准噶尔盆地南缘古近纪—新近纪前陆盆地沉积格局与演变

Depositional setting and evolution of the Paleogene—Neogene foreland basin of southern margin of Junggar Basin

针对准噶尔盆地南缘古近系和新近系碎屑岩沉积体,运用野外露头宏观分析与岩心、薄片微观描述来"定岩相和沉积相";依据地震相的不同特点及相变的不同位置,刻画湖岸线演化,从而对沉积体"定边界";根据重矿物组合特征及砂岩等厚图来"定主次物源"的方法,综合研究前陆盆地的沉积相特征。在此基础上,分析了准噶尔盆地南缘湖盆沉积格局与演变,认为准噶尔盆地南缘古近系紫泥泉子组沉积时期,湖平面较低,天山山前带发育4个规模较大的扇三角洲朵状体;至安集海河组沉积时期,湖平面上升,山前带扇三角洲发生退积,仅沉积3个规模变小的朵状体,霍尔果斯地区扇三角洲朵状体不发育。新近系沙湾组沉积时期,由于逆冲推覆构造作用,山前带地形高差大、坡度陡且气候干旱,随着湖平面的迅速下降,山前带发育更大规模进积型扇三角洲沉积。准噶尔盆地南缘古近系—新近系2个主要物源分别是中部东湾—吐谷鲁—玛纳斯背斜、西部西湖—独山子背斜;2个次要物源分别为东部呼图壁背斜和中西部霍尔果斯背斜,此4个物源流向是由南向北。北部卡因迪克地区则是来自前陆隆起区的重要物源。

Good ways are found in studying clastie deposits of the Paleogene and Neogene in southern margin of Junggar Basin. The ways are ① Lithofacies and sedimentary facies are distinguished by outcrop analyses and core and thin section description, ② The boundaries of deposits are identified by recognition of shoreline evolution according to different characteristics of seismic facies and different locations of facies change and ③ The main and minor provenances are distinguished by characteristics of heavy mineral assemblages and isopach maps of sandstones. Characteristics of sedimentary facies have been studied by this comprehensive method. The depositional framework and evolution of the southern margin of Junggar Basin were analyzed on this basis. The results indicate that during the deposition of the Paleogene Ziniquanzi Formation, 4 large scale fan delta deposits were developed in thrust belt of the Tianshan Mountains and the lake level was lower. During the deposition of the Anjihaihe Formation, 3 fan delta deposits with decreasing sizes were developed in front of the Tianshan Mountains due to the lake level rising and the fan delta retrogration. Fan delta was not developed in Huoerguosi area. During the deposition of the Early Neogene Shawan Formation, fan deltas with larger scales were developed in front of the Mountains, the topography differences were large, the slope was steep and the climate was arid due to lake level quick falling. There are 2 main sedimentary provenances and 2 minor ones from the Paleogene to Neogene in southern margin of Junggar Basin. The main provenances are the Dongwan-Tugulu-Manas anticline in central area, the Xihu-Dushanzi anticline in western area. The minor sedimentary provenances are respectively the Hutubi anticline in eastern area and the Huoerguosi anticline in central western area. These four provenances are distributed in south-north direction. There is a very important provenance in Kayindike area whieh is from the foreland uplifting area.