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Evidence for large Late Triassic impact (free pdf)
From: Ben Creisler
A new paper in open access that may be of interest:
Honami Sato, Tetsuji Onoue, Tatsuo Nozaki & Katsuhiko Suzuki (2013)
Osmium isotope evidence for a large Late Triassic impact event.
Nature Communications 4, Article number: 2455
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.