Sr isotope excursion across the Precambrian-Cambrian boundary in the Three Gorges area, South China

Yusuke Sawaki, Takeshi Ohno, Yusuke Fukushi, Tsuyoshi Komiya, Tomoko Ishikawa, Takafumi Hirata, Shigenori Maruyama

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    53 Citations (Scopus)

    Abstract

    The Precambrian/Cambrian (PC/C) boundary is one of the most important intervals for the evolution of life. However, the scarcity of well-preserved outcrops across the boundary leaves an obstacle in decoding surface environmental changes and patterns of biological evolution. In south China, strata through the PC/C boundary are almost continuously exposed and contain many fossils, suitable for study of environmental and biological change across the PC/C boundary. We undertook deep drilling at four sites in the Three Gorges area to obtain continuous and fresh samples without surface alteration and oxidation. 87Sr/86Sr ratios of the fresh carbonate rocks, selected based on microscopic observation and geochemical signatures of Mn/Sr and Rb/Sr ratios, aluminum and silica contents, and δ13C and δ18O values, were measured with multiple collector-inductively coupled plasma-mass spectrometric techniques. The chemostratigraphy of 87Sr/86Sr ratios of the drilled samples displays a smooth curve and a large positive anomaly just below the PC/C boundary between the upper part of Baimatuo Member of the Dengying Formation and the lower part of the Yanjiahe Formation. The combination of chemostratigraphies of δ13C and 87Sr/86Sr indicates that the 87Sr/86Sr excursions preceded the δ13C negative excursion, and suggests that global regression or formation of the Gondwana supercontinent, possibly together with a high atmospheric pCO2, caused biological depression.

    Original languageEnglish
    Pages (from-to)134-147
    Number of pages14
    JournalGondwana Research
    Volume14
    Issue number1-2
    DOIs
    Publication statusPublished - Aug 1 2008

    Keywords

    • Gondwana
    • Precambrian-Cambrian boundary
    • Sr isotope
    • δC, chemostratigraphy

    ASJC Scopus subject areas

    • Geology

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  • Cite this

    Sawaki, Y., Ohno, T., Fukushi, Y., Komiya, T., Ishikawa, T., Hirata, T., & Maruyama, S. (2008). Sr isotope excursion across the Precambrian-Cambrian boundary in the Three Gorges area, South China. Gondwana Research, 14(1-2), 134-147. https://doi.org/10.1016/j.gr.2007.11.002