Multiple S-isotopic constraints on paleo-redox and sulfate concentrations across the Ediacaran-Cambrian transition in South China
Multiple S-isotopic constraints on paleo-redox and sulfate concentrations across the Ediacaran-Cambrian transition in South China
复制标题
华南埃迪卡拉纪-寒武纪过渡期古氧化还原和硫酸盐浓度的多重硫同位素限制
DOI：
10.1016/j.precamres.2019.105500
复制
发表时间：
2020-10-01
影响因子：
3.8
通讯作者：
Shen, Yanan
中科院分区：
文献类型：
--
作者：
Li, Dandan;Zhang, Xiaolin;Shen, Yanan
海洋化学条件的变化经常被认为是地球历史上生物多样化和大规模灭绝事件的主要驱动力。在埃迪卡拉-寒武纪过渡期，两个主要的生物事件，包括埃迪卡拉生物群的灭绝和寒武纪大爆发，发生了大约与碳和硫循环的扰动。这些戏剧性的生物变化和同时代的地球化学事件通常被认为是有联系的，但它们的因果关系仍然存在争议。本文报道了华南埃迪卡拉-寒武系过渡段小滩剖面黄铁矿δ S-34（py）和δ S-33（py）的多种硫同位素组成。我们的同位素结果表明，负三角洲S-33（py）值，以及正三角洲S-34（py）值，发生在埃迪卡拉-寒武系边界。负三角洲S-33（py）数据表明，在含硫沃茨上涌至含氧浅水沃茨期间，来自深水沃茨的硫化物发生了混合。负三角洲S-33（py）和埃迪卡拉生物群灭绝的大致时间之间的巧合意味着古氧化还原扰动可能导致了埃迪卡拉生物群的消失。在寒武系忠义村段沉积磷块岩时，δ S-33（py）值为负，δ S-34（py）值为正，表明富营养硫化物深层沃茨的上涌与磷块岩在含氧陆棚区的沉积有密切联系。此外，使用箱模型和化学计量学计算，我们定量估计了有机质和黄铁矿的埋藏速率升高的基础上平行的正三角洲C-13（carb），三角洲S-34（py）和三角洲（33）间谍在寒武纪阶段2内观察到的偏移。我们的质量平衡模拟结果提供了一个独立的约束硫酸盐浓度为4毫米或更低的寒武纪早期海洋。黄铁矿和有机物的埋藏增强可能导致氧气水平的增加，这可能为早期动物提供了更适合居住的环境，从而为寒武纪早期动物的辐射铺平了道路。
Changes in oceanic chemical conditions are frequently invoked as a primary driver of biodiversification and mass extinction events in Earth history. During the Ediacaran-Cambrian transition, two major biological events, including the extinction of the Ediacaran biota and the Cambrian explosion, occurred approximately coincident with perturbations of the carbon and sulfur cycle. These dramatic biological changes and coeval geochemical events are commonly thought to be linked, but their causal relationships remain controversial. Here we present multiple S-isotopic compositions of pyrite (delta S-34(py) and Delta S-33(py)) from the Xiaotan section spanning the Ediacaran-Cambrian transition interval in South China. Our isotopic results show that negative Delta S-33(py) values, together with positive delta S-34(py) values, occurred across the Ediacaran-Cambrian boundary. The negative Delta S-33(py) data suggest mixing of sulfide from deep waters during the upwelling of sulfidic waters into oxygenated shallow waters. The coincidence between the negative Delta S-33(py) and the approximate timing of the extinction of the Ediacaran biota implies that paleo-redox perturbations may have contributed to the disappearance of the Ediacaran biota. Negative Delta S-33(py) values coupled with positive delta S-34(py) values were also observed in the Cambrian Zhongyicun Member when the phosphorites were deposited, suggesting a strong linkage between the upwelling of nutrient-rich sulfidic deep waters and the deposition of the phosphorites in oxygenated shelf areas. In addition, using box models and stoichiometry calculations, we quantitatively estimated elevated burial rates of organic matter and Pyrite based on the parallel positive delta C-13(carb), delta S-34(py) and Delta(33)Spy excursions observed at Xiaotan within Cambrian Stage 2. Our mass balance modelling results provide an independent constraint on sulfate concentrations which were 4 mM or lower in the early Cambrian oceans. The probable increase in oxygen levels resulting from the enhanced burial of pyrite and organic matter could have provided a more habitable environment for early animals and thus paved the way for the radiation of early Cambrian animals.