A Miocene impact ejecta layer in the pelagic Pacific Ocean

Tatsuo Nozaki*, Junichiro Ohta, Takaaki Noguchi, Honami Sato, Akira Ishikawa, Yutaro Takaya, Jun Ichi Kimura, Qing Chang, Kazuhiko Shimada, Jun ichiro Ishibashi, Kazutaka Yasukawa, Katsunori Kimoto, Koichi Iijima, Yasuhiro Kato


研究成果: Article査読

16 被引用数 (Scopus)


Meteorite impacts have caused catastrophic perturbations to the global environment and mass extinctions throughout the Earth’s history. Here, we present petrographic and geochemical evidence of a possible impact ejecta layer, dating from about 11 Ma, in deep-sea clayey sediment in the Northwest Pacific. This clay layer has high platinum group element (PGE) concentrations and features a conspicuous negative Os isotope anomaly (187Os/188Os as low as ~0.2), indicating an influx of extraterrestrial material. It also contains abundant spherules that include pseudomorphs suggestive of porphyritic olivine as well as spinel grains with euhedral, dendritic and spherical forms and NiO contents as great as 23.3 wt%, consistent with impact ejecta. Osmium isotope stratigraphy suggests a most plausible depositional age of ~11 Ma (Miocene) for this layer, as determined by fitting with the seawater evolution curve. No large impact crater of this age is known on land, even within the relatively large uncertainty range of the relative Os age. Thus, we suggest that an unrecognised impact event in the middle or late Miocene produced the impact ejecta layer of the Northwest Pacific.

ジャーナルScientific reports
出版ステータスPublished - 2019 12月 1

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