Normal fault in limestone in the Pennsylvanian of Ohio, USA. (geology hammer for scale)

The grayish-brown bed at left in the above photo is the Lowellville Limestone, a marine horizon of fossiliferous limestone first described from Lowellville, Pennsylvania (the type locality). It has also been identified in outcrops in northeastern Ohio. It is correlative with the Poverty Run Limestone of eastern Ohio.

The black-colored material at right is calcareous shale (here nicknamed the "Lowellville Shale"). This is in fault contact with the Lowellville Limestone, but occurs stratigraphically above the limestone. Just above the Lowellville Limestone, the Lowellville Shale is fissile to flaggy, fossiliferous, black calcareous shale. Above that is non-flaggy, sparsely-fossiliferous, incompetent, black calcareous shale.

The Lowellville Limestone and overlying shale unit are part of the Pottsville Group, a Pennsylvanian-aged cyclothemic succession in eastern Ohio that contains nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Member (?).

The Lowellville Limestone at the site shown above (= Beach City Dam outcrop in northwestern Tuscarawas County, Ohio) is medium grayish to gray-brown on weathered surfaces and very dark gray to black on crack surfaces. It is moderately fossiliferous, dominated by brachiopods. A medium-sized plant stem was also observed at this locality. The rocks here are gently folded and minor normal faulting is also present (see above photo for an example of this) - the faults are probably relaxational structures.

Faults are fractures in rocks along which differential displacement has occurred. Dip-slip faults are those involving movement of rocks in non-horizontal directions. Strike-slip faults involve movement of rocks in horizontal directions. The two common types of dip-slip faults are normal faults and reverse faults. The fault shown above is a low-angle normal fault, which is formed by extensional stress. Slickenlines are present on the fault plane. The black shale at right has moved downward. The limestone at left has moved upward.

Stratigraphy: Lowellville Limestone, Pottsville Group, upper Lower Pennsylvanian