There are current debates around the extent of global ocean oxygenation, particularly from the late Neoproterozoic to the early Paleozoic, based on analyses of various geochemical indices. We present a temporal trend in excess barium (Baexcess) contents in marine organic-rich mudrocks (ORMs) to provide an independent constraint on global ocean redox evolution. The absence of remarkable Baexcess enrichments in Precambrian (>ca. 541 Ma) ORMs suggests limited authigenic Ba formation in oxygen- and sulfate-deficient oceans. By contrast, in the Paleozoic, particularly the early Cambrian, ORMs are marked by significant Baexcess enrichments, corresponding to substantial increases in the marine sulfate reservoir and oxygenation level. Analogous to modern sediments, the Mesozoic and Cenozoic ORMs exhibit no prominent Baexcess enrichments. We suggest that variations in Baexcess concentrations of ORMs through time are linked to secular changes in the marine dissolved Ba reservoir associated with elevated marine sulfate levels and global ocean oxygenation. Further, unlike Mo, U, and Re abundances, significant Baexcess enrichments in ORMs indicate that the overall ocean oxygenation level in the early Paleozoic was substantially lower than at present.

中文翻译：

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用海洋泥岩中的自生钡富集重新审视逐步海洋氧化

基于对各种地球化学指数的分析，目前围绕全球海洋氧化的程度存在争论，特别是从晚新元古代到早古生代。我们提出了海洋富含有机质泥岩 (ORM) 中过量钡 (Baexcess) 含量的时间趋势，以提供对全球海洋氧化还原演化的独立约束。在前寒武纪（>约 541 Ma）ORM 中没有显着的 Baexcess 富集表明在缺氧和缺硫酸盐的海洋中自生 Ba 形成有限。相比之下，在古生代，特别是早寒武世，ORM 的特征是显着的 Baexcess 富集，对应于海洋硫酸盐储层和氧化水平的大幅增加。与现代沉积物类似，中生代和新生代 ORM 没有表现出明显的 Baexcess 富集。我们认为，随着时间的推移，ORM 的 Baexcess 浓度的变化与海洋溶解 Ba 水库的长期变化有关，这些变化与海洋硫酸盐水平升高和全球海洋氧化有关。此外，与 Mo、U 和 Re 丰度不同，ORM 中显着的 Baexcess 富集表明早古生代的整体海洋氧化水平大大低于目前。