NEW DATA ON SILICIFIED PROTEROZOIC MICROFOSSILS FROM THE JIUDINGSHAN FORMATION OF JIANGSU AND NORTHERN ANHUI, CHINA

The Middle to Late Proterozoic Jiudingshan formation of Jiangsu and northern Anhui provinces contains abundant laminar and nodular cherts that have revealed a diverse and well preserved microfossil assemblage in thin sections: The assemblage is dominated by 12 genera, represented by 16 species in all, among which are 6 genera-with 10 species-of filamentous forms and three genera and species of coccoidal ones. These 9 genera and 13 species are probably all cyanobacteria: Siphonophycus septatum, S. robustum, S. typicum, S. kestron, Oscillatoriopsis vermiformis, O. obtusa, Cephalophytarion grande, Salome sp., Veteronostocale amoenum, Paleolyngbya sp., Gloeodiniopsis suxianensis, Eoentophysalis cumulus and Nanococcus vulgaris. Another three genera and species are regarded here as incertae sedis: Myxococcoides minor, Leiosphaeridia sp. and Brachypleganon khandanum. The occurrences of Oscillatoriopsis vermiformis, O. obtusa, Cephalophytarion grande, Salome sp., Veteronostocale amoenum, Paleolyngbya sp. and Nanococcus vulgaris are the first to be recorded from this region of China. The important mat-building elements Siphonophycus and Oscillatoriopsis always appeared to be associated together in the present study, supporting an interpretation that the two may be closely related. Previously only Siphonophycus has been found in this locality, without any associated Oscillatoriopsis. Palaeoecologically, the occurrence of a large number of Oscillatoriopsis filaments lacking heterocysts in the Jiudingshan Formation implies that environmental conditions were anaerobic. Oscillatoriopsis filaments lacking heterocysts in the Jiudingshan formation imply that environmental conditions were anaerobic. This new discovery of microfossils from the Jiudingshan Formation is systematically significant in amplifying and extending our knowledge – providing a more complete understanding of Proterozoic microbial communites worldwide and also giving us a more complete understanding of their environments. It reveals that prokaryotic organisms clearly played the most important role in the microbial community of shallow benthic marine environments in this locality prior to the onset of the Neoproterozoic glaciation.