准噶尔盆地百口泉油田八道湾组三段辫状河三角洲的识别与沉积特征

THE BRAIDED FLUVIAL DELTAIC DEPOSITS IN THE 3RD MEMBER OF BADAOWAN FORMATION AND THEIR DEPOSITIONAL CHARACTERISTICS,BAIKOUQUAN AREA,JUNGGAR BASIN

针对前人提出准噶尔盆地百口泉地区下侏罗统八道湾组三段为曲流河三角洲沉积的观点,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,其沉积环境属于辫状河三角洲沉积。通过对研究区沉积特征进行综合研究,认为该区辫状河三角洲发育3种亚相和6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,辫状河三角洲前三角洲泥。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,研究区内主要发育辫状河三角洲前缘和平原沉积;八道湾组三段沉积晚期,湖平面继续下降,主要发育辫状河三角洲平原沉积。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。

Previous studies suggested that the 3rd Member of Badaowan Formation of the Lower Juras sic in the Baikouquan area of Junggar Basin be a meandering fluvial delta. According to the texture, sedimentary structure and distribution pattern of the sandstones, the authors believed that it is the product of a traction current with fairly strong hydrodynamic conditions and belonging to a braided fluvial delta. Three subfacies and six microfacies were recognized, including subfacies of distrihutary channel, flood plain and swamp, subaqueous distributary channel, interdistributary bay, mouth bar and prodelta clay. Based on the distribution pattern of sedimentary facies and its evolution, it is re vealed that the braided fluvial deltaic system was formed during a water level falling period. In the early stage, the study area was occupied by the braided delta front and braided delta plain; and in the middle stage, the water level continued to fall, the study area was covered by a braided deltaic plain. The northwest Halaalate Mountains, Delun Mountains and Zhayier Mountains were the main prove- nance of sediments.