Anomalous mercury enrichment in Early Cambrian black shales of South China: Mercury isotopes indicate a seawater source
Anomalous mercury enrichment in Early Cambrian black shales of South China: Mercury isotopes indicate a seawater source
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华南早寒武世黑色页岩汞异常富集：汞同位素表明海水来源
DOI：
10.1016/j.chemgeo.2017.08.010
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发表时间：
2017-09
期刊：
影响因子：
3.9
通讯作者：
Ruizhong Hu
中科院分区：
文献类型：
--
作者：
Runsheng Yin;Lingang Xu;Bernd Lehmann;Ryan Lepak;James Hurley;Jingwen Mao;Xinbin Feng;Ruizhong Hu
在中国南部扬子地台早寒武世黑色页岩层序最下部的富含硫化物的黑色页岩和磷岩中，汞含量极高，达到μg g−1范围。在这项研究中，汞同位素被用来帮助解决这种异常汞浓缩的来源。观察到汞同位素的质量无关分馏特征，Δ199Hg值为0.13~0.24‰，Δ200Hg值为0.05~0.10‰，表明海水是汞的重要来源。我们假设，从公海涌出的营养丰富的水域导致了光区的高生物生产力，同时也伴随着对海水中汞的清除。与现代海水相比，生物量的高级腐烂和缺氧至正己烷条件下的再矿化，加上极低的碎屑输入，导致汞和其他氧化还原敏感的广谱生物金属的富集度高达107。以前只有在含氧深海环境，即锰结壳/结核中，才能观察到这种壮观的氢金属富集区。
Extremely elevated Hg levels up to the μg g− 1range were found in sulfide-rich black shale and phosphorite in the lowermost part of the Early Cambrian black shale sequences on the Yangtze Platform in South China. In this study, mercury isotopes were used to help resolve the origin of this anomalous Hg enrichment. Mass independent fractionation signatures of Hg isotopes with positive Δ199Hg values of 0.13 to 0.24‰ and positive Δ200Hg values of 0.05 to 0.10‰ were observed, indicating seawater is an important source of Hg. We hypothesize that upwelling of nutrient-rich waters from the open ocean resulted in high bioproductivity in the photic zone with concomitant scavenging of Hg from seawater. Advanced decay of biomass and remineralization under anoxic to euxinic conditions combined with very low clastic input led to enrichment of Hg and a broad spectrum of other redox-sensitive and biogenic metals up to 107compared to modern seawater. Such spectacular hydrogenous metal enrichment has previously been observed in the oxic deep-sea environment only, i.e. manganese crusts/nodules.
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