Japan Geoscience Union Meeting 2022

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[J] Oral

B (Biogeosciences ) » B-CG Complex & General

[B-CG05] Decoding the history of Earth: From Hadean to the present

Sun. May 22, 2022 1:45 PM - 3:15 PM 304 (International Conference Hall, Makuhari Messe)

convener:Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo), convener:Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Katsuhiko Suzuki(Submarine Resources Research Center, Japan Agency for Marine-Earth Science and Technology), convener:Kentaro Nakamura(Department of Systems Innovation, School of Engineering, University of Tokyo), Chairperson:Yuki Tomimatsu(Department of Earth and Planetary Sciences, Kyushu University), Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo)

2:15 PM - 2:30 PM

[BCG05-15] Conodont and radiolarian biostratigraphic age constraints on Carnian (Upper Triassic) chert-hosted stratiform manganese deposits from Panthalassa: Formation of deep-sea mineral resources during the Carnian pluvial episode

★Invited Papers

*Yuki Tomimatsu1, Tetsuji Onoue1, Manuel Rigo2 (1.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, 2.Department of Geosciences, University of Padova)

Keywords:Stratiform manganese deposit, Chert, Conodont, Radiolaria, Carnian pluvial episode, Wrangellia Large Igneous Province

Numerous stratiform manganese deposits occur in the Permian to Jurassic bedded chert successions of the Jurassic accretionary complexes of the Chichibu, Mino–Tamba, and North Kitakami belts, which is considered to have accumulated in a pelagic, open-ocean setting within the Panthalassa Ocean. Although a number of previous studies investigated the depositional age and process of Permian and Jurassic manganese deposits in these accretionary complexes, very few studies have focused on the Triassic bedded chert–hosted stratiform manganese deposits. We thus investigated the occurrence and stratigraphic distribution of Triassic stratiform manganese deposits in Japan, constraining their ages by means of integrated conodont–radiolarian biostratigraphy. This study investigated the stratiform manganese deposits in the following four accretionary complexes; (i) the Takahira section, in the Chichibu Belt; (ii) the Tamaiwa section in the Tamba Belt; (iii) the Kanzaki section in the Mino Belt; and (iv) the Otaniyama section in the North Kitakami Belt. In these sections, the Triassic stratiform manganese deposits range in thickness from 30 to 150 cm and generally occur intercalated within chert sequence. The chert samples from each studied section yielded abundant conodonts and radiolarians representing the same faunal assemblages. On the basis of the conodont and radiolarian biostratigraphies, the depositional age of the Triassic manganese deposits was constrained to the latest Julian to earliest Tuvalian (mid-Carnian).This age indicates that the formation of the Triassic manganese deposits occurred contemporaneously with the last eruptive phase of the Wrangellia Large Igneous Province (LIP) volcanism and subsequent changes in the deep-sea redox conditions in the Panthalassa Ocean during the Carnian pluvial episode. Therefore, the Carnian manganese deposits may have been formed with the hydrothermal processes associated with the Wrangellia LIP volcanism and/or the changes in redox conditions on the ocean floor.