有机硫化合物
δ34S
硫黄
干酪根
沉积有机质
化学
硫化物
环境化学
硫酸盐
有机质
沉积岩
同位素分析
同位素特征
地质学
稳定同位素比值
地球化学
烃源岩
有机化学
总有机碳
构造盆地
海洋学
古生物学
物理
流体包裹体
石英
量子力学
作者
M. R. Raven,Jess F. Adkins,Josef P. Werne,Timothy W. Lyons,Alex L. Sessions
标识
DOI:10.1016/j.orggeochem.2015.01.002
摘要
Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are 34S-enriched relative to coexisting sulfide, and experiments have produced 34S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography – inductively coupled plasma mass spectrometry, to measure the compound-specific sulfur isotopic compositions of volatile organosulfur compounds over a 6 m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in 34S relative to coexisting kerogen and porewater sulfide. We hypothesize that this 34S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon–sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary porewater. The 34S-depleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.
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