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中晚三叠世(延长期)鄂尔多斯盆地发育两种不同构造类型的盆地边缘,其中西南缘为强烈逆冲导致的挠曲沉降背景下发育的前陆盆地,北中部为稳定沉降的克拉通内盆地.中上三叠统延长组可划分为四4个区域性的三级层序,它们均由微角度不整合或区域性冲刷面所分隔,内部自下而上由低位体系域、湖进体系域和高位体系域构成,但盆地西南缘和北中部的层序构成在沉积样式上存在明显差异:西南缘由于逆冲造山而发育巨厚的砾岩带和不整合,北中部稳定沉降的克拉通则发育加积的河流相砂、砾岩和平行不整合.西南缘的沉积构成反映了从逆冲挠曲沉降到回弹上隆的演化过程,层序界面的形成与回弹隆起、剥蚀和冲断作用有关.前陆盆地的层序地层格架和体系域的配置受褶皱冲断带活动控制,其层序序列反映了中晚三叠世造山带向前陆盆地不断逆冲的过程.北中部的层序演化反映克拉通缓坡背景下的河流-三角洲沉积序列,由底部的粗碎屑辫状河沉积、中部的曲流河沉积和顶部的细碎屑河漫滩沉积构成,受湖平面升降变化控制.在缓坡背景下的低位体系域沉积期,由于可容纳空间有限,大量的河流沉积物只能通过侧向迁移、侵蚀和搬运,在冲积平原上形成砂体的侧向复合加积,构成特定的侵蚀不整合边界.
Middle and Late Triassic (Extended) Ordos Basin developed two different types of basin margins, of which the southwestern margin of the foreland basin developed in the context of flexural and subsidence caused by strong thrusting, and the middle of the north craton Basin.The Upper Triassic Yanchang Formation can be divided into four or four regional third-order sequences separated by micro-angle unconformity or regional scouring surface, the interior is composed of lowstand system tract and lake from bottom to top System tract and highstand system tract. However, the sequence composition of the southwestern margin and the north central of the basin is obviously different in sedimentary style: the southwestern margin of the southwestern margin is thick with thick conglomerate zones and unconformity, and the stable settlement in the north central part Sedimentary facies sand, conglomerate and parallel unconformity are developed in the craton, and the sedimentary composition in the southwestern margin reflects the evolution from the thrust deflection to the uplift, the formation and rebound of the sequence boundary, And the thrusting action.The sequence stratigraphic framework and system domain configuration of the foreland basin are controlled by the fold-thrust belt activity, and the sequence sequence reflects the continuous thrusting process of the Middle Triassic orogen to the foreland basin North Central The sequence evolution reflects the river-delta sedimentary sequence in the gentle craton of gentle craton. It is composed of the bottom of the coarse braided river sediments, the middle meandering river sediments and the top of the fine river sediment deposition, controlled by the elevation of the lake. During the depositional period of the lowstand system tract in the gentle slope, due to limited space, a large number of river sediments can only form side-by-side composite addition of sand bodies on the alluvial plain through lateral migration, erosion and handling, forming specific Eroded unconformity borders.