Appalachian Basin Framework Geology and Petroleum Systems: Insights from New Regional Geologic Cross Sections, Thermal Maturity Maps, and Burial History Models

Robert T. Ryder, Christopher S. Swezey, Robert C. Milici, John E. Repetski, Leslie F. Ruppert, Elisabeth L. Rowan, Robert D. Crangle, and Michael H. Trippi
U.S. Geological Survey, Reston, VA

Three new regional geologic cross sections combined with new thermal maturity maps and burial history models have improved understanding of the Appalachian basin framework geology and petroleum systems. The cross sections extend from the Findlay arch in northwestern Ohio, through the Rome trough in Pennsylvania and West Virginia, to the Allegheny structural front and adjoining Valley and Ridge in south-central Pennsylvania and eastern West Virginia. The cross sections show a complex history for the basin that involved a graben system, carbonate-dominated continental margins, and foreland basins. Styles of deformation range from basement-involved extensional faults that formed during Middle Cambrian late-stage opening of the Iapetus sea to thin-skinned contractional structures of Alleghanian origin. The Rome trough may have locally experienced mild inversion during the Alleghanian orogeny. Unconformities shown on the cross section represent major drops in eustatic sea level and (or) major tectonic events.

Petroleum systems recognized in the 2002 USGS assessment of oil and gas resources of the Appalachian basin are readily identified on the cross sections. The more important source rocks are Ordovician black shale, Devonian black shale, and Pennsylvanian coal beds. Ordovician and Middle Devonian conodont color alteration index (CAI) and Pennsylvanian vitrinite reflectance (%Ro) maps complement the cross sections by showing the degrees of thermal maturity achieved by the source rocks. Moreover, prominent salients in the CAI and %Ro isograds identify areas that may have been overprinted by westward migrating hot fluids. Burial history models suggest that Ordovician source rocks entered the oil window between the Devonian and Permian, whereas the Devonian and Pennsylvanian source rocks entered the oil window between the Mississippian to Permian.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas