Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

B (Biogeosciences) » B-CG Complex & General

[B-CG10] Phanerozoic biodiversity change: Extinction and diversification

Mon. May 21, 2018 10:45 AM - 12:15 PM 102 (1F International Conference Hall, Makuhari Messe)

convener:Yukio Isozaki(Department of Earth Science and Astronomy, Multi-disciplinary Sciences - General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo), Yusuke Sawaki(The University of Tokyo), Chairperson:Sawaki Yusuke(The University of Tokyo)

11:05 AM - 11:20 AM

[BCG10-08] Clues to extraterrestrial material in old sedimentary rocks: A case study on helium-3 from the Permian/Triassic boundary

★Invited Papers

*Naoto Takahata1, Tetsuji Onoue2, Mitsutaka Miura3, Yuji Sano1, Yukio Isozaki4 (1.Atmosphere and Ocean Research Institute, the University of Tokyo, 2.Faculty of Advanced Science and Technology, Kumamoto University, 3.Graduate School of Science and Technology, Kumamoto University, 4.Department of Earth Science and Astronomy, the University of Tokyo)

Keywords:P/T boundary, mass extinction, extraterrestrial material, helium isotope

Helium is suitable to detect extraterrestrial material in marine sediments as well as platinum group elements such as iridium because helium is much enriched in extraterrestrial matter compared to the Earth’s surface. In this study we tried to detect extraterrestrial material in old sedimentary rocks collected from the Permian/Triassic (or P/T) boundary section. Becker et al. (2001) reported an anomaly in 3He trapped in fullerene from P/T boundary rocks in Japan and China, which in turn suggested a possible extraterrestrial impact as the cause of the P/T boundary mass extinction. However no one have ever found evidence for extraterrestrial 3He after their finding. Although the approach of using the 3He signature appears promising, their results are doubtful. We checked their finding using new samples collected from a better P/T boundary section.
We collected pelagic deep-sea sediments in the ancient Pacific Ocean (Panthalassa Ocean) in the Mino Belt, central Japan. Layers we collected the sediments include the P/T boundary section. Much higher 3He/4He ratios (up to 150 Ra; 1Ra = the atmospheric ratio) were observed at the extraction temperatures of 750-950 degree Celsius in bulk samples and acid-insoluble residues. These high 3He/4He ratios may infer existence of extraterrestrial helium carried in fullerenes or interplanetary dust particles. Bulk 3He concentrations we obtained from Mino section samples are enough higher than the detection limit and relatively higher below the P/T boundary. This is the first report on distribution of extraterrestrial 3He across a large P/T boundary section. Based on sedimentation rate calculated from zircon ages, influx of extraterrestrial material was estimated. It may have increased to more than ten times higher during a hundred of thousands of year before the P/T boundary, which is equivalent to the influx at the K/Pg boundary because of long duration. This increase may have caused global cooling leading to mass extinction.

Reference: Becker et al. (2001), Science, 291, 1530-1533.