鄂尔多斯盆地及周缘地区中二叠统沉积特征

Sedimentary characteristics of the middle Permian in Ordos Basin and its adjacent areas

鄂尔多斯盆地及周缘地区上古生界天然气资源丰富,中二叠统石盒子组是主力勘探层位,明确其沉积相及沉积特征对于该区油气勘探具有重要的意义。在野外剖面踏勘及钻井岩心观察的基础上,对研究区石盒子组地层及岩性特征、沉积相类型及沉积演化等进行系统分析。结果表明:研究区中二叠统石盒子组主要发育粗粒陆源碎屑岩系。中二叠世研究区仍存在间歇性局部海侵,石盒子组主要以陆相沉积体系为主,包含冲积扇沉积相、河流沉积相、湖泊沉积相、三角洲沉积相等,同时发育障壁海岸沉积体系。研究区自北向南石盒子组依次发育冲积扇、河流、三角洲、滨浅湖等沉积,南缘、西南缘发育浅水三角洲沉积,南缘、东南缘障壁海湾中发育潟湖和障壁沙坝沉积。

The Ordos Basin and its adjacent areas are rich in natural gas resources in the upper Paleozoic. The middle Permian Shihezi Formation is the main exploration interval,and its sedimentary characteristics are of great significance for oil and gas exploration. Based on the outcrop investigation and drilling core observation,this paper makes a comprehensive analysis of the stratigraphic and lithologic characteristics,sedimentary facies types and depositional patterns of the Shihezi Formation. The results show that the middle Permian Shihezi Formation mainly developed coarse-grained terrestrial clastic rock series. Intermittent local marine transgression still exists in the study area in the middle and late Permian.The Shihezi Formation is mainly dominated by continental sedimentary systems,including alluvial fan facies,river facies,lake facies,and delta deposits,and barrier island-coastal systems. From the north to the south,the Shihezi Formation successively developed alluvial fans,rivers-deltas,shallow lakes and other deposits. The southern and southwestern margins developed shallow water delta deposits,whereas the southern and southeastern margins developed lagoons and barrier bar sands in restricted barrier bays.