First absolute zircon SHRIMP age

AGUIRRE URRETA, M.P. PAZOS, P.J. M. FANNING, Y LITVAK VANESA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

ELSEVIER

Año: 2008 vol. 26 p. 91 - 99

0895-9811

A high-resolution ion-microprobe (SHRIMP) U–Pb zircon age from a tuff layer intercalated in the ammonoid bearing sedimentary12 succession of the Neuque´n Basin in Argentina provides a robust geochronologic date to add to the absolute ages and to improve the13 relative chronology of the Early Cretaceous Hauterivian stage. The tuff layer appears interbedded between shales of the upper member14 (Agua de la Mula) of the Agrio Formation within the Spitidiscus riccardii ammonoid zone (base of the Late Hauterivian) yielding a date15 of 132.5 ± 1.3 Ma. This date confirms and supports an accurate correlation between the ammonoid biostratigraphy of the Neuque´n16 Basin with the Western Mediterranean Province of the Tethys during the Early Cretaceous and matches with the most recently published17 time scale. It also casts doubts on the validity of K–Ar ages on glauconite-grains recently reported from the Lower Cretaceous of the18 Vocontian Basin of France.