Molybdenum isotope constraints on the extent of late Paleoproterozoic ocean euxinia
Molybdenum isotope constraints on the extent of late Paleoproterozoic ocean euxinia
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DOI：
10.1016/j.epsl.2011.05.019
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发表时间：
2011-07-15
影响因子：
5.3
通讯作者：
Anbar, Ariel D.
中科院分区：
文献类型：
--
作者：
Kendall, Brian;Gordon, Gwyneth W.;Anbar, Ariel D.
缺氧和硫化物（euxinic）深海的扩张可能解释全球大型铁建造（IF）沉积的终止在类似1.85 Ga，但晚古元古代海洋euxinia的面积范围是不好的限制。在这里，我们使用了来自038的黑色页岩的钼（Mo）同位素组成（δ Mo-98/95）和黄铁矿Fe与高活性Fe（Fe-PY/Fe-HR通常为0.8）和Fe-HR/Fe-T（>0.38）的比值，这意味着持续的水柱euxinia。游离硫化物的浓度可能足以导致四硫代钼酸盐的形成接近定量，并从底层沃茨中去除。观察到的δ Mo-98/95的窄范围为1.19 +/- 0.28 ppm。(250)由此推断，由大多数富氧页岩定义的Mo同位素组成代表了古元古代晚期全球海水的Mo同位素组成。质量平衡模型表明，富有机质沉积物下euxinic底部沃茨的海洋钼汇在1.8 Ga的一个重要组成部分。模拟结果表明，沿着晚古元古代洋缘普遍存在缺氧海洋环境。这些环境可能是缺氧深层沃茨中Fe-（aq）（2+）上涌的有效汇。因此，Mo同位素数据与Fe形态和其他地球化学证据相一致，这些证据表明，在类似于1.85 Ga之后，富氧环境的扩张导致全球大型IF沉积的停止。(C)2011爱思唯尔有限公司版权所有。
The expansion of anoxic and sulfidic (euxinic) deep oceans may explain the termination of global large iron formation (IF) deposition at similar to 1.85 Ga, but the areal extent of late Paleoproterozoic ocean euxinia is poorly constrained. Here, we use the molybdenum (Mo) isotope composition (delta Mo-98/95) of black shales from the 038) and ratios of pyrite Fe to highly reactive Fe (Fe-PY/Fe-HR typically 0.8) and Fe-HR/Fe-T (>0.38), which implies persistent water column euxinia. Concentrations of free sulfide may have been sufficient to result in near-quantitative formation of tetrathiomolybdate and its removal from bottom waters. The observed narrow range in delta Mo-98/95 of 1.19 +/- 0.28 parts per thousand. (250) defined by most euxinic shales is thus inferred to represent the Mo isotope composition of late Paleoproterozoic global seawater. Mass-balance modeling suggests that organic-rich sediments deposited beneath euxinic bottom waters represented a substantial fraction of the oceanic Mo sink at 1.8 Ga. The modeling results suggest that euxinic marine environments were common along late Paleoproterozoic ocean margins. These environments could have served as efficient sinks for Fe-(aq)(2+) upwelling from anoxic deeper waters. Hence, the Mo isotope data are consistent with Fe speciation and other geochemical evidence that suggest an expansion of euxinic environments led to the cessation of global large IF deposition after similar to 1.85 Ga. (C) 2011 Elsevier B.V. All rights reserved.