Abstract The end-Permian mass extinction (EPME; ca. 251.94 Ma) is the most severe mass extinction in the geological record. Detailed paleobiological investigations show a very rapid EPME event, and recently published δ238U data show a large negative excursion and thus a massive shift to globally expanded anoxia at the main extinction phase in the latest Permian. The negative shift in δ238U is in correlation with a globally characterized negative δ13C excursion near the Permian-Triassic boundary (PTB). In some highly expanded PTB carbonate sections, however, there are two distinct negative δ13C excursions whereas uranium isotopes (δ238U) from such sections have not yet been examined, leaving a gap in the understanding of the global perturbations of marine redox conditions immediately following the EPME. Here, we present a new δ238U study of syn-depositional dolostones from a well-characterized and highly expanded drill core, which recorded two pronounced negative δ13C excursions across the PTB, from the Carnic Alps, Austria. This drill core extends 331-meters across the PTB and provides a unique opportunity to explore the detailed timing, duration, and extent of marine redox chemistry changes before, during, and immediately after the EPME. Our new δ238U record shows two negative shifts, which are correlated with the two negative δ13C excursions. The first negative δ238U excursion preceding the EPME confirms the recently published δ238U records from across the EPME and support that syndepositional marine dolostones can record δ238U trends of seawater similar to that of limestones. Modeling of uranium isotope cycling in the latest Permian and earliest Triassic oceans suggests two distinct stages of expanded marine anoxia separated by a brief interval (∼100 kyr) of reoxygenation across the PTB. The first anoxic episode lasted for ∼ 60 kyr while anoxic seafloor area expanded to cover >18% of the entire seafloor, coeval with the main EPME horizon, agreeing with marine anoxia as a proximate kill mechanism for the EPME. The second anoxic event was less intense compared to the first anoxic pulse but sustained for a longer duration. A global modeling of coupled C, P, and U cycles show that two pulses of volcanic carbon injection that drives global warming and increased phosphorus weathering rate can reasonably reproduce our data to match two phases of anoxia. The model also demonstrates that the loss of terrestrial vegetation in the EPME is crucial to generating an intervening interval of oxygenated ocean. Our new study adds to a growing body of evidence that the global marine redox conditions underwent rapid oscillations during the EPME event and continued afterward, which may have played a central role in delaying the marine ecosystem recovery in the Early Triassic.

中文翻译：

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海洋白云岩中的铀同位素证明了二叠纪-三叠纪危机期间两次不同的海洋缺氧事件

摘要 二叠纪末大灭绝（EPME；ca. 251.94 Ma）是地质记录中最严重的大灭绝。详细的古生物学调查显示了一个非常快速的 EPME 事件，最近公布的 δ238U 数据显示了一个大的负偏移，因此在最近二叠纪的主要灭绝阶段向全球扩大的缺氧大规模转变。δ238U 的负移与二叠纪-三叠纪边界 (PTB) 附近的全球特征性负 δ13C 偏移有关。然而，在一些高度膨胀的 PTB 碳酸盐部分，有两个明显的负 δ13C 偏移，而来自这些部分的铀同位素 (δ238U) 尚未被检查，这在 EPME 之后立即对海洋氧化还原条件的全球扰动的理解方面留下了空白. 这里，我们提出了一项新的 δ238U 研究，对来自奥地利卡尼克阿尔卑斯山的一个特征良好且高度扩展的钻芯的同沉积白云岩进行了研究，该岩芯记录了两次明显的 δ13C 负偏移穿过 PTB。该钻芯在 PTB 上延伸 331 米，提供了一个独特的机会来探索 EPME 之前、期间和之后海洋氧化还原化学变化的详细时间、持续时间和程度。我们新的 δ238U 记录显示两个负移，这与两次负 δ13C 偏移相关。EPME 之前的第一次负 δ238U 偏移证实了最近发布的来自整个 EPME 的 δ238U 记录，并支持同沉积海相白云岩可以记录类似于石灰岩的海水 δ238U 趋势。在最近的二叠纪和最早的三叠纪海洋中对铀同位素循环进行建模表明，扩展的海洋缺氧的两个不同阶段被跨 PTB 的短暂再充氧间隔 (~100 kyr) 隔开。第一次缺氧事件持续了约 60 kyr，而缺氧海底区域扩大到覆盖整个海底的 18% 以上，与主要 EPME 层位同时期，这与海洋缺氧作为 EPME 的近似杀死机制一致。与第一次缺氧脉冲相比，第二次缺氧事件强度较低，但持续时间更长。耦合 C、P 和 U 循环的全球模型表明，推动全球变暖和磷风化率增加的两次火山碳注入脉冲可以合理地再现我们的数据以匹配缺氧的两个阶段。该模型还表明，EPME 中陆地植被的丧失对于产生含氧海洋的干预间隔至关重要。我们的新研究增加了越来越多的证据，表明全球海洋氧化还原条件在 EPME 事件期间经历了快速振荡并在此后持续，这可能在延迟早三叠世海洋生态系统恢复方面发挥了核心作用。