1:45 PM - 2:00 PM
[MIS09-13] A working hypothesis on the accumulation of methane hydrate in gas chimneys developed in the eastern margin of Japan Sea
Keywords:shallow methane hydrate, carbonate nodule, Japan Sea, drilling, active fault
A series of observation of the recovered cores by necked eyes, X-ray CT photography and experiments such as sieving of carbonate nodules from mud clarified the close association of carbonate nodules and gas hydrate in the sediments of gas chimneys. This combination of carbonate nodules and gas hydrate occurs periodically and the calculated cycles are around 15 ky.
Preceding studies clarified the following subjects.
1. Carbonate nodules in the gas hydrate field of Japan Sea are interpreted to be formed in the sulfate-methane interface (SMI).
2. The carbon and oxygen isotopic ratios of the carbonate nodules demonstrated the thermogenic methane from the deep largely contributes the formation of the nodules.
3. Active faults and folds develop in the mobile belt of the eastern margin of Japan Sea and form many topographic highs.
Combining the above-mentioned preceding studies and acquired data, we propose the following working hypothesis: Methane gas has been periodically supplied from the depth by the movements of active faults, and the gas repeatedly formed both carbonate nodules and methane hydrate at around the depth of SMI that existed at or in the shallow depth of the seafloor.
Further studies are required if the proposed mechanism of the accumulation of shallow gas hydrate would be applied generally to the other gas hydrate-bearing topographic highs that distribute in the eastern margin of Japan Sea.
We express sincere gratitude to all the persons in JOGMEC who engaged to operate R/V Hakurei in 2014. X-ray CT photos of cored samples are taken under the cooperation program between Kochi Core Center and Akihiro Hiruta (14B013). This research is a part of the shallow methane hydrate exploration project of METI.