[B-CG04] Decoding the history of Earth: From Hadean to the present

[BCG04-03] Geochemistry of the Kawame ferromanganese deposit in the Hayachine Belt: Implications for the oceanic environment in the Late Devonian

*Yusuke Kuwahara¹, Koichiro Fujinaga^2,3, Tatsuo Nozaki^4,3,5,2, Junichiro Ohta^3,2, Kazutaka Yasukawa^3,1,2, Kentaro Nakamura¹, Yasuhiro Kato^3,1,2,4 (1.Department of Systems Innovation, School of Engineering, The University of Tokyo, 2.Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 3.Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, 4.Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology, 5.Department of Planetology, Graduate School of Science, Kobe University)

Keywords:Umber, Accretionary complex, Osmium isotopic ratio

It is widely accepted that hydrothermal ferromanganese sediment is a useful recorder of ocean chemistry. Because the ancient ferromanganese sediments were subducted and then accreted onto the continental crust, onshore hydrothermal ferromanganese deposits (termed umbers) are regarded as an important key to understand the chemistry of the ancient ocean. The Late Devonian umber, the oldest umber in Japan, can be observed at the Kawame Quarry in the Hayachine Belt, Northeast Japan. Here we investigate the bulk chemical composition and osmium isotopic composition (¹⁸⁷Os/¹⁸⁸Os) of the Kawame umber. In the presentation, we will report the geochemical features of the Kawame umber and ¹⁸⁷Os/¹⁸⁸Os of the Late Devonian seawater, and discuss their paleoceanographic implications.