Carnets de Géologie / Notebooks on Geology - Memoir 2005/02, Abstract 04 (CG2005_M02/04) Main changes in microfossil communities throughout the Upper Proterozoic of Russia. [Changements majeurs dans les assemblages de microfossiles au cours du Protérozoïque supérieur de Russie] Elena GOLUBKOVA1 Elena RAEVSKAYA2 Key Words: Microfossils; Upper Proterozoic; East-European and Siberian platforms GOLUBKOVA E. & RAEVSKAYA E. (2005).- Main changes in microfossil communities throughout the Upper Proterozoic of Russia. In: STEEMANS P. & JAVAUX E. (eds.), Pre-Cambrian to Palaeozoic Palaeopalynology and Palaeobotany.- Carnets de Géologie / Notebooks on Geology, Brest, Memoir 2005/02, Abstract 04 (CG2005_M02/04) Mots-Clefs : Microfossiles ; Protérozoïque supérieur ; plates-formes est-européenne et sibérienne Introduction The Early - Middle Riphean (R1-R21) assemblages More than 50 years of study have resulted in the description of hundreds of taxa of A long interval embracing the Early Riphean Precambrian microfossils from the different and the bulk of the Middle Riphean does not regions of Russia. These forms are usually show much diversity in the microfossil preserved either as silicified or organic-walled populations. remains and generally are morphologically simple and stratigraphically long-ranging. The The most representative assemblages of this systematics of Precambrian microorganisms still age (1,650-1,250 Ma), all of them on the needs a serious revision, although efforts by Siberian platform, are from the Billyakh Group specialists from all over the world to solve these of the Anabar Uplift (VEIS et alii, 2001; SERGEEV problems have helped to clarify the biological et alii, 1995 and others), the Kyutingde and assignment of some taxa. Debengda formations of the Olenek Uplift, and the Omackhta Fm of the Uchur-Maya region. Distinctive, exceptionally diverse and well- But more diverse Early Riphean microbiotas preserved microbiotas were found at several were described from the Burzyan Group of the locations on the East-European and Siberian Bashkirian meganticlinorium, Southern Urals, Platforms. They occur at discrete stratigraphical adjacent to the East-European Platform. levels and are geographically sporadic. However, a comprehensive analysis based on These assemblages are dominated by the published data and original material (Fig. 1) cyanobacteria. The most common are the permitted the drawing of an evolutionary trend ellipsoidal akinetes Archaeollipsoides in the main taxonomical changes that occurred (Nostocacea or Stigonematacea), in the organic world throughout the Upper chroococcacean cyanobacterium Eoentophysalis Proterozoic of Russia. (Entophysalidacea) and empty sheaths Siphonophycus (Oscillatoriacea or Nostocacea). For the present study the only records we In addition, the less abundant taxa of various used were from strata controlled either by cyanophyta such as Circumvaginalis, isotopic data or other evidence of age. Both Oscillatoriopsis, Filiconstrictosus, Partitiofilum, silicified and organic-walled microfossils were Palaeolyngbia, Eosynechococcus, analyzed taxonomically. Only species with real Sphaerophycus, Myxococcoides and some biological meaning or biostratigraphical others occur in these assemblages. Although significance were used to define noteworthy the representatives of Archaeollipsoides, stages in the development of Upper Proterozoic Eoentophysalis and Siphonophycus were microorganisms. Five main stratigraphical reported from the older sediments levels, characterized by the FAD of distinctive (approximately 1,900-2,000 Ma) of the Belcher species or by the occurrence of new Supergroup and the Epworth Group of Canada, morphological forms have been distinguished they became the dominant components of (Fig. 2). microbiotas only in the Early-Middle Riphean. 1 Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Makarova emb. 2, 199034 Saint-Petersburg (Russia) [email protected] 2 Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Makarova emb. 2, 199034 Saint-Petersburg (Russia) 21 Carnets de Géologie / Notebooks on Geology - Memoir 2005/02, Abstract 04 (CG2005_M02/04) Figure 1: Geographical locations of the most distinctive Upper Proterozoic microbiotas of Russia. The list of common taxa present in these Turukhansk Uplift, Siberia (SERGEEV, 1994 and assemblages includes the following: others). Among organic-walled microfossils the Leiosphaeridia, Eomarginata, Simia, first appearances of the spherical striate Pterospermopsimorpha, Satka, Konderia, eukaryote form Valeria lophostriata JANKAUSKAS, Germinosphaera, Palaeopleurocapsa and others. 