title: Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic.
abstract: The 34-million-year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., end-Triassic extinction event), but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits. Here, we report evidence for an impact event (platinum group elements anomaly with nickel-rich magnetite and microspherules) from the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridium-enriched ejecta layers of the Late Triassic may be found on a global scale. The ejecta deposit is constrained by microfossils that suggest correlation with the 215.5-Mya, 100-km-wide Manicouagan impact crater in Canada. Our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine planktons. However, such an event has been reported among marine faunas and terrestrial tetrapods and floras in North America. We, therefore, suggest that the Manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm.
authors.affiliation: Department of Earth and Environmental Sciences, Kagoshima University, Kagoshima 890-0065, Japan. onoue@sci.kagoshima-u.ac.jp
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Onoue
authors.forename: Honami
authors.initials: H
authors.lastname: Sato
authors.forename: Tomoki
authors.initials: T
authors.lastname: Nakamura
authors.forename: Takaaki
authors.initials: T
authors.lastname: Noguchi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hidaka
authors.forename: Naoki
authors.initials: N
authors.lastname: Shirai
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Ebihara
authors.forename: Takahito
authors.initials: T
authors.lastname: Osawa
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Hatsukawa
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Toh
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Koizumi
authors.forename: Hideo
authors.initials: H
authors.lastname: Harada
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Orchard
authors.forename: Munetomo
authors.initials: M
authors.lastname: Nedachi
mesh_terms: D053476:Extinction, Biological; D052203:Ferrosoferric Oxide / Q000737:chemistry; D005843:Geography; D007564:Japan; D019110:Meteoroids; D009532:Nickel / Q000737:chemistry; D009792:Oceans and Seas; D010163:Paleontology; D010984:Platinum / Q000737:chemistry; D013997:Time Factors
chemical_list: D010984:Platinum; D009532:Nickel; D052203:Ferrosoferric Oxide