BURIAL AND THERMAL HISTORY MODELS OF THE CENTRAL APPALACHIAN BASIN, OHIO, PENNSYLVANIA, AND WEST VIRGINIA

Three regional-scale, 2D cross-sectional burial and thermal history models have been constructed for the undeformed north-central Appalachian basin. The models integrate thermal and geologic data to provide a geologically constrained burial history. The sections extend from the Allegheny structural front in West Virginia and Pennsylvania northwestward across the Rome trough and Dunkard basin and terminate to the northwest near the crest of the Findlay Arch in Ohio. The Dunkard is a ‘sub-basin' within the larger Appalachian basin and a late Paleozoic depocenter with present day depths to basement approaching 30,000 ft.

The models incorporate sedimentation, compaction, uplift, and erosion, and they assume a basement heat flow of 52 mW/m2. Well logs were used to identify and quantify lithologies. Relatively low thermal conductivities were assigned to Pennsylvanian coals (0.2 W/mºC) and Devonian kerogen-rich shales (0.9–1.2 W/mºC) based on published values from the region. Corrected bottom hole temperatures and measurements of conodont color alteration index (CAI) and vitrinite reflectance (Ro%) from Ordovician, Devonian, and Pennsylvanian rocks constrain model temperatures and thermal maturities.

To match the measured thermal maturities, the models required deposition of additional sediment, subsequently removed by erosion. We assumed that maximum burial occurred during the Permian (~270 Ma based on recent apatite and zircon fission track studies) with deposition of a wedge of sediment 10,000 – 13,000 ft thick at the southeast end and thinning to the northwest. Published temperatures from fluid inclusions in sphalerite veinlets in Devonian shale at sites deeper in the basin can be readily accounted for by the burial model. In contrast, published fluid inclusion temperatures from the Findlay Arch are significantly higher than predicted by the burial models. However, the results of fluid flow modeling show that westward flow and advective heat transport from deeper in the basin provide a possible explanation for these high temperatures. The burial/thermal history models permit the thermal maturities of individual hydrocarbon source beds to be calculated across the region. The models also provide the regional temperature and pressure framework needed to model hydrocarbon migration.