Rare earth element and Sr-Nd isotope geochemistry of phosphate nodules from the lower Cambrian Niutitang Formation, NW Hunan Province, South China
Rare earth element and Sr-Nd isotope geochemistry of phosphate nodules from the lower Cambrian Niutitang Formation, NW Hunan Province, South China
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湘西北下寒武统牛蹄塘组磷酸盐结核的稀土元素和Sr-Nd同位素地球化学
DOI：
10.1016/j.palaeo.2013.10.002
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Chen Yong-Quan
中科院分区：
文献类型：
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作者：
Zhu Bi;Jiang Shao-Yong;Yang Jing-Hong;Pi Daohui;Ling Hong-Fei;Chen Yong-Quan
中国南部扬子地台早寒武世黑色页岩层序中广泛分布着磷矿结核。本文对湖南省中国南部两个PC-C剖面中的磷酸盐结核进行了X射线衍射、主量元素、稀土元素和锶单键Nd同位素研究。根据稀土元素和稀土元素的同位素特征，可以识别出两种不同类型的磷酸盐结核：类型1具有海水状稀土配分模式，εND(T)值较高；类型2具有帽状稀土配分模式和更负的εND(T)值。我们认为，这两种类型的稀土配分模式和Nd同位素组成的差异，反映了早期成岩作用中孔隙水地球化学从以海水为主向以成岩流体为主转变。大多数样品中都显示出Eu正异常，这不仅可能记录了早寒武世中国南部地区的缺氧环境，而且可能记录了海底喷气热液的参与。
Phosphate nodules are widely distributed in the early Cambrian black shale sequence in Yangtze platform, South China. In this study, we carried out X-ray diffraction, major element, rare earth element, and Srsingle bondNd isotopic studies on phosphate nodules from two PC-C sections in Hunan Province, South China. Two different types of phosphate nodules can be recognized based on REE and Nd isotopic characteristics: type 1 with seawater-like REE patterns, higher εNd(t) values; and type 2 with hat-shaped REE patterns and more negative εNd(t) values. We suggest that the difference in REE patterns and Nd isotopic compositions between the two types reflects changes in pore water geochemistry from seawater-dominated towards diagenetic fluid-dominated conditions during early diagenesis. Positive Eu anomalies are displayed in most samples, and are likely to record not only the anoxic environments but also the involvement of submarine exhalative hydrothermal fluids which prevailed in South China during early Cambrian.