Anatomy of an intruded coal, II: effect of contact metamorphism on organic δ13C and implications for the release of thermogenic methane, Springfield (No. 5) Coal, Illinois Basin

The relatively high VM contents of the intruded coals (compared to coals that have undergone normal burial maturation) and the lack of any trend in δ13Corg approaching the intrusion raises questions about previously published models of the effects of large-scale igneous intrusions on atmospheric composition and δ13Corg excursions associated with oceanic anoxic events. This study underscores the importance of the use of organic petrography in combination with isotope geochemistry to determine if contact metamorphosed coals and organic-rich shales could have released a significant amount of 13Corg-depleted volatiles leading to negative δ13Corg excursions in the sedimentary record.