The Effect of Elemental Sulfur on the Thermal Evolution of Steroids

Summary Steroids are one of the most important families of biomarkers, and have been widely used in petroleum exploration, paleoenvironment reconstruction and the research of eukaryotic evolution in early Earth, etc. The general evolution pathways of natural steroids were initially speculated on from their distribution in geological samples. Previous researchers further clarified the evolutionary pathways of steroids through laboratory thermal simulation experiments. However, the role of sulphur/sulphur-bearing compounds on the thermal evolution of steroids was still not well understood. We therefore carried out research on the thermal evolution pathway of steroids with and without elemental sulfur using gold tube pyrolysis experiments. The results show that elemental sulfur significantly accelerated the thermal evolution process of steroid compounds, and can induce aromatization starting with the C-ring monoaromatic steroids. The common coexistence of sterols, sterenes, steranes and aromatic steroid compounds in many immature geological samples may also be the result of the presence of sulfur. The isomerization of steranes was significantly different with and without sulfur. Therefore, when using sterane isomerization parameters to evaluate the maturity of geological samples, it is necessary to take more factors into consideration such as the lithofacies, including the presence of sulfur.