准噶尔盆地南缘侏罗纪沉积相演化与盆地格局

Sedimentary facies evolution and basin pattern of the Jurassic in southern margin area of Junggar Basin

通过对准噶尔盆地南缘侏罗系5条剖面的沉积特征对比,结合钻井资料和地震资料,确定了准噶尔盆地南缘侏罗纪盆地边界、沉积相演化及盆地格局。头屯河剖面和后峡剖面的沉积相对比及古流向测量表明二者在早、中侏罗世形成于同一沉积体系。在早、中侏罗世,沉积相逐渐从以辫状河—三角洲—湖泊相为主过渡到以河流—湖泊相为主,沉积水体逐渐变浅;其中三工河组沉积时期盆地沉积范围达到最大,西山窑组沼泽相发育,车排子—莫索湾凸起自西山窑组沉积时期开始构成相对高地并遭受部分剥蚀。早、中侏罗世的盆地边界至少位于后峡以南附近,此时不存在地理分割明显的天山山脉。晚侏罗世—早白垩世早期,沉积相从辫状河—滨浅湖相为主迅速演变为以辫状河—冲积扇相为主。在此期间盆地边界明显向北迁移,天山山脉明显隆升并造就天山南北沉积环境的巨大差异,博格达山构成盆地南缘的又一重要物源体系。

Mainly, the basin boundary of the Jurassic in southern margin area of Junggar Basin, the sedimentary facies evolution and basin pattern are determined by analysis of sedimentary facies correlation of 5 sections of the Jurassic combined with seismic data and well data. The sedimentary facies correlation and paleocurrent measure of Houxia section and Toutunhe river section show that the two sections were formed in the same sedimentary system during the Early-Middle J urassic. The sedimentary facies of southern margin of Junggar Basin changed from braided river-braided river delta-lacustrine facies to fluvial-lacustrine facies during the Early-Middle Jurassic. During the sedimentary period of Sangonghe Formation of Middle Jurassic, the basin boundary migrated southward to Houxia area and the sedimentary area came to be the biggest. Swampy facies was well developed during the sedimentary period of Xishanyao Formation, and the Chepaizi-Mosowan horseback came into a relative highland from then on.The Junggar Basin and Tarim Basin were not geographically separated during the Early-Middle Jurassic by the Tianshan Mountains. From the Late Jurassic to the early age of Early Cretaceous, the sedimentary facies was characterized by rapid evolution from braided river facies-shore-shallow lacustrine facies to braided river-alluvial fan facies.The distribution of the alluvial fan conglomerates of the Upper Jurassic shows the tectonically active background and obvious uplift of the Tianshan Mountains during the Late Jurassic to the early age of Early Cretaceous, which led to the widely different sedimentary environments of the Tarim Basin and southern margin area of the Junggar Basin. The southern Junggar Basin shrank northward obviously during the Late Jurassic to the early period of Early Cretaceous and the Bogeda Mountains became another important provenance system of southern margin area of Junggar Basin.