Anisian (Middle Triassic) ammonoids from North America: quantitative biochronology and biodiversity

摘要: This study synthesizes and revises the ammonoid zonations as well their correlation with each other for western Nevada (USA), British Columbia (Canada), Sverdrup Basin (Canada) by utilizing unitary association method. Based on a standard- ized taxonomy, Anisian in studied areas contains 13, 10, 3 zones total of 174, 90, 7 species, respectively. The are correlated means 'common taxa zonation', which includes all common to basins. leads new more precise correlations, at slight variance those literature. Hence, Buddhaites hagei Zone corre- lates only Intornites mctaggarti Subzone (Nevada) not entire Acrochordiceras hyatti (Nevada). Tetsaoceras hayesi appears correlate Unionvillites hadleyi Nevadisculites taylori Zone. Hollandites minor than likely correlates rather Balatonites shoshonensis is usually acknowledged. method enables us quantify diachronism taxa, affects about 67% genera 18% species Columbia. Therefore, this significant its value should be overlooked. Finally, diversity analysis based revised performed. reveals that major event occurred during (early Middle Anisian), Columbia, records highest richness enhanced exchanges be- tween latitudinally restricted faunas. may reflect changes climate or oceanic circulation time.