尼玛盆地南部古近系牛堡组沉积特征及其地质意义

对西藏尼玛盆地南部查昂巴古近系牛堡组实测剖面的沉积相研究识别出2种沉积相类型:扇三角洲相与湖泊相.根据沉积物岩性、结构、构造、颜色等特征,扇三角洲相可进一步划分为扇三角洲平原(包括辫状河道与河道间湾2个沉积微相)、扇三角洲前缘(包括水下分流河道与分流间湾2个沉积微相)与前扇三角洲3个沉积亚相;湖泊相可进一步划分为滨湖、...

Sedimentary Characteristics and Geological Significance of Paleogene Niubao Formation, Southern Nyima Basin

Two types of sedimentary facies,fan delta facies and lacustrine facies,are identified in measured section of the Paleogene Niubao Formation at Chaangba area,Nyima basin,Tibet.According to the lithology,structure and color of sediments,the fan delta facies can be subdivided into fan delta plain subfacies（including braided channel macro-ficies and riverway inter-bay macro-facies）,fan delta front subfacies（including underwater distributary channel macro-facies and distributary inter-bay macro-facies）,and pre-fan delta subfacies;while the lacustrine facies can be subdivided into shore lake subfacies,shallow lake subfacies and semi-deep（or deep） lake subfacies.The finding of ripple index and stripping lineation of sandstones in fan delta front subfacies indicated that the sediments of Niubao Formation of Chaangba section come from the Gaize-Selingcuo thrust block,southern Nyima basin.Chaangba section can be divided into three deposition cycles： cycleⅠas an upward-coarsening depositional cycle,is composing of lacustrine facies transition to fan delta facies;cycle Ⅱ is composing of a ＂coarse-fine-coarse＂ sedimentary cycle;cycle Ⅲ is also composing of a ＂coarse-fine-coarse＂ sedimentary cycle,transition from fan delta facies to lacustrine facies.The sedimentary cycle subdivision of the Paleogene Niubao Formation at Chagangba area has great significance for the research of uplift mechanism,palaeogeograhpic reconstruction and oil exploration of Qinghai-Tibet plateau.