西藏羌塘盆地东部中-上侏罗统沉积特征及沉积相划分

CHARACTERISTICS AND SEDIMENTARY FACIES OF THE MIDDLE-UPPER JURASSIC CLASTIC ROCKS IN QIANGTANG BASIN, TIBET

详细野外剖面测量基础上,对羌塘盆地东部中-上侏罗统剖面主要岩类的宏观特征(颜色和构造)、物质组分、结构及磁化率等特征进行系统研究,研究区碎屑岩主要为砾岩、砂岩、粉砂岩和泥岩等岩类,磁化率值呈现低→高→低→高→低(雀莫错组→布曲组→夏里组→索瓦组→雪山组)的规律性变化。综合沉积特征显示雀莫错组和雪山组主要为河流相-河控三角洲相沉积,布曲组为碳酸盐缓坡相沉积为主,夏里组主要为潮坪-泻湖相沉积,索瓦组主要为混积陆棚-泻湖-潮坪相沉积,中-晚侏罗世羌塘盆地古水深在下降的总趋势中呈现浅→深→浅→深→浅的升降旋回,盆地沉积中心由东向西迁移,区域构造演化和全球海平面变化共同控制了盆地沉积面貌。

The middle-upper Jurassic elastic rocks in Qiangtang basin, north Tibet are characterized by their great thickness. In this paper, we report the palaeogeography of the elastic rocks based on a systematic study of the sedimentary characteristics of the middleupper Jurassic in eastern Qiangtang Basin. Our results show that the elastic rocks mainly include conglomerates, sandstones, sihstones and mudstones. The data of magnetic susceptibility manifest two main cycles from low throughhigh andagain to low, from the Quemocuo Formation through the Buqu Formation, the Xiali Formation, the Suowa Formation to the Xueshan Formation. We believe that the Quemocuo and Xueshan Formations were dominantly formed in a river and river delta environment whereas the Buqu Formation was produced in a carbonate ramp setting. In coutrast, the Xiali and Suowa Formations could have been established in tidaldeha or continental shelftidallagoon environment, respectively. Clearly, the eastern Qiangtang basin could have been continually subsiding during the Jurassic. Meanwhile, the sedimentary center of the basin could have been moving westward. The Jurassic sediment environment of the Qiangtang basin could have been controlled by the regional tectonics and global sea level change.