Influence of goethite nanophase on rare-earth element patterns and enrichment in marine phosphates during early diagenesis

被引：0

作者：

Xing, Jieqi ^{[1
,2
,3
]}

Li, Shan ^{[1
,2
,3
]}

Wei, Hongyan ^{[1
,2
,3
]}

Xi, Jiaxin ^{[1
,2
,3
]}

Lin, Xiaoju ^{[1
,2
]}

Yang, Yiping ^{[1
,2
]}

Xian, Haiyang ^{[1
,2
]}

Tan, Wei ^{[1
,2
]}

Wei, Jingming ^{[1
,2
]}

Zhu, Jianxi ^{[1
,2
,3
]}

机构：

[1] CAS Key Laboratory of Mineralogy and Metallogeny, Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou,510640, China

[2] CAS Center for Excellence in Deep Earth Science, Guangzhou,510640, China

[3] University of Chinese Academy of Sciences, Beijing,100049, China

来源：

Chemical Geology | 2024年 / 653卷

基金：

中国国家自然科学基金;

关键词：

Carbonates - Electron energy levels - Electron energy loss spectroscopy - Electron scattering - High resolution transmission electron microscopy - Nanotechnology - Phosphates - Rare earth elements - Rare earths - Seawater - Submarine geology;

D O I：

暂无

中图分类号：

学科分类号：

摘要：

Although rare-earth elements (REEs) in authigenic phosphates and carbonates derived from marine sediments are potential proxies (e.g., REE patterns) for reconstructing paleoenvironmental conditions, the REE patterns appear to be inconsistent. Some marine authigenic phosphates show a bell-shaped pattern with an enrichment of the middle REEs (MREEs; Nd–Ho), while others exhibit a modern seawater-like pattern characterized by a strong depletion in cerium and an enrichment in heavy REEs (Er–Lu, Y, and Sc). Although the origin of the bell-shaped pattern in phosphates has been extensively debated, the evidence is often ambiguous; therefore, the origin of the pattern remains unclear. In this study, we investigate the microscale and nanoscale mineralogical and geochemical characteristics of the REE-enriched Early Cambrian phosphorites. In situ elemental analyses reveal that the codeposited phosphates (bell-shaped REE pattern) and carbonates (modern seawater-like pattern) have different REE patterns. A microscale investigation shows that phosphate grains contain some dispersed goethite nanophase, and a nanoscale investigation using transmission electron microscopy coupled with electron energy-loss spectroscopy shows that Fe2+ is distributed along the rim of the goethite nanophase, indicating that the goethite were reduced. These findings suggest that the REE pattern and concentration in phosphates could have been influenced by the release of REEs during the reduction of Fe (oxyhydr)oxide in the early diagenetic process before the final deposition. Although additional evidence is required, our results are important for understanding the effects of Fe redox cycling on the REE pattern and enrichment in marine authigenic phosphates. In addition, our results suggest that compared with authigenic phosphates, authigenic carbonates would provide a more reliable reconstruction of paleoenvironmental conditions. © 2024 Elsevier B.V.

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