Tracking the redox history and nitrogen cycle in the pelagic Panthalassic deep ocean in the Middle Triassic to Early Jurassic: Insights from redox-sensitive elements and nitrogen isotopes
Tracking the redox history and nitrogen cycle in the pelagic Panthalassic deep ocean in the Middle Triassic to Early Jurassic: Insights from redox-sensitive elements and nitrogen isotopes
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DOI：
10.1016/j.palaeo.2016.01.039
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发表时间：
2016-05-01
影响因子：
3
通讯作者：
Maruyama, Shigenori
中科院分区：
文献类型：
--
作者：
Fujisaki, Wataru;Sawaki, Yusuke;Maruyama, Shigenori
为了阐明中三叠世（安尼纪）至早侏罗世（托阿尔纪）泛海洋中部的氧化还原历史，我们测定了日本西南部犬山深海燧石互层暴露良好的页岩中的常量、微量和稀土元素以及有机碳和总氮同位素的丰度。在跨越 Tr-J 边界的过渡层序中检测到了明显的正 Ce 异常，伴随着高 Mn 和弱 Mo 富集，这表明沉积物处于比研究剖面中任何其他时期都更富氧的条件下。好氧期持续130-170 kyr，并且与三叠纪末期的动物更替同时发生。另一方面，安尼阶和托阿尔阶黑色页岩中 U、V、Mo、TOC 和 TN 的强烈富集表明这两个层段都存在深海缺氧。一些黑色页岩中高浓度的钼含量表明远洋泛海深海中存在真核。与其他页岩相比，富含氧化还原敏感元素的黑色页岩的 delta N-15(TN) 值较低，低至 -2.0 ppm。在安尼西亚期经常发生的海洋缺氧事件中，这种低 Delta N-15(TN) 值可能表明铵的强烈同化，但不能排除固氮增强的可能性，特别是对于托阿尔期缺氧事件。这项工作基于页岩中的氧化还原敏感元素，首次记录了从中三叠世到早侏罗世的远洋泛海深海的长期氧化还原历史，并揭示了海洋氧化还原变化与生物活动之间可能的联系。 (C) 2016 Elsevier B.V. 保留所有权利。
In order to clarify the redox history of the central Panthalassic Ocean in the Middle Triassic (Anisian) to Early Jurassic (Toarcian), we determined the abundances of major, trace and rare earth elements, and organic carbon and total nitrogen isotopes from well-exposed shales interbedded with deep-sea cherts from Inuyama, southwest Japan. A distinct positive Ce anomaly accompanying high Mn and weak Mo enrichments was detected in the transitional sequence across the Tr-J boundary, which indicates deposition under a more oxic condition than at any other period in the study section. The oxic period lasted for 130-170 kyr, and coincided with a faunal turnover at the end of the Triassic. On the other hand, strong enrichments of U, V, Mo, TOC and TN in Anisian and Toarcian black shales suggest deep ocean anoxia in both intervals. Highly concentrated Mo contents in some black shales indicate euxinia in the pelagic Panthalassic deep ocean. delta N-15(TN) values are low, down to -2.0 parts per thousand, in such black shales enriched in redox-sensitive elements, compared with other shales. This low delta N-15(TN) values during recurrent oceanic euxinic events in the Anisian may indicate strong assimilation of ammonium, but the possibility of enhanced nitrogen fixation cannot be ruled out especially for the Toarcian anoxic event. This work provides the first documentation of the long-term redox history in the pelagic Panthalassic deep ocean, from the Middle Triassic to the Early Jurassic, based on redox-sensitive elements in shales, and it reveals probable links between oceanic redox changes and biological activity. (C) 2016 Elsevier B.V. All rights reserved.