Abstract 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) low 187Os/188Osi ratios during the late Julian; and (iii) an abrupt increase in 187Os/188Osi ratios at the end of the Julian. The decrease in 187Os/188Osi ratios 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.

中文翻译：

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远洋泛塔拉萨海洋卡尼阶“雨季”（晚三叠世）期间的海洋锇同位素记录

摘要 卡尼期雨季事件（CPE）是发生在卡尼期（晚三叠世）的全球环境变化和生物危机。CPE 期间的气候以短暂的极端降雨为特征，已知在最近的儒略纪（即卡尼纪早期）发生了海洋分类群的灭绝。尽管这些事件被认为是由兰格利亚洪水玄武岩 (FB) 火山作用引起的，但现有研究几乎没有发现直接证据来支持这一点。我们使用高分辨率微化石生物地层学和来自日本增生复合体的上三叠统层状燧石序列的古海水 Os 同位素数据研究了兰格利亚 FB 喷发与 CPE 之间的时间关系，积累在泛海区赤道地区的远洋深海环境中。我们基于牙形石和放射虫以及锇同位素数据的生物地层分析显示：(i) 在朱利安早期，初始 Os 同位素比 (187Os/188Osi) 持续下降；(ii) 朱利安晚期的低 187Os/188Osi 比率；(iii) 在 Julian 结束时 187Os/188Osi 比率突然增加。整个 Julian 中 187Os/188Osi 比率的下降表明，Wrangellia FB 喷发导致非放射性 Os 输入海洋的输入增加。此外，V 和 U 等氧化还原敏感元素在朱利安末期突然增加，这是在远洋深海泛塔拉萨洋中 CPE 期间条件减少的第一个证据。朱利安晚期的海洋缺氧事件已被确认为黑色页岩和富含有机质的泥灰岩在中浅水特提斯剖面的广泛沉积。因此，在 Wrangellia FB 火山活动结束时，特提斯浅大陆边缘以及远洋深海 Panthalassa 洋发生了缺氧条件。