日本地球惑星科学連合2018年大会

講演情報

[JJ] ポスター発表

セッション記号 B (地球生命科学) » B-CG 地球生命科学複合領域・一般

[B-CG09] 地球史解読:冥王代から現代まで

2018年5月22日(火) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:小宮 剛(東京大学大学院総合文化研究科広域科学専攻)、加藤 泰浩(東京大学大学院工学系研究科システム創成学専攻)、鈴木 勝彦(国立研究開発法人海洋研究開発機構・海底資源研究開発センター)

[BCG09-P07] 27億年前の浅海堆積物における炭素同位体負異常の起源

*Kim Beomsik1上野 雄一郎1,2,3Gilbert Alexis1,2 (1.東京工業大学理学院地球惑星科学系、2.東京工業大学地球生命研究所、3.海洋研究開発機構)

キーワード:太古代、炭素同位体、ストロマトライト、メタン資化菌、Organic haze

Sedimentary organic carbon in some Late Archean rocks are anomalously depleted in 13C (δ13Corg = -45 to -60‰). The origin of the isotope anomaly is still unknown and is possibly resulted from biological uptake of methane (methanotrophy) or deposition of hydrocarbon haze. To test the hypotheses, small-scale isotopic analyses of both inorganic and organic carbon were conducted for various lithologies of 2.7 Ga sedimentary rocks in Fortescue Group, Western Australia. For this purpose, a new analytical method was developed for measuring small samples. As a result, low δ13C organic matter occurs not only in stromatolite as previously pointed out, but also in black laminated mud. Also, the δ13Corg seems not correlated with δ13Ccarb value as opposed to the case expected when methanotrophs are active because methanotrophs typically produce not only very 13C-depleted organic matter but also CO2. These results do not support the methanotrophy scenario. Furthermore, a relationship between δ13Corg value and TOC contents is consistent with a mixing of two organic end-members with different isotopic ratios. The observed δ13Corg-TOC trend appears to occur in each lithology of the sedimentary rocks, suggesting that the source of the low δ13Corg distributed uniformly irrespective to the depositional environment. This may suggest that the anomalously 13C-depleted organics could have been deposited from atmosphere at about 2.7 Ga.