Organic sulfur compounds formed during early diagenesis in Black Sea sediments

Abstract

Sediments from Units I and II of the Black Sea were analyzed to assess the early diagenetic formation of organic sulfur compounds (OSC). A series of isomeric C 28-2,4-dialkylthiophenes was found at low concentrations in surface sediments. OSC with C 25-highly branched isoprenoid (RBI) skeletons were not found in surface sediments even though there was a rapid decrease in the concentrations of C 25-HBI alkenes in the same sediments, nor were OSC found which contained carbon skeletons derived from C 37–C 39 alkenes which are also abundant in the sediment. As depth increased in Unit I, concentrations of the C 28-2,4-dialkylthiophenes decreased while C 25- and C 30-HBI thiolanes appeared at the bottom of Unit I and increased in concentration into Unit II. Treatment of macromolecular material from sediment extracts with Raney nickel yielded phytane as the dominant hydrocarbon as well as series of C 25- and C 30-HBI hydrocarbons, β-carotane, and isorenieratane. These latter two components were generally absent from the free hydrocarbon fractions. These results indicate that sulfur incorporation into functionalized lipids can occur during the very early stages of sedimentary diagenesis, even at the sediment-water interface. On the other hand, the rapid loss of C 25-HBI alkenes in surface sediments could not be accounted for by sulfur quenching, and other potential OSC-precursors, such as C 37-C 39 alkenes, also apparently did not incorporate sulfur into readily-analyzable material.