湘中龙潭组北型沉积相及聚煤特征

湘中地区晚二叠世龙潭组北型地区为一套灰黑色泥岩、粉砂岩、细砂岩、煤层等沉积组合，具有砂泥薄互层层理、透镜状层理、水平层理及大型交错层理等沉积构造。根据野外剖面及岩心沉积学分析，在龙潭组中识别出残积平原-潟湖、潮坪和滨外陆棚沉积体系，总体上反映为海平面持续抬升、水体逐渐变深的沉积过程。煤层的形成受古构造和古环境等因素控制，煤层发育于煤系沉积早期的渴湖环境（2煤）和中期的潮坪环境（1煤），从西向东2煤厚度减小，硫分及灰分产率增大；1煤仅在部分地区可见，其硫分、灰分产率均比2煤高，说明受海水影响较大。

Sedimentary Facies and Coal Accumulation of Northern Type Longtan Formation in Central Hunan

The northern type Longtan formation of the Late Permian in central Hunan is dominated by an assemblage of greyish black mudstone, siltstone, fine sandstone, and coals, and contains a variety of thin sandstone-mudstone interbedded bedding, lenticular beddings, horizontal beddings and large-scaled cross beddings. The basal part of the coal measures was developed with residual plain facies and overlying lagoon facies, The middle to upper part is dominated by tidal flat facies and the top part is represented by an offshore shelf facies. The coal accumulation is controlled by paleotectonics and paleoenvironment. The coal-forming swamps were developed on the lagoon environment of the initial stage of deposition of coal measures （NO.2 coal） and on the tidal flat environment of middle stage of deposition of coal measures （NO. 1 coal）. The NO.2 coal is the major industrial coal in the research area, and from west to east, its thickness decreased and the content of sulfur and ash increased. The NO.1 coal is developed locally and the contents of sulfur and ash are higher than that of the NO.2 coal, showing a stronger influence from marine water than the NO.2 coal.