Decoupled oxygenation of the Ediacaran ocean and atmosphere during the rise of early animals
Decoupled oxygenation of the Ediacaran ocean and atmosphere during the rise of early animals
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DOI：
10.1016/j.epsl.2022.117619
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发表时间：
2022-08
影响因子：
5.3
通讯作者：
W. Shi;Benjamin J. W. Mills;Chao Li;S. Poulton;Alexander J. Krause;Tianchen He;Ying Zhou;Cheng Men
中科院分区：
文献类型：
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作者：
W. Shi;Benjamin J. W. Mills;Chao Li;S. Poulton;Alexander J. Krause;Tianchen He;Ying Zhou;Cheng Men
埃迪卡拉纪（635 - 541 Ma）见证了后生动物的早期多样化和辐射，以埃迪卡拉生物群的形式出现。这场生物学革命始于1575 Ma，被广泛归因于一个时间上有限的深海氧合事件，可能是由同期大气氧水平的上升引起的。然而，缺乏对埃迪卡拉纪大气和海洋氧化还原演化的定量地球化学记录驱动的估计，因此海洋和大气氧化作用之间可能的联系仍然是推测性的。在这里，筛选可能的沉积后蚀变后，我们利用来自中国南方，阿曼和美国-墨西哥的古地理多样性的碳和硫同位素记录，开发一个地球化学同位素质量平衡模型，以量化埃迪卡拉大气氧和海洋硫酸盐演化。来自三大洲的模型结果表明，埃迪卡拉纪大气中的氧含量在20630 Ma和20590 Ma之间单调上升，随后在埃迪卡拉纪的其余部分保持相对稳定，约为0.6现在的大气水平。相比之下，海洋硫酸盐储层似乎保持相对稳定之前，575马，与随后的大脉冲硫酸盐浓度上升到108毫米。这些定量结果表明，埃迪卡拉海洋和大气的氧化解耦，这是与已发表的地球化学记录。我们认为，埃迪卡拉纪早期大气氧含量的上升，由有机碳和黄铁矿的净埋藏增加驱动，可能没有建立广泛的深海氧化。相反，后来来自大陆的氧化力（主要是硫酸盐）的脉冲输入驱动了海底氧化的短暂事件，伴随着埃迪卡拉生物群的辐射。
The Ediacaran Period (∼635 to 541 Ma) witnessed the early diversification and radiation of metazoans, in the form of the Ediacaran Biota. This biological revolution, beginning at ∼575 Ma, has been widely attributed to a temporally restricted episode of deeper ocean oxygenation, potentially caused by a contemporaneous rise in atmospheric oxygen levels. However, quantitative geochemical-record-driven estimates of Ediacaran atmospheric and oceanic redox evolution are lacking, and hence possible links between oceanic and atmospheric oxygenation remain speculative. Here, after screening for possible post-depositional alteration, we utilize paleogeographically-diverse carbon and sulfur isotope records from South China, Oman and USA-Mexico, to develop a biogeochemical isotope mass balance model to quantify Ediacaran atmospheric oxygen and oceanic sulfate evolution. Model results from all three continents indicate that Ediacaran atmospheric oxygen levels rose monotonically between ∼630 Ma and ∼590 Ma, and subsequently remained relatively stable at around 0.6 present atmospheric level for the remainder of the Ediacaran. By contrast, the marine sulfate reservoir appears to have remained relatively stable before ∼575 Ma, with a subsequent large pulse where sulfate concentrations rose to ∼8 mM. These quantitative results indicate that Ediacaran oceanic and atmospheric oxygenation were decoupled, which is consistent with published geochemical records. We propose that the early Ediacaran rise of atmospheric oxygen levels, driven by increased net burial of organic carbon and pyrite, may not have established widespread deep-ocean oxygenation. Instead, later pulsed input of oxidizing power (mainly sulfate) from the continents drove transient episodes of seafloor oxygenation that accompanied radiations of the Ediacaran Biota.