Does large igneous province volcanism always perturb the mercury cycle? Comparing the records of Oceanic Anoxic Event 2 and the end-Cretaceous to other Mesozoic events
Does large igneous province volcanism always perturb the mercury cycle? Comparing the records of Oceanic Anoxic Event 2 and the end-Cretaceous to other Mesozoic events
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DOI：
10.2475/08.2018.01
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发表时间：
2018-10
影响因子：
2.9
通讯作者：
L. Percival;H. Jenkyns;T. Mather;A. Dickson;S. Batenburg;M. Ruhl;S. Hesselbo;R. Barclay;I. Jarvi
中科院分区：
文献类型：
--
作者：
L. Percival;H. Jenkyns;T. Mather;A. Dickson;S. Batenburg;M. Ruhl;S. Hesselbo;R. Barclay;I. Jarvi
汞（Hg）越来越多地被用作大火成岩省（LIP）火山活动的沉积示踪剂，并支持几个LIP的形成与大规模灭绝和重大环境扰动事件之间的巧合的假设。然而，许多重要的问题仍然需要回答之前，汞可以声称为一个明确的指纹LIP火山活动，以及理解为什么一些沉积记录文件明确的汞富集信号，而其他人没有。特别重要的是评估不同火山类型对全球汞循环的影响，以及沉积过程在记录全球汞循环扰动方面所发挥的作用。本文给出了白垩纪第二次海洋缺氧事件（OAE 2：194 Ma）和白垩纪晚期（167 ~ 66.0Ma）的汞记录。OAE 2与多个主要是海底LIP的侵位有关;最晚的白垩纪与德干圈闭的陆上火山活动有关。这两种联系都得到了先前发表的全球分布的沉积记录中非放射性锇（Os）同位素值趋势的有力支持。这两个事件的汞数据显示，不同地点之间存在相当大的差异，这归因于不同沉积物类型在记录汞信号方面的有效性，与石灰岩到粘土岩或富含有机物的页岩等岩性发生重大变化的部分相比，岩性均质的记录记录更清楚地记录了汞的富集。至关重要的是，有没有地理上一致的信号沉积汞富集的地层记录OAE 2或最新的白垩纪相匹配的Os同位素证据LIP侵位，表明火山活动并没有造成全球汞扰动整个喷发历史的LIP在这些时候形成的。据建议，OAE 2的记录中的锇同位素和汞的趋势之间的差异是由有限的分散范围的汞从海底火山相比，全球范围内的分布Os。类似的缺乏这两个代理之间的相关性在最上层的白垩纪地层表明，虽然陆上火山活动可以扰乱全球汞循环，并不是所有的陆上喷发会这样做。这些结果突出了不同的火山过程对汞在地球仪上扩散效率的不同影响。可能影响LIP喷发对全球汞循环的影响的因素包括海底与陆上火山活动、火山强度或爆炸性，以及上升岩浆与周围富含有机物的沉积物之间反应产生的生热汞的潜在贡献。
Mercury (Hg) is increasingly being used as a sedimentary tracer of Large Igneous Province (LIP) volcanism, and supports hypotheses of a coincidence between the formation of several LIPs and episodes of mass extinction and major environmental perturbation. However, numerous important questions remain to be answered before Hg can be claimed as an unequivocal fingerprint of LIP volcanism, as well as an understanding of why some sedimentary records document clear Hg enrichment signals whilst others do not. Of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle, as well as the role played by depositional processes in recording global Hg-cycle perturbations. Here, new mercury records of Cretaceous Oceanic Anoxic Event 2 (OAE 2: ∼94 Ma) and the latest Cretaceous (∼67–66.0 Ma) are presented. OAE 2 is associated with the emplacement of multiple, predominantly submarine, LIPs; the latest Cretaceous with subaerial volcanism of the Deccan Traps. Both of these connections are strongly supported by previously published trends towards unradiogenic osmium- (Os) isotope values in globally distributed sedimentary records. Hg data from both events show considerable variation between different locations, attributed to the effectiveness of different sediment types in registering the Hg signal, with lithologically homogeneous records documenting more clear Hg enrichments than sections with major changes in lithology such as limestones to claystones or organic-rich shales. Crucially, there is no geographically consistent signal of sedimentary Hg enrichment in stratigraphic records of either OAE 2 or the latest Cretaceous that matches Os-isotope evidence for LIP emplacement, indicating that volcanism did not cause a global Hg perturbation throughout the entire eruptive history of the LIPs formed at those times. It is suggested that the discrepancy between Os-isotope and Hg trends in records of OAE 2 is caused by the limited dispersal range of Hg emitted from submarine volcanoes compared to the global-scale distribution of Os. A similar lack of correlation between these two proxies in uppermost Cretaceous strata indicates that, although subaerial volcanism can perturb the global Hg cycle, not all subaerial eruptions will do so. These results highlight the variable impact of different volcanogenic processes on the efficiency of Hg dispersal across the globe. Factors that could influence the impact of LIP eruptions on the global mercury cycle include submarine versus subaerial volcanism, volcanic intensity or explosivity, and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic-rich sediments.