Japan Geoscience Union Meeting 2016

Presentation information

Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS13] Evolution of the Pelagic Realm

Mon. May 23, 2016 9:00 AM - 10:30 AM 203 (2F)

Convener:*Atsushi Matsuoka(Department of Geology, Faculty of Science, Niigata University), Toshiyuki Kurihara(Graduate School of Science and Technology, Niigata University), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Tetsuji Onoue(Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University), Katsunori Kimoto(Japan Agency for Marine-Earth Science and Technology), Tatsuo Nozaki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Hayato Ueda(Department of Geology, Niigata University), Kenta Kobayashi(Department of Geology, Faculty of Science, Niigata University), Takashi Hasegawa(Division of Global Environmental Science and Engineering, Graduate School of Natural Science and Technology, Kanazawa University), Chair:Atsushi Matsuoka(Department of Geology, Faculty of Science, Niigata University), Toshiyuki Kurihara

9:30 AM - 9:45 AM

[MIS13-03] Reconsideration of sedimentary place of the Triassic Muyinhe Formation in the Changning–Menglian belt of Southwest China

*Tsuyoshi Ito1, Xin Qian2, Qinglai Feng2 (1.Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 2.China University of Geosciences, Wuhan)

Keywords:Geochemistry, Triassic, siliceous rock, radiolaria, Paleotethys, Changning–Menglian belt

Siliceous rocks of the Triassic Muyinhe Formation in the Changning–Menglian belt in southwestern Yunnan Province in Southwest China had been considered to be pelagic deposits. We observed them and analyzed their geochemistry, and recosidered the sedimentary place.
The observation revealed that the siliceous rocks are characterized by inclusion of abundant radiolarian test (e.g., Triassocampe Dumitrica, Kozur, and Mostler, Pseudostylosphaera Kozur and Mostler, Eptingium Dumitrica, and Paroertlispongus) and the lack of rhythmical bedding. The geochemical results are as follows: the samples have high concentrations of SiO2; most of the samples were plotted in the non-hydrothermal field on the Al–Fe–Mn diagram; most of the samples were plotted in the continental margin field on the Fe2O3/TiO2–Al2O3/(Al2O3+Fe2O3) and (La/Ce)N–Al2O3/(Al2O3+Fe2O3) diagrams. In addition, the samples show a flat rare earth element pattern normalized to North America shale composite.
These observational and geochemical results strongly suggest that the siliceous rocks are unlikely to represent pelagic deposits, indicating that the extent of the pelagic ocean basins in the Paleotethys during the Triassic is probably less than previously believed. These non-pelagic deposits may represent the closure stage of the Paleotethys.