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