Abstract The history of oceanic oxygenation from the late Neoproterozoic to the early Cambrian is currently debated, making it difficult to gauge whether, and to what extent environmental triggers played a role in shaping the trajectory of metazoan diversification. Uranium isotope ( δ 238 U) records from carbonates have recently been used to argue for significant swings in the global marine redox state from the late Neoproterozoic to the early Cambrian. However, geochemical signatures in carbonates—the U isotope archive most commonly employed to argue for redox shifts—are susceptible to diagenetic alteration and may have variable offsets from seawater values. Therefore, there is an impetus to reconstruct seawater U isotopic evolution using another sedimentary archive, in order to verify that these excursions can indeed be linked to global shifts in marine redox landscape. Here we report new U isotope data from two fine-grained siliciclastic upper Ediacaran to lower Cambrian (ca. 551–515 Ma) successions in South China. We find large δ 238 U swings between − 0.63 ‰ and + 0.39 ‰ for calculated values of authigenic U in the siliciclastic rocks, consistent with correlative records from the carbonates. The replication of these patterns in both carbonate and siliciclastic units provides confirmatory evidence that the early Cambrian seawater was characterized by highly variable U isotope compositions. These new δ 238 U data also provide higher-resolution records of global oceanic redox conditions during Cambrian Age 3, coeval with a critical interval of the Cambrian explosion. These δ 238 U data bolster the case that the Ediacaran-Cambrian transition experienced massive swings in marine redox state, providing a dynamic environmental backdrop for and potentially even a key driver of the emergence and radiation of metazoans.

中文翻译：

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通过自生 δ238U 记录突出显示的寒武纪爆炸中的高动态海洋氧化还原状态

摘要 从新元古代晚期到寒武纪早期的海洋氧化历史目前存在争议，因此很难判断环境触发因素是否以及在多大程度上影响了后生动物多样化的轨迹。来自碳酸盐的铀同位素 (δ 238 U) 记录最近被用来论证从新元古代晚期到寒武纪早期的全球海洋氧化还原状态的显着波动。然而，碳酸盐中的地球化学特征——最常用于论证氧化还原位移的 U 同位素档案——容易受到成岩改变的影响，并且可能与海水值有不同的偏移。因此，有动力利用另一个沉积档案重建海水 U 同位素演化，为了验证这些远足确实与海洋氧化还原景观的全球变化有关。在这里，我们报告了来自华南两个细粒硅质碎屑上埃迪卡拉纪到下寒武纪（约 551-515 Ma）序列的新 U 同位素数据。我们发现，对于硅质碎屑岩中自生 U 的计算值，δ 238 U 在 − 0.63 ‰ 和 + 0.39 ‰ 之间波动，这与碳酸盐岩的相关记录一致。这些模式在碳酸盐和硅质碎屑单元中的复制提供了确凿的证据，即早期寒武纪海水的特征是高度可变的 U 同位素组成。这些新的 δ 238 U 数据还提供了寒武纪 3 期全球海洋氧化还原条件的更高分辨率记录，与寒武纪爆发的关键间隔同时期。