Identification and Geochemical Implication of Sulfur Compounds in an Immature Lacustrine Shale Oil

The organic sulfur compounds were isolated from an immature shale oil in Hetao Basin, northern China, and characterized by Fourier transform ion cyclotron resonance mass spectrometry and gas chromatography–mass spectrometry. Various sulfur-containing biomarkers were identified, including C15, C20, and C25 isoprenoid thiophenes and benzothiophenes, C13 bicyclic terpenoid sulfide, and C37/C38 n-alkylated sulfur compounds. The molecular composition indicates that the sulfurization occurred in the early stages of diagenesis through bacterial sulfate reduction, which contains a wealth of geochemical information. In addition, a series of novel spirosterene-derived sulfur compounds were identified in combination with desulfurization results. The spirosterene skeletons are considered originating from the rearrangement of cholestenes with the presence of clay minerals. The unstable spirosterene skeletons were preserved through sulfurization, and the derived sulfides are potential molecular markers