Geology around Natural Reactors and Birthplace of Eukaryotes
Geology around Natural Reactors and Birthplace of Eukaryotes
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DOI：
10.5026/jgeography.128.549
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发表时间：
2019-08
期刊：
影响因子：
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通讯作者：
Y. Sawaki;Tomohiko Sato;W. Fujisaki;Hisahiro Ueda;H. Asanuma;S. Maruyama
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文献类型：
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作者：
Y. Sawaki;Tomohiko Sato;W. Fujisaki;Hisahiro Ueda;H. Asanuma;S. Maruyama
真核生物的进化是生命史上最重要的问题之一。古生物研究发现了加蓬古元古代弗朗西维利亚群中最古老的真核化石。为了阐明加蓬古沉积盆地的特殊特征，总结了弗兰切维利群的地质证据，并提出了新的大地构造模式。该模型对地幔上涌给予了很大的重视，这可以解释为什么弗兰西维利亚盆地只有天然反应堆。古元古代的大氧化事件不仅在真核生物的演化中发挥了重要作用，而且在天然反应堆的形成中也发挥了重要作用。受与羽流有关的火山作用的影响，大陆地壳的还原风化作用将富铀矿物输送到弗兰西维利安群的沉积物中，而不溶解铀。随后的氧化事件使铀酰离子在氧化破裂的裂谷盆地内聚集，并在fl或OOR海上沉积了大量有机质。弗兰西维利安群内的热液循环沉淀了高铀矿石，这些矿石在大约2.0Ga时成为天然反应堆，并可能在fl促进了该盆地中真核生物的演化。在很大程度上，海洋-大气系统的氧化程度与沉积岩的数量有关。这样，2.7Ga的地幔翻转形成了巨大的陆壳，是影响真核生物进化的关键事件之一。
The evolution of eukaryotes is one of the most important issues in the history of life. Paleon-tological studies discovered the oldest eukaryotic fossil from the Paleoproterozoic Francevillian Group in Gabon. To clarify specific features of ancient sedimentary basins in Gabon, geologic evidence for the Francevillian Group is summarized and a new geotectonic model is proposed. The model gives much weight to the upwelling of mantle plume, which can explain why the Francevillian basin only hosted natural reactors. The Great Oxidation Event in the Paleoproterozoic played an important role in not only the evolution of eukaryotes but also in the formation of natural reactors. Reductive weathering of the continental crust, which was affected by plume-related volcanisms, transported Uranium-rich minerals into sediments of the Francevillian Group without dissolution of Uranium. The subsequent oxidation event enabled uranyl ions to accumulate within an oxic failed rift basin, and settled large quantities of organic matter on the seafloor. Hydrothermal circulation within the Francevillian Group precipitated highly Uranium-rich ores, which became natural reactors at approximately 2.0 Ga, and might have influenced the evolution of eukaryotes in this basin. In a large sense, the degree of oxidation of the ocean-atmosphere system has been linked to the amount of sedimentary rocks. In that way, mantle overturn in 2.7 Ga, which created a large continental crust, was one of the crucial events that affected the evolution of eukaryotes.