Colonial cyanobacteria of the genus ostiana (microcystis) from the upper vendian of Arkhangelsk region

The study of organic films from Zimnie Gory Beds, Ust'-Pinega Formation (Upper Vendian) permits to identify numerous colonial coccoid cyanobacteria of genus Ostiana Hermann (O. microcystis and O. aphanotece sp. nov.). Spheroid acritarchs of genus Leiospheridia Eis. (L. tenuissima and L. ternata) are occasionally found together with the colonial microfossils. Pyritized organic films with filamentous Leiotrichoides tipicus were found in some layers of Ust'-Pinega formation. Phytoleims with numerous colonial coccoid micrfossils assiged to the genus Ostiana Hermann, 1976, were found in the Upper Vendian terrigenous deposits (Zimnegorsk Beds, Ust'-Pinega Formation) in the Borehole 1000-1 (depth: 470 - 475 m). The fossils are represented with minute (from 1 to 10 - 12 micron in diameter rarely larger) spherical or ellipsoid forms with thin, smooth or rough envelope and slightly thickened margin. The colonies are claster-like, rounded or irregular in shape. The cells are usually tightly placed in colony to form the thickened outline or overlap each other. Sometimes the cluster-like colonies are connected by the rows of smaller cells forming threads (table I, fig. 1; tabl. II, fig. 2,4). The phytoleims with microfossils are mostly thin, transparent, but darker ones with uneven margin and distinct meshes of various shape and size resembling cellular structures can be found (tabl. I, fig. 2). Piritized organic films were found in some layers Ust'-Pinega Formation. Framboids of pyrite are deployed of over decomposed organic matter signaling the activities of sulphatereducing bacteria. Together with the colonial cyanobacteria occasional spheroid mocrofossils (acritarchs) were discovered and assigned to two species: Leiosphaeridia ternata (Timofeev, 1966) emend. Mikhailova et Jankauskas, 1989 and Leiosphaeridia tenuissima Eisenack, 1958. L. ternata has a dense dark, opaque envelope with specific radial crack on an exterior edge. The diameter is 20 to 30 mm (table II, fig. 1). Thin-walled acritarchs with smooth wall and rare flexibility folding are assigned to L. tenuissima Eisenach, 1958. The diameter of the envelopes varies from 15 - 20 to 150 - 200 mm (table II, fig. 6). Varions groups of numerous microfossils differing in size, shape of colonies and cells are assigned to genus Ostiana Hermann, 1976. Two species of colonial cyanobacters: Ostiana microcystis and Ostiana aphanothece sp. nov. are described from the material studied.