Radiolarian Biostratigraphy Of Mélangein Yarlu Zangbo Suture Zone

A sand-mud-dominant sedimentary mélange which is significant to the initial time of India-Asia collision and the close of Tethys Ocean outcrops in the south of Yarlung-Zanapo Suture Zone(YZSZ) in southern Tibet. This thesis is based on radiolarian assembly yielded from the YZSZ mélange, and is aimed at the YZSZ mélange’s geological time range and distribution, paleogeographic outline, recovering of forming process and mechanism. Furthermore, it provides new evidences of collision of India-Asia and evolution of Tethys Ocean.During this research period, the author and his team carried out a lot of stratigraphic work in Chuangde-Beijia section in Gyangze and Sangdanlin Section in Jilong and discovered two different abundant radiolarian assemblies. After systematic authentication and research, we found that Chuangde-Beijia section includes 121 species of 72 genus, and 5 radiolarian biozones are recognized: ①Holocryptocapsa fallax- Tethysetta boesii assemblage zone, ②Holocryptocanium barbui- Trimulus fossilis assemblage zone, ③Guttacapsa gutta zone, ④Diacanthocapsa brevithorax- Excentropylomma cenomana assemblage zone, ⑤ Pseudoacanthosphaera spinosissima- Pseudodictyomitra pseudomacrocephala assemblage zone, ⑥Acaeniotyle starka- Immersothorax cyclops assemblage zone. At the same time, Sangdanlin section include 91 species of 58 genus, and 6 radiolarian biozones are recognized: ①Rhopalosyringium magnificum zone, ②Immersothorax cyclops zone, ③Homeoarchicorys eiformigum zone, ④Mita regina- Phaseliforma subcarinata assemblage zone, ⑤Diploplegma somphum- Phormocyrtis turgida assemblage zone.The radiolarian assembly yielded from sand-mud-dominant matrix of Chuangde section indicates a Campanian age of late Cretaceous, while the radiolarian assembly yielded from rock pieces, which made of conglomerate, sandstone, carbonatite, siliceous rock, demonstrates a broader and older age(Aptian- Turonian). These strata belong to sand-mud-dominant sedimentary mélange of late Cretaceous Zongzhuo formation in the northern sub-zone of Tethys-Himalaya sedimentary zone.Sangdanlin section includes two unconformable formations which is non-siliceous sand-mud-dominant lower Zongzhuo formation(radiolarian reveals a Campanian age of late Cretaceous) and siliceous sand-mud-dominant upper Sangdanlin formation(radiolarian indicates a Thanetian age of Paleocene). The older formation members recognized from Sangdanlin formation show that this formation is not a successive sedimentation but a sedimentary mélange mixed of older strata during the collision of India-Asia in Thanetian.The two contemporaneous-heteropical deposits of Jiachala formation and Sangdanlin formation in Gyangze and Sangdanlin show that the collision of India-Asia has already occurred in the eastern Tibet in late paleocene, while it has not in the western. The collision of India-Asia occurred earlier in the east then later to the west along the YZSZ in Tibet.