鄂尔多斯盆地侏罗系直罗组砂岩发育特征

Distributional and Sedimentary Characteristics of Sandstones in Jurassic Zhiluo Formation,Ordos Basin

根据岩性旋回结构,在全盆地范围将直罗组划分为上、下两段。分段制图表明,直罗组上、下段地层厚度展布规律与全组厚度展布规律基本一致,均表现为西厚东薄;上段地层较下段厚。下段砂岩层数少、单层厚度大;而上段砂岩以层多、层薄为特点。直罗组砂岩总体成熟度较低,区域制图和碎屑组分等反映周缘存在多个源区。砂岩粒度分布表现为河道和分流河道等沉积特征。直罗组砂岩发育多种反映陆上河流沉积环境的层面和层理构造。综合分析认为,在今残留盆地范围内,直罗组下段以辫状河、曲流河沉积为主,东北部可见三角洲平原沉积。上段以辫状河、曲流河、三角洲和湖泊沉积为主。直罗组下段辫状河道砂岩具有良好的渗透性、连通性和成层性,是砂岩型铀矿和石油的良好储层。

According to the cycle architecture of lithology, the Zhiluo Formation is divided into two members （ named upper and lower ones） in the scale of whole basin. The figures about member thickness, sandstone thickness and layer numbers of sandstone indicate that： the thickness distribution patterns of sandstone about both upper and lower members are consistent with that of the whole formation, all of them show it is thicker in the west while thinner in the east ; the thickness of upper member are thicker than that of lower member, generally. The lower member has less layer numbers of sandstone and bigger thickness of single sandstone layer, while the upper member holds the opposite characteristics. The analysis of detrital components, detritus type, supporting style and regional mapping indicate that： the sandstone of Zhiluo Formation has the characteristics of multi-provenances and proximal deposition. The analysis of grain size shows that the sandstone has the characteristic of fluvial channel deposition. Several types of surface and bedding structures existed in the sandstone of Zhiluo Formation, which reflect the fluvial deposit environment. The vertical sequence of lower member has the typical characteristic of braided stream system, while the upper member reflects the combination characteristic of superimposition of multiple phase meandering-braided stream system. Via comprehensive analysis, it is considered that the main sedimentary facies of lower member of Zhiluo Formation is braided stream system, and transited to meandering river at latter in the residual basin. While that of the upper member are mainly braided-meandering stream system, delta and lake. The sandstone deposited in braided channel of lower member of Zhiluo Formation has excellent permeability, connectedness and well bedding, so it is the well reservoir of sandstone-type uranium deposits and hydrocarbon.