Long-term sedimentary recycling of rare sulphur isotope anomalies
Long-term sedimentary recycling of rare sulphur isotope anomalies
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DOI：
10.1038/nature12021
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发表时间：
2013-04
期刊：
影响因子：
64.8
通讯作者：
C. Reinhard;N. Planavsky;T. Lyons
中科院分区：
文献类型：
--
作者：
C. Reinhard;N. Planavsky;T. Lyons
大气中大量氧气的积累已经控制了地球表面的化学和生态结构。岩石记录中的非质量相关（NMD）硫同位素异常是用于重建早期大气氧化还原历史的核心工具。这些异常的产生和最初传递到海洋沉积物需要低大气 O2 分压（参考文献），而 23.2 亿年前 NMD 异常从岩石记录中消失，被认为标志着在地球历史的大约前 20 亿年中，大气氧含量持续偏低（低于当前大气含量的 10−5 倍）。在这里，我们提出了一项模型研究，旨在描述地壳 NMD 异常的长期表面再循环，并表明，随着大气增加超过该阈值，这种地球化学信号的记录可能会表现出“地壳记忆效应”。一旦 NMD 异常被埋藏在上地壳中，它们就极难被清除，只有通过在含氧地球表面上的连续风化、稀释和埋藏循环才能被消除。这种循环导致在同位素信号的同步大气生成停止很久之后，NMD异常残留地并入沉积记录中，在大气增加到当前大气水平的10-5倍以上之后，动态和可测量的信号可能会存活长达10-1亿年。我们的结果可以将氧气产生和瞬时积累的地球化学证据与早期地球上 NMD 异常的维持相一致，并建议未来的工作应该研究这样一种观念，即大气中新的 NMD 硫同位素异常的时间连续生成很可能早在它们最终从岩石记录中消失之前就已经停止了。
The accumulation of substantial quantities of O2 in the atmosphere has come to control the chemistry and ecological structure of Earth’s surface. Non-mass-dependent (NMD) sulphur isotope anomalies in the rock record are the central tool used to reconstruct the redox history of the early atmosphere. The generation and initial delivery of these anomalies to marine sediments requires low partial pressures of atmospheric O2 (; refs,), and the disappearance of NMD anomalies from the rock record 2.32 billion years ago, is thought to have signalled a departure from persistently low atmospheric oxygen levels (less than about 10− 5 times the present atmospheric level) during approximately the first two billion years of Earth’s history. Here we present a model study designed to describe the long-term surface recycling of crustal NMD anomalies, and show that the record of this geochemical signal is likely to display a ‘crustal memory effect’following increases in atmospheric above this threshold. Once NMD anomalies have been buried in the upper crust they are extremely resistant to removal, and can be erased only through successive cycles of weathering, dilution and burial on an oxygenated Earth surface. This recycling results in the residual incorporation of NMD anomalies into the sedimentary record long after synchronous atmospheric generation of the isotopic signal has ceased, with dynamic and measurable signals probably surviving for as long as 10–100 million years subsequent to an increase in atmospheric to more than 10− 5 times the present atmospheric level. Our results can reconcile geochemical evidence for oxygen production and transient accumulation with the maintenance of NMD anomalies on the early Earth,,,, and suggest that future work should investigate the notion that temporally continuous generation of new NMD sulphur isotope anomalies in the atmosphere was likely to have ceased long before their ultimate disappearance from the rock record.