The Late Ordovician and Early Silurian periods experienced glaciation and mass extinctions. However, debates exist regarding the factors that initiated the glaciation and the subsequent delay in biotic recovery. To uncover the relationships between paleoclimate, marine redox states, and biotic recovery in the Early Silurian, temporal variations in Zinc (Zn) isotopic compositions along with other multi-geochemical proxies were analyzed for a carbonate-dominated section in South China. A stratigraphic δZn trend was found in studied section, indicating a widespread disturbance to the marine Zn cycle. A significant negative shift in δZn by up to ∼0.7 ‰ was observed immediately following the Hirnantian Glaciation and HICE, which can be attributed to a combination of reduced burial efficiency of organic carbon, fast weathering of large igneous provinces and increased riverine Zn input. This was followed by a ∼ 0.4 ‰ rise in δZn values, alongside a sharp decrease in δC values, indicating an increase in sulfide precipitation (e.g., ZnS, FeS) due to expansions of euxinia. Subsequently, a notable rise in δZn values by up to ∼1.1 ‰ is interpreted as an increase in organic carbon burial, given the concurrent variation of δZn and δC during this period. The findings suggest that the increase in organic carbon burial, a reduction in reverse weathering, or a combination of them contributed to the glaciation in Silurian. Furthermore, the weathering-induced high primary productivity led to anoxic water conditions in the latest Hirnantian and Rhuddanian. This prolonged marine anoxia in seawater thus caused the deposition of organic-rich sediments and hindered biotic recovery in the Rhuddanian.

中文翻译：

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早志留世大陆风化和有机碳埋藏增强的锌同位素证据


奥陶纪晚期和志留纪早期经历了冰川作用和大规模灭绝。然而，关于引发冰川作用和随后生物恢复延迟的因素存在争议。为了揭示早志留世古气候、海洋氧化还原状态和生物恢复之间的关系，对华南碳酸盐岩为主的地区锌（Zn）同位素组成以及其他多种地球化学指标的时间变化进行了分析。在研究剖面中发现了地层 δZn 趋势，表明海洋锌循环受到广泛干扰。在赫南蒂安冰川作用和 HICE 之后，立即观察到 δZn 显着负移高达 ∼0.7 ‰，这可归因于有机碳埋藏效率降低、大型火成岩省的快速风化和河流锌输入增加的综合作用。随后，δZn 值上升约 0.4 ‰，同时 δ13C 值急剧下降，表明由于 euxinia 的扩张，硫化物沉淀（例如 ZnS、FeS）增加。随后，考虑到这一时期 δZn 和 δ13C 的同时变化，δZn 值显着上升约 1.1 ‰，被解释为有机碳埋藏量的增加。研究结果表明，有机碳埋藏的增加、逆风化的减少或它们的组合促成了志留纪的冰川作用。此外，风化引起的高初级生产力导致赫南阶和鲁丹阶晚期的缺氧水体状况。海水中长期的海洋缺氧导致了富含有机物的沉积物的沉积，并阻碍了鲁丹期的生物恢复。