大同煤田太原组含煤岩系基准面旋回与聚煤作用

Coal-accumulating processes and base level cycles of the Taiyuan Formation in the Datong coalfield

结合大量钻孔岩心、测井、井田地震资料,按照基准面旋回理论原理对大同煤田石炭系太原组含煤层系高分辨率层序地层发育特征与聚煤作用进行分析。将太原组划分为1个长期基准面旋回,3个中期基准面旋回和7个短期基准面旋回,分析了不同中期基准面旋回沉积相序、短期旋回结构类型、叠加样式及其煤层聚集的控制因素,明确了中期旋回地层格架内砂体与煤层的分布规律及其响应特征。研究认为弱伸展、缓慢沉降的古构造背景以及温暖潮湿的古气候条件是太原组成煤的基础条件,中期基准面变化及所处的位置是聚煤的主控因素,在中期基准面旋回上升晚期,易发育厚度大,横向分布稳定的主力可采煤层;上升早中期或下降中晚期,多发育中薄层炭质泥岩与薄层煤层,煤层多零星分布,横向连续性差。

Based on the base- level cycle principle, the authors studied high- resolution sequence stratigraphic characteristics and coal accumulation of Taiyuan Formation in the Datong coalfield by using borehole, logging and geological data. One long- term base level cycle, three medium-term base level cycles and seven short-term base level cycles were identified. Various sedimentary facies sequences, structure and stacking pattern of short cycle sequences and controlling factors for coal accumulation in different middle cycle sequences were analyzed emphatically and, as a result, the distribution features and log responses of sand bodies and coal seams in the interior were obtained. The research results also show that the accumulation of the coal of Taiyuan Formation was controlled by medium-term base-level changes under the conditions of slight extension and slow subsidence of tectonic setting and humid climate. The late rising half medium- term base- level was favorable for depositing wide and thick coal seams, while thinlayers of carbonaceous mudstone and coal were developed in the early-to-middle period of the rising half medium-term base level or the late period of the falling half level, where the coal seams were distributed sporadically with poor continuity laterally.