浑江煤田石炭二叠纪含煤岩系层序地层与聚煤作用

Sequence Stratigraphy and Coal Accumulation for Coal Measures of the Carboniferous-Permian in Hunjiang Coal Field

运用层序地层学有关理论和方法,分析了浑江煤田石炭系-二叠系含煤岩系的层序,探讨了聚煤作用的控制因素。石炭纪-二叠纪含煤地层共识别出4个层序边界,划分为3个三级层序。为分析煤层厚度与地层厚度及砂岩百分含量的关系,绘制了三维相关图。研究表明,层序2地层厚度在40-70 m时,层序3地层厚度在50-80 m时,煤层发育较厚,而此时砂岩百分含量小于50%,表明有利于煤层聚积的环境是沉降速率中等、陆源碎屑供给相对较少的沉积环境,主要是三角洲间湾以及下三角洲平原地区。研究区含煤岩系层序地层格架中,不同层序沉积时期,煤层的分布有所不同,对于层序2来说,主要可采煤层分布在最大海泛带两侧,而层序3主要可采煤层分布在海侵面附近,此时较低的泥炭堆积速率与较慢的可容空间增加速率相平衡,从而形成该煤层。

The principle of sequence stratigraphy has been used to reconstruct the sequence stratigraphic framework of the Carboniferous-Permian coal measures in Hunjiang coal field. The controls of sequence stratigraphy on the coal accumulation in this coal field have been discussed. Four sequence boundaries, which divided these Carboniferous-Permian coal measures into three the third-order sequences, have been identified. A three-dimensional correlogram was drawn to analysis relations among the thickness of coal, the thickness of strata and the content of sandstones. The results show that the thickest coal seams occur in the areas with strata thicknesses of 40--70m for Sequence II and of 50-80m for sequence III, and the content of sandstones is less than 50%, implying that coalforming environments are those with moderate rates of subsidence and little input of coarse-grained sediments, mainly interdelta bays and lower delta plains. The distributions of coal in the sequence stratigraphie frameworks of this study area are different during different sedimentary periods： during sequence II, the thick coal seams were developed at the both sides of the maximum flood belt, where the moderate accommodation increasing rate and the peat accumulation rate were about equal; during sequence III, the coal seams were developed near the transgression surface, where the low accommodation increasing rate and the peat accumulation rate were about equal.