Authors
Urs Schaltegger, Jean Guex, Annachiara Bartolini, Blair Schoene, Maria Ovtcharova
Publication date
2008/3/1
Journal
Earth and Planetary Science Letters
Volume
267
Issue
1
Pages
266-275
Publisher
Elsevier
Description
New precise zircon U–Pb ages are proposed for the Triassic–Jurassic (Rhetian–Hettangian) and the Hettangian–Sinemurian boundaries. The ages were obtained by ID-TIMS dating of single chemical-abraded zircons from volcanic ash layers within the Pucara Group, Aramachay Formation in the Utcubamba valley, northern Peru. Ash layers situated between last and first occurrences of boundary-defining ammonites yielded 206Pb/238U ages of 201.58±0.17/0.28 Ma (95% c.l., uncertainties without/with decay constant errors, respectively) for the Triassic–Jurassic and of 199.53±0.19 / 0.29 Ma for the Hettangian–Sinemurian boundaries. The former is established on a tuff located 1 m above the last local occurrence of the topmost Triassic genus Choristoceras, and 5 m below the Hettangian genus Psiloceras. The latter sample was obtained from a tuff collected within the Badouxia canadensis beds. Our new ages …
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U Schaltegger, J Guex, A Bartolini, B Schoene… - Earth and Planetary Science Letters, 2008