The Carboniferous-Triassic Sediment And Biota Evolutions In Tibet And Their Geological Significances

The spatio-temporal distributions and evolutions of the Caboniferous-Triassic sediment and biota in Tibet and West Yunnan are studied. And their origins and geological implications are discussed too. The sequence of the Pangduo Group in the Lhasa area was further described; the lithostratigraphic formations at the Deriangma-Xiala section in Xainza area was clarified; A new Triassic section was discovered at Dibucuo in Cuoqin area, and the Jiangrang Formation was suggested to it; The Dibucuo Formation and the Jianzhanong Formation was revised to be the Late Triassic -Early Jurassic instead of the Late Permian previously. Based on the investigation and analyse on more than 10 sections on the Qinghai-Xizang(Tibet) Plateau and West Yunnan, the sequence through the Carboniferous to the Triassic was revised.The conodont sequence from the Late Carboniferous to the Late Triassic was primarily established in the Gongdise-Nyainqentanglha Stratigraphic Region. The Late Carboniferous Neognathodus fauna, the Middle Permian Vjalovognathus fauna and Rabeignathus fauna, the Late Permian Clarkina fauna were discovered. The Triassic conodont was found in the Zuozuo Formation in Shiquanhe area. Sereral conodont zones through the Early Triassic to the Late Triassic were recognized in the Jiangrang Formation in the Cuoqin area.The mixed palynological assemblage of the lower part of the Yongzhu Formation, Xianza District, Northern Xizang (Tibet) was found. The Late Triassic-Early Jurassic palynological assemblage was found from the Dibucuo Formation and the Jianzhanong Formation, which were thought to be Late Permian previously. The brachiopod fossils were systemically collected at the Deriangma-Xiala section in Xainza area, and its correlation with conodont zones was recognized too. And based on the correlation between the conodonts and brachiopods, the conflict of the division of the Late Carboniferous-Early Permian between the Gondwana and Tethys was discovered. The reason and solution of the conflict was discussed theoretically too.The characteristics, the spatio-temporal distributions, origin and tectonic backgroud of the glaciomarine deposition, diamictite, pebbly slates were studied too.Based on the analyse of the form, structure and their provincilism of the coral, brachiopod and conodont at the Deriangma-Xiala section, the biota through the Early Carboniferous to the middle Permian displayed a series of the Warm fauna-mixed fauna-Cool fauna-mixed fauna-Warm fauna. The analyse on the characteristic of the deposition and sedimentary facies showed the same evolutionary trend. Based on the spatio-temporal distributions and evolutions of the Caboniferous-Triassic sedimentary assemblage and biota, the relationships and effects among the Caboniferous-Permian Ice Age, the Gondwana glacier, and the rift system at the northern margin of the Gondwana were discussed.Based on the spatio-temporal distributions and evolutions of the Caboniferous-Triassic sedimentary assemblage and biota, the Qiangtang Block was thought to be at the northern margin of the Gondwana Continent during the Late Carboniferous to the Early Permian. It was pushed northwards during the Middle and early of Late Permian by the rift of the South tethys. At the end of the Late Permian, it was collided to be the southern margin of the Euro-Asia Continent. During the Triassic, it underwent the the transgression and regression of the sea-level, at the end of the Triassic it was uplifted to be land again with the Gondise Block. Based on the analyse of the stratigraphic sequence of the Triassic and its covering strata and the Index of the Organic Metamorphic Maturity of conodont, the Triassic of the northern margin of the Gongdise-Nyainqentanglha Stratigraphic Region and the South of the Qiantang Stratigraphic Region was a promising target for the oil exploration.