--> --> Abstract: Provenance of Sandy Sediments and Their Possibility of Hosting Gas Hydrate in the Eastern Margin of Japan Sea, by Takashi Uchida, Isao Takashima, Tomoya Ito, and Ryo Matsumoto; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Provenance of Sandy Sediments and Their Possibility of Hosting Gas Hydrate in the Eastern Margin of Japan Sea

Takashi Uchida1; Isao Takashima1; Tomoya Ito1; Ryo Matsumoto2

(1) Earth Science and Technology, Akita University, Akita, Japan.

(2) University of Tokyo, Tokyo, Japan.

The MD179 project was undertaken in the eastern margin of Japan Sea by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments older than 300 ka in order to develop geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles.

Sediment samples below the seafloor were obtained in the Umitaka Spur, the Joetsu Channel and other areas by the UT09 and KY09-05 cruises in 2009 as well as the MD179 cruise. They have been mainly composed of muddy sediments with a small amount of sandy sediments. Thin sandy layers are intercalated with thick muddy sediments, which are often strongly bioturbated with burrows and pellets. Those sandy sediments consist of fine- to medium-grained sand grains, and are sometimes tuffaceous. The results of pore-size distribution measurements and thin-section observations indicate that porosities of muddy sediments are around 50 % but those of arenites range from 42 to 52 % of which mean pore sizes and permeabilities are larger than those of siltstones and mudstones. While the presence of gas hydrate in intergranular pores is not confirmed, the soupy occurrence in recovered sandy sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands.

So as to know the time of deposition of coarse-grained sediments, thermoluminescence (TL) dating of constituent quartz grains and grain-size distributions are analyzed. It has been inferred that methane in gas hydrate and methane plumes are of thermogenic origin in the study area, which show the occurrences of mounds, nodules, veins, pore fillings etc. Permeable intergranular pore systems of arenite sand, fractures, faults as well as gas chimneys may have played an important role as conduits for deep thermogenic hydrocarbon gas migration.

The geological modeling of the gas hydrate formation and evolution system is concerned for energy resource potential in the Japan Sea as well as the Nankai Trough areas. Although the chimney type accumulation may be dominated and is characterized by massive concentration of nodular and fracture filling hydrates, the sandy sediments hosting gas hydrate in their intergranular pore system may likely occur.

This study was performed as a part of the MH21 Research Consortium on methane hydrate in Japan.