2000 Fiscal Year Final Research Report Summary
The Neoproterozoic Snowball Earth hypothesis : Tests from the cap carbonates of Namibia
| Project/Area Number |
11640414
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体地球物理学
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| Research Institution | Gifu University |
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Principal Investigator |
KAWAKAMI Shin-ichi Gifu University Associate Professor, 教育学部, 助教授 (80183036)
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| Co-Investigator(Kenkyū-buntansha) |
OHNO Terubumi The University Museum, Kyoto University Professor, 総合博物館, 教授 (40194245)
TAKANO Masao Graduate School of Science, Nagoya University Associate Professor, 大学院・理学研究科, 助教授 (90262849)
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| Project Period (FY) |
1999 – 2000
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| Keywords | Earth History / Neoproterozoic / Snowball Earth hypothesis / Ice Age / Climate Change / carbonate / geochemisty / Shima-shima gaku |
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| Research Abstract |
The close association of Neoproterozoic glacial deposits and overlying cap carbonates has long been regarded as enigma, but now can be reasonably explained by the snowball Earth hypothesis (Hoffman et al., 1998). The basal part (rhythmite ; 14.2 m in thickness) of the Neoproterozoic Rasthof cap carbonate overlying Chuos diamixtite, in the Otavi Group, Namibia was continuously sampled. Chemical profiles of the sequence were obtained by the analysis using the X-ray fluorescence microscope (SXAM). Carbon, oxygen, and strontium isotopic profiles were also measured. We divided it into three successive intervals based on the different characteristics in the chemical profiles. In the lower interval I (1.6 m in thickness), there are no fluctuations in Ca and Mn profiles with relatively small Fe contents. Cyclic changes of Ca and Mn are remarkable in the middle interval. The nature of banding and their possible origin, and cyclicities have been discussed. If the sub-mm scale banding is annual rhythm, the meter-scale banding represent millennial-scale cycles. The time scale of carbon isotopic excursions observed in interval I is estimated to be 103-104 years, which is about 1 or 2 order of magnitude smaller than the LPTM event.
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