A new assemblage of morphologically complex, ornamented and large organic-walled microfossils (acritarchs) from the Ura Formation in the Patom Uplift, East Siberia, is identified and taxonomically described as a continuation of the previous studies (Nagovitsin et al., 2004; Sergeev et al., 2011). Nine new species and three new genera are recognised; 10 other species are known from occurrences in the Ediacaran strata of Australia, China, the Siberian Platform (SP), and the East European Platform (EEP). The new species are morphologically advanced phenotypes, showing innovative elements of vesicle ornamentation and variable symmetry, and internal bodies within zygotic cyst-like vesicles that are indicative of the sexual reproduction stage of the microorganism. The morphological features and the preliminarily recognised cell wall ultrastructure are characteristic of phytoplankton; thus the described microfossils are identified as green microalgae. The relative age of the Ura assemblage, by comparison to microfossil records elsewhere and estimated in the regional geologic context of the Dalniaya Taiga (containing the Ura Formation) and the Zhuya (overlying) groups, is suggested to be early Ediacaran. Radiation of the Ura-type microorganisms pre-dates the records of Ediacaran microbiota from Australia (the Pertatataka association/Ediacaran Complex Acanthomorphic Palynoflora), the Siberian Plat form (Khamaka-type assemblages), and the EEP (Vychegda association) but is preceded by the appearance of certain species recorded in China at the base of the Doushantuo Formation. The stratigraphic ranges of genera co-occurring in these palaeocontinents (Appendisphaera, Cavaspina, Ceratosphaeridium, Gyalosphaeridium, Labruscasphaeridium, Multifronsphaeridium, Tanarium, and Variomargosphaeridium) are extended by their lower record in the Patom Uplift and may span a major portion of the Ediacaran Period. The refined stratigraphic distribution of microfossils may provide a means for zoning the entire Ediacaran System in addition to the upper zones established in Australia. (C) 2011 Elsevier B.V. All rights reserved.
