EXPLORATION FOR HYDROCARBONS IN THE SOUTHERN APPALACHIAN BASIN - AN OVERVIEW

Successful assessment of oil and gas resources in the southern Appalachian basin requires an understanding of the regional stratigraphy and geologic structure in order to identify potential petroleum systems, including source beds, reservoir beds, seals, favorable levels of thermal maturation, and the timing of structural and stratigraphic traps. In general, the region may be divided into five structural provinces, the Blue Ridge structural (and physiographic) province, the eastern low-angle thrust and imbricate thrust structural provinces in the Valley and Ridge Physiographic Province, and the foreland thrust, and foreland basin structural provinces in the Appalachian Plateaus Physiographic Province, each structural province with its own variation of the regional stratigraphic framework.

The Paleozoic stratigraphy of the region reflects four major episodes of tectonic deformation: the late Proterozoic-early Paleozoic Iapetan event, which resulted in continental extension and the formation of faulted transitional crust; followed by the Taconic (Ordovician), Acadian (Devonian), and Alleghanian (Carboniferous) compressional orogenies and their associated foreland basin deposits. Only the siliciclastic strata related to the Iapetan and Taconic orogenies are indigenous to the southern Appalachian basin, as Devonian and Alleghanian siliciclastic strata were derived largely from tectonically active regions to the north and south.

Each of these major orogenic events resulted in the formation of a regionally extensive petroleum system, and source rocks range in age from Cambrian (Rome trough) to Pennsylvanian (coalbed methane). Thermal maturation isolines commonly trend across geologic structure, and hydrocarbon generation in the region may have occurred as early as Silurian (Rome trough) and as late as Permian. In the eastern part of the southern Appalachian basin, petroleum systems generated hydrocarbons prior to, during, and probably after major Alleghanian structural deformation. For example, in the eastern low-angle thrust belt, hydrocarbons apparently were generated from Ordovician source rocks sometime during the Devonian and may have migrated from their initial traps to their present locations in structural traps during Alleghanian deformation.