古地貌恢复及其对重力流沉积砂体的控制作用: 以鄂尔多斯盆地三叠系延长组长73亚段为例

鄂尔多斯盆地三叠系延长组长7₃亚段沉积体系和砂体成因类型及展布特征受湖盆底部形态控制明显，不同地区砂体类型、成因及空间展布各异。根据岩心、钻井、测井等资料运用印模法与沉积学方法精确地恢复了鄂尔多斯盆地三叠系延长组长7₃亚段的古地貌，并对微古地貌单元进行精细刻画，在此基础上分析了古地貌对盆地延长组长7₃亚段沉积体系和砂体成因类型及展布特征的控制作用。研究表明:长7₃期古地貌整体呈东缓西陡的不对称坳陷形态，明确了研究区发育高地、坡折带、湖底深洼（凹）、湖底平原、湖底古隆、湖底古脊和古沟道7个微古地貌单元。研究区延长组长7₃亚段重力流沉积体系受古地貌控制较明显，从湖盆边缘至湖盆中心依次发育三角洲前缘沉积、沟道型重力流沉积、半深湖-深湖沉积，从坡折带至湖盆中央，重力流沉积类型逐渐从砂质碎屑流沉积转换为浊流沉积。古地貌形态控制着研究区延长组长7₃亚段重力流砂体的整体展布，而高地、坡折带及古沟道等微古地貌单元则进一步控制重力流砂体的物源方向、成因类型、运输方向、横向连通性及展布形态等。 

Paleogeomorphological restoration and its control on gravity flow sand bodies: A case study of the Chang 73 submember of the Triassic Yanchang Formation in the Ordos Basin

The bottom morphology of the lake basin controlled the sedimentary system, genetic types, and distribution characteristics of sand bodies in the Chang 7₃ submember of the Triassic Yanchang Formation in the Ordos Basin. The types, genesis, and spatial distribution of sand bodies in different regions differ. In this study, according to cores, drilling, logging, and other data, the paleogeomorphology of the Chang 7₃ submember was accurately restored by the impression method and sedimentology method, and the micro paleogeomorphology units were finely characterized. On this basis, the authors analyze the paleogeomorphology control on the sedimentary system, genetic types, and distribution characteristics of sand bodies in the Chang 7₃ submember. The result shows that the paleogeomorphology of the Chang 7₃ period is an asymmetrical depression in the east and a steep depression in the west. Seven micro paleogeomorphic units, including the highland, the slope break zone, the lakebed deep depression, the lakebed plain, the lakebed paleouplift, the ancient lakebed ridge, and the ancient channel, are identified in the study area. The paleogeomorphology obviously controlled the gravity flow deposition system of the Chang 7₃ submember in the study area. From the margin to the center of the lake basin, delta front deposition, channel-type gravity flow deposition, and semideep-deep lake deposition successively developed. From the slope break zone to the center of the lake basin, the gravity flow deposition type gradually changed from sandy debris flow deposition to turbidity flow deposition. The paleogeomorphology controls the overall distribution of the gravity flow sand body in submember 7₃ in the study area, while the micro paleogeomorphology units such as the highland, the slope break zone, and the ancient channel further control the provenance direction, genetic type, transportation direction, lateral connectivity and distribution pattern of the gravity flow sand bodies.