Abstract
Mineralogical and chemical compositions of carbonate nodules associated with methane hydrates, which were collected from the Sea of Japan by MD179 research cruise during the June 2010, were investigated to clarify the mechanism of the formation of the nodules. The predominant minerals of the nodules were aragonite and calcite with subordinate amounts (10-30%) of quartz, feldspars, pyrite and clay minerals such as illite. The calcites are high-Mg calcite with an average of about 4% (maximum 8%) MgO. The average sodium content (2,500m/g) of aragonites in the nodules is about half as compared with that of aragonites which are formed under ordinary shallow marine environments, indicating the different mechanism of aragonite formation in the carbonate nodules associated with methane hydrates.
