The paper, for which Research Scientist Azami is the first author and was co-authored by Senior Research Scientist Fujinaga, Principal Research Scientist Kato, and others, has been published in Ore Geology Reviews. 

 In northeastern Hokkaido, Japan, a geological unit known as the Tokoro Belt, composed of rocks formed on the seafloor during the Jurassic to Cretaceous periods, is distributed. The Tokoro Belt contains many iron oxide and manganese oxide deposits, which were previously mined. 

 This study revealed that the iron oxide deposits were formed by hydrothermal activity at mid-ocean ridges during the Jurassic period, while the manganese oxide deposits were formed by hydrothermal activity at hotspot seamounts during the Cretaceous period. Furthermore, it was found that the manganese oxide deposits formed during the midst of a major oceanic anoxic event known as OAE1a. 

 Although the extent of oceanic deoxygenation during OAE1a was previously unclear, this study has clarified that the deep-sea environments of pelagic regions in the Pacific Ocean were not deoxygenated. 

 The paper can be accessed here. 

 The press release can also be accessed here.