The contribution of bacteria to organic matter in coal-measure source rocks

Abstract

On the basis of GC–MS analysis, a suite of nine coal-measure source rocks (Ro 0.51%–0.63%) from the southern margin of Junggar basin was found to contain many biomarkers for bacterially-generated hydrocarbons: hopane, sesquiterpene, C23+ monomethyl alkanes (even carbon predominance), and C24+ alkyl cyclohexane. Rock–eval and microscope analysis indicate that vitrinite (especially desmocollinite and homocollinite) plays a significant role in the generation of hydrocarbons in coal-measure source rocks. Vitrinite performs this role by absorbing ultramicroscopic organic matter, generally in the form of resins or bacterial plastids. C23+ monomethyl alkanes (even carbon predominance) and C24+ alkyl cyclohexane series compounds are derived from bacterial metabolites of higher plants. The ultramicro organic matter adsorbed by vitrinite source rocks in the study area is probably ultramicro bacterial plastids. Because the organic matter of higher plants with low hydrogen content has been transformed into organic matter rich in hydrogen by bacteria, the hydrocarbon generation capacity of source rocks is greatly improved. In other words, in coal-measure source rocks, bacteria play an important role in hydrocarbon generation.