Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742.
Proc Natl Acad Sci U S A. 2013 Oct 29;110(44):17638-43. doi: 10.1073/pnas.1218851110. Epub 2013 Feb 13.
It is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the Neoarchean. It is puzzling, therefore, that the sulfur isotope record of the Neoarchean is characterized by a signal of atmospheric mass-independent chemistry rather than a strong overprint by sulfate reducers. Here, we present a study of the four sulfur isotopes obtained using secondary ion MS that seeks to reconcile a number of features seen in the Neoarchean sulfur isotope record. We suggest that Neoarchean ocean basins had two coexisting, significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record. One of these pools is suggested to be a soluble (sulfate) pool, and the other pool (atmospherically derived elemental sulfur) is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide. We suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite-forming environments. We also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record.
一般认为硫酸盐还原代谢作用较为古老，可能在新太古代之前就已经建立。因此，令人费解的是，新太古代的硫同位素记录的特征是大气质量独立化学的信号，而不是硫酸盐还原菌的强烈叠加。在这里，我们使用二次离子质谱（secondary ion MS）研究了获得的四个硫同位素，试图调和新太古代硫同位素记录中看到的一些特征。我们认为，新太古代的海洋盆地有两个共存的、规模相当大的硫库，并且形成黄铁矿前体的途径在确定每个硫库的同位素特征如何传递到沉积岩记录方面发挥了重要作用。其中一个库被认为是可溶（硫酸盐）库，而另一个库（大气衍生的元素硫）在与硫化氢反应之前，主要是不溶和无反应的。我们认为，这些库对黄铁矿形成的相对贡献取决于不溶库的积累和黄铁矿形成环境中硫化物产生的速度。我们还认为，大量反应性硫的非硫酸盐库的存在掩盖了硫酸盐还原菌在岩石记录中广泛活动的同位素证据。
