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鄂尔多斯盆地中部奥陶系马家沟组赋存有丰富的天然气资源,前人研究多集中于顶部与风化壳相关的储集层。文中基于岩心、薄片及阴极发光分析,将鄂尔多斯盆地中部奥陶系马五盐下碳酸盐岩-蒸发岩划分为10种岩石类型。根据各岩类的宏观、微观特征以及它们在纵横向上的组合与分布特点,利用岩石类型组合的方法,将研究区划分为局限-蒸发潟湖、台内滩、滩间海、微生物丘和台坪5种沉积环境。根据各亚段岩石类型发育的差异性及统计结果发现,研究区马五盐下具有蒸发岩与碳酸盐岩间互的旋回性沉积演化与海平面升降特征,每个亚段都代表一次海侵或海退的旋回沉积。其中,马五6、马五8和马五10亚段为海退期沉积,以纹层状云质膏岩、泥晶云岩构成的局限-蒸发潟湖沉积为主,蒸发岩矿物含量高,反映沉积环境相对闭塞、能量较低且盐度较高;马五7和马五9亚段为海进期沉积,以相对高能的台内滩或微生物丘沉积为主,并与相邻的局限-蒸发潟湖和台坪沉积构成较完整的向上变浅米级沉积旋回,表明该阶段水体循环相对更好,整体沉积环境开阔且能量较高。
The Ordovician Majiagou Formation in central Ordos Basin is rich in natural gas resources. Previous researches mainly focused on reservoirs related to weathered crust at the top. Based on the analysis of cores, thin slices and cathodoluminescence, carbonate rock-evaporites of Ordovician Ma Wu salt in central Ordos Basin are divided into 10 types of rocks. According to the macroscopic and microcosmic features of the rocks and the combination and distribution of them in the vertical and horizontal directions, the study area is divided into limited-evaporation lagoon, inland beach, intertidal sea, microbial pool and terrace by means of rock type combination 5 kinds of sedimentary environment. According to the differences of rock types and statistical results in each sub-segment, it is found that there are cycles of swirling sedimentary evolution and sea-level rise and fall between evaporites and carbonate rocks in Mawu salt area of the study area. Each sub-segment represents a sea Invasion or regression of cyclonic deposition. Among them, the Ma Wu 6, Ma Wu 8 and Ma Wu 10 sub-sea sediments for the retrograde deposition to laminar clouds of gypsum, mud and crystalline dolomite constitute the limitations - the evaporation of lagoon deposits, mainly high mineral content of the evaporite, Reflecting the relative occlusion of sedimentary environment, low energy and high salinity; Ma5 and Ma5-9 sub-stages of the deposition of the sea-phase deposition, relatively high-energy inland beaches or microbial deposits, and with the adjacent limitations - Evaporation lagoons and Tai Ping sediments form a relatively complete upper-rising shallow-m-scale sedimentary cycle, indicating that the water cycle at this stage is relatively better and the overall depositional environment is open with higher energy.