TY - JOUR
T1 - Sr isotope excursion across the Precambrian-Cambrian boundary in the Three Gorges area, South China
AU - Sawaki, Yusuke
AU - Ohno, Takeshi
AU - Fukushi, Yusuke
AU - Komiya, Tsuyoshi
AU - Ishikawa, Tomoko
AU - Hirata, Takafumi
AU - Maruyama, Shigenori
N1 - Funding Information:
We thank Takanori Kiguchi, Hiroshi Matsuo and Hitomi Tokimori for technical advice (ICP-OES) at the Center for Advanced Materials Analysis in the Tokyo Institute of Technology. We also thank Dr. Takahiro Wakabayashi for assistance (ICP-MS) in the acquisition of analytical data. This work was partly supported by grants for “secular variation of seawater composition (No. 16740284)”, and for “Coevolution of surface environment and solid earth from the Neoproterozoic Snowball Earth to Cambrian explosion events (No. 18740318)” from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
PY - 2008/8
Y1 - 2008/8
N2 - 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.
AB - 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.
KW - Gondwana
KW - Precambrian-Cambrian boundary
KW - Sr isotope
KW - δC, chemostratigraphy
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U2 - 10.1016/j.gr.2007.11.002
DO - 10.1016/j.gr.2007.11.002
M3 - Article
AN - SCOPUS:46149104363
VL - 14
SP - 134
EP - 147
JO - Gondwana Research
JF - Gondwana Research
SN - 1342-937X
IS - 1-2
ER -