A NEW INTERPRETATION FOR THE GEOLOGY OF CENTRALIA, PA

A series of duplexes characterized by small anticlines and synclines adjacent to a series of NE-SW trending subparallel blind thrust faults and reverse faults provides a revised interpretation for geologic structures in part of the Ashland, Pennsylvania 7.5 Minute Quadrangle. The Llewellyn Formation (Middle Pennsylvanian) was described and subdivided into several varying siliciclastic lithologies that were mapped in the surrounding region Centralia. The lithologies of the Llewellyn Formation in the region are composed of multistoried coarse- and medium-grained quartz conglomerates and sandstone, medium-grained reddish-brown to greenish-gray shaley-sandstone, dark gray silty-shale, and coal. From this work a stratigraphic column, geologic map, and cross-section were produced.

The variable lithologies of the Llewellyn Formation, stratigraphically overlying the Pottsville Conglomerate, exhibit the typical structures observed in other parts of the Appalachians in Pennsylvania. Less competent shale and coal lithologies allowed structural deformation to progress throughout the mapping region. The extent of folding ranged from open (coarser lithologies) to closed (finer lithologies) folds that are slightly overturned and plunge predominantly to the east. The Locust Gap and Germantown thrust faults provide the ramps along which the duplex systems formed. The rocks were highly fractured, cleaved, and exhibit evidence of flexural slip.

Geologic mapping in Centralia, the location of an underground mine fire, may be helpful in understanding the distribution of anthracite fuel and structural complexity of the rocks through which the fire burns. Previous geologic interpretations for this region do not include either a subdivision of the lithologies in the Llewellyn Formation or duplex structures riding over the Pottsville Conglomerate.