The occurrence and distribution of phenylphenanthrenes, phenylanthracenes and binaphthyls in Palaeozoic to Cenozoic shales from China

The distributions of phenylphenanthrenes, phenylanthracenes and binaphthyls in sediment extracts have been investigated in a set of lacustrine shales from the Eocene Shahejie Formation (well SG 1) in the western Depression of Liaohe Basin, East China. All isomers of these phenyl substituted polycyclic aromatic hydrocarbons (PAHs) have been identified in the m/z 254 mass chromatograms by comparison of the mass spectra and standard retention indices with those published elsewhere. The 2,2′-binaphtyl/1,2′-binaphthyl ratio values show a linear increase with increasing maturity, and have a good correlation with Tmax (°C). Therefore, they can be used as an effective maturity indictor for source rocks in this study. In the main phase of the oil generation window, the 3-phenylphenanthrene and 2-phenylphenanthrene prevail over other isomers, and some thermodynamically unstable isomers including all phenylanthracenes, 4-phenylphenanthrene and 1,1′-binaphthyl are present at very low concentrations or below the detection limit in the m/z 254 mass chromatograms. The absolute concentrations of individual phenylphenanthrene and binaphthyl isomers were obtained by comparison of the peak areas with that of internal standard phenanthrene-d10. All isomers are present at low concentrations at low maturity stages and then show an abrupt increase at a depth of ≈3100 m, corresponding to the onset of the intensive C15+ hydrocarbon generation. The Phenylphenanthrene Ratio (2- + 3-PhP)/[(2- + 3-PhP) + (4- + 1- + 9-PhP)] shows a reverse change with increasing maturity at the low maturity stage. It displays a drastic increase at a depth of ≈3100 m and then remains at a nearly constant value. This study can expand the understanding of the formation and distribution of phenyl substituted PAHs in sedimentary organic matter deposited in various environments.