STABLE ISOTOPE GEOCHEMISTRY OF A MIDDLE PENNSYLVANIAN COAL

Macerals are the individual organic subcomponents of coal and have distinct physical and chemical properties, which reflect differences in original plant material, alteration during deposition and diagenesis, and the degree of coalification or rank. The distributions of the different maceral types within a particular coal significantly control coal properties and, as a consequence, the environmental and technological problems associated with the use of coal.

The present study is undertaken to evaluate the controls on carbon isotope variability in macerals from Illinois coals. We separated macerals by using density-gradient centrifugation techniques. In this way we were able to concentrate relatively pure macerals within a single coal (purities up to 99%) and measure their isotopic composition.

Our preliminary carbon isotope results of macerals separated from an individual sample of the Springfield No. 5 coal show that significant differences exist among macerals. We measure an increase in ä13C values from liptinites (ä13C resinite = -27.2 ‰ and ä13C sporite = -26.9 ‰) to inertinites [ä13C fusinite = -25.3 ‰ and ä13C semifusinity = -25.2 ‰] and finely to vitrinites (ä13C vitrinite = -24.9 ‰). These results confirm previous findings that significant isotope differences exist among different macerals within a single coal, likely recording the original composition of plant tissues from which the macerals originated and the changes that occur during coalification.