Document Type

Book Chapter

Publication Date


Journal / Book Title

Pétrologie Organique, Recueil des Communications, Colloque International des Pétrographes Organiciens Francophones


Density gradient centrifugation (DGC) is a physical method for the separation of sedimentary organic matter into its constituents. Using DGC, it is possible to prepare maceral concentrates from a single sample, which are amenable to microanalysis. DGC fractions from a coal sample from the Illinois Basin (Herrin No. 6, Upper Carboniferous) and from the kerogen of a marine shale sample from the Paris Basin (Lower Toarcian) were analyzed by flash pyrolysis-gas chromatography-mass spectrometry, after extraction by CH2Cl2.

Chemical differences between the coal DGC fractions are the easiest to recognize, indicating very distinctive biological precursors. For example, the liptinite fraction (𝜌 = 1.12 g ml-1) is dominated by long-chain aliphatic compounds (n-alkanes and n-alkenes) along with alkylbenzenes and alkylphenols. Vitrinite (1.29 g ml-1) shows a predominance of alkylbenzenes and phenolic compounds. Polyaromatic hydrocarbons (especially naphthalene, phenanthrene, anthracene and their pseudohomologues) are major compounds in the pyrolyzate of fusinite (1.45 g ml-1). In contrast, there is less variety of organic compounds in the Toarcian sample. Petrographically, this kerogen is primarily amorphous. However, a main DGC peak (𝜌 = 1.18 g ml-1) with two shoulders (1.15 and 1.23 g ml-1) is resolved using multi-step centrifugation. The chemical differences between these fractions are subtle but significant. Concentrations of alkylbenzenes, alkylthiophenes, alkylpyrroles and phenolic compounds increase with density, relative to the aliphatics. This indicates that this kerogen, probably of algal and bacterial origin, is partially separable by DGC.

Book Publisher

Bulletin des Centres de Recherches Exploration-Production Elf Aquitaine

Book Editor(s)

Curnelle, R. and Sévérac, J.-P.

Published Citation

Stankiewicz, B. A., Kruge M. A., and Crelling, J. C., 1994, Geochemical characterization of maceral concentrates from Herrin No. 6 coal (Illinois Basin) and Lower Toarcian shale kerogen (Paris Basin). In, Curnelle, R. and Sévérac, J.-P., eds., Pétrologie Organique, Recueil des Communications, Colloque International des Pétrographes Organiciens Francophones, Publ. Spéc., Bull. Centres Rech. Explor.-Prod. Elf Aquitaine, Vol. 18, p. 237-251.