The δ³⁴S values of the early-cleaved sulfur upon low temperature pyrolysis of a synthetic polysulfide cross-linked polymer

Closed and open kinetic pyrolysis experiments were conducted at 200°C on synthetic sulfur cross-linked polymer. Sulfur isotopic analyses of the released H₂S and the residual organic sulfur revealed large discrimination (6-9.5‰) between the early-formed, isotopically light H₂S and the residual organic sulfur. This indicates that there is a relatively large kinetic isotope effect during thermal alteration of organic sulfur. This large discrimination decreases as the reaction time increases. Isotope exchange between organic sulfur and inorganic sulfur species rapidly occur under closed system conditions. Therefore, we suggest that the early isotopic discrimination in closed system is minimized due to both gradual release of heavier sulfur isotope and isotopic exchange processes as the pyrolysis experiments advance. These results have significant geochemical implications for source rock-oil-H₂S correlations.