Geochemical Records Reveal Protracted and Differential Marine Redox Change Associated With Late Ordovician Climate and Mass Extinctions
Geochemical Records Reveal Protracted and Differential Marine Redox Change Associated With Late Ordovician Climate and Mass Extinctions
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DOI：
10.1029/2021av000563
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发表时间：
2022-02-01
期刊：
影响因子：
8.4
通讯作者：
Young, Seth A.
中科院分区：
文献类型：
--
作者：
Kozik, Nevin P.;Gill, Benjamin C.;Young, Seth A.
奥陶纪（Hirnantian; 445 Ma）经历了地球历史上第二次最严重的物种大灭绝，与冈瓦南冰期和海洋缺氧的地球化学证据增加相吻合。目前尚不清楚是冷却、扩大的缺氧，还是两者共同导致了晚奥陶纪大灭绝（LOME）。本文利用三个全球分布的碳酸盐序列的碘和硫同位素地球化学数据来约束局部和全球海洋氧化还原条件的变化。碘记录表明，局部缺氧条件可能普遍存在于浅层碳酸盐架子上，而硫同位素表明全球缺氧（缺氧和硫化物）条件减少。晚卡田硫酸盐-硫同位素数据显示，在海平面上升期间开始并持续到希尔南田冰期高峰的一个大的负偏移。地球化学盒模拟表明，黄铁矿埋藏的减少和风化作用的增加共同驱动了观测到的负偏移，表明晚奥陶世期间全球海底含氧量减少了3%。硫数据集提供了进一步的证据，表明在这一趋势之后，含氧量增加，这与随后在希尔南天晚期冰川消退期间海平面上升的上升相吻合。大陆架缺氧的持续与全球缺氧减弱和增强的背景有关，这与两个LOME脉冲有关。这些结果对整个晚奥陶世的局部和全球海洋氧化还原条件提出了重要的限制，并表明非硫化物大陆架缺氧-以及冰川上升海平面和气候变冷-是恶化海洋动物条件的重要环境压力因素，导致了地球历史上第二大物种大灭绝，也是唯一一个在冰窖气候下的例子。
The Ordovician (Hirnantian; 445 Ma) hosts the second most severe mass extinction in Earth history, coinciding with Gondwanan glaciation and increased geochemical evidence for marine anoxia. It remains unclear whether cooling, expanded oxygen deficiency, or a combination drove the Late Ordovician Mass Extinction (LOME). Here, we present combined iodine and sulfur isotope geochemical data from three globally distributed carbonate successions to constrain changes in local and global marine redox conditions. Iodine records suggest locally anoxic conditions were potentially pervasive on shallow carbonate shelves, while sulfur isotopes suggest a reduction in global euxinic (anoxic and sulfidic) conditions. Late Katian sulfate-sulfur isotope data show a large negative excursion that initiated during elevated sea level and continued through peak Hirnantian glaciation. Geochemical box modeling suggests a combination of decreasing pyrite burial and increasing weathering are required to drive the observed negative excursion suggesting a similar to 3% decrease of global seafloor euxinia during the Late Ordovician. The sulfur datasets provide further evidence that this trend was followed by increases in euxinia which coincided with eustatic sea-level rise during subsequent deglaciation in the late Hirnantian. A persistence of shelf anoxia against a backdrop of waning then waxing global euxinia was linked to the two LOME pulses. These results place important constraints on local and global marine redox conditions throughout the Late Ordovician and suggest that non-sulfidic shelfal anoxia-along with glacioeustatic sea level and climatic cooling-were important environmental stressors that worsened conditions for marine fauna, resulting in the second-largest mass extinction in Earth history and the only example during an icehouse climate.