石西地区八道湾组三段辫状河三角洲的识别与沉积特征研究

摘要

The sedimentary facies of 3rd Member of Lower Jurassic Badaowan Formation in Shixi area of Junggar Basin was previously regarded as meandering river delta. The authors consider it to be the product of tractive current under fairly strong hydrodynamic conditions, as evidenced by the texture, sedimentary structure and distribution characteristics of the sandstone. Its sedimentary environment belongs to the braided fluvial delta. Based on a synthetic study of its sedimentary characteristics, the authors identified 2 subfacies and 5 microfacies in the study area, which include the braided delta distributary channel, braided delta flood plain swamp, braided delta subaqueous distributary channel, tributary bay, and mouth bar. The distribution characteristics and evolution processes of sedimentary facies are inferred as follows: during the early stage the water level fell, the study area developed braided delta front; in the middle stage the water level continued falling, the study area developed braided delta plain; in the late stage the water level rose, and the sediments became thinning. The northwest Halaalate Mountain, Delun Mountain and Zhayier Mountain located in the margin of the study area constituted the main material sources.%针对前人提出准噶尔盆地腹部石西地区下侏罗统八道湾组三段为曲流河三角洲沉积的观点,笔者根据碎屑岩的结构、沉积构造及砂体的空间展布等特征,认为八道湾组三段是在较强水动力条件下牵引流沉积的产物,其沉积环境应属于辫状河三角洲沉积.通过对研究区八道湾组三段辫状河三角洲的沉积特征进行综合研究,认为该区辫状河三角洲发育2种亚相和5种微相:辫状河三角洲平原分流河道、河漫沼泽,辫状河三角洲前缘水下分流河道、支流间湾、河口砂坝.并分析了其展布特征与演化过程,推测该区八道湾组三段沉积早期湖平面下降,研究区内发育辫状河三角洲前缘沉积;中期湖平面继续下降,发育辫状河三角洲平原沉积；晚期湖平面上升,沉积物有所变细.西北部哈拉阿拉特山—德仑山及扎伊尔山物源体系是其主要物源区.