Paleobiology of the Neoproterozoic (Upper Riphean) Shorikha and Burovaya silicified microbiotas, Turukhansk Uplift, Siberia

Diverse assemblages of silicified microfossils have been detected in lenses of black chert within peritidal carbonates of the Neoproterozoic (Upper Ri phean) Shorikha and Burovaya formations, Turukhansk Uplift, northeastern Si beria. These microbiotas are represented by 19 species of simple filamentou s and coccoidal microfossils, multicellular trichomes, and thick-enveloped sphaeromorphic and acanthomorphic acritarchs. Microfossils include both pro karyotic (possibly cyanobacterial) and eukaryotic (mainly phytoplanktonic) microorganisms. The eukaryotes in these formations are relatively diverse-t he result of an explosive radiation near the Meso-Neoproterozoic boundary. The discovery of abundant phytoplanktonic microorganisms in the Shorikha an d Burovaya cherts increases the biostratigraphical potential of Proterozoic silicified microbiotas and fills a gap in the paleontological record of th e Turu-khansk Uplift, a potential candidate for the stratotype of the Meso- Neoproterozoic boundary. The affinities of the formally described tars are postulated as follows: Oscillatoriaceae: Eomicrocoleus crassus Horodyski an d Donaldson, 1980; Oscillatoriopsis obtusa Schopf and Blacic, 1971; O. medi a Mendelson and Schopf, 1982; Oscillatoriaceae or Nostocaceae: Siphonophycu s robustum (Schopf, 1968); S. typicum (Hermann, 1974); S. solidum (Golub, 1 979); Nostocaceae or Stigonemataceae: Alchaeoellipsoides minor (Golovenoc a nd Belova, 1984); Chroococcaceae: Gloeodiniopsis lamellosa Schopf, 1968, Eo synechococcus grandis Hofmann, 1976; Incertae sedis: Scissilisphaera gradat a Green, Knell and Swett, 1989; Myxococcoides minor Schopf, 1968; M, inorna ta Schopf, 1968; M. stragulescens Green, Knell, and Swett, 1989; Myxococcoi des sp.; Pterospermopsimorpha? sp.; Shorikhosphaeridium knolli new genus an d species; Leiosphaeridia jacutica (Timofeev); problematic ellipsoidal form s; and problematic spiny forms.