宇宙から降る塵の歴史を解読～三畳紀の地層から宇宙塵の降下量変動を初めて復元～

2026-05-11 九州大学

約2億1500万年前の地球へ降下した宇宙塵が、ジュラ紀付加体中にみつかるまでの模式図。かつての深海堆積物に降り積もった宇宙塵は、現在は付加体中の層状チャート中に保存されている。

＜関連情報＞

• https://www.kyushu-u.ac.jp/ja/researches/view/1467
• https://www.jstage.jst.go.jp/article/pjab/102/5/102_pjab.102.012/_article/-char/en

日本の遠洋性層状チャートに記録された三畳紀における地球外起源の³Heフラックスの変動Extraterrestrial 3He flux variability during the Triassic recorded in pelagic bedded cherts of Japan

Tetsuji ONOUE , Kohei SETOYAMA, Honami SATO, Takuma SHIOHARA, Naoto TAKAHATA
Proceedings of the Japan Academy,Series B  Published: May 11, 2026
DOI:https://doi.org/10.2183/pjab.102.012

Abstract

Interplanetary dust particles are highly enriched with ³He implanted by the solar wind, enabling the reconstruction of extraterrestrial dust fluxes to Earth from sedimentary ³He records. However, the fluxes of extraterrestrial dust during periods predating the Cretaceous remain poorly constrained. In this study, we present the first comprehensive reconstruction of extraterrestrial ³He fluxes for much of the Triassic period (approximately 246–212 Ma) based on pelagic-bedded cherts preserved in Jurassic accretionary complexes in Japan. We reconstructed extraterrestrial ³He fluxes after correcting for dilution by radiolarian-derived biogenic silica. The records reveal long-term flux enhancements during the Ladinian and late Carnian (Tuvalian) intervals, reaching amplitudes approximately 2–3 times the background level and persisting for ∼3–4 Myr. These features are inconsistent with short-lived influx events, such as comet showers or asteroid breakups, and are instead comparable to long-term background variations in the Cretaceous and Cenozoic records. A sharp ³He flux peak at ∼215–216 Ma is accompanied by elevated ³He/⁴He ratios, indicating a sudden influx of fine-grained extraterrestrial material. The timing of this excursion closely coincides with the Manicouagan impact event (215.4 Ma), suggesting a link between asteroid disruption and enhanced dust production during the Triassic.