ABSTRACT

Regional face cleats cutting Pennsylvanian and Permian coal seams in the Allegheny Plateau of West Virginia can be divided into domains separated by boundaries that are sharply defined along most of their lengths. Domains and domain boundaries are established based on cleat trends, number of regional cleat sets, and relative chronology of cleat-set development. Regional cleats of each set show a common trend, and abutting relationships between multiple sets within a domain describe a progressive history of changing stress fields and cleat development. Boundaries dividing the in-situ directions of horizontal principal stress are coincident with cleat domain boundaries suggesting a common and persistent controlling factor. Uniform trends of face cleats within domains and abrupt changes in cleat signature across domain boundaries can be spatially related to regional basement structures and a depositional hinge line within the coal-bearing and underlying Mississippian rocks. In addition, fold structures in coal and underlying sedimentary rocks across the Allegheny Plateau commonly terminate or change trend abruptly at joint domain boundaries. In some cases, regions of common fold trends in coal bearing rocks are contained within specific domains. Face-cleat trends commonly differ from joint trends in rocks immediately bounding coal seams. However, one domain boundary in coal can be traced into Mississippian rocks through the unconformity at the base of the Pennsylvanian section. In this case, Mississippian and Pennsylvanian joint trends differ. It follows that joint domain boundaries can extend downward through rocks of different lithologies, as well as coincidewith conformable and unconformable stratigraphic boundaries.

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