Wednesday, November 21, 2012

Bollide Impact During the Triassic and Exonerated of Marine Mass Extinction

Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic


1. Tetsuji Onoue (a,*)
2. Honami Sato (a)
3. Tomoki Nakamura (b)
4. Takaaki Noguchi (c)
5. Yoshihiro Hidaka (d)
6. Naoki Shirai (d)
7. Mitsuru Ebihara (d)
8. Takahito Osawa (e)
9. Yuichi Hatsukawa (e)
10. Yosuke Toh (e)
11. Mitsuo Koizumi (e)
12. Hideo Harada (e)
13. Michael J. Orchard (f)
14. Munetomo Nedachi (g)


a. Department of Earth and Environmental Sciences, Kagoshima University, Kagoshima 890-0065, Japan

b. Department of Earth and Planetary Material Sciences,Tohoku University, Miyagi 980-8578, Japan

c. Department of Science, Ibaraki University, Mito 310-8512, Japan

d. Department of Chemistry, Tokyo Metropolitan University, Tokyo 192-0397, Japan

e. Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1195, Japan

f. Geological Survey of Canada, Vancouver, BC, Canada V6B 5J3

g. Division of Instrumental Analysis, Frontier Science Research Center, Kagoshima University, Kagoshima 890-0065, Japan

*. To whom correspondence should be addressed. E-mail:


The 34-million-year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., end-Triassic extinction event), but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits. Here, we report evidence for an impact event (platinum group elements anomaly with nickel-rich magnetite and microspherules) from the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridiumenriched ejecta layers of the Late Triassic may be found on a global scale. The ejecta deposit is constrained by microfossils that suggest correlation with the 215.5-Mya, 100-km-wide Manicouagan impact crater in Canada. Our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine planktons. However, such an event has been reported among marine faunas and terrestrial tetrapods and floras in North America. We, therefore, suggest that the Manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm.

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