Effects of extreme heating on the elemental and isotopic compositions of an Upper Cretaceous coal

Intrusion of igneous sills into coal seams in the Maastrichtian Vermejo Formation of Colorado-New Mexico rapidly and severely altered the organic matter content of the coal. Organic carbon concentrations drop from 65% in coal samples distant from sills to between 5 and 38% in coal samples close to a sill. Changes in organic matter C/N ratios and δ13C values relative to distance from the sill indicate preferential losses of isotopically light forms of carbon from the coal. The relatively high TOC concentration, elevated C/N ratio and more negative δ13C value of coal closest to the sill suggest that rapid pyrolysis immobilized the thermal products as partially graphitized or mineral forms of carbon.