Diagenesis of Ediacaran − early Cambrian phosphorite: Comparisons with recent phosphate sediments based on LA-ICP-MS and EMPA

作者：Haiying Yang, Jiafei Xiao, Yong Xia, Zhifang Zhao, Zhuojun Xie, Shan He, Shengwei Wu · 发表于：Ore Geology Reviews · 年份：2022 · DOI：10.1016/j.oregeorev.2022.104813 · 被引用次数：30 · 研究领域：Geochemistry and Elemental Analysis、Geological and Geochemical Analysis、Paleontology and Stratigraphy of Fossils

“Old phosphorite” deposits (Ediacaran to early Cambrian) located in Central Guizhou, South China, are hosted in carbonate and represent the earliest phosphogenesis. These old phosphorites, as well as Pliocene to Pleistocene and modern phosphate sediments (recent phosphorite) have been extensively studied. However, the possibility of recent phosphorite being the incipient stage of long-time phosphorite remains uncertain. Taking Weng’an (Ediacaran) and Zhijin (early Cambrian) phosphorites as examples, this study conducted in situ geochemical and mineralogical analyses of phosphate minerals (old apatites). Analogies between recent and old apatites were determined by comparing geochemistry based on rare earth elements (REE) and yttrium (REE + Y). Old phosphorite could be divided into authigenic grains and biodetritus, both comprising closely accumulated apatite nanocrystals. REE + Y concentrations (∑REE + Y) were much higher in the outer rim than in the inner core of biodetritus, whereas the authigenic grains showed relatively homogeneous REE + Y distributions. Three REE + Y patterns were observed: (1) “left-inclined” type, with no Ce anomalies; (2) shale-like pattern, with weak MREE enrichment and slightly negative Ce anomalies; (3) “hat-shaped” pattern, with notable MREE enrichment, evident HREE depletion, and remarkable negative Ce anomalies. Positive La, Gd, and Y anomalies, as well as MREE enrichment increased from type (1) to type (3), which can be explained by increasing d...