Early incorporation of polysulphides in sedimentary organic matter

Abstract

The increase in sulphur content of organic matter with depth in Recent sediments has been attributed to incorporation of either H₂S or polysulphides or to a combination of both. Indeed, the widespread occurrence of organic sulphur compounds with carbon skeletons that bear an unambiguous link with natural precursors indicates that organic matter may act as a sink for inorganic sulphur species with an efficacy second only to reactive iron minerals. Laboratory and field observations indicate that all compounds identified so far are consistent with incorporation of H₂S; molecular evidence for incorporation of polysulphides has previously been lacking. Here we report the identification of homologous series of cyclic disulphides with a linear carbon skeleton and of a cyclic di- and trisulphide with a C₂₀ isoprenoid carbon skeleton in sediments of Quaternary to Pliocene age. Although incorporation of H₂S can still explain the presence of cyclic disulphides, the cyclic trisulphide implies incorporation of inorganic polysulphides in sedimentary organic matter at the earliest stages of diagenesis.