Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean.
Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean.
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DOI：
10.1111/gbi.12091
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发表时间：
2014-09
期刊：
影响因子：
3.7
通讯作者：
E. Sperling;A. Rooney;L. Hays;V. N. Sergeev;N. G. Vorob’eva;N. D. Sergeeva;D. Selby;D. Johnston-D.-John
中科院分区：
文献类型：
--
作者：
E. Sperling;A. Rooney;L. Hays;V. N. Sergeev;N. G. Vorob’eva;N. D. Sergeeva;D. Selby;D. Johnston-D.-John
大量证据表明，中元古代海洋盆地的地下水体通常是缺氧的，要么是富氧的（硫化物），要么是含铁的（游离亚铁）。为了进一步记录氧化还原变化，在此期间，多代理地球化学和古生物学的调查进行了约1000米厚的中元古代（下里菲）的阿尔兰成员的Kalkovic组，俄罗斯中部。铁形态地球化学，有机地球化学，氧化还原敏感的微量元素丰度和黄铁矿硫同位素值的支持下，表明盆地石灰质页岩的阿兰成员下的含氧水柱沉积，并与此解释一致，真核微化石丰富的盆地相。阿兰页岩的铼-锇（Re-Os）系统学给出了序列底部附近两个层位的沉积年龄为1414±40和1427±43 Ma，与先前提出的相关性一致。游离氧在盆地环境中的存在增加了一个重要的端员元古宙氧化还原不均匀性，需要根据以前的数据从时间相当的盆地解释。阿兰段有机碳总含量极低可能是关键-含氧深水沃茨更有可能（在任何大气O2水平下）处于出口产量低的贫营养系统。地下沃茨中氧化还原不均匀性的全方位记录和局部氧化还原控制的存在表明，没有一个单一的地层剖面或盆地可以充分捕获元古代海洋的平均氧化还原剖面及其在任何给定时间点的变化。
A substantial body of evidence suggests that subsurface water masses in mid-Proterozoic marine basins were commonly anoxic, either euxinic (sulfidic) or ferruginous (free ferrous iron). To further document redox variations during this interval, a multiproxy geochemical and paleobiological investigation was conducted on the approximately 1000-m-thick Mesoproterozoic (Lower Riphean) Arlan Member of the Kaltasy Formation, central Russia. Iron speciation geochemistry, supported by organic geochemistry, redox-sensitive trace element abundances, and pyrite sulfur isotope values, indicates that basinal calcareous shales of the Arlan Member were deposited beneath an oxygenated water column, and consistent with this interpretation, eukaryotic microfossils are abundant in basinal facies. The Rhenium-Osmium (Re-Os) systematics of the Arlan shales yield depositional ages of 1414±40 and 1427±43 Ma for two horizons near the base of the succession, consistent with previously proposed correlations. The presence of free oxygen in a basinal environment adds an important end member to Proterozoic redox heterogeneity, requiring an explanation in light of previous data from time-equivalent basins. Very low total organic carbon contents in the Arlan Member are perhaps the key--oxic deep waters are more likely (under any level of atmospheric O2) in oligotrophic systems with low export production. Documentation of a full range of redox heterogeneity in subsurface waters and the existence of local redox controls indicate that no single stratigraphic section or basin can adequately capture both the mean redox profile of Proterozoic oceans and its variance at any given point in time.