The relatively high positive gamma-ray response and corresponding low-compensated density of black shales facilitated extension of outcropping Upper Devonian black shales (the Rhinestreet Shale Member of the West Falls Formation, the Pipe Creek Shale Member of the Java Formation, and the Dunkirk Shale Member of the Perrysburg Formation) southward in the subsurface beneath the Appalachian Plateau about 500 mi (800 km) to wells in the Greendale syncline in southwestern Virginia.

Subsurface mapping clearly outlines an arcuate area from western New York through northwestern Pennsylvania, eastern Ohio, and western West Virginia to southwestern Virginia, in which the black shales are laterally continuous. Presumably, depositional environments were also uniform throughout this area at any given time during the accumulation of these dark rocks.

Regionally, the black shales delineate an offshore part of the extensive Upper Devonian delta complex, although their distribution is somewhat restricted by a westward-expanding Middle Devonian unconformity against which the Rhinestreet and Pipe Creek Shale Members feather out. However, the Dunkirk Shale Member equivalent is present in outcrop as the lower part of the Huron Member of the Ohio Shale in Ohio and northern Kentucky, and in the corresponding part of the Gassaway Member of the Chattanooga Shale in central Tennessee and contiguous southern Kentucky.

To the east, in the Appalachian basin, the black shales grade laterally into an eastward-thickening sequence of gray shale and siltstone turbidite beds. In the absence of extensive key beds, the thick sequence of coarser grained clastic rocks cannot be divided stratigraphically.

End_of_Article - Last_Page 1167------------