*WINNER* Microstructures in faulted sandstone near Spencer, Tennessee


  • Joel Baker


Road construction along State Route 111 north of Spencer, Tennessee exposed 150 meters of fresh outcrop of Pennsylvanian Sewanee Conglomerate. Here, the Sewanee is a 40-meter thick cross-bedded conglomeratic quartz sandstone that is yellowish-gray to yellowish-brown in color. The outcrops on the east and west side of the road contain numerous strike-slip and thrust faults associated with Alleghenian deformation and the formation of the Appalachian Mountains. Fault-damage zones of white friable cataclasite occur in proximity to closely spaced strike-slip faults. These zones may represent internal deformation of the regional Cumberland Plateau overthrust. Point-counting analysis of nine samples collected from the outcrop reveals that pressure-solution microstructures are the most common microstructure, affecting nearly 95% of the quartz grains. Microcracks, representing brittle deformation microstructures, affect 25-52% of the grains and are most abundant in fault-damage zones. Cataclastic bands are localized zones of intense brittle deformation and are associated with faulting. The assemblage of microstructures indicates that rock deformation during the Alleghanian orogeny occurred at low temperature (<300°C) and shallow depth (<10 km).





Earth Sciences