Relationship between crustal degassing and microbial mineralization in active mud volcanoes, hydrocarbon seeps, and other environments
【研究キーワード】
authigenic carbonate / noble gas / helium isotopes / protodolomite / EPS / microbial methane / thermogenic methane / Mud volcano / Methane / Dolomite / Noble gas / Stable Isotope
【研究成果の概要】
During this year, we have completed analysis of noble gas inclusions in methane derived authigenic carbonates from samples recovered in shallow sediments in both Joetsu Basin, Sea of Japan, and from offshore Sakhalin Island, in Tatar Strait and Brejo du Espinho, Brazil (Snyder and Takahata, AORI, Univ. Tokyo). These samples show different amounts of mantle-derived helium as well as helium derived in the crust, providing some information as to the origin of gases that produced the carbonates, as well as where they were formed. In addition, Shiraishi (Hiroshima Univ.) prepared microdolomite sections using focused ion beam (FIB), followed by observation using scanning transmission X-ray microscopy (STXM) and a transmission electron microscopy (TEM). These sections reveal inclusions of extracellular polymeric substances (EPS), as well as protodolomite inclusions. Two field excursions were taken this year to the Mobara gas field area in Chiba Prefecture (Snyder, AORI; Matsumoto, Meiji U.; and Tomaru, Chiba U.) to collect gas samples as well as sediment and water near the seep sites that may potentially yield microbial carbonates. Sample analysis is still ongoing, although we have determined the stable carbon isotope signature of carbon dioxide present in the gases, which we will later compare with the stable isotopic composition of the associated microbial carbonates
【研究代表者】