Chemistry of Maceral and Groundmass Density Fractions of Torbanite and Cannel Coal
Microscopically, torbanite and cannel coal are composed of coarser macerals set in a fine-grained to amorphous groundmass. It is often assumed that the amorphous groundmass is genetically related to the distinct macerals. The separation of macerals and groundmass from 14 late Paleozoic torbanite, cannel, and humic coals permits the analysis of individual constituents using elemental analysis and flash pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Cluster and principal component analyses of the Py-GC/MS data further reveal the chemical similarities and differences between the various constituents. Pyrolyzates of Botryococcus-related alginites are characterized by an abundance of normal alkadienes, alkenes, and alkanes. Even their alkylbenzenes and alkylnaphthalenes exhibit a relatively higher concentration of isomers with a single, linear alkyl side-chain than do other macerals and groundmass. In contrast, vitrinite pyrolyzates are dominated by phenolic and aromatic compounds. Sporinites are enriched in aliphatic, aromatic, and phenolic structures, especially the short chain aliphatics and alkylbenzenes. They are also CharacteriZed by a predominance of 1,2-dimethylbenzene and 1-ethyl-2-methylbenzene. The groundmass is further divided into lamalginitic, bituminitic, and vitrinitic. The chemistry of the brightly-fluorescing lamalginitic groundmass is basically similar to that of alginite, but also resembles other groundmass types in normal hydrocarbon and alkylphenol distributions. The vitrinitic groundmass can be described as an 'aliphatic-rich' vitrinite. The pyrolyzate of the bituminitic groundmass is characterized by the predominance of long chain normal hydrocarbons. Their pyrolyzates have a chemical nature intermediate between alginite and vitrinite. The relatively higher contents of hopanoids in their pyrolyzates and elemental nitrogen suggest a bacterial role in the formation of the groundmass. Chemical analysis and subsequent multivariate statistical analysis suggest that the groundmass is likely to be a mixture of bacterially-degraded algal and humic organic matter. The proportions of the two primary components vary from sample to sample, as does the extent of degradation. Bacterially-produced hopanoids are also incorporated.