Notes on the origin of altered macerals in the Ragged Edge of the Pennsylvanian (Asturian) Herrin coalbed, Western Kentucky

• The marine margin of the No. 11 coal in western Kentucky is brecciated.
• The coal breccia is mineralized and has attained a high vitrinite reflectance.
• Geochemistry suggests thermal fluids caused the mineralization and metamorphism.

The Ragged Edge of the Herrin (Western Kentucky No. 11) coal bed has a variety of maceral textures and assemblages that do not fit in the conventional vitrinite and inertinite definitions as established by the International Committee for Coal & Organic Petrology. Within a narrow zone at the marine margin of the coalbed, the coal is brecciated and cemented by carbonate with some of the brecciated clasts metamorphosed to anthracite-level vitrinite reflectances. This is in contrast to the ambient high volatile C bituminous coal rank in the region. Low-rank peat-like textures are preserved in the clasts, suggesting that the metamorphism took place soon after deposition of the peat. Geochemical and mineralogical evidences suggest that the increase in reflectance was the consequence of the channeling of hydrothermal fluids through the breccia. The narrow zone of metamorphism and, further, the juxtaposition of breccia clasts of varying degrees of metamorphism suggest that the hydrothermal influx occurred at shallow depths of burial, perhaps shortly following deposition of the peat.