| 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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| 引用本文：蒋立阳,余烨,王莉.2025.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[J].地球学报,46(6):1135-1148. |
| DOI：10.3975/cagsb.2024.112221 |
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| 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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| 中文摘要:为了明确湘中南地区中奥陶统烟溪组黑色岩系南北差异的成因模式, 以7条剖面20个黑色岩系样品为研究对象, 采用剖面观察、薄片鉴定、矿物成分及地球化学分析方法, 对其物质来源、形成环境和成因机制进行了分析。结果表明: 烟溪组黑色岩系具有海相硅质岩典型的微晶-粉晶结构, 北部区域发育大量笔石化石, 中部区域和南部区域发育大量放射虫化石; 稀土元素配分模式与澳大利亚后太古宙平均页岩(PAAS)的基本相似, 表现为LREE相对富集、HREE相对平缓、Ce正异常及明显Eu负异常的特征; 稀土总量介于6.06×10–6~290.44×10–6之间, 其中北部区域稀土总量较高, 而中部和南部区域稀土总量较低; 烟溪组黑色岩系以生物成因硅为主, 同时也受到了热液富硅流体和陆源碎屑硅输入的控制, 其中热液富硅流体对中部和南部区域黑色岩系形成的影响较大, 而陆源碎屑硅输入对北部区域黑色岩系形成的影响较大; 该套黑色岩系主要形成于水体滞留、缺氧还原的环境, 其中中部和南部区域厌氧还原程度较高, 而北部区域厌氧还原程度略低。热液富硅流体的SiO2沉淀和放射虫等底栖生物的发育促进了中部和南部区域大陆边缘-深海盆地的黑色岩系的形成; 陆源碎屑硅、细粒物质及笔石等浮游生物促进了北部区域大陆边缘的黑色岩系的形成。 |
| 中文关键词:黑色岩系 沉积环境 成因机制 烟溪组 中奥陶统 湘中南地区 |
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| Geochemical Characteristics and Petrogenesis Analysis of the Middle Ordovician Yanxi Formation Black Rock Series, Central-Southern Hunan |
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| Abstract: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. |
| keywords:black rock series sedimentary environment origin mechanism Yanxi Formation Middle Ordovician cen-tral-southern Hunan |
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