二连盆地群下白垩统含煤地层聚煤特征分析

Analysis of coal-accumulating characteristics in the lower cretaceous coal-containing strata of the Erlian basin group

内蒙古二连盆地群含有丰富的煤及煤层气资源,早白垩世巴彦花群是该盆地群的主要含煤地层,本文分析了该盆地群含煤岩系的沉积环境、沉积序列和控煤因素,提出巴彦花群的层序地层划分方案、煤系区域展布特征和典型断陷的聚煤模式。将巴彦花群划分为3个三级层序及相应的体系域,3个层序分别对应阿尔善组+腾格尔组一段、腾格尔组二段和赛汗塔拉组,煤层主要发育在层序Ⅱ,Ⅲ的湖侵体系域;在含煤岩系中识别出滨浅湖、扇三角洲平原、三角洲平原、河流泛滥平原等4种有利的聚煤环境类型,认为滨浅湖沼泽聚煤最好,(扇)三角洲平原沼泽、河流泛滥平原沼泽次之;通过分析古气候、古构造、古地理的控煤作用,提出区深水型半地堑型、浅水型半地堑型以及地堑型等3种断陷盆地聚煤模式,其中深水半地堑型断陷的缓坡带和浅水半地堑型断陷的中部聚煤最好,地堑型断陷聚煤较差。综合研究表明,煤层在区域上分布东部各断陷优于西部、北部优于南部,在垂向上上含煤段含煤性优于下含煤段.

The Erlian basin group in eastern Inner Mogolia is developed with abundant coal and coalbed methane resources. The Bayanhua group of the Early Cretaceous is the major coal measures. This paper has analyzed the depositional environments, sedimentary sequence and controlling factors of coal accumulation of the Bayanhua group, and has proposed the sequence stratigraphic framework, regional distribution of coal measures and the coal-accumulating mod- els of typical faulting basin in the Erlian area. A total of 3 third-order sequences and corresponding systems tracts have been subdivided, with sequence I, sequence II and sequence III corresponding to Aershan formation and first member of Tenggeer formation, Second member of Tenggeer formation, Saihantala formation in ascending order. The lacustrine transgressive systems tracts in sequence II and III were developed with major coals. Coal-forming swamps were developed from coastal and shallow lacustrine environments, the fan delta nlain and nor-mal delta plain environments, and the fluvial flood plain envionments, with the swamps devel- oped from coastal and shallow lacustrine being the most favorable coal-forming environments. The controlling factors of coal accumulation, including paleoclimates, paleotectonics and paleo- geography, have been discussed, and three types of the faulting basin coal accumulating model have been classified, including the deep water half-graben, shallow water half-graben, full grahens. It is suggested that the gentle slope side of the deep water half-graben and the central zone of the shallow water half-graben were the best coal-forming area, while the full graben has poor coal-forming potentials. This comprehensive study have revealed that regionally the coal seams in Bayanhua group in the Erlian area are developed better in the east and north than in the west and south, and vertically the upper coal-bearing member has a better coal-bearing property than the lower coal-bearing member.