青龙寺井田主采煤层古泥炭沼泽演化规律研究

Study on evolution law of ancient peat swamp from main coal seam in Qinglongsi Minefield

煤相及相关地球化学特征可揭示主采煤层形成时古泥炭沼泽的水介质条件及演化序列,为煤炭清洁利用、富油煤的赋存特征等研究提供地质依据。基于神府矿区青龙寺井田主采煤层5^(-2)煤的显微组分特征、煤化学性质和元素地球化学等测试分析结果,划分了宏观煤岩类型,总结了煤化学特征,重点对该煤层的煤相及微量元素分布特征开展了精细研究。结果表明:从底板至顶板方向,5^(-2)煤层垂向显微组分含量构成6个演化旋回,对应煤相演化的6个阶段,其中第Ⅰ阶段至第Ⅲ阶段,成煤作用由湖泊湿地沼泽相开始,至下三角洲平原低位沼泽相或山前冲积平原干燥森林沼泽相结束。第Ⅳ阶段至第Ⅵ阶段,成煤作用主体经历了湖泊湿地沼泽相。时间序列上,5^(-2)煤层的沼泽水体的水介质条件呈现出波动式变化,第Ⅰ、第Ⅱ和第Ⅳ阶段水动力条件经历了由强变弱的演化过程,第Ⅲ阶段水动力条件经历了由强变弱再增强的演化过程,第Ⅴ阶段至第Ⅵ阶段水动力条件由弱至强的演化趋势,阶段内部存在不同程度的波动变化。单个旋回多表现为底部盐度低、顶部盐度高的特征,且各演化阶段盐度变化的趋势与煤岩学参数指示的水动力条件变化趋势基本一致。

Coal facies and related geochemical characteristics can reveal the water medium conditions and evolution sequence of ancient peat swampwhen the main coal seam was formed,and provide a geological basis for the study of clean coal utilization and the occurrence characteristics of oil-rich coal.Based on the test and analysis results of the micro-composition characteristics,coal chemical properties and element geochemistry of the main coal seam 5-2 in Qinglongsi mine field in Shen-Fu mining area,this paper divided the macro coal and rock types,summarized the coal chemical characteristics,and focused on detailed research on the coal facies and trace element distribution characteristics of the coal seam.The results show that:from the floor to the roof,the vertical microscopic composition of No.5-2 coal seam constitutes 6 evolutionary cycles,corresponding to the six stages of coal facies evolution.From stageⅠto stageⅢ,coal formation starts from the lake wetland swamp facies and ends with the lower swamp facies in the lower delta plain or the dry forest swamp facies in the alluvial plain of the mountain piedmont.From stage IV to stage VI,the main body of coal formation experiences the lake,wetland and swamp facies.In the time series,the water medium conditions of the marsh water body of the No.5^(-2) coal seam shows a fluctuating change.The hydrodynamic conditions of the first,second and fourth stages experienced an evolution process from strong to weak,and the hydrodynamic conditions in the third stage have undergone an evolutionary process from strong to weak and then strengthened.From stageⅤto stageⅥ,the evolution trend of hydrodynamic conditions is from weak to strong with varying degrees of fluctuations within the stages.A single cycle is mostly characterized by low bottom salinity and a high top salinity,and the trend of salinity change in each evolution stage is basically consistent with the change trend of hydrodynamic conditions indicated by coal and rock parameters.