EARLY JOINTING IN COAL AND BLACK SHALE: EVIDENCE FOR AN APPALACHIAN-WIDE STRESS FIELD AS A PRELUDE TO THE ALLEGHANIAN OROGENY

Early ENE striking joints (present coordinates) within both Pennsylvanian coal and Devonian black shale of the Central and Southern Appalachians define an approximately rectilinear stress field with a dimension > 1500 km. This Appalachian-wide stress field (AWSF) dates from the time of joint propagation when both the coal and shale were buried to the oil window during the 10-15 My period straddling the Pennsylvanian-Permian boundary. The AWSF was generated during the final assembly of Pangea as a consequence of plate-boundary tractions from either (1) late-stage convergence where maximum horizontal stress, SH, was parallel to the slip vector of Gondwana relative to Laurentia or (2) dextral slip of Gondwana relative to Laurentia where SH is ≈ 30° from the plate-bounding transcurrent fault. An overprint of Alleghanian joints marks the disruption of the AWSF by local stress fields associated with stratigraphically controlled décollement tectonics of the conventional Alleghanian orogeny.