Coalification patterns of the Pittsburgh coal: their origin and bearing on hydrocarbon maturation

The coalification pattern of the Pittsburgh coal as established by isoreflectance contours has an overall trend which intersect with the prevailing structural trend of the Dunkard basin. Reflectance values increase from 0.53% in southeastern Ohio to 1.57% in the Maryland panhandle. Divergences of the reflectance contour pattern from the overall trend coincide in part with the present areas of high geothermal gradient. Crustal radiogenic heat, or regional geothermal heating, was probably the dominant heat source responsible for the coalification of the Pittsburgh coal in the Dunkard basin.A time-temperature, Lopatin-type diagram, which was constructed for the Dunkard basin near Wheeling, West Virginia, delineates conditions on maturation of sediments and provides clues to the times of petroleum migration and to the possible source beds. Silurian strata matured during subsidence and burial prior to the orogeny. The Mississippian and Pennsylvanian strata matured during or after the orogeny. The Pennsylvanian strata west of the Dunkard basin, as suggested by vitrinite reflectance values, are apparently still immature.