1982 and of the spiral prokaryotes Obruchevella and Glomovertella are documented from the The most diverse organic-walled assemblage Katanga saddle, the Baikit syneclise and the is from the Ust'-Il'ya and Kotuikan formations Patom Uplift of the Southern Siberia of the above-mentioned Billyakh Group (1,490- (NAGOVITSIN, 2001). The acanthomorphic 1,250 Ma). Here, in addition to cyanobacteria acritarch Tappania, assigned by BUTTERFIELD and the remains of what are probably (2005) to fungi, recently was reported from the eukaryotic microorganisms, there are large uppermost Middle Riphean sediments of spherical forms of Chuaria circularis WALCOTT, southwestern Siberia (NAGOVITSIN, 2001). 1899 (400-800 µm in diameter), large Tappania was first described in the early filamentous fragments of Elatera (Eosolena) Mesoproterozoic Ruyang Group of China (YIN, and spheroids bearing one long process 1998) and the Roper Group of Ausralia (JAVAUX (considered as reproductive structure of fungi et alii, 2001) but differs in various aspects from or algae) of Caudosphaera (VEIS et alii, 2001). the younger (~800 Ma) Tappania described by BUTTERFIELD (JAVAUX, pers. comm.). The Microfossil assemblages of the branching multicellular talloms of Ulophyton, terminal part of the Middle Riphean provisionally attributed by HERMANN (pers. 2 (R2 ) comm.) to red algae, occur in the coeval strata The uppermost Middle Riphean (1,250-1,000 of the Totta Fm in the Uchur-Maya region. Ma) is marked by the appearance of several new forms. The stalk-forming cyanobacterium The Late Riphean (R3) assemblages Polybessurus bipatitus FAIRCHILD, 1975, ex The base of the Upper Riphean GREEN et alii, 1987 occurs in silicified (approximately 1,000 Ma) is one of the most microbiotas from the Southern Urals and the important levels in the evolution of Upper 22 Carnets de Géologie / Notebooks on Geology - Memoir 2005/02, Abstract 04 (CG2005_M02/04) Proterozoic microbiotas. This is expressed by becomes common in the Upper Riphean incoming morphological innovations, including a assemblages of every region. In the Lakhanda remarkable increase in the diversity and size of biota from the Neryuen Fm of the Lakhanda eukaryotes. Group (the Uchur-Maya region, eastern Siberia) diverse and abundant microorganisms The most distinctive and diverse microbiotas belonging to fungi, algae and several are known from the Uchur-Maya Region (the problematic groups are known, including Lakhanda and Ui groups, HERMANN, 1981, 1990 possible animals (HERMANN & PODKOVYROV, 2002). and others), the Turukhansk Uplift (the Some taxa (Eosacchoromyces, Mucorites and Derevninya, Shorikha and Miroedikha Mycosphaeroides, HERMANN, 1990) are classified formations, VEIS et alii, 1998; SERGEEV, 2001 as fungi while some others have definite algal and others) and the Yenisey Ridge (the Seryi affinities. The latter include green algae, such Kluch and Dashka formations, NAGOVITSIN, as Archaeoclada (attributed to 2000) of Siberia, from the Southern Urals (the Siphonocladales), Lomentunella (probably Zil'merdak, Nugush, and Inzer formations, VEIS belonging to Ulotrichales), Palaeovaucheria et alii, 2003 and others) and the Mesen' (assigned to Vaucheriales of a xanthophyte syneclise (Vashkin Fm.) of the East-European algae), and Ulophyton and Bangiomorpha Platform (VEIS et alii, 2004). interpreted as red algae (BUTTERFIELD, 2000). In More than 50 species of microfssils are the silicified Siberian microbiotas there are the described from the Upper Riphean assemblages coccoidal microfossils Glenobotrydion, of Russia. The spherical acanthomorphic Palaeastrum and Myxococcoides attributed to acritarch Trachyhystrichosphaera is of a green algae of the order Chlorococcales particular interest, because it appears and (NAGOVITSIN, 2000 and others). Figure 2: Cambrian acritarch-based biostratigraphy of the East-European Platform and stratigraphical positions of recorded acritarch data from the Siberian Platform. The Early? - Late Vendian (V1?-V21) Vychegoda Fm of the Mesen' syneclise, in the northeastern part of the East-European assemblages Platform (VEIS, pers. comm.). These The microfossil assemblages of Early? - Late assemblages are stratigraphically below the Vendian age (0.6-0.55 Ma) are recorded from first appearance of Metazoa. The large spherical the Kursov and Parshin formations of the Nepa- acritarchs (100 - 200 µm in diameter, probably Botuoba region and from the Turkut Fm of the green algae, MOCZYDLOWSKA, 2004), ornamented Lena-Anabar depression of Siberia (RUDAVSKAYA with various processes, are the most & VASIL'EVA, 1989; MOCZYDLOWSKA, 2004). There characteristic features of these assemblages. is but one report of what is probably a Among them species of the genera Tanarium contemporaneous microbiota from the (as Goniosphaeridium), Cavaspina, 23 Carnets de Géologie / Notebooks on Geology - Memoir 2005/02,