New U-Pb zircon ages integrated with ammonite biochronology from the Jurassic of the Canadian Cordillera

摘要: The accuracy of published Jurassic time scales is compromised by a paucity sufficiently accurate and stratigraphically well-constrained isotopic dates. U–Pb dating volcaniclastic rocks within fossiliferous marine successions method suitable providing additional useful calibration points. Stikinia Wrangellia, two the major accreted terranes Canadian Cordillera, comprise volcanosedimentary assemblages magmatic arc origin. Within them we selected sections from which report 14 new zircon ages that are integrated with ammonite biochronology at zonal level. Poor recovery complex systematics made it difficult to obtain precise for many samples. following were determined (with 2σ errors): 194.0+9.1–1.8 Ma Plesechioceras? harbledownense Assemblage (upper Sinemurian), 191.5 ± 0.8 Sinemurian) Whiteavesi Zone (lower Pliensbachian), 185.6+6.1–0.6 Frebo...