Content distribution and isotopic composition characteristics of sulfur in marine source rocks in Middle-Upper Yangtze region

Marine hydrocarbon source rocks in the Middle-Upper Yangtze region are rich in sulfur compared with terrestrial source rocks. Significant differences exist in sulfur content of source rocks in different formations or in the same formation with different lithology. There are obvious positive correlations between sulfur content and TOC of source rock. Sulfur in marine source rock exists mainly in form of organic sulfur and pyritic sulfur. Elemental sulfur is common in soluble extracts of marine source rock, but it has a variable content and occupies a lower percentage of total sulfur content. The δ³⁴S value of sulfur in marine source rock has a broad variation range from -35‰ to 30‰. The average values of δ³⁴S of organic sulfur and elemental sulfur are negative with -8. 68‰ and -5. 65‰ respectively, and those of pyritic sulfur and sulfate sulfur are positive with 4. 15‰ and 2. 19‰ respectively.