大柳塔煤矿活鸡兔井田侏罗系延安组高分辨率层序地层及聚煤规律研究

High-Resolution Sequence Stratigraphy and Coal Accumulation Law of Jurassic Yan’an Formation in the Huojitu Minefield of the Daliuta Coal Mine

根据高分辨率层序地层学理论对大柳塔煤矿活鸡兔井田侏罗系延安组进行层序地层划分,并结合沉积环境分析,研究延安组煤系地层的聚煤规律。研究结果表明:活鸡兔井田侏罗系延安组可以划分出3个长周期基准面旋回,8个中周期基准面旋回,15~18个短周期基准面旋回。长周期基准面旋回对应于陆相坳陷盆地初始沉降、扩张、萎缩过程,其地层组合序列记录了湖水超覆、扩展以及退缩的沉积地质历史。延安组煤层形成于三角洲泛滥平原沼泽及三角洲湖泊沼泽两种沉积模式,其中:5煤、2-2上煤、1-2煤、1-2上煤形成于三角洲泛滥平原沼泽环境,主要位于短、中周期沉积基准面上升半旋回的晚期或下降半旋回的早期,可容纳空间增加与沉积物供给速度较平衡,沉积厚度较大,分布较稳定,但经历了异地搬运,局部冲刷现象明显,为三角洲泛滥平原沼泽沉积模式;而4煤、3-1煤、2-2煤则形成于三角洲湖泊沼泽,主要位于短、中周期基准面下降半旋回,沉积物供给难以满足可容纳空间的增长速度,煤层厚度较薄,分叉、合并现象明显,空间分布不稳定,未经历异地搬运沉积,无冲刷现象发生,为三角洲湖泊沼泽沉积模式。

Based on the theory of high-resolution sequence stratigraphy,strata division is made to the Jurassic Yan’an Formation in the Huojitu minefield of the Daliuta coal mine.In combination with analysis of the sedimentary environment,the coal accumulation law of this formation is studied.Results show that this set of strata can be divided into three long-period base-level cycles,eight medium-period base-level cycles and 15 ~ 18 short-period base-level cycles.The long-period base-level cycle corresponds to the initial subsidence,expansion and shrinkage of continental depression basins.Its stratigraphic sequence assemblage recorded the sedimentary geological history of lake water overlap,expansion and retreat.Coal seams of Yan’an Formation were formed in delta flood swamp and delta lakes swamp settings,of which 5 coal,2-2 uppercoal and 1-2 uppercoal were formed in delta plain swamps,mainly in the late stage of the rising half cycle and the early stage of the falling half cycle of the short-period sedimentary base level cycle where the accommodation space was balanced with the supply of sediment,so the sedimentary thickness was larger and the distribution was stable,but the sediments were transported from place to place,so the local flushing phenomenon was obvious,so it is attributed to a delta flood swamp sedimentation.While 3-1 coal,4 coal and 2-2 coal were formed in delta lake swamps,in which marshes were mainly located in the descending half cycle of short-period base level cycle,the growth rate of sediment supply was difficult to meet accommodation space,so the coal seam thickness was relatively thin and the spatial distribution was unstable in which the phenomenon of bifurcation and merger was obvious. It had not experienced material transportation and deposition between different places and there was no flushing phenomenon,so which can be explained by a delta lake swamp sedimentary model.