Integrated study of seafloor methane hydrate and gigantic methane seeps in the eastern margin of Japan Se a

日本海东缘上越海盆存在极高的甲烷通量。在盆地中还观察到浅层气烟囱型天然气水合物和强烈的甲烷渗漏。深层热成因甲烷通过管道（气烟囱）迁移到海底，并积累成大量的天然气水合物矿床。在末次盛冰期发生了大规模的离解，与海平面下降相对应，并引起了严重的环境变化。类似的机制可以解释在奥陶纪-志留纪边界的大规模灭绝。

Extremely high methane flux has been identified in the Joetsu basin, eastern margin of Japan Sea. Shallow, gas chimney type gas hydrates and strong methane seepages have been also observed in the basin. Deep-seated thermogenic methane migrated through conduits (gas chimney) to the seafloor and accumulated as massive gas hydrate deposits. Massive dissociation occurred at the LGM, corresponding to the sea level fall, and caused serious environmental change. Similar mechanism may explain mass extinction at the Ordovician-Silurian boundary.