柴北缘鱼卡地区侏罗纪含煤地层层序地层学研究

运用钻井岩心、测井及层序地层学有关理论、方法,对青海柴北缘鱼卡地区侏罗纪含煤地层进行了层序地层学研究。共识别出4个层序界面,将侏罗系含煤地层划分为3个三级层序,分别对应于中侏罗统大煤沟组、石门沟组下段和石门沟组上段;研究区层序界面主要包括区域不整合面(古风化壳)、三角洲平原分流河道下切谷、河道间古土壤和盆地内基准面下降—暴露—上升旋回的转折点;与海相含煤盆地不同,厚煤层在层序格架内的发育具有多样性。在古隆起和盆地内部,厚煤层常靠近初始湖泛面发育(煤7);在盆地边缘河流—三角洲平原,厚煤层常靠近最大湖泛面发育(煤5)。总体来看,陆相含煤盆地三级层序中,湖侵体系域聚煤最好。

A sequence stratigraphic analysis of the Jurassic coal measures in Yuqia region of Northern Qaidam basin

The principle of the sequence stratigraphy in well logs and outcrops has been used to reconstruct sequence stratigraphic framework of the Jurassic coal measures in Yuqia area of Northern Qaidam basin.Four sequence boundaries have been identified,which divide the Jurrasic coal measures into 3 third-order sequences,corresponding to Dameigou Formation,Lower Member of Shimengou Formation and Upper Member of Shimengou Formation,respectively.The main types of sequence boundary in the research area include regional unconformity surface(paleoweathering crust),incised valley fill of distributary channels,paleosols in the interfluvial area and the shallowing-upward to deepening-upward transforming surface of the depositional systems.The distribution of thick coal seams in the Jurassic continental lacustrine sequence stratigraphic framework is various compared with the paralic coal measures.The thick coal seam,represented by Coal Seam 7,developed near the transgressive surface of Sequence I in the basinal area and the paleo-uplift area,but in the marginal fluvial delta plain such as in Sequence II,the thick coal seem(Coal Seam 5) developed around the maximum flooding surface.In overall,in the continental third-order sequences,the thickest coal seams tend to develop in the transgressive systems tract.