The Oldest Trace Fossils in Association with an Ediacara-Type Biota in the Upper Vendian of the South Urals

Abstract

Trace fossils and palaeopascichnids have been studied in the Basa Formation of the Vendian Asha Group of the South Urals (southwestern periphery of the Suleiman Anticline, Shubino quarry in Ust’-Katav, Chelyabinsk Region of Russia). The general morphology and preservation of ichnofossils have been shown to be similar to the Late Vendian–Early Cambrian subhorizontal bilobate burrows of Didymaulichnus. The paleontological remains have been found to be confined to extremely shallow deposition settings and located stratigraphically below the volcanic tuff layer with a zircon U–Pb isotopic age of 578 ± 7 Ma. Until now, the first occurrence of ichnofossils and the associated “Agronomic Revolution” were dated at ~560–550 Ma. According to our study results, mobile benthos and biological mixing of sediments could have occurred 20–30 Ma earlier. The hypothesis that the onset of the “First Agronomic Revolution” and the “Cambrian Explosion” were far from being close in time was confirmed.