The Permian Lucaogou Formation oil shale in the southeast of the Junggar Basin is the oldest oil shale in China. In this study, the biodegradation characteristics of the oil shale are investigated based on organic geochemistry. The analytical results show that the biodegraded oil shale contains large humps of unresolved complex mixtures (UCMs) and is depleted of n-alkanes and acyclic isoprenoids (pristine (Pr), phytane (Ph), iC18, iC17, iC16, iC15 and iC14). Furthermore, C14–C16 bicyclic terpanes are completely preserved. It can be concluded that the biodegradation level of the Lucaogou Formation oil shale is PM1–PM2. In addition, the values of aromatic hydrocarbon proxies (methyldibenzothiophene/dibenzothiophene (MDBT/DBT), dimethyldibenzothiophene/methyldibenzothiophene (DMDBT/MDBT), 1,2,7-trimethylnaphthalene/1,3,6-trimethylnaphthalene (1,2,7-TMN/1,3,6-TMN) and 1,2,4-trimethylnaphthalene/1,6,7-trimethylnaphthalene (1,2,4-TMN/1,6,7-TMN)) also reflect a low bio-degradation level. The well-preserved TMN derivatives indicate that the biodegradation level of the Lucaogou Formation oil shale is below PM3.
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