Revisión de la edad del Grupo de Asha en los Urales meridionales

Abstract

The Asha Group of the South Urals, initially erected by Albert Olli as Palaeozoic sedimentary complex, more than half a century ago was considered as a key section for the Vendian (Ediacaran) of the western slope of the South Urals. However, the ca. 1700 m-thick terrigenous sedimentary sequence is characterised by unusual low biodiversity of Ediacaran macrofossils, which might be explained by relatively young age of the Asha Group and possible mass extinction event in the end of Ediacaran Period. The relatively young age was confirmed by the U-Pb zircon date of 547.6±3.8 Ma obtained from the tuff in the lower part of the Basa Formation as well as finding of ichnospecies Didymaulichnus tirasensis in the upper part of Zigan formation. However, in 2018 it has been documented there the mass appearing of D. tirasensis in the lowermost part of the Basa Formation. Therefore, the Vendian (Ediacaran) age of the Asha Group of the South Urals can be revisited in favour to terminal Ediacaran- Cambrian or even early Cambrian.