Coupled δ44/40Ca, δ88/86Sr, and 87Sr/86Sr geochemistry across the end-Permian mass extinction event
Coupled δ44/40Ca, δ88/86Sr, and 87Sr/86Sr geochemistry across the end-Permian mass extinction event
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DOI：
10.1016/j.gca.2019.07.035
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发表时间：
2019-10
影响因子：
5
通讯作者：
Jiuyuan Wang;A. Jacobson;Hua Zhang;J. Ramezani;B. Sageman;M. Hurtgen;S. Bowring;S. Shen
中科院分区：
文献类型：
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作者：
Jiuyuan Wang;A. Jacobson;Hua Zhang;J. Ramezani;B. Sageman;M. Hurtgen;S. Bowring;S. Shen
我们报告了中国南方眉山和大江碳酸盐岩层系跨越二叠纪-三叠纪边界 (PTB) 的高分辨率、高精度 δ44/40Ca、δ88/86Sr 和 87Sr/86Sr 记录。该研究的目的是了解地球历史上一段以严重的生物和环境扰动为特征的时期钙和锶同位素的行为，包括大规模灭绝、洪水玄武岩火山活动、海洋酸化和海平面波动。大江在主灭绝视界和PTB之间的<60 kyr时间范围内显示负δ44/40Ca和δ88/86Sr偏移以及不变的87Sr/86Sr比率。眉山δ44/40Ca和δ88/86Sr记录普遍偏向较高值，并显示出相对于大江的同步和异步趋势。此外，眉山的 87Sr/86Sr 比值显着升高，并且没有定义明确的长期模式。我们借助支持元素和同位素测量（例如 Sr/Ca、δ13C 和 δ18O）以及顺序浸出实验，协调数据集的不同概念模型。综合证据表明，大江沉积物在岩石缓冲条件下经历了重结晶和新形态，保留了原始信号。相比之下，眉山记录显示了初级和次级过程的影响，包括分馏的局部差异、流体缓冲的早期海洋成岩作用和晚期成岩叠印。大江的三个同位素记录以及眉山的δ44/40Ca和δ88/86Sr记录在一定程度上保存了二叠纪末海水的地球化学信息。我们发现海平面下降期间陆架碳酸盐的风化增强为海水 δ44/40Ca 和 δ88/86Sr 值快速下降提供了最好的解释，而不影响 87Sr/86Sr 比率。
We report high-resolution, high-precision δ44/40Ca, δ88/86Sr, and87Sr/86Sr records spanning the Permian-Triassic boundary (PTB) from the Meishan and Dajiang carbonate successions in south China. The goal of the study was to understand the behavior of Ca and Sr isotopes during a time period in Earth history characterized by severe biological and environmental perturbations, including a major mass extinction, flood basalt volcanism, ocean acidification, and sea level fluctuations. Dajiang displays negative δ44/40Ca and δ88/86Sr excursions and invariant87Sr/86Sr ratios in the <60 kyr timeframe between the main extinction horizon and the PTB. The Meishan δ44/40Ca and δ88/86Sr records are generally shifted to higher values and display both synchronous and asynchronous trends relative to Dajiang. In addition,87Sr/86Sr ratios at Meishan are significantly elevated and do not define a clear secular pattern. We reconcile diverse conceptual models for the dataset with the aid of supporting elemental and isotope measurements (e.g., Sr/Ca, δ13C, and δ18O), as well as sequential leaching experiments. The combined body of evidence indicates that Dajiang sediments experienced recrystallization and neomorphism under rock-buffered conditions that preserved primary signals. In contrast, the Meishan records display influences from both primary and secondary processes, including local differences in fractionation, fluid-buffered early marine diagenesis, and late stage diagenetic overprinting. The three isotopic records for Dajiang, and to some extent, the δ44/40Ca and δ88/86Sr records for Meishan, preserve information about the geochemistry of end-Permian seawater. We find that enhanced weathering of shelf carbonates during sea level fall provides the best explanation for rapidly decreasing seawater δ44/40Ca and δ88/86Sr values without affecting87Sr/86Sr ratios.