Based on field outcrop observations and microscopic thin section analysis, the microfacies types, microfacies associations, and the evolution of sedimentary environments controlled by relative sea-level changes of the oil and gas reservoirs in the western Ordos Basin are studied. The results show that 13 types of microfacies (MF) can be identified in the Middle-Upper Cambrian of the study area, including argillaceous limestone MF, micritic limestone MF, bioclastic wackstone MF, bioclastic packstone MF, wormkalk, oolitic grainstone MF, intraclastic grainstone MF, intraclastic-bioclastic grainstone MF, mictric-fine crystalline dolomite MF, fine-medium crystalline dolomite MF, argillaceous dolomite MF, mudstone MF, and shale MF. The spatial distribution characteristics of microfacies indicate that this set of carbonate rocks has seven types of microfacies associations, representing restricted platform muddy dolomite flats (MA1), restricted platform dolomite flats (MA2), open platform intra-platform shoals (MA3), open platform inter-shoal sea (MA4), platform margin shoals (MA5), upper slope (MA6), and lower slope facies belts (MA7). From bottom to top, the Middle-Upper Cambrian in the study area successively develops MA5, MA6, MA7, MA3, MA4, MA1, and MA2, which correspond to the platform margin shoals, upper slope, lower slope, open platform intra-platform shoals, inter-shoal sea, restricted platform muddy dolomite flats, and dolomite flats. This sequence indicates that the sedimentary environment becomes more restricted vertically from bottom to top, with the water body becoming shallower. Laterally, the sedimentary environment transitions from slope to platform margin, then to open platform, and finally to restricted platform from west to east, representing a change from deep water to shallow water with a gradual increase in water energy. The sedimentary environment changes revealed by microfacies are jointly controlled by relative sea-level fluctuations and tectonic movements: the sedimentary period of the Zhangxia Formation was mainly controlled by sea-level changes, characterized by sea-level rise. The sedimentary period of the Sanshanzi Formation was controlled by both sea-level changes and tectonic movements. The tectonic uplift in the southwestern part of the basin gradually intensified, leading to a significant drop in relative sea level, thus forming the sedimentary environment transition from slope to platform margin, open platform, and restricted platform from bottom to top. 

通过野外观察和显微镜下薄片分析, 研究鄂尔多斯盆地西部油气储层的微相类型、微相组合及相对海平面控制下的沉积环境演化规律。结果表明, 研究区中–上寒武统可识别出13类微相: 泥质灰岩、泥晶灰岩、生屑粒泥灰岩、生屑泥粒灰岩、竹叶状灰岩、鲕粒颗粒灰岩、内碎屑颗粒灰岩、内碎屑生屑颗粒灰岩、泥晶–粉晶白云岩、细晶–中晶白云岩、泥质白云岩、泥岩和页岩。微相的空间分布特征表明, 该套碳酸盐岩具有7种微相组合类型, 分别代表局限台地泥云坪(MA1)、局限台地云坪(MA2)、开阔台地台内滩(MA3)、开阔台地滩间海(MA4)、台地边缘滩(MA5)、上斜坡(MA6)和下斜坡相带(MA7)。研究区中–上寒武统从下往上依次发育MA5, MA6, MA7, MA3, MA4, MA1和MA2微相组合, 表征台地边缘滩、上斜坡、下斜坡、开阔台地台内滩、滩间海、局限台地泥云坪和云坪相带, 反映沉积环境在纵向上从下往上变得更具局限性, 水体变得更浅; 横向上从西向东呈现为斜坡→台地边缘→开阔台地→局限台地沉积环境的转变, 即从深水向浅水变化, 水体能量逐渐升高。微相揭示的沉积环境变化受相对海平面升降和构造运动共同控制。张夏组沉积期主要受海平面变化控制, 以海平面上升为特点; 三山子组沉积期受海平面变化和构造运动共同控制, 盆地西南部构造隆升逐渐加强, 使得相对海平面显著下降, 形成自下而上为斜坡、台地边缘、开阔台地和局限台地的沉积环境变化规律。