鄂尔多斯盆地三叠系延长组沉积体系特征及湖盆演化

Sedimentary system characteristics and lake basin evolution of Triassic Yanchang Formation in Ordos Basin

通过近年来新补充的大量的野外露头及钻井岩心观察和薄片鉴定等资料,对鄂尔多斯盆地延长组沉积体系类型及特征、各期沉积相特征以及湖盆演化进行研究。结果表明,河流沉积、湖泊沉积以及三角洲沉积为区内主要的沉积体系类型。长10期以浅湖亚相和三角洲相沉积为主;长9期发生湖侵,并出现油页岩沉积;长8期湖盆进一步发展,中心以浅湖亚相为主;长7期湖盆发育达到鼎盛,发育张家滩页岩;长6期沉积作用增强,湖泊三角洲建设进程加快;长4+5期发生又一次短暂的湖侵,三角洲建设进程减缓;长3期湖盆开始收缩,发生全区的三角洲建设;长2期湖盆收缩加剧,区内北部大部分冲积平原化,西缘、西南缘、东缘和东南缘具有不同程度的地层剥蚀;长1期盆地内仅残留3个内陆闭塞的浅水湖泊。研究认为,研究区延长组湖盆面积及深湖面积在长7期均达到最大,之后开始逐渐萎缩,长3期湖盆面积急剧减小,长1期湖盆面积达到最小,深湖已基本消失。

Based on a large number of newly additional field outcrops and drilling core observations, thin section identification, the type and characteristics of sedimentary systems, the features of sedimentary facies and the evolution of lake basin of the Yanchang Formation in Ordos Basin were studied. The result shows that the sedimentary systems mainly include river, lake and delta. The 10th member of Yanchang Formation is mainly shallow lake and deltaic sediments. The 9th occurs lake construction, in which the oil shale deposits appear; The study shows that the lake basin further develops in the 8th period and the center is mainly the shallow lake subfacies. The Zhangjiatan shale emerged in the 7th period, in which the lake basin developed to its peak. The sedimentation enhanced in the 6th member of Yanchang Formation, which promoted the construction speed of the lake delta. Another short lake dipping occurred in the 4＋5th period, which slowed down the delta construction process. The lake basin began to gradually shrink and disappear in the 3rd period, which led to the regional construction of delta. The lake basin contracted intensively in the 2nd period, in which most of the northern area become alluvial plains, and the western, southwestern, eastern and southeastern margin have suffered different degree strata denudation. Three inland shallow-water lakes formed in 1st period. The lake basin and deep lake area in the 7th period reached the maximum, then began to shrink gradually, the area in the 3rd period decreased sharply, and in the 1st period reached the minimum, in which the deep lake has basically disappeared.