Revisiting stepwise ocean oxygenation with authigenic barium enrichments in marine mudrocks
Revisiting stepwise ocean oxygenation with authigenic barium enrichments in marine mudrocks
复制标题
重新审视海洋泥岩中自生钡富集的逐步海洋氧合
作者：
Guang-Yi Wei;Hong-Fei Ling;Graham A. Shields;Simon V. Hohl;Tao Yang;Yi-Bo Lin;Feifei Zhang
根据各种地球化学指标的分析，目前围绕着全球海洋氧化的程度，特别是从新元古代晚期到早古生代，存在着争论。我们提出了海洋富有机质泥岩（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。在前寒武纪没有明显的Baexcess富集（>ca. 541 Ma）ORM表明，有限的自生Ba形成在氧和硫酸盐缺乏的海洋。相比之下，在古生代，特别是早寒武世，ORM的标志是显着的Baexcess富集，相应的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、新生代有机质不存在明显的钡过量富集。我们认为，随着时间的推移，在Baexcess浓度的ORM的变化与海洋溶解钡水库与海洋硫酸盐水平升高和全球海洋氧合的长期变化。此外，不像Mo，U和Re的丰度，显着的Baexcess富集在ORM表明，在早古生代的整体海洋氧化水平大大低于目前。
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 organicrich 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.