Deformation Bands in sandstones of the lower Pennsylvanian Raccoon Mountain Formation are well exposed at the Pinnacles, a promontory along the Cumberland Escarpment near Sewanee, TN. The well-defined N 40 E cliff on the southern side of the Pinnacles closely corresponds to the strike of the deformation bands. The strain-hardened shear zones are part of the Alleghenian Cumberland Overthrust. 168 measured bands are exposed in cross section as glassy quartz veins 0.1-5mm thick, and also as fault surfaces that vary from a few cm² to many m². Deformation bands in thin-section are marked by cataclasis with angular quartz grains ranging from less than 0.05mm to 0.1mm. Subgrain development and undulating extinction of quartz grains are evident both within the bands and the general matrix of the medium-grained sandstone. Prominent NE- striking subvertical joints were reactivated as faults and developed deformation bands now marked with down dip slickenlines that trend N 53W, 75. Smaller bands are typically subparallel and feather into the larger surfaces. Subhorizontal slickenlines on larger surfaces appear to overprint vertical ones. The N 67 W transport direction for the Cumberland Overthrust is recorded by a set of gently dipping faults without bands at the top of the Raccoon Mountain Fm.