青海木里煤田外力哈达矿区侏罗系层序地层与聚煤作用

Sequence stratigraphy and coal accumulation of the Jurassic in Wailihada mining area of Muli Coalfield in Qinghai Province

利用钻孔岩心数据,对青海北部木里煤田外力哈达矿区侏罗纪湖盆相陆源碎屑含煤岩系进行了层序地层学和聚煤作用的研究。研究区侏罗系共划分出5个三级层序及相应的体系域。在每个层序中,低位体系域由河道相或分流河道相灰白色粗砂岩、细砂岩组成,湖侵体系域由泛滥盆地相或分流间湾相砂质泥岩组成,高位体系域由湖泊相或分流间湾沼泽相泥岩和碳质泥岩组成。厚煤层主要形成于层序S1的湖侵体系域中期,高位体系域和低位体系域基本没有煤层发育。这主要是在湖侵体系域中期,由于可容空间增加速率与泥炭堆积速率相平衡,因此,在三角洲平原分流间湾环境易形成较厚的煤层。

Sequence stratigraphy and coal accumulation of the Jurassic lacustrine clastic coal measures in the Wailihada mining area of northeastern Qinghai were studied using borehole data.A total of 5 third-order sequences and corresponding systems tracts were subdivided.Within each sequence,the lowstand systems tract（LST）is composed of grayish white coarse-grained sandstones of fluvial or distributary channel facies,the transgressive systems tract（TST）consists of sandy mudstones of flood basin and interdistributary bay facies,and the highstand systems tract（HST）is dominated by the mudstone and carbonaceous mudstones of the lacustrine and interdistributary bay facies.Thick coal was formed in the middle stage of the TST of sequence S1,and no major coals were formed in the LST and HST.This is mainly due to a balanced development of accommodation space rates and peat accumulation rates during middle stage of the TST,when the interdistributary environments favored the accumulation of thick coals.