| 湘中南中奥陶统烟溪组黑色岩系地球化学特征及成因分析 |
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| 关键词:black rock series sedimentary environment origin mechanism Yanxi Formation Middle Ordovician cen-tral-southern Hunan |
| 基金项目:湖南省自然科学基金项目(编号: 2023JJ30239; 2023JJ30231)；湖南省教育厅资助科研项目“湘中南地区中奥陶统烟溪组古海洋环境演化与有机质富集”(编号: 23B0467) |
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| Geochemical Characteristics and Petrogenesis Analysis of the Middle Ordovician Yanxi Formation Black Rock Series, Central-Southern Hunan |
| The source, sedimentary environment, and genetic mechanism of 20 black rock series samples from 7 profiles of the Middle Ordovician Yanxi Formation in central-southern Hunan were comprehensively analyzed to clarify the genetic model of north–south differences based on profile observations, thin section identification, mineral composition, and geochemical analysis. The results were as follows: The black rock series of the Yanxi Formation presents a microcrystalline and powder crystal structure typical of marine siliceous rocks. A substantial number of graptolite fossils are developed in the northern region of the study area, while numerous radiolarian fossils are developed in the central and southern regions. The distribution pattern of rare earth elements (REEs) is similar to that of the post-Archean average shale (PAAS), characterized by relatively enriched light REEs, a relatively gentle heavy REE slope, positive Ce anomalies, and distinct negative Eu anomalies. The total concentration of REEs in the black rock series ranged from 6.06×10–6 to 290.44×10–6, with higher REE contents in the northern region and lower REE contents in the central and southern regions. The black rock series of the Yanxi Formation which were simultaneously controlled by hydrothermal silicon-rich fluids and the inputs of terrestrial detrital silicon were primarily composed of biogenic silicon. In particular, hydrothermal silicon-rich fluids had a greater impact on the formation of the black rock series in the central and southern regions, whereas terrestrial detrital silicon inputs had a more significant impact on the formation of the black rock series in the northern regions. In general, the black rock series of the Yanxi Formation formed mainly in an oxygen-deficient environment with water retention, and the degree of anaerobic reduction was slightly higher in the central and southern regions than in the northern regions. The precipitation of SiO2 from hydrothermal silicon-rich fluids, along with the development of benthic organisms such as radiolarians, contributed to the formation of the black rock series in the continental margin and deep-sea basins of the central and southern regions. Simultaneously, terrestrial detrital silicon, fine-grained material, and planktonic organism such as graptolites, facilitated the construction of the black rock series on the northern continental margin. |
| Jiang Liyang,YU Ye,WANG Li.2025.Geochemical Characteristics and Petrogenesis Analysis of the Middle Ordovician Yanxi Formation Black Rock Series, Central-Southern Hunan[J].Acta Geoscientica Sinica,46(6):1135-1148. |
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