Phyllosilicate orientation demonstrates early timing of compactional stabilization in calcite-cemented concretions in the Barnett Shale (Late Mississippian), Fort Worth Basin, Texas (USA)

Calcite-cemented zones in the prolific gas-producing Barnett Shale (Ft. Worth Basin, Texas) preserve very early compactional fabrics that contrast markedly with fabrics in the enclosing host-rocks. The compactional state of these zones, based upon alignments of phyllosilicates as determined by High-resolution X-ray goniometry (HRXTG), complemented by X-ray powder diffraction (XRPD), back-scattered electron imaging, and elemental X-ray mapping, points to a prelithification, near-syndepositional timing of initial authigenic calcite emplacement. Thus, these carbonate-cemented zones are of particular interest for the information they provide on the character of grain assemblages and sediment types at the time of deposition and also on the early post-depositional environmental chemistry of the Barnett Shale strata. (D 2008 Elsevier B.V. All rights reserved.