Schaltegger, Urs U-Pb zircon age determinations on volcanic ash beds in the Pucara Formation (Utcubamba Valley): a precise age for the Triassic-Jurassic and the Hettangian-Sinemurian boundaries - Lima Sociedad Geológica del Perú 2008 - 6 p. ilus. Subjects--Topical Terms: BIOESTRATIGRAFIACENIZA VOLCANICADATACION U-PBEXTINCION MASIVAHETANGIANOJURASICOLIMITE ESTRATIGRAFICOPALEOCLIMATOLOGIAROCAS VOLCANICASTRIASICOVOLCANISMO Subjects--Geographic Terms: AMAZONASCHACHAPOYASPERUUTCUBAMBA Subjects--Index Terms: GRUPO PUCARA