Evidence of a Large Impact in the Norian Triassic

Osmium isotope evidence for a large Late Triassic impact event

Authors:

1. Honami Sato (a)
2. Tetsuji Onoue (a)
3. Tatsuo Nozaki (b)
4. Katsuhiko Suzuki (b)

Affiliations:

a. Department of Earth and Environmental Sciences, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan

b. Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

Abstract:

Anomalously high platinum group element concentrations have previously been reported for Upper Triassic deep-sea sediments, which are interpreted to be derived from an extraterrestrial impact event. Here we report the osmium (Os) isotope fingerprint of an extraterrestrial impact from Upper Triassic chert successions in Japan. Os isotope data exhibit a marked negative excursion from an initial Os isotope ratio (187Os/188Osi) of ~0.477 to unradiogenic values of ~0.126 in a platinum group element-enriched claystone layer, indicating the input of meteorite-derived Os into the sediments. The timing of the Os isotope excursion coincides with both elevated Os concentrations and low Re/Os ratios. The magnitude of this negative Os isotope excursion is comparable to those found at Cretaceous–Paleogene boundary sites. These geochemical lines of evidence demonstrate that a large impactor (3.3–7.8 km in diameter) produced a global decrease in seawater 187Os/188Os ratios in the Late Triassic.