2001 Fiscal Year Final Research Report Summary
Paleoenvironmental reconstruction of the oldest microfossils from the 3.5Ga Pilbara craton, western Australia
| Project/Area Number |
11691119
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
地球化学
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
MARUYAMA Shigenori Tokyo Institute of Technology Professor, 大学院・理工学研究科, 教授 (50111737)
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| Co-Investigator(Kenkyū-buntansha) |
KATO Yasuhiro Yamaguchi University Assoc. Professor, 理学部, 助手 (40221882)
TERABAYASHI Masaru Kagawa University Assoc. Professor, 工学部, 助教授 (40243745)
ISOZAKI Yukio University of Tokyo Professor, 大学院・総合文化研究科, 教授 (90144914)
HIROSE Kei Tokyo Institute of Technology Assoc. Professor, 大学院・理工学研究科, 助教授 (50270921)
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| Project Period (FY) |
1999 – 2001
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| Keywords | hydrothermalcirculation / microfossi / western Australia, Pilbara / mid-oceanic ridge / Archean / Early .life / barite / photo-synthesis |
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| Research Abstract |
Geologic mapping and systematic samplings have been completed in the Pilbara area, Australia in this calendar year. They are, (1) the 3.5 Ga old North Pole region where the oldest microfossils have been recognized, (2) 3.0 Ga old Cleaverville region, and (3) 2.7 Ga old Richmond region where shallow marine black shale and stromatolite are present. The collected samples were all thin-sectioned, and observed under the microscope. Some were chemically analyzed in major and trace elements by XRF, as well as REE by laser ICP-MS. Separated zircons were dated by laser ICP-MS at TIT. Metamorphic mineral assemblages were determined and their P-T conditions were estimated. Fluid inclusions were also investigated to make it clear the physico-chemical environment of early life. The results are as follows.
(1) The microfossil-bearing unit forms a part of accretionary complex.
(2) The physico-chemical environment where microfossils were survived was reconstructed ; it was at 2000m deep under XCO2-rich hyfrothermal system.
(3) Microfossils are not cyanobacteria but chemo-fossils which had already differentiated to some extent by 3.5 Ga.
(4) Microfossils formed a sub-seafloor community down to 800m along the fracture system related to hydrothermal fluid circulation.
(5) New micro fossils were found from the 3.0 Ga Cleaverville region. Those are extremely large and well-preserved, suggesting a possibility of birth of eukaryotes at 3.0 Ga.
(6) New microfossils were also identified from the 3.5 Ga seamount-top sediments. These may be fossils which may have begun photo-synthesis under the shallow marine environment.
(7) Paleoenvironment of stromatolite-bearing unit at 2.7 Ga was reconstructed (presented at AGU, 2001 ).
(8) Paleoenvironmental reconstruction of 2.7 Ga old sediments from shallow marine to deep-sea. The microfossils were newly found from those deep-sea sediments.
(9) A brief summary of the history of life and the Earth was published.
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[Publications] Ueno, Y., Yurimoto, H., Yoshioka, H., Komiya, T., Maruyama, S.: "Ion microprobe analysis of graphite from ca 3.8 Ga metasediments, Isua supracrustal belt, West Greenland : Relationship between metamorphism and carbon isotopic composition"Geochim.Cosmochim.Acta.. 66. 153-164 (2002)
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