Boreskov

CYANO‐BACTERIAL MATS OF HOT SPRINGS IN BARGUZIN BASIN(BAIKAL RIFT ZONE) AS A MODEL FOR STUDYING EARLY ECOSYSTEMAND MINERAL FORