准噶尔盆地西北缘八区下侏罗统八道湾组, 大多数人认为属于辫状河沉积。笔者通过对研究区岩石类型、特征、沉积相标志研究后认为, 八道湾组沉积属于辫状河三角洲和湖相沉积体系, 并对八道湾组沉积相展布与演化特征进行了系统研究, 论证了该区继晚三叠世末期的湖平面大幅度下降, 伴随湖盆的衰亡, 八道湾组进入早期( J₁b₅³) 广泛的沼泽沉积环境, 随着泥沙的带入, 沼泽逐渐消亡, 而河流作用加强, 地层逐渐由东向西超覆, 主要发育辫状河沉积; 至J₁b₅ 亚期晚时( J₁b₅¹) 湖平面开始迅速上升, 发育了大片的浅湖及辫状河三角洲沉积环境; 在J₁b₄ 亚期湖平面又迅速下降, 导致浅湖沉积退出研究区; J₁b ₂₊₃亚期再次发生湖侵作用, 以大面积的浅湖沉积为特征; 而J₁b₁ 亚期伴随着湖平面的再次下降, 河流作用逐渐减弱, 泥质沉积日渐增多, 在八道湾组末期重新又形成了大片的沼泽沉积环境。

The sedimentation of Badaowan Formation in the 8th block in northwest margin of Junggar Basin is regarded as braided river facies. Based on the analysis of the rock type, features and sedimentary facies marks, it is believed that Badaowan Formation is braided river delta and lacustrine sedimentation. The sedimentary distribution and evolution of Badaowan Formation are systematically studied. The result shows that the lake level descended since Late Triassic and swamp deposit widely developed in Badaowan Formation by the extinction of the lake basin, with the inputting of alluvium and the shrinking of swamp, strata overlapped from east to west and braided river developed; shallowlacustrine and braided river delta developed well with the ascending of the lake level in sub-stage of J₁b₅¹; the lake level descended swiftly since the sub-stage of J₁b₄, which resulted in the extinction of the shallow lacustrine in the study area; during the sub-stage of J₁b ₂₊₃, lake transgression emerged once more, and it was characterized by a large scale of shallow lacustrine; the lake level descended again since the sub-stage of J₁b₁, shale increased with the attenuation of fluviation, and swamp widely developed at the last stage of Badaowan Formation.