[M-ZZ46] Marine Manganese Deposits: Origin, Exploration, and Development

[MZZ46-P01] Detrital minerals in hydrogenetic ferromanganese crusts as an alternative tool for archiving marine geological environments

*Akira Usui¹, Takashi Ito², Hirokuni Oda³, Hitoshi Hasegawa⁴ (1.Marine Core Research Center, Kochi University, 2.Ibaraki University, 3.AIST, 4.Kochi University)

Keywords:paleoceanography, manganese crusts, ocean sediments

Since iron and manganese oxides have been precipitated in the world oceans since 20Ma or older, most of the deep-sea floors are covered with ferromanganese crusts and nodules. The hydrogenetic ferromanganese crusts are in particular noted as potential paleoceanographic archives as well as future metal resources. They can be used as a tape recorder for deciphering the historical changes in marine geological environments, as indicators of environmental changes. We have reported laminated structure or compositional changes of major chemical composition on various scales and their regional changes. However, most of the data that read the variations are growth structure of major iron-manganese oxide only, which is the principal hydrogenetic components. In this study, we paid special attention to other minor components useful to read the history. The goal is to utilize better techniques for further research and development for more reliable criteria for identification of mineral particles similarly to marine sediment cores. The target materials are the substrate rocks on the seafloor, terrigenous mineral particles (river output, eolian dust), remains and traces of organisms, extraterrestrial materials, volcanic ash, hydrothermal precipitates, and authigenic precipitates. We tried to identify the materials using high-resolution optical/electron microscopes, microscale analysis, X-ray CT, analysis software, acid leach, gravity separation, etc. As a result, together with the earlier reports on magnetic minerals, we found that microfossil assemblage, cosmic spherules, weathering products, chemical precipitates. We have several issues in the processes of separation, age models, and identification of the factors of the spatiotemporal fluctuations, but expect better future in archiving the paleoenvironmental information from the detrital components in marine manganese deposits.