Abstract The radiation of macroscopic animals in the Early Cambrian, commonly be called as ‘Cambrian explosion’, had a close relationship with Earth oxygenation. These macrofossils are widely preserved within the Early Cambrian in the northern and western Yangtze Craton. In order to show the casual relationship between animal evolution and Earth redox environment, Mo content and isotopic composition analyses have been conducted on dolomites of the Tianzhushan Formation and the black shales of the Shuijingtuo Formation from the lowermost Cambrian profile in the eastern Huangling dome, northern Yangtze Craton. The calcitic dolostones from the Tianzhushan Formation display lower concentrations of Mo contents (0.055–0.666 ppm) than that of the black silty shales from the Shuijingtuo Formation (6.0–172 ppm). This magnitude difference is most likely related to the different lithologies due to Mo enrichment in shales. The Mo isotope values (δ98/95Mo) of the calcitic dolostones for the Tianzhushan Formation vary from −0.73‰ to 0.41‰. In comparison, the black sandy shales from the Shuijingtuo Formation exhibit δ98/95Mo of −1.04–1.84‰, including 5 samples from the earliest Shuijingtuo Formation displaying systematically higher δ98/95Mo values (0.09–1.84‰) than those of the other 5 samples from upper layers (δ98/95Mo = −1.04 to −0.19‰). These geochemical data suggest that the redox environment of the early Cambrian is fluctuating, and the peak oxygenation of the ocean had already reached a level similar to modern environments. According to the Mo concentrations and δ98/95Mo data, the sedimentary succession can be divided into five intervals, which are closely correlated to the episodic evolution of early life in the Cambrian. Together with the available published data from other profiles in the Yangtze Craton, our new data reveal that the higher oxidation environment had a positive effect on the evolution of early life.

中文翻译：

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华南黄陵地区寒武系沉积剖面钼同位素变化：寒武系爆发对应氧化还原环境的证据

摘要 早寒武世宏观动物的辐射，俗称“寒武纪大爆发”，与地球的氧化作用密切相关。这些大型化石广泛保存在扬子克拉通北部和西部的早寒武世。为揭示动物演化与地球氧化还原环境之间的偶然关系，对黄陵穹窿东部最下部寒武系剖面天柱山组白云岩和水井沱组黑色页岩进行钼含量和同位素组成分析。扬子克拉通。天柱山组方解石白云岩的钼含量（0.055-0.666 ppm）低于水井沱组黑色粉质页岩（6.0-172 ppm）。由于页岩中钼的富集，这种幅度差异很可能与不同的岩性有关。天柱山组方解石白云岩的Mo同位素值(δ98/95Mo)在-0.73‰～0.41‰之间变化。相比之下，水井沱组黑色砂质页岩δ98/95Mo含量为-1.04～1.84‰，其中水井沱组最早5个样品的δ98/95Mo值（0.09～1.84‰）系统高于其他5个样品从上层（δ98/95Mo = -1.04 到 -0.19‰）。这些地球化学数据表明，早寒武世的氧化还原环境是波动的，海洋的氧化峰值已经达到了与现代环境相似的水平。根据Mo浓度和δ98/95Mo资料，可将沉积序列划分为5个层段，这与寒武纪早期生命的情节演化密切相关。连同来自扬子克拉通其他剖面的已发表数据，我们的新数据表明，较高的氧化环境对早期生命的演化产生了积极影响。