Matsumoto(1987)による〔『Origin of manganese nodules in the Jurassic siliceous rocks of the Inuyama district, central Japan』(181p)から〕


Middle Jurassic radiolarian siliceous shale and bedded chert of the Inuyama district, central Japan, yield abundant manganese nodules at a particular horizon. The nodules are composed mainly of spherulitic rhodochrosite with subordinate apatite. Spherules are 0.2 mm to1.6 mm in diameter. Carbon and oxygen isotope ratios of rhodochrosite are -5.63‰ to -9.32‰ Peedee belemnite (PDB) and +0.47‰ to -1.85‰ PDB, respectively. Isotopic compositions suggest precipitation of rhodochrosite at 12-23゜C from interstitial water having -0.5‰ to -3‰δ18O standard mean ocean water (SMOW) and under the influence of methane fermentation. Judging from the minor element concentrations and the rare-earth element (REE) patterns through a manganese nodule and surrounding host rocks, Mn contained in the nodules is considered to have been contained originally in the host sediment probably as hydrogenous manganese that later migrated and concentrated into a zone of nodules during burial diagenesis.』

Geologic setting

Occurrence of manganese and dolomite nodules
Bulk mineralogy and chemistry of manganese nodule and host rocks
Chemical composition of rhodochrosite and dolomite
Isotopic composition of rhodochrosite and dolomite
Formation of manganese nodules
Origin of manganese
Comparison with other Japanese manganese deposits
 Distribution of chert-hosted manganese deposits in Japan
 Temporal comparison
 Genetic comparison