Organic geochemistry of the Late Permian coal from the Songhe Mine, Guizhou

The Late Permian coal samples selected from Songhe Mine, Guizhou Province, were investigated by organic geochemical methods. Optical microscopy was used to observe coal components and determine vitrinite reflectance. Saturated hydrocarbons and aromatic hydrocarbons in coals were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS), and the related organic geochemical parameters were calculated. The results show that the content of vitrinite in Songhe coal samples is the highest, with the average vitrinite reflectance (R_o) 1.21%. The carbon number of n-alkanes ranges from C₁₂ to C₂₉, and the main peak carbon is C₁₄ or C₁₅. The value of ∑C_21-/∑C₂₂₊ is higher, and the value of odd-even predominance (OEP) is close to 1, and the pristane/phytane (Pr/Ph) ratio is from 1.40 to 2.65. There are many kinds of aromatic hydrocarbons detected. The contents of naphthalene and phenanthrene compounds derived from resins are predominant, and the isomers of aromatic hydrocarbons with higher thermodynamic stability has an advantage position. The data analyses indicate that the coal-forming parent material is mainly from terrestrial higher plants, accompanied by the contribution of marine phytoplankton. The coal sample has higher maturity. The relative higher contents of fluorenes and benzonaphthothiophenes indicate that coal seams were mainly formed in reducing environment.