日本地球惑星科学連合2014年大会

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セッション記号 U (ユニオン) » ユニオン

[U-05_30PO1] 生命-水-鉱物-大気相互作用

2014年4月30日(水) 18:15 〜 19:30 3階ポスター会場 (3F)

コンビーナ:*大竹 翼(北海道大学大学院工学研究院 環境循環システム部門)、鈴木 庸平(東京大学大学院理学系研究科)、白石 史人(広島大学大学院理学研究科地球惑星システム学専攻)、高井 研(海洋研究開発機構極限環境生物圏研究センター)、上野 雄一郎(東京工業大学大学院地球惑星科学専攻)、長沼 毅(広島大学大学院生物圏科学研究科)、掛川 武(東北大学大学院理学研究科地学専攻)、横山 正(大阪大学大学院理学研究科宇宙地球科学専攻)、中村 謙太郎(独立行政法人海洋研究開発機構 (JAMSTEC) システム地球ラボ プレカンブリアンエコシステムラボユニット)

18:15 〜 19:30

[U05-P05] カナダオンタリオ州、ガンフリント層(19億年前)中の初生鉱物と続成作用による変化

*二階堂 映美1掛川 武1 (1.東北大学大学院理学研究科)

キーワード:続成作用, 酸化的環境, 還元的環境, 閉じた系

Some microfossils in the 1.9 Ga Gunflint Formation show clear morphology of aerobic microorganisms. However, carbon isotope compositions of microfossils and other geochemical characteristics suggest the activity of anaerobic microorganisms in the same rock sample. This leads to the skepticism if the 1.9 Ga surface ocean environments were essentially anoxic and oxic environments were very limited.
In order to examine if oxic world were more common or anoxic world were more common, shallow water sedimentary rocks were collected from Kakabeka (the bottom of the Gunflint) and Telly Fox (the top of the Gunflint) areas. The following features were found in the present study. (1) Chemistry of carbonate change into either Fe-rich or Mg-rich from calcite during diagenesis. Fe-rich feature is only found at the bottom of the Gunflint Formation, suggesting wide injection of reduced fluids in sediments. (2) Carbon isotope compositions were similar to cyanobacteria value, and feature of anaerobic bacteria were not detected. This suggests that previous report of carbon isotope compositions of anaerobic bacteria was limited in a few places and not widespread in the Gunflint Formation. Therefore, aerobic microorganism was the major life forms. (3) Sulfur isotope compositions of pyrite range from -2 to +15 per mil, suggesting closed system sulfate reduction. The closed system was most likely isolated oxic seawater from anoxic sediments, probably high sedimentation of SiO2 and CaCO3. In addition, isolated sediments were anaerobic bacterial world, where organic matter from the oxic world was largely consumed.