Mass extinction and extensive black shale deposition were associated with widespread ocean anoxia during the Ordovician–Silurian transitional interval, yet uncertainty among trace-metal proxies has precluded an improved understanding of redox dynamics at this time of Earth history and their relationship with animal evolution and accumulation of organic-rich shale. Herein, we describe results of a geochemical investigation of the Qianqian #1 section of South China that preserves the stratigraphic record of the inner shelf of the Upper Yangtze Platform. Specifically, newly acquired total organic carbon (TOC), total sulfur (TS), iron (Fe) speciation, and major element and trace metal abundances are considered with existing data from the studied section. Our results reveal that redox trends suggested by Fe speciation data are generally consistent with those based on C_org/P ratios and redox-sensitive trace element (RSTE) enrichment. However, documented differences among redox histories based on Fe speciation, C_org/P ratios, and RSTE enrichment may reflect the influence of high-frequency redox fluctuations. Comparison of bimetal ratios (U/Th, V/Cr, Ni/Co, and V/(V + Ni)) to Fe speciation, C_org/P ratios, and RSTE enrichment suggest that commonly cited thresholds of bimetal ratios for various redox states are unreliable, though variations in U/Th, V/Cr, and Ni/Co may provide a more robust indication of relative redox changes. A documented strong correlation of changing redox conditions and fossil distributions suggests that largely dynamic and ferruginous, perhaps euxinic, conditions contributed to biotic crisis and recovery. A strong coupling of TOC and redox proxies suggests that protracted anoxia or euxinia is critical to the accumulation and preservation of organic matter. Our study demonstrates that redox evaluations that rely upon a single geochemical proxy or elemental ratio are likely to be uncertain. Rather, multiple geochemical proxies are required to explore relationships among redox states, animal evolution, and deposition and preservation of organic-rich shale.

在奥陶纪-西陆纪过渡期，大规模灭绝和广泛的黑页岩沉积与广泛的海洋缺氧有关，但是痕量金属代理之间的不确定性使人们对地球历史时期的氧化还原动力学及其与动物进化和积累的关系的认识有所改善。有机丰富的页岩。在此，我们描述了华南前钱1号段的地球化学调查结果，该结果保留了上扬子平台内陆架的地层记录。具体而言，将根据研究部分的现有数据考虑新获得的总有机碳（TOC），总硫（TS），铁（Fe）形态以及主要元素和痕量金属的丰度。_org / P比值和氧化还原敏感微量元素（RSTE）富集。但是，基于铁的形态，C _org / P比和RSTE富集的氧化还原历史之间的已记录差异可能反映了高频氧化还原波动的影响。双金属比（U / Th，V / Cr，Ni / Co和V /（V + Ni））与铁形态的比较，C _org/ P比和RSTE富集表明，尽管U / Th，V / Cr和Ni / Co的变化可能提供相对可靠的相对氧化还原变化的更可靠指示，但各种氧化还原状态的双金属比的常用阈值并不可靠。氧化还原条件和化石分布的变化之间有很强的相关性，这表明在很大程度上动态和铁质的，可能是富营养的条件导致了生物危机和恢复。TOC和氧化还原代理之间的强耦合表明，长期的缺氧或游氧不足对有机物的积累和保存至关重要。我们的研究表明，依赖于单一地球化学特征或元素比的氧化还原评估可能不确定。而是需要多个地球化学代理来探索氧化还原状态，动物进化，