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TitreSedimentary record of a Late Triassic impact event in an ancient Pacific pelagic site: Manicouagan impact ejecta?
AuteurOnoue, T; Sato, H; Nakamura, T; Noguchi, T; Hatsukawa, Y; Osawa, T; Toh, Y; Koizumi, M; Orchard, M J; Nedachi, M; Ebihara, M
SourceProceedings of the 21st Canadian Paleontology Conference; par Haggart, J W (éd.); Smith, P L (éd.); Canadian Paleontology Conference Proceedings no. 9, 2011 p. 39-40
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120093
Réunion21st Canadian Paleontology Conference; Vancouver; CA; août 19-22, 2011
Documentpublication en série
Lat/Long OENS135.0000 137.0000 35.5000 34.5000
SujetsTrias supérieur; cratères météoriques; spinelle; argilites; chailles; biostratigraphie; fossiles; Paléogène; Norien; Radiolarie; Structure d'impact de Manicouagan ; Tertiaire; Crétacé
Programmebassins sédimentaires du Yukon, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
We present evidence for an impact event (microspherules, nickel-rich spinels, and anomalous concentrations of platinum-group elements) from a deep-sea claystone layer in an Upper Triassic bedded chert succession of the Sakahogi section, Inuyama area, central Japan. The strata were deposited in a deep Paleo-Pacific (Panthalassa) basin. The claystone contains anomalously high contents of iridium, up to 40 ppb, comparable to the levels found at the Cretaceous/Paleogene boundary (e.g. 36 ppb at Stevens Klint, Denmark). Radiolarian and conodont biostratigraphy indicate that the chert succession is middle to late Norian in age. The radiolarian fossils show no evidence of a mass extinction event across the impact layer. Of the 14 radiolarian species
identified within the claystone, only one species disappears within this layer. Although there are no radiometric age data for the middle to late Norian, it has been assigned an age range of 216.4-209.8 Ma based on biostratigraphy and the astronomically tuned geomagnetic polarity time-scale (Hüsing et al., 2011). The Manicouagan impact structure (Canada) would appear to be related to deposition of the ejecta deposit described in the present study, because 1)the age of crater formation (215.5 Ma) is within the range of the age of the chert succession, and 2) the Manicouagan impact was large enough to produce a global distribution of ballistic ejecta within ~30/ paleolatitude of the crater. Our results suggest that distal ejecta layers, possibly linked to the Manicouagan impact, will be found at other middle to late Norian sites worldwide. The application of an event-stratigraphic approach at such sites is required to confirm the distribution of ejecta and constrain the location of the source crater for the ejecta deposits.