| 寒武纪第十期早期海洋氧化还原波动：来自U 同位素的证据 |
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| 引用本文： | 邱晨,魏广祎,闵思雨,陈曦,凌洪飞.寒武纪第十期早期海洋氧化还原波动：来自U 同位素的证据[J].高校地质学报,2022,28(1):40-50. |
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| 作者姓名： | 邱晨 魏广祎 闵思雨 陈曦 凌洪飞 |
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| 作者单位： | 南京大学 地球科学与工程学院，内生金属矿床成矿机制研究国家重点实验室，南京 210023 |
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| 摘 要： | 寒武纪晚期到奥陶纪早期的海洋动物多样性整体水平较低，生物地球化学研究认为可能与海洋氧化还原状态波动有关，但仍证据较少。保存良好的海相碳酸盐岩沉积被认为能够记录古代海水的地球化学信息，其铀同位素组成 (δ238U) 可用来反映全球海洋的氧化还原状态。文章测定了华南瓦儿岗剖面寒武系第十阶底部海相碳酸盐岩的δ238U值，结果显示在寒武纪第十期早期U同位素组成可能存在三次负漂移，对应的δ238U值分别为-0.8‰、-0.55‰和-0.60‰，指示三个海洋缺氧时段。通过U同位素质量平衡模型计算得出，三个缺氧时段全球海洋底层水体分别约有22％、3.5%和5%的缺氧面积。初步推断第一次缺氧可能与风化输入营养元素增强致初级生物生产力提高有关，而其后的两次缺氧可能与原先的海底缺氧水体在海侵阶段上涌扩散有关。
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| 关 键 词： | 铀同位素 氧化还原 寒武系第十阶 海洋缺氧 |
Marine Redox Fluctuation during the Early Cambrian Age 10: Evidence from U Isotopes |
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| QIU Chen,WEI Guangyi,MIN Siyu,CHEN Xi,LING Hongfei.Marine Redox Fluctuation during the Early Cambrian Age 10: Evidence from U Isotopes[J].Geological Journal of China Universities,2022,28(1):40-50. |
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| Authors: | QIU Chen WEI Guangyi MIN Siyu CHEN Xi LING Hongfei |
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| Institution: | State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China |
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| Abstract: | The marine animal diversity was generally low during late Cambrian and early Ordovician. Biogeochemical studies suggest that it may have been related with fluctuations in oceanic redox conditions, despite still lack of evidence. Well-preserved marine carbonates could record the geochemical characters of ancient seawater, and their uranium isotope compositions (δ238U) can be used to reconstruct the global oceanic redox conditions. In this study we analyzed the uranium isotope compositions of marine carbonates of the basal Cambrian Stage 10 from Wa’ergang section, South China. Our data show that the δ238U profile has three negative excursions with minima of -0.8‰ , -0.55‰ and -0.60‰ , respectively, which indicates three intervals of oceanic anoxia expansion. Modeling results based on the uranium isotope mass balance model suggest that about 22%, 3.5% and 5% of the global sea-floor were covered by anoxic water during these three intervals, respectively. We speculate that the first anoxic interval may have been related with increase in primary productivity due to enhanced weathering input of nutrients, and the latter two may have been induced by upwelling of deep anoxic water during the transgressions. |
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| Keywords: | U isotopes redox Cambrian Stage 10 oceanic anoxia |
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