Abstract To study the possible role of base-level oscillations in the formation of thick coal seams in coastal plain (paralic) environments, the Early Permian Shanxi Formation No.21 thick coal seam was investigated in 3 cores spanning a distance of 29 km in the Anhe (Anyang-Hebi) coalfield, Henan Province using sedimentology, sequence stratigraphy, and coal petrology. The accommodation condition and origin of the peatland can be interpreted from maceral and mineral composition in the No.21 coal seam. Coals that accumulated in a low accommodation peat of ombrotrophic origin are characterized by relatively high inertinite content and relatively low mineral matter abundance. Coals accumulated in a balanced accommodation peat of rheotrophic origin are characterized by high vitrinite content and low abundances of inertinite and mineral matter. Coals with relatively high vitrinite content and relatively low inertinite content are interpreted to have accumulated in a high accommodation peat of rheotrophic origin. The No.21 coal seam was developed as part of a transgressive systems tract (TST) and displays maximum thickness in the central Anhe coalfield due to the local rapid subsidence of the formative delta plain. Six types of key stratigraphic surfaces are recognized in the coal seam, including terrestrialization (TeS), paludification (PaS), give-up transgressive (GUTS), accommodation-reversal (ARS), exposure (ES), and flooding (FS) surfaces. The No.21 coal seam consists of at least three drying-up and wetting-up cycles defined by these surfaces, with each cycle spanning from 20 ka to 30 ka. The variation of peatland type from rheotrophic through ombrotrophic and back to rheotrophic peat in the landward area implies the role of high-frequency climatic fluctuations, and the water level changes in the central and seaward areas may reflect sea-level fluctuations due to the hydrological connection to the sea and the change in rainfall to evaporation rates. These cycles arrived at a period close to that of climatic precession for Milankovitch cycles during the early Permian. The oscillating high and low summer insolation would have caused the alternating wet and dry climate periods that were then recorded as the wet-dry cycles in the coal seams. The results of this study can provide insights for research addressing hydrological conditions in ancient peatlands, and paleoclimate and sea-level fluctuations recorded in thick paralic coal seams.

中文翻译：

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近岸环境厚煤层层序地层分析——以河南安河煤田早二叠世山西组为例

摘要 为研究沿海平原（近海）环境中基底水平振荡对厚煤层形成的可能作用，对山西早二叠世山西 21 组厚煤层进行了 3 个跨距 29 km 的岩心研究。河南省安河（安阳-鹤壁）煤田利用沉积学、层序地层学和煤岩学。泥炭地的容纳条件和成因可以从21号煤层的矿物成分和矿物成分来解释。积聚在嗜碱性成因的低适应泥炭中的煤具有相对较高的惰性物质含量和相对较低的矿物质丰度的特征。堆积在流变源的平衡适应泥炭中的煤的特征是镜质体含量高，惰性和矿物质丰度低。具有相对高镜质体含量和相对低惰性含量的煤被解释为在流变成因的高适应性泥炭中积累。21 号煤层是海侵系统域 (TST) 的一部分，由于形成的三角洲平原局部快速下沉，安河煤田中部的煤层厚度最大。煤层中识别出六种关键地层表面，包括陆化（TeS）、泥化（PaS）、放弃海侵（GUTS）、适应反转（ARS）、暴露（ES）和洪水（FS）表面. 21 号煤层由这些表面定义的至少三个干涸和润湿循环组成，每个循环跨度从 20 ka 到 30 ka。陆上地区泥炭地类型从变养型到变养型再到变养型泥炭的变化暗示了高频气候波动的作用，中部和临海地区的水位变化可能反映了由于水文联系引起的海平面波动。到海洋和降雨量对蒸发率的变化。这些周期到达的时期接近二叠纪早期米兰科维奇周期的气候岁差。波动的高低夏季日照会导致交替的干湿气候周期，然后记录为煤层中的干湿循环。这项研究的结果可以为解决古代泥炭地水文条件的研究提供见解，