华南晚二叠世层序—古地理及聚煤规律*

晚二叠世是地质历史中重要的成煤时期,在中国南方多个省区都形成了可采煤层。受海平面变化的影响,华南地区晚二叠世发育一套完整的陆相—海陆过渡相—海相含煤岩系。通过对野外露头及钻孔剖面资料分析,识别出了区域不整合面、下切谷底部冲刷面、河道间古土壤层和沉积相转换面等关键层序地层界面,以及依据海相石灰岩标志层横向分布规律反映的区域最大海泛面,同时结合前人关于华南地区地层对比及煤层对比方面的成果,将华南上二叠统划分为3个三级层序及9个体系域。利用单因素分析多因素综合作图法恢复了各层序中岩相古地理及煤层分布规律,结果表明:层序Ⅰ中煤层主要形成于潮控下三角洲平原以及潟湖潮坪环境,厚煤层的展布受这些沉积相带控制;层序Ⅱ中三角洲平原环境中煤层最厚,开阔台地煤层最薄,平面上煤层厚度表现为西部厚、中部次之、东部无煤的阶梯式递变;层序Ⅲ中煤层主要形成于三角洲平原环境,此时聚煤作用主要发生于华南西部的康滇古陆东侧,在华南中部及东部大部地区发育的浅海台地和深水盆地均不利于聚煤作用发生。

Sequence-palaeogeography and coal accumulation of the Late Permian in South China

The Late Permian is a significant period for coal accumulation,and during this period minable coal seams were formed in the most parts in South China. Impacted by sea level changes,a full range of facies were developed in the coal-bearing successions,including terrestrial,terrestrial-marine transitional,and marine facies. By means of data from outcrop section and borehole cores,some key sequence stratigraphic surfaces were recognized which including regional unconformities,basal surface of incised valley fills,inter-fluvial paleosol horizons,and facies-reversal surfaces. The maximum flooding surfaces were also recognized by the reginal distribution of marine limestone beds towards palaeo-continent. Combined with the achievements made by previous research on stratigraphic sub-correlation and regional coal correlation in South China,the Upper Permian are subdivided into three third-order sequences and nine systems tracts. The single factor analysis and multifactor comprehensive mapping method was used to reconstruct the lithofacies palaeogeography of each third sequence. The results showed that the coals in sequence I were formed in tide-influenced lower delta plain and lagoon-tidal flat facies belts,with distribution of the thick coal seams being controlled by these facies belts. In sequence Ⅱ,thick coals were developed in delta plain facies belts and the thin coals were formed in the open platform facies belts. The total thickness of coal seams in sequence Ⅱ decreased stepwise from west to east in South China,displaying that the coal in the western part were thickest,the coals in the central part were thin,while no coal were formed in the eastern part. The coals in sequence Ⅲ were formed mainly in delta plain facies belt which was mainly developed in the western part of South China,mainly in the eastern part of the Kangdian Oldland. During this period,the central and eastern parts of South China were occupied by the shallow marine carbonate platform and deep marine facies belts which were not favorable for coal accumulation.