Paleoenvironmental reconstruction of the oldest microfossils from the 3.5Ga Pilbara craton, western Australia

西澳大利亚 3.5Ga 皮尔巴拉克拉通最古老微化石的古环境重建

• 批准号: 11691119
• 负责人: MARUYAMA Shigenori
• 金额: $ 8.63万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11691119/
• 关键词: hydrothermalcirculation; microfossi; western Australia, Pilbara; mid-oceanic ridge; Archean; Early .life; barite; photo-synthesis; 世界最古微化石; 海水組成; 地下生物圏; 二酸化炭素濃度; 深海

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.

本历年在澳大利亚皮尔巴拉地区完成了地质绘图和系统取样。它们是：（1）3.5Ga的北极地区，已确认的最古老的微体化石，（2）3.0Ga的Cleaverville地区，（3）2.7Ga的里士满地区，存在浅海相黑色页岩和叠层石。将采集的样品均进行薄切片，并在显微镜下观察。一些化学分析的主要和微量元素的XRF，以及稀土元素的激光ICP-MS。分离的锆石在TIT的激光ICP-MS定年。确定了变质矿物组合，并估算了它们的P-T条件。流体包裹体的研究，以明确早期生命的物理化学环境。结果如下。(1)含微体化石单元是加积杂岩的一部分。(2)重建了微体化石生存的物理化学环境，为2000 m深处富XCO 2的热液系统。(3)微体化石不是蓝藻，而是3.5Ga就已发生一定程度分化的化学化石。(4)微体化石沿着与热液循环有关的断裂系统形成了一个下至沿着800 m的亚海底群落。(5)在3.0 Ga Cleaverville地区发现了新的微化石。它们非常大，保存完好，表明真核生物可能在3.0 Ga诞生。(6)新的微体化石也被确定从3.5 Ga的沉积物。这些化石可能是在浅海环境下开始光合作用的化石。(7)重建了2.7Ga时含叠层石单元的古环境（发表于AGU，2001）。(8)从浅海到深海2.7Ga古沉积物的古环境重建这些微体化石是在这些深海沉积物中新发现的。(9)出版了关于生命和地球历史的简要摘要。

项目成果

Maruyama, S., Isozaki, Y., Nakashima, S., Windley B.F.: "History of the Earth and life. In Geochemistry and the Orign of Life (ed.S.Nakshima et al.)"Universal AcademyPress, Tokyo, Japan (in press). (2002)

Maruyama, S.、Isozaki, Y.、Nakashima, S.、Windley B.F.：“地球和生命的历史。地球化学和生命的起源（编辑 S.Nakshima 等人）”环球学院出版社，东京，日本

Ueno, Y., Yurimoto, H. Yoshioka, H., Komiya, T., and Maruyama, S.: "Ion microprobe analysis of graphite from ca 3.8 Ga metasediments, Isua supracrustal belt. West Greenland: Relationship between metamorphism and carbon is otopic composition"Geochim. Cosmo

Ueno, Y.、Yurimoto, H. Yoshioka, H.、Komiya, T. 和 Maruyama, S.：“Isua 上壳带约 3.8 Ga 变质沉积物中石墨的离子微探针分析。西格陵兰：变质作用与碳之间的关系是

Kitajima, K., Maruyama, S., Utsunomiya, S., Liou, J.G.: "Seafloor hydrothermal alteration at Archean mid-ocean ridge. Journal of Metamorphic"Geology. 19. 583-600 (2001)

Kitajima, K.、Maruyama, S.、Utsunomiya, S.、Liou, J.G.：“太古代洋中脊的海底热液蚀变。变质杂志”地质学。

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

Ueno, Y.、Yurimoto, H.、Yoshioka, H.、Komiya, T.、Maruyama, S.：“西格陵兰伊苏亚表壳带约 3.8 Ga 变质沉积物中石墨的离子微探针分析：变质作用与碳同位素之间的关系

Maruyama, S., Isozaki, Y., Nakashima, S., Windley B.F.: "History of the Earth and life. In Geochemistry and the Origin of Life (ed. S. Nakshima et al.)"Universal Academy Press, Tokyo, Japan (in press). (2002)

Maruyama, S.、Isozaki, Y.、Nakashima, S.、Windley B.F.：“地球和生命的历史。地球化学和生命的起源（S. Nakshima 等编辑）”Universal Academy Press，东京，