Elevated sedimentation of clastic matter in pelagic Panthalassa during the early Olenekian
Elevated sedimentation of clastic matter in pelagic Panthalassa during the early Olenekian
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DOI：
10.1111/iar.12485
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发表时间：
2023-01
期刊：
影响因子：
1.5
通讯作者：
Shun Muto;S. Takahashi;S. Yamakita
中科院分区：
文献类型：
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作者：
Shun Muto;S. Takahashi;S. Yamakita
二叠纪末期的大灭绝被认为极大地改变了生物地球化学循环。早三叠世泛大洋（深海燧石缺失带）低纬度远洋深海沉积层序中燧石缺失且黏土岩占主导，一直被认为记录了放射虫的灭绝以及由此导致的生物源二氧化硅产量的下降。然而，近期研究表明，深海燧石缺失带的上部沉积速率高于层状燧石，这意味着是碎屑输入增加，而非生物源二氧化硅输入减少，导致了这种异常的岩性。在本研究中，我们聚焦于赤森 - 2剖面，该剖面保存了一个罕见的沉积层序，涵盖了深海燧石缺失带黏土岩下部的大部分。我们获取了牙形刺化石，这使得该剖面能够与中国南方有众多定年凝灰岩的剖面进行对比。通过将凝灰岩的年代投射到我们所测的剖面，我们表明深海燧石缺失带下部的沉积速率也高于层状燧石。因此，深海燧石缺失带的大部分是在碎屑输入增加的情况下形成的，这可能记录了陆地景观的扰动，可能是干旱化和/或干旱地区季节性增强，导致了输送到远洋的沙尘通量增加。另一方面，深海燧石缺失带记录了大灭绝事件对放射虫的持续影响这一观点无法解释深海燧石缺失带的高沉积速率。考虑到早三叠世海洋中生物源二氧化硅的埋藏效率，以及黏土沉积增加对放射虫保存的影响，之前受青睐的这一场景需要重新考虑。
The end‐Permian mass extinction is thought to have greatly altered biogeochemical cycles. The absence of chert and dominance of claystone in low‐latitude pelagic deep‐sea sedimentary sequences of Early Triassic Panthalassa (the deep‐sea chert gap) has been believed to record radiolarian die‐off and consequent decline in biogenic silica production. However, recent studies showed that the upper portion of the deep‐sea chert gap has sedimentation rates higher than bedded chert, meaning that increased clastic inputs, rather than decreased biogenic silica inputs, resulted in the anomalous lithology. In this study, we focus on the Akkamori‐2 section, which preserves a rare sedimentary sequence spanning a large part of the lower portion of the claystone of the deep‐sea chert gap. We obtained conodont fossils that allow correlation with sections in South China that have numerous dated tuffs. By projecting the dates of the tuffs to our measured sections, we show that sedimentation rates of the lower portion of the deep‐sea chert gap is also higher than bedded chert. Hence, most of the deep‐sea chert gap was formed under increased clastic inputs, which likely records disturbance in the terrestrial landscape, probably aridification and/or increased seasonality in arid areas, that lead to elevated dust flux to the pelagic ocean. On the other hand, the idea that the deep‐sea chert gap records lingering effects of the mass extinction event on radiolarians cannot explain the high sedimentation rates of the deep‐sea chert gap. This previously favored scenario needs to be reconsidered, taking into account the burial efficiency of biogenic silica in the Early Triassic ocean, and also effects of increased clay deposition on preservation of radiolarians.