鄂尔多斯白垩系自流水盆地水文地质特征与岩相古地理

Hydrogeological Characteristics and Lithofacies Palaeogeography of Cretaceous Artesian Basin,Ordos

鄂尔多斯白垩系盆地是一特大型自流水盆地,发育洛河、环河华池和罗汉洞三个含水岩组。通过分析早白垩世的盆地古构造、古地理、沉积环境和岩石特征、划分含水岩组沉积相类型,探讨沉积相与含水岩组发育分布规律以及含水性之间的关系,认为岩相古地理是控制含水岩组分布特征、含水性以及水质变化的重要因素,受其影响,在盆地边缘,含水岩组由多期冲积扇、河流和三角洲平原分流河道相砂砾岩和砂岩组成,不同沉积期次的砂砾岩层叠置,形成巨厚含水层,泥岩隔水层不发育,地下水循环系统性好,矿化度低;在盆内,洛河和罗汉洞组风成相砂岩,产状稳定、组份和结构成熟度高、易溶组份少,顶底板及边界隔挡岩性匹配合理,是最理想的含水岩组。环河华池组含水砂体,由三角洲水下分流河道以及滨湖滩坝相长石石英细砂岩组成,呈孤立透镜体状,含水性差,孔喉结构复杂,水溶蚀作用强,矿化度高;早白垩世形成的鄂尔多斯东西不对称湖盆结构既控制当时含水层的发育和分布,又是现今自流水盆地结构形成的基础。

Ordos basin is only the largest artesian basin in China during Cretaceous. Characteristics of early Cretaceous lithofacies palaeogeographic are significant factors that influence distributing features, aquosity and quality change of three water-bearing Formations, Luohe, Huanhe-Huachi and Luohandong Formation. Through analyzing palaeotectonic, palaeogeographic, sedimentary environment and litho-feature, sedimentary facies types of mainly water-bearing formation are divided in this article, and relationships between sedimentary facies with aquosity and distributing rule of water-bearing formation have been discussed further. It is considered that water-bearing formations lain in the margin of basin, composed of alluvial fans, rive facies and distributary channel of delta plain, have characteristics of different episode of sedimentary granulite superposition, thicker water-bearing layers, less water-resisting layers of mudstones, optimum circle system of groundwater and low mineralization degree ; and there are two types in the inside of basin, wind-bearing facies sandstones of Luohe Formation and Luohandong Formation are the best of water-bearing formation with charateristics of stabile occurrence, high maturation in component and structure, low solube component and reasonably spatial matching relation of roof and floor lithology and boundary isolated barrier lithology; on the other hand, water-bearing sand boies of Huanhe-Huachi Formation, composed of feldspar-quartz fine-sand of bar and lakefront, occurs isolated lens and has charateristics of poor aquosity, complex pore-throat texture, strong corrosion and high mineralization degree. Asymmetrical lake-basin structure of Ordos basin in EW way, formed in early Cretaceous, not only control development and distribution of main water-beating bed, but also is the basis of structure forming of artesian basin nowadays.