COAL BED DECOLLEMENT-RELATED STRUCTURAL CONTROLS ON ROOF STABILITY IN EASTERN COAL MINES

Slickensides are commonly associated with potentially hazardous ground conditions in underground coal mines. In the coal mining industry, slickensides have generally been regarded as randomly oriented features, ubiquitous to coal mine roof, that formed by differential compaction of shale or coal around sand channels. In contrast, investigations by the Mine Safety and Health Administration’s Roof Control Division indicate that consistently oriented slickensides commonly represent bedding plane faults, drag folds, listric faults, and duplexes that formed during coal bed decollement. Coal bed decollement refers to a style of detachment faulting that occurs in shale units that directly overlie coal seams, and are a common but largely unrecognized feature in the Appalachian Basin. Several kinds of slickensides observed in coal mines are interpreted to have formed in response to regional tectonic stresses, and are interpreted as contemporaneous with the formation of folds and thrust faults that define a structural grain in the Appalachian fold-and-thrust belt. When regarded as structural geologic features, these styles of slickensides can be understood through mapping efforts.

The geographically widespread observations suggest the relation of structural-style slickensides observed in the Appalachian Basin to deformation during the Late Pennsylvanian-Permian Alleghanian orogeny. Because the slickensides discussed represent regional structural geologic features, controls on coal mine ground instability can be regarded in a regional context. It is suggested that mine-wide structural geologic mapping can be used to project zones of slickenside occurrences so that miners can be prepared for adverse ground conditions.