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Sulfur Isotopic Verification of Phanerozoic Ocean Anoxic Events

显生宙海洋缺氧事件的硫同位素验证

基本信息

批准号：
06804028
负责人：
KAJIWARA Yoshimichi
金额：
$ 1.28万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

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

最近，本研究人员提出了一个识别海洋缺氧历史的可靠的硫同位素定位法。它是基于从自然和实验室系统中的一些经典和最新检查中获得的微生物硫地球化学信息。其基础是世界地层学记录中公认的沉积和/或成岩硫化物中显着的硫同位素双峰性。这种双峰型最合理的解释是与微生物栖息地的区别有关的环境氧化还原条件的剧烈变化。在无氧缺氧条件下，硫酸盐还原完全是由于没有任何有效的氧化剂而发生的，硫化物相对于同期海水硫酸盐的34S/32S分馏程度应限制在厌氧硫还原细菌异化硫酸盐还原过程中，即在ra…中的动力学同位素效应范围内。更多-25；双加&gt；10*的nge。然而，在需氧菌相对占优势的普通含氧盆地中，分馏的程度预计或多或少会超过这个范围，从而得到现代海洋沉积物中通常观察到的-50&lt；Double Plus&gt；10*范围内的值，因为最初的硫化物一旦产生，就会被好氧硫氧化菌或其他氧化剂(如溶解游离氧)重新氧化，然后在沉积和埋藏成岩过程中并入到随后的氧化还原循环中。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-缺氧环境提供了可靠的地球化学判据。应用这一原理，对显生界一些重要地质事件的古大洋氧化还原环境进行了评价。结果表明，地球上的大灭绝和层控型成矿作用几乎总是与海洋的强烈缺氧密切相关。这将为模拟地球历史提供一个新的附加约束。较少