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International Journal of Coal Geology


The thermal maturity and organofacies sensitivity of polycyclic aromatic compound (PAC) distributions was explored by examination of the aromatic fractions of solvent extracts from a diverse set of 53 shales, coals and kerogen macerals which have undergone either natural or artificial maturation and which represent all three principal sedimentary organic matter (OM) types. Systematic changes with maturation were observed in the following groups of isomers: tri- and tetramethylnaphthalenes, methyl- and dimethylphenanthrenes, methyl- and dimethyldibenzothiophenes, methylpyrenes, and methylchrysenes. The maturity differences were quantified by mathematical ratios of the relative concentrations of the more thermally stable isomers to the less stable, on the basis of theoretical considerations and empirical observations. The PAC maturity parameters, unlike those derived from saturate biomarker stereoisomers, are typically effective across the entire oil generation window. To compensate for the effects of OM type on the maturity parameters, they were combined using principal components analysis. The resulting first principal component was in good agreement with independent indicators of maturity. The relative distributions of C0-C3 alkylphenanthrenes, dibenzothiophene, methyldibenzothiophenes and methyldibenzofurans were evaluated by a separate principal components analysis. The results permitted an independent grouping of the samples by OM type and suggested additional, simple molecular ratios that allow graphical recognition of OM type, including the ratio of dibenzothiophenes to dibenzofurans and a ratio using C2-alkylphenanthrene isomers.


To overcome the limitations of the optical and biomarker methods, it is advantageous to have supplementary techniques for maturity assessment and organic matter type determination. With that in mind, the objective of this study was to test the suitability of the distributions of polycyclic aromatic compounds in ascertaining thermal maturity levels and OM type for a large, heterogeneous sample set.


Published Citation

Kruge M.A. (2000) Determination of thermal maturity and organic matter type by principal components analysis of the distributions of polycyclic aromatic compounds. Int. J. Coal Geol. 43:27-51.