Bedding-plane faults and shear bodies
Slickensided, horizontal thrust faults or bedding-plane faults have been encountered above undeformed coal beds in both the Illinois (see, for example, Krausse and Nance, 1980) and Appalachian (see, for example, Millici and others, 1982) Basins. Phillipson (2005) reported slickensided drag folds along bedding above the Springfield (W. Ky. No. 9) coal in western Kentucky and above the Elkhorn No. 3, Kellioka, Upper Harlan, Blue Gem, and Harlan coals in eastern Kentucky.
Bedding-plane faults are fault planes across which horizontal movement has occurred. In many cases, the fault plane (decollement) is the top of the coal bed; small thrust faults sometimes develop upward into overlying shales, where the fault ramps upward into the roof (Molinda, 2003; Elizalde and others, 2016). Phillipson (2005) noted similar shapes and scales of slickensided drag folds along bedding above the Springfield coal in the Illinois Basin (including a mine in western Kentucky) and coals of the Appalachian Basin. Phillipson (2005) noted that drag folds (wedge-shaped slickensides) were commonly oriented parallel to the structural grain (trend) of the Allegheny front in Virginia, eastern Kentucky, and Pennsylvania, which indicates that they may have formed by tectonic movement west of Appalachian mountain building at the end of the Pennsylvanian Period. Bedding-plane faults in mines in the Pine Mountain Thrust Sheet may be associated with residual horizontal stresses.