准格尔煤田西南缘太原-山西组层序地层与聚煤规律

Sequence stratigraphy and coal accumulation law of Taiyuan-Shanxi Formation in southwest of Jungar Coalfield

为了探讨厚煤层在层序格架中的分布规律和聚煤作用的控制因素,采用高分辨率层序地层理论和方法,对准格尔煤田西南缘太原-山西组含煤地层进行研究。研究结果表明:以区域不整合面、海侵方向转换面、下切谷冲刷面、古土壤等层序界面,将太原-山西组地层划分为3个三级层序和5个四级层序。研究区煤层主要分布于高位体系域,其次为海侵体系域,此时基底沉降缓慢,可容空间增加速率与泥炭堆积速率基本保持平衡,有利成煤。高位体系域厚煤层是由多期基准面升降形成的煤层复合体。通过进一步对三级层序SⅢ2地层、煤层厚度和砂岩百分含量的分析可知,厚煤层形成于基底沉降速率中等、砂岩含量较少的泥炭沼泽环境。近海地区基准面升降控制着潜水位变化,最终控制泥炭堆积和保存。

In order to discuss the thick seam distribution law in the sequence stratigraphy framework and the control factors of the coal accumulation role,the high resolution sequence stratigraphy theory and method were applied to the study on the coal measures of TaiyuanShanxi Formation at the southwest of Jungar Coalfield. The study results showed that based on the regional unconformity surface,the turn around surface in the transgression direction,the erosion surface of the incised valley,the paleosol and other sequence stratigraphy surface,the stratigraphy in Taiyuan-Shanxi Formation were divided into three three-grade sequence stratigraphy and five fourth-grade sequence stratigraphy. The seams in the study region mainly distributed in the high level system region and secondary were the transgressive system region. At this moment,the foundation subsidence was gently slow,the accommodation space increased rate and the peat accumulation rate was basically kept in the balances and would be favorable to the coal formation. The thick seams in the high level system region were composed with the seam complex formed with the multi cycles of the base level. The further analysis on the three grade sequence SⅢ2 stratigraphy,seam thickness and the percentage content of the sandstone showed that the thick coal seam was formed in the peat swamp environment with a medium settlement rate of the base floor and a less content of the sandstone. The base level of the offshore region controlled the variation of the groundwater level and would finally control the peat accumulation and preservation.