鄂尔多斯盆地西部晚三叠世原型盆地恢复及其改造演化

Restoration and tectonic reworking of the Late Triassic basin in western Ordos Basin

恢复鄂尔多斯晚三叠世原型盆地是评价盆地西缘上三叠统油气勘探前景的重要问题。研究认为,在三叠纪延长组沉积期,鄂尔多斯盆地西部受秦祁褶皱带和阿拉善古陆控制,六盘山西缘大断裂和贺兰山西缘断裂分别构成晚三叠世沉积盆地的西南与西北边界;走廊过渡区与盆地本部沉积具有连通性,形成向西开口、南深北浅、主体为北西-南东向的大型不对称坳陷盆地,银川盆地、六盘山盆地是鄂尔多斯盆地的一部分,盆地西缘前人所称的“南北古脊梁”不起沉积分割作用。延长组沉积期湖盆西部从南到北发育汭水河—镇原、景泰—环县、窑山—甜水堡和汝箕沟—盐定4个三角洲沉积体系,受不同物源影响,各体系沉积特征不同,并且经后期构造运动改造,在盆地西缘冲断带上盘残存不全。但在现今冲断带以东及其掩覆地区延长组保存较完整,延长组残余沉积分布广泛,勘探前景广阔。

Restoring prototype basin is an important issue for evaluating oil and gas prospect of Upper Triassic in west Ordos Basin. The authors point out that the Qin-Qi Fold Belt and Alashan ancient land controlled the borderline of the western Ordos prototype basin in Later Triassic. The large borderline faults of west Liupanshan and west Helanshan were the southwest and northwest borderlines of the Upper Triassic prototype basin. There is no clear boundary line between the Hexi Corridor and the cadre of the basin. The prototype basin is a large NW-SE asymmetric depressed basin, which is deep in south and shallow in north. The Yinchuan Basin and Liupanshan Basin.are part of the prototype basin in the Yanchang stage of Upper Triassic. There are four delta sedimentary systems, which are Ruishuihe-Zhenyuan, Jingtai-Huanxian, Yaoshan-Tianshuipu and Rujigou-Yanding delta sedimentary systems, with different sedimentary characteristics from south to north in western Upper Triassic basin. These delta sedimentary systems were altered in Late Indosinian, Mid-Yanshanian, Late Yanshanian and Himalayan, denudated badly in the hanging wall of the west thrust belt, and conserved integrally in the east of the present thrust belt. The extensive residual Yanchang Formation sedimentary system has good prospecting.