准噶尔盆地南缘浅表层砾岩层成因及分布特征

准噶尔盆地南缘浅表层巨厚砾岩层普遍发育,导致浅表层及以下地层地震成像质量差,下伏目的层构造形态及高点难以准确落实。通过对准噶尔盆地南缘新近纪以来构造、沉积演化及古地貌分析,明确浅表层砾岩层地质结构,构建砾岩层成因模式,落实砾岩层宏观分布。研究表明,准噶尔盆地南缘浅表层砾岩层纵向可划分为低速和高速2套砾岩层;受喜马拉雅期多幕构造运动、古构造、沉积物供给量等因素控制,发育横向古凸分割、纵向早期多级扇叠合进积、晚期快速堆积的成因模式;砾岩层宏观分布受车排子古凸起分割,总体发育东部和西部2大冲积扇群,可进一步细分为5大冲积扇,整体南厚北薄,高速砾岩层较厚,低速砾岩层薄,东部冲积扇群受3排正向构造带控制,南北向发育3排砾岩带。

Genesis and Distribution of Shallow Conglomerates in the Southern Margin of Junggar Basin

The hugely thick conglomerates are widely developed in the shallow layers of the southern margin of Junggar basin,which leads to the poor seismic imaging quality of the shallow layers and the difficulties in accurate determination of the structural high and configura?tion of the underlying target zone.Based on the analysis of the structure,sedimentary evoluation and ancient landform in the southern mar?gin of Junggar basin since Neogene,the paper identifies the geological framework,establishes the genetic model and determines the distri?bution of the conglomerate layer.The study shows that the conglomerate in the southern margin of Junggar basin can be divided into low?speed conglomerate and high?speed conglomerate vertically.A geological genetic model of“segmented by the ancient swell horizontally,multistage fan overlapping and progradation in the early period and rapid accumulation in the late period vertically”is established,which was controlled by multistage tectonic movements,paleostructure and sediment supply during the Himalayan period.The conglomerate layer is segmented by the ancient Chepaizi swell,where 2 alluvial fan groups are developed in the east and west,respectively and can be further divided into 5 alluvial fans.The conglomerate layer is thick in the south and thin in the north,among which the high?speed conglomerate is relatively thick and low?speed conglomerate is relatively thin.The eastern alluvial fan group is controlled by 3 rows of positive tectonics and 3 N?S trending conglomerate belts are developed in the eastern fan group.