Intensive Ocean anoxia and large δ13Ccarb perturbations during the Carnian Humid Episode (Late Triassic) in Southwest China
Intensive Ocean anoxia and large δ13Ccarb perturbations during the Carnian Humid Episode (Late Triassic) in Southwest China
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DOI：
10.1016/j.gloplacha.2022.103942
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发表时间：
2022-09
影响因子：
3.9
通讯作者：
Z. Zhang;M. Joachimski;S. Grasby;Y.D. Sun
中科院分区：
文献类型：
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作者：
Z. Zhang;M. Joachimski;S. Grasby;Y.D. Sun
卡尼期湿润事件(CHE)代表了晚三叠世气候由干向湿的戏剧性转变。这种气候变化的表现及其相关的生物和环境反应尚不完全清楚。在此，我们在中国西南卧龙岗进行了碳酸盐碳同位素、痕量金属和黄铁矿框体分析，以追踪这一关键时期的古环境变化。卧龙岗CHE的特征是在朱连一世末期强烈生物扰动的朱干坡灰岩之上发育了细小的层状碳质粉砂岩和黑色页岩。这种岩性变化伴随着两次负的δ~(13)C碳漂移，氧化还原敏感的痕量金属U和Mo的强烈富集，以及丰富的平均直径为1~5μm的小黄铁矿框体的发育。沉积和地球化学证据共同表明，碳酸盐产量急剧下降和主要的碳循环扰动，与强烈的海洋缺氧和洞穴动物群的大量死亡相吻合。与西特提斯的其他地区不同，卧龙港的车的余波以长期的海洋缺氧为特征，碳酸盐生产疲软至少持续到图瓦卢晚期。瓦窑组沉积了细碎片状粉质碳酸盐、泥灰岩和碳质粉砂岩以及稀有的底栖生物化石，证明了这一点。我们的研究表明，在扬子地台西南边缘和南盘江盆地广泛发育的缺氧-正己烷环境可能是造成CHE期间海相动物群丧失的原因之一。
The Carnian Humid Episode (CHE) represents a dramatic dry to wet climate transition in the Late Triassic. Manifestations of this climate shift and its associated biological and environmental responses are not fully understood. Here, we carried out carbonate carbon isotope, trace metal, and pyrite framboid analyses at Wolonggang in southwest China to trace palaeoenvironmental changes during this critical interval. The CHE at Wolonggang is marked by the development of fine laminated carbonaceous siltstones and black shales overlying the intensely bioturbated Zhuganpo limestone deposited in the latest Julian 1. This lithological change is accompanied by two negative δ13Ccarbexcursions, a strong enrichment of redox-sensitive trace metals U and Mo, and the development of abundant small pyrite framboids with an average diameter < 5 μm. The sedimentary and geochemical evidence collectively suggest a sharp decrease in carbonate production and a major carbon cycle disturbance, coinciding with the onset of intense ocean anoxia and the mass mortality of burrowing faunas. Unlike other areas in the western Tethys, the aftermath of the CHE at Wolonggang is characterized by long-lasting ocean anoxia, with weak carbonate production persisting at least to the late Tuvalian. This is evidenced by the deposition of finely laminated silty carbonates, marls, and carbonaceous siltstones with rare benthic fossils in the Wayao Formation. Our study suggests that anoxic-euxinic environments widely developed along the southwest margins of the Yangtze Platform and in the Nanpanjiang Basin, probably contributing to the loss of marine faunas during the CHE.