Sulfur Isotopic Verification of Phanerozoic Ocean Anoxic Events

最近，本研究者提出了一个用于识别海洋缺氧-缺氧历史的硫同位素的合理定位方法。它是基于从自然和实验室系统中的一些经典和最新的检查获得的微生物硫地球化学信息。其基础是在世界范围内的地层记录中发现的沉积和/或成岩硫化物中显著的硫同位素双峰性。这种双峰现象可以最合理地解释为环境氧化还原条件的急剧变化与微生物栖息地的歧视。在无氧缺氧盆地中，由于缺乏有效的氧化剂，硫酸盐还原只发生在该盆地中，硫化物相对于同期海水硫酸盐的~（34）S/~（32）S分馏程度应限制在目前已证实的厌氧硫还原菌异化硫酸盐还原过程中的动力学同位素效应范围内，即限制在厌氧硫还原菌异化硫酸盐还原过程中的~（34）S/~（32）S分馏范围内，即限制在厌氧硫还原菌异化硫酸盐还原过程中的~（34）S/~（32）S分馏范围内。 关于我们 -25 10 * 的nge<double plus>。然而，在需氧菌相对占优势的普通好氧盆地中，分馏的程度预计或多或少会超过这个范围，得到的值通常在<double plus>现代海洋沉积物中通常观察到的-50 10 * 范围内，由于初始硫化物一旦产生就被需氧硫再氧化，氧化细菌或其他氧化剂如溶解的游离氧，然后在沉积和埋藏成岩过程中掺入sebetary氧化还原循环。因此，沉积和/或成岩硫化物的同位素组成为识别和重建大洋缺氧-缺氧环境提供了一个良好的地球化学判据。应用这一原理，我们试图对古生代一些重要地质事件的古海洋氧化还原环境进行评价。结果表明，世界上的块状构造和层控型成矿作用几乎都与海洋缺氧密切相关。这将为模拟地球历史提供一个新的附加约束。少

Very recently, a sound sulfur isotopic oriterion for recognizing the ocean oxic-anoxic history has been proposed by the present investigator. It is based on information on microbial sulfur geochemistry obtained from some classical and latest examinations in natural and laboratory systems. The basis is the remarkable sulfur isotopic bimodalism in sedimentary and/or diagenetic sulfides recognized in the worldwide stratigraphic record. This bimodalism can most reasonably be accounted for by a drastic chage of environmental redox condition associated with discrimination of microbial habitat. In an aerobe-free anoxic basin where the sulfate reduction exclusively occurs because of the absence of any effective oxidants, the extent of 34S/32S fractionation of sulfide, with respect to contemporaneous seawater sulfate, shold be restricted within the currently confirmed range of kinetic isotope effect during dissimilatory sulfate reduction by anaerobic sulfur-reducing bacteria, that is, in the ra … More nge of -25 <double plus> 10 *. In an ordinary oxic basin where aerobes are relatively predominant, however, the extent of fractionation is expected to more or less exceed this range to give the values typically in the range of -50 <double plus> 10 * as generally observed in the modern oceanic sediments, since the initial sulfide once produced is reoxidized by aerobic sulfur-oxidizing bacteria or by other oxidants such as dissolved free oxygen and then incorporated in a sebsequent redox cycle during sedimentary and burial diagenetic processes. Thus, the isotopic composition of sedimentary and/or diagenetic sulfide provides a sound geochemical criterion for recognizing and reconstructing the oceanic oxic-anoxic hiApplying this principle, an attempt has been made to evaluate paleoceanic redox settings of some important geologic events in Phanerozoic time. The results reveal that the mass extinctions and the stratabound type mineralizations in the world are almost always associated intimately with intense oceanic anoxia. This would provide a new additional constraint on modeling the earth history. Less