丸山・廣瀬・上野研のメンバー

澤木　佑介/ Sawaki Yusuke

卒業論文タイトル：

スコットランド、南中国の地質

修士論文タイトル：

Environmental change in Ediacaran period :estimated from radiogenic Sr isotope ratios preserved in strata at Three Gorges, South China 　　　　　　　　　　　　　　　　 　　　　　　　　　　　　　　　　

博士論文タイトル(Ph-D thesis)：

Surface environment in the Ediacaran and the Cambrian: Evidenced from Sr and Ca isotope ratios.

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Affiliation and Contact
Present
東京工業大学　理工学研究科　地球惑星科学専攻　Department of Earth and Planetary Science, Tokyo Institute of Technology.
in the Past
海洋研究開発機構　地球内部ダイナミクス領域　(IFREE, JAMSTEC) (2011.4〜2012.3) 日本学術振興会　特別研究員PD
東京工業大学　理工学研究科　地球惑星科学専攻　Department of Earth and Planetary Science, Tokyo Institute of Technology. (2002.4〜2011.3)

Please contact me using following address.
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My study
Our group is interested in the linkage betwenn life evolution and surface environmental changes.
We are performing systematic analyses of several isotic ratios in order to estimate past environment.
In our group, I am analyzing 87Sr/86Sr and 88Sr/86Sr ratios of the fresh carbonate rocks.

Ediacaran period The Ediacaran period was one of the most important times for the evolution of life. However, the scarcity of well-preserved outcrops of Ediacaran rocks still leaves ambiguity in decoding ambient surface environmental changes and biological evolution.

Locality of our study Our group conducted geological survey in Scotland(U.K.), Three Gorges(South China), Altai(Russia) and Svalbard in order to collect Ediacaran flesh carbonate rocks. The Ediacaran strata in South China are almost continuously exposed, comprise mainly carbonate rocks with subordinate black shales and sandstones, and they contain many fossils, suitable for study of environmental and biological changes in the Ediacaran. We conducted drilling at four sites in the Three Gorges area to obtain continuous, fresh samples without surface alteration and oxidation. I joined geological surveys at Pilbara (in Australia in 2010) and Labrador (in Canada in 2011).

Result The weathering influx from continents is thought to be a major influence on the change in composition of ancient seawater and on biological evolution. Its flux can be estimated from the 87Sr/86Sr ratio of carbonate rocks. We analyzed 87Sr/86Sr and 88Sr/86Sr ratios of the fresh carbonate rocks, selected on the basis of microscopic observations and the geochemical signatures of Sr contents, Mn/Sr and Rb/Sr ratios, and δ18O values, with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS). The chemostratigraphy of the 87Sr/86Sr ratios of the drilled samples displays a smooth curve and three large positive shifts during Ediacaran and Cambrian time. The combination of the detailed chemostratigraphies of δ13C, δ18O and 87Sr/86Sr values and Mn and Fe contents enables us to decode the surface environmental changes and their causes (see Sawaki et al., 2008a and Sawaki et al., 2010b).

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Recent Publications
1, Y. Sawaki, et al., 2008a. Sr isotope excursion across the Precambrian-Cambrian boundary, in the Three Gorges area, South China: Gondwana Research, vol. 14, p. 134-147.
2, Y. Sawaki, et al., 2008b. Internal structures and U-Pb zircon dating of a tuff layer in the Meishucunian Formation, Yunnan Province, South China: Gondwana Research, vol. 14, p. 148-158.
3, Y. Sawaki, et al., 2010a. Imbricated ocean-plate stratigraphy and U-Pb zircon ages from tuff beds in cherts in the Ballantrae complex, SW Scotland. Geological Society of America, Bulletin, vol. 122, p. 454-464.
4, Y. Sawaki, et al., 2010b. The Ediacaran radiogenic Sr isotope excursion in the Doushantuo Formation in the Three Gorges area, South China. Precambrian Research, vol. 176, p. 46-64.
5, Y. Sawaki, et al., 2010c. 87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian carbonates below the Port Askaig Glaciogenic Formation, Scotland. Precambrian Research, vol. 179, p. 150-164.

うさぎ/ My friend