L’article “A new 40Ar/39Ar age from volcanic events in the Rosso Ammonitico Veronese as a tie-point for the Late Jurassic” par Pellenard et al. publiée à Geological Magazine

Pierre Pellenard sur le terrain

L’étude “A new 40Ar/39Ar age from volcanic events in the Rosso Ammonitico Veronese as a tie-point for the Late Jurassic” par P. Pellenard, S. Nomade, L. Martire, F. De Oliveira Ramalho, F. Monna, H. Guillou, vient d’être publiée à Geological Magazine, 150, 1136-1142 [pdf].

L’échelle des temps géologiques pour la fin du Jurassique est peu précise, en particulier parce que les datations obtenues par des méthodes radiométriques sont rares. Dans cet article, Pierre Pellenard (Pierre.Pellenard@u-bourgogne.fr) du laboratoire Biogéosciences utilise la méthode 40Ar/39Ar, appliquée à des niveaux de cendres volcaniques scellés dans l’enregistrement sédimentaire, ceci afin de contraindre chronologiquement l’Oxfordien. 

Abstract: Eight volcanic ash layers, linked to large explosive events caused by subduction-related volcanism from the Vardar Ocean back arc, interbedded with limestones and cherts, have been identified in the Rosso Ammonitico Veronese Formation (north-eastern Italy). The thickest ash layer, attributed to the Gregoryceras transversarium ammonite biozone (Oxfordian Stage) , yields a precise and reliable ⁴⁰Ar/³⁹Ar age of 156.1 ± 0.89 Ma which is in better agreement with the GTS2004 boundaries, than the current GTS2012 . This first biostratigraphically well-constrained Oxfordian age is proposed as a new radiometric  tie-point to improve the Geologic Time Scale for the Late Jurassic whose ammonite-bearing radiometric ages are particularly scarce .