Marine osmium isotope record during the Carnian “pluvial episode” (Late Triassic) in the pelagic Panthalassa Ocean
Marine osmium isotope record during the Carnian “pluvial episode” (Late Triassic) in the pelagic Panthalassa Ocean
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DOI：
10.1016/j.gloplacha.2020.103387
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发表时间：
2021-02
影响因子：
3.9
通讯作者：
Y. Tomimatsu;T. Nozaki;Honami Sato;Y. Takaya;J. Kimura;Q. Chang;H. Naraoka;M. Rigo;T. Onoue
中科院分区：
文献类型：
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作者：
Y. Tomimatsu;T. Nozaki;Honami Sato;Y. Takaya;J. Kimura;Q. Chang;H. Naraoka;M. Rigo;T. Onoue
卡尼期雨期（CPE）是发生在卡尼期（晚三叠世）的一次全球性环境变化和生物危机。CPE期间的气候特征是短暂的极端降雨，海洋生物群的灭绝发生在最后的朱利安（即卡尼早期）。虽然这些事件被认为是由弗兰格利亚洪水玄武岩（FB）火山作用引起的，但现有的研究几乎没有发现直接证据支持这一点。我们研究了爆发的Wrangellia FB和CPE之间的时间关系，使用高分辨率的微体化石生物地层学和古海水Os同位素数据的上三叠统层状硅质岩继承在日本的增生复杂，积累在大洋深海环境中的泛地中海的赤道地区。根据牙形石、放射虫和锇同位素资料，我们的生物地层学分析表明：（i）早儒略历时期的初始Os同位素比值（187 Os/188 Osi）持续下降;（ii）晚儒略历时期的187 Os/188 Osi比值较低;（iii）早儒略历末期的187 Os/188 Osi比值突然上升。整个朱利安的187 Os/188 Os比值的下降表明，从弗兰格利亚FB的爆发到海洋的非放射成因的Os输入增加。此外，氧化还原敏感的元素，如V和U，突然增加的朱利安，这是第一个证据的减少条件期间的CPE在深海泛萨大洋的结束。从中浅水特提斯剖面广泛沉积的黑色页岩和富含有机质的泥灰岩中，可以认识到朱利安晚期的海洋缺氧事件。因此，在Wrangellia FB火山作用结束时，特提斯浅海大陆边缘以及深海泛萨拉萨洋都出现了贫氧状态。
The Carnian Pluvial Episode (CPE) was a global environmental change and biotic crisis that occurred during the Carnian (Late Triassic). The climate during the CPE was characterized by a short-lived period of extreme rainfall, and an extinction of marine taxa is known to have occurred during the latest Julian (i.e. early Carnian). Although these events are considered to have been caused by the Wrangellia Flood Basalt (FB) volcanism, existing studies have found little direct evidence to support this. We investigated the temporal relationship between the eruption of Wrangellia FB and CPE using high-resolution microfossil biostratigraphy and paleo-seawater Os isotope data of an Upper Triassic bedded chert succession from an accretionary complex in Japan, which accumulated in a pelagic deep-sea environment in an equatorial region of the Panthalassa Ocean. Our biostratigraphic analysis, based on conodonts and radiolarians, and osmium isotope data show: (i) a continuous decline of initial Os isotope ratios (187Os/188Osi) in the early Julian; (ii) low187Os/188Osiratios during the late Julian; and (iii) an abrupt increase in187Os/188Osiratios at the end of the Julian. The decrease in187Os/188Osiratios throughout the Julian suggests an increased input of unradiogenic Os from the eruption of the Wrangellia FB into the ocean. Moreover, redox-sensitive elements, such as V and U, increased abruptly at the end of the Julian, which is the first evidence of reducing conditions during the CPE within the pelagic deep-sea Panthalassa Ocean. Marine anoxic event in the late Julian has been recognized from widespread deposition of black shales and organic-rich marls in intermediate to shallow water Tethyan sections. Thus, oxygen-depleted conditions occurred at the Tethyan shallow continental margin, as well as in the pelagic deep-sea Panthalassa Ocean, at the end of Wrangellia FB volcanism.