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U.S. Geological Survey Open-File Report 2004-1445

Initial Results of a 2D Burial/Thermal History Model, Central Appalachian Basin, Ohio and West Virginia

By E. L. Rowan, R. T. Ryder, J. E. Repetski, M. H. Trippi, and L. F. Ruppert

A preliminary model of burial/thermal history and hydrocarbon generation is presented for a regional-scale (354 km) geologic cross section oriented approximately perpendicular to the Appalachian basin axis. The section extends through relatively undeformed strata, from the Rome trough in central West Virginia, northwestward to the Findlay arch in northwestern Ohio. The model incorporates sedimentation, compaction, uplift, and erosion, and assumes a constant basement heat flow of 60 mW/m2. Relatively low thermal conductivities are assigned to coals (0.2 W/m°C) and to kerogen-rich black shales (0.9 W/m°C). Thermal maturity measurements of conodont color alteration index (CAI) and vitrinite reflectance (Ro%) from Ordovician, Devonian, and Pennsylvanian rocks constrain the model. Even with the low thermal conductivities, the model requires the deposition of additional Permo-Triassic sediment, subsequently removed by erosion, in order to match measured thermal maturity values. In this model, maximum burial is assumed to have occurred at the end of the Middle Triassic (230 m.y.), with deposition of a wedge of Permo-Triassic sediment. The added sediment is 7200 ft (2195 m) thick at the southeast end of the section, thins to the northwest, and pinches out at the western margin of the basin. The additional, modeled, Permo-Triassic sediment is completely eroded by present day, leaving only the current, measured formation thicknesses.

An important goal of the study is to predict the timing of thermal maturation of key hydrocarbon source rocks. We present calculations for two source rock intervals, Middle-Upper Devonian shales and the Ordovician Utica Shale. The Devonian shales have generated predominantly gas and lesser amounts of oil. These hydrocarbons are trapped in sandstones of Devonian and Mississippian age as well as in fractured intervals of Devonian shale. The Utica Shale is a 100-200 ft (30-60 m) thick, laterally extensive, source rock that generated petroleum that is now trapped in Cambrian-Silurian carbonates and sandstones.


  Index map of the study area
Locations of some of the major structural and geologic features in the vicinity of the model cross section.

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