Keywords:gas hydrate, Japan Sea, gravel
Some subseafloor core samples were obtained in the scientific cruise HR14 performed by the JOGMEC-Hakurei in the eastern margin of Japan Sea. Sediments in most of the sites are mainly composed of muddy fine clastics, and can be often found accompanied by a small amount of very fine to medium grained sandy layers, which are usually observed as thin laminations in muddy layers. The gravel layer was observed thicker than 20 cm associated with the massive methane hydrate layer longer than 130 cm in the RC1403 (Sec. 7). Over than 1,100 gravels were obtained, of which major size, minor size, aspect ratio, roundness, sphericity, lithology and color were investigated. These are generally pebble (average 8.29mm). They are composed only of very well-rounded, greyish white to dark grey calcareous mudstone. According to the probability plot of their grain-size distribution, it consists of one segment showing the normal distribution, which may indicate gravel transportations by a high energy flow.
This research is a part of the METI project entitled "FY2014 promoting research and development on methane hydrate."