Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. We report high-resolution U-isotope (δ²³⁸U) data from carbonates of the uppermost Permian to lowermost Middle Triassic Zal section (Iran) to characterize the timing and global extent of ocean redox variation during the Early Triassic. Our δ²³⁸U record reveals multiple negative shifts during the Early Triassic. Isotope mass-balance modeling suggests that the global area of anoxic seafloor expanded substantially in the Early Triassic, peaking during the latest Permian to mid-Griesbachian, the late Griesbachian to mid-Dienerian, the Smithian-Spathian transition, and the Early/Middle Triassic transition. Comparisons of the U-, C-, and Sr-isotope records with a modeled seawater PO₄^3- concentration curve for the Early Triassic suggest that elevated marine productivity and enhanced oceanic stratification were likely the immediate causes of expanded oceanic anoxia. The patterns of redox variation documented by the U-isotope record show a good first-order correspondence to peaks in ammonoid extinctions during the Early Triassic. Our results indicate that multiple oscillations in oceanic anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction.

中文翻译：

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在最近的二叠纪大灭绝之后，海洋广泛缺氧的多次发作与全球变暖和大陆风化有关。

解释最新的二叠纪大灭绝之后的海洋生物恢复延误了500万年，这是现生代最大的生物危机，这对地质和生物科学都是一个根本性的挑战。海洋氧化还原扰动可能在这种延迟的恢复中发挥了关键作用。然而，对早期三叠纪海洋缺氧细节（例如时间，持续时间和程度）的定量限制缺乏，使海洋状况与延迟的生物恢复之间的联系变得模棱两可。我们报告了从最上层的二叠纪碳酸盐岩到最下层的三叠纪Zal剖面（伊朗）的碳酸盐的高分辨率U同位素（^δ238 U）数据，以表征三叠纪早期海洋氧化还原变化的时间和全球范围。我们的^δ238U记录揭示了三叠纪早期的多个负向变化。同位素质量平衡模型表明，缺氧海底的全球面积在三叠纪早期就大为扩展，在最新的二叠纪至格里斯巴赫中期，晚期的格里斯巴赫纪至二叠纪中期，史密斯一斯一世至过渡期以及早三叠世/中三叠纪达到峰值。过渡。U，C和Sr同位素记录与模拟海水PO ₄ ^3-的比较三叠纪早期的浓度曲线表明，海洋生产力的提高和海洋分层的增强可能是扩大海洋缺氧的直接原因。U同位素记录所记录的氧化还原变化模式显示出与三叠纪早期氨化灭绝峰的良好一阶对应关系。我们的结果表明，在最近的二叠纪大灭绝之后，海洋缺氧的多次振荡调节了海洋生态系统的恢复。