Life on the way out of Shuram Excursion: new locality of Ediacaran biota in the Ura Uplift of the southern Siberian Platform

The Ura Uplift section in the Patom Highlands area of Siberia is one of the most complete Neoproterozoic carbonate-siliciclastic succession with excellent chemostratigraphic records (δ13С and 87Sr/86Sr). Present study reveals the first finds of Ediacaran macrofossils within thick siliciclastic/carbonate succession of the Chencha and Zherba formations with well-established negative δ13С anomaly attributed to the Shuram Excursion in this section. The fossils are preserved in glauconitic and quartz sandstone horizons in shallow-marine tide-influenced nearshore environment and share many taphonomic and morphological features with the White Sea-and Nama-type biotas. On the one hand, stratigraphic position of some of fossils within the uppermost Shuram Excursion falls into the time interval ~ 573-567 Ma and therefore is correlative to the Avalon-type fossil assemblage. On the other hand, the new fossil assemblage indicates to the earlier appearance of some Nama-type species, such as erniettomorphs, than it was thought. In addition, the new assemblage is characterised by low-diversity metazoan community dominated by microbial textures. It potentially supports the hypothesis that the Ediacaran shallow water fossil assemblages were significantly less species-rich than their deeper water counterparts. The discovery of the oldest macrofossils in South Siberia both opens a new window to understand their palaeoecology and taphonomy, and demonstrates that palaeontological potential of such a vast region has not entirely been realised.