The development of large paleobiological databases has provided an opportunity to reassess the pattern and timing of marine biodiversity changes during the Late Ordovician, which has newly revealed a major decline in biodiversity during the middle to late Katian Stage (448.7–446.7 Ma) and a rapid faunal recovery during the latest Hirnantian to early Telychian stages (444.7437.1 Ma), herein termed the “Katian Extinction” (KE) and the “Early Silurian Recovery” (ESR), respectively. Being only recently recognized, the kill mechanism of the KE and the environmental conditions associated with the ESR have received little attention to date. Here, we report whole-rock iron isotopic compositions (δFe) for the YD-1 drillcore in South China and, combined with other geochemical proxies, use them to investigate environmental influences on the KE and ESR. Iron isotopes are more sensitive to fluctuations in the oxic-to-suboxic part of the redox spectrum than commonly used proxies (e.g., Fe-speciation and trace-metal data) because sediment δFe increases in the oxic zone as a result of Fe uptake by Fe(III), whereas it decreases in the suboxic zone due to fractionation in favor of Fe during dissimilatory iron reduction. The Katian Extinction coincided with decreasing δFe (from +0.35‰ to 0.00‰) as well as increasing C/P and Mo, supporting an anoxia-driven biocrisis. Enhanced rates of organic carbon accumulation (OCAR) and biogenic silica accumulation (SiAR) from the Rhuddanian to mid-Aeronian were potentially induced by widespread upwelling in the Yangtze Sea linked to the post-Hirnantian eustatic transgression. Our study provides insight into the causes of the Katian Extinction, which was an integral part of the multi-phased Late Ordovician Mass Extinction, and documents the environmental conditions in the Yangtze Sea in which the Early Silurian Recovery occurred.

中文翻译：

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生产力和氧化还原对奥陶纪晚期“卡蒂安灭绝”和“志留纪早期恢复”的影响

大型古生物学数据库的发展为重新评估晚奥陶世海洋生物多样性变化的模式和时间提供了机会，新揭示了卡蒂阶中晚期（448.7~446.7 Ma）生物多样性的大幅下降和生物多样性的快速下降。赫南特纪晚期到特利奇纪早期（444.7437.1 Ma）期间动物群的恢复，本文分别称为“卡蒂安灭绝”（KE）和“志留世早期恢复”（ESR）。 KE 的杀伤机制以及与 ESR 相关的环境条件直到最近才被认识到，迄今为止还很少受到关注。在此，我们报告了华南 YD-1 钻芯的全岩铁同位素组成 (δFe)，并结合其他地球化学指标，利用它们来研究环境对 KE 和 ESR 的影响。铁同位素对氧化还原光谱的含氧到含氧部分的波动比常用的代理（例如铁形态和痕量金属数据）更敏感，因为沉积物 δFe 在含氧区中增加，这是由于铁吸收的结果。 Fe(III)，而在低氧区则由于异化铁还原过程中 Fe 的分馏而减少。卡蒂安灭绝与δFe的减少（从+0.35‰到0.00‰）以及C/P和Mo的增加同时发生，支持了缺氧驱动的生物危机。从鲁丹纪到中期埃隆纪有机碳积累（OCAR）和生物硅积累（SiAR）速率的增加可能是由与后赫南特海平面海侵有关的长江海广泛上升流引起的。我们的研究深入了解了卡蒂安灭绝的原因，卡蒂安灭绝是多阶段晚奥陶世大规模灭绝的一个组成部分，并记录了发生早志留世恢复的长江海的环境条件。