Niu Z.-J.,Yichang Geological Survey Center |
Duan Q.-F.,Yichang Geological Survey Center |
Wang J.-X.,Yichang Geological Survey Center |
He L.-Q.,Yichang Geological Survey Center |
Bai Y.-S.,Yichang Geological Survey Center
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2010
The studied area is situated at the origin of the Yangtze River in the Tanggula Mountain of southern Qinghai, which was a part of the Qamdo Block of the East Tethyan tectonic domain during the Late Palaeozoic and is bounded by the Jinshajiang suture to the north and the Lantsang-Lungmo Co suture to the south. The Permian strata is widespread in the area with various sedimentary facies, and separated by numerous and complicated faults, especially Lower Permian influenced by volcanic activity. As a result of complex regional tectonics and depositional types, there has been much controversy over the Lower Permian (Cisuralian) classification and correlation, which mainly involves issues including succession, age and regional correlation of volcanic rocks. According to the study of lithographic association of sedimentary environment and fauna of lithostratigraphical unit (especially volcanic rocks), the sequences in volcanic-sedimentary setting are refined in this paper. The Jiushidaoban and Nuoribagaribao formations are diachronous in southern Qinghai according to the fusulinid data. The Permian succession indicates that the Zharigen Formation composed mostly of carbonate rocks occupied the main part of the southern Qinghai, belonging to a stable platform during early stage of the Early Permian. The Luodianian strong volcanic eruption led to a depositional differentiation, forming the Qadikao Formation and contemporaneous Nuoribaribao Formation. As a result of volcanic product and sedimentary process, a complex volcanic-sedimentary landform occurred on sea floor and controlled the distribution of sedimentary facies. Four sedimentary types were recognized based on detailed field mapping and analysis of lithographic association. Jiushidaoban Formation mainly characterized by carbonate rock is widespread in southern Qinghai, which is a representative of platform facies during the intermission period between volcanic activities, which shows that the complex palaeogeographic structure of alternate volcano island and shallow marine has been transferred into a uniform and stable shallow-water carbonate platform since Xiangboan.