新疆吐哈盆地中、下侏罗统含煤岩系层序地层及古地理

Sequence stratigraphy and palaeogeography of the Lower and Middle Jurassic coal measures in Turpan-Hami Basin

在吐哈盆地中、下侏罗统含煤岩系层序地层分析的基础上,对聚煤期古地理特征及其与聚煤作用的关系进行了研究。结果表明,吐哈盆地中、下侏罗统含煤岩系形成于河流—三角洲—湖泊沉积体系,其中共发育4个三级层序,分别对应于八道湾组、三工河组、西山窑组一、二段和三、四段。吐哈盆地从层序Ⅰ到层序Ⅳ,先后经历了沼泽(层序Ⅰ)—湖泊(层序Ⅱ)—沼泽(层序Ⅲ)—湖泊(层序Ⅳ)过程。在对应于最大湖泛面的湖侵体系域末期和高位体系域早期,较快的可容空间增加速率与泥炭堆积速率相平衡,从而有利于厚煤层的堆积。煤层厚度、碳质泥岩厚度与砂砾岩含量呈负相关关系,即砂砾岩含量越少,煤和碳质泥岩厚度越大;地层厚度300～500m(层序Ⅰ)和400～550m之间(层序Ⅲ)时,煤层厚度最大,说明有利于煤和碳质泥岩聚集的环境是沉降速率中等、陆源碎屑供给相对较少的三角洲间湾、湖湾以及下三角洲平原环境,层序Ⅰ和层序Ⅲ的聚煤中心如艾维尔沟、柯尔碱、桃树园、七泉湖、柯柯亚、鄯善、艾丁湖、沙尔湖、大南湖和三道岭等均属于这类环境。

This paper analyses the sequence stratigraphy and palaeogeography of the Lower and Middie Jurassic coal measures in the Turpan-Hami Basin, northwestern China. The controls of the palaeogeography and sequence stratigraphy on the coal accumulation in this Basin have been discussed. The results show that the coal measures were formed in a fluvial - delta - lacustrine sedimentary system, and a total of 4 third-order sequences were developed, corresponding to the Badaowan Formation, Sangonghe Formation, the Members 1, 2 and 3,4 of the Xishanyao Formation, respectively. The Turpan-Hami Basin had experienced the swamping （ Sequence Ⅰ ） --lake flooding（ Sequence Ⅱ ） --swamping（ Sequence Ⅲ ） --lake flood- ing（Sequence Ⅳ ） processes. The thick coal seams were developed during the deposition of the late transgressive systems tract and the early highstand systems tract corresponding to the maximum flood surface, when the rate in creation of accommodation kept balance with the peat accumulation rate. There is a negative correlation between the thickness Of coal and carbonaceous mudstone and the content of sandstones and conglomerates, i.e. the thicker coals are associated with the lower contents of sandstones and conglomerates. This implies that the coal-forming environments are inter-delta bays, lower delta plains and back swamps in the fluvial system. The thickest coal seams occur in areas with a strata thickness ranging between 300 - 500 m for Sequence Ⅰ and between 400 - 550 m for Sequence Ⅲ. This suggests that the most ideal sites for coal accumulation are those with moderate rates of subsidence and relatively little input of coarse-grained sediments, which favors the development of inter-delta bays, lower delta plains and back swamps in fluvial systems. The coal-accumulating centers during the deposition of sequence Ⅰ and sequence Ⅲ in the Turpan-Hami Basin, such as Ewirgol, Kerjian, Taoshuyuan, Qiquanhu, Kekeya, Shanshan, Aidinghu, Shaerhu, Dananhu and Sandaoling, were developed in these environments.