The Oldest Vendian (Ediacaran) Fossils of Eurasia: U-Pb Isotope Age of the Basa Formation (Asha Group, Southern Urals)

摘要

U-Th-Pb (SHRIMP II) isotopic dating of accessory zircons from Vendian (Ediacaran) ash tuffs of the Basa formation section (Asha Group, Southern Ural) was performed for the first time. The concordant age obtained (573.0 +/- 2.3 Ma) can be interpreted as the upper age limit of the onset of the Timan Orogeny in the structure of the Southern Urals. Fossil remains of Kuckaraukia multituberculata and several paleopascichnids, belonging to the genera Palaeopascichnus and Orbisiana, were previously found in the rocks of the Upper Basa Subformation, and the first occurrence of Arumberia banksi was established. The age obtained indicates a more ancient age of this Vendian assemblage compared to the previously accepted one.