Comparison of hydrocarbon compositions in a sequence of humic coals, cannel coals and oil shales from the Pictou Coalfield, Nova Scotia
DOI:
https://doi.org/10.4138/1674Abstract
Thirty oil shale, cannel coal and humic coal samples from die Pennsylvanian Stellarton Group, Nova Scotia, Canada have been investigated in this study by means of organic geochemical methods including gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Hydrocarbon compositions of the solvent extracts were found to vary significantly with lithology and facies. Analysis of the saturated hydrocarbon fractions revealed that the relative amounts of long-chain alkanes (>C20) compared to those of short-chain alkanes (<C20) are higher in the humic coal than in the cannel coal and oil shale samples. Moreover, the humic coal is characterized by the presence of homodrimane as the dominant bicyclic alkane. In the oil shale and cannel coal samples, on the other hand, C15-bicyclancs are present as major sesquiterpenoid hydrocarbons. Compounds such as biphenyl, dibenzofuran, fluorene and their mono-mediylated and di-metfiylated homologues were shown to occur almost exclusively in the aromatic hydrocarbon fractions of the humic coal samples. Presumably, these compounds are products of die degradation of lignin during diagenesis. The bitumen compositions of cannel coal and oil shale samples are quite similar. RÉSUMÉ Trente échantillons de schiste bitumineux, de charbon de spores et pollens, et de charbon humique provenant du Groupe de Stellarton (Pennsylvanien de la Nouvelle-Écosse, Canada) ont été analysés dans cette étude à l'aide de méthodes de géochimie organique comprenant la chromatographic en phase gazeuse (GC) et le couplage chromatographic en phase gazeuse -spectrométrie de masse (GC/MS). On constata que les compositions d'hydrocarbures des extraits en solvent varient fortement selon la lithologie et le faciès. Une analyse des fractions à hydrocarbures satures révèla que la proportion des alcanes à longue chaine (>C20) par rapport aux alcanes à chaine courte (<C20) est plus élevée dans le charbon humique que dans les échantillons de charbon de spores et pollens et de schiste bitumineux. De plus, le charbon humique est caractérisé par la présence d'homodrimane comme alcane bicyclique principal. Par centre, dans les échantillons de schiste bitumineux et de charbon de spores et pollens, on note la présence de C15j-bicyclanes comme hydrocarbures sesquiterpénoiides majeurs. Certains composes, tels le biphényle, le dibenzofurane, le fluorène el leurs homologues mono- et diméthylés, se retrouvent presqu'exclusivement dans les fractions à hydrocarbures aromatiques des échantillons de charbon humique. Ces composés serai ent leproduit de la dégradation de la lignine durant ladiagenèse. Les compositions bituminiques des échantillons de charbon de spores et pollens et des schiste bitumineux se ressemblent beaucoup. [Traduit par le journal]Downloads
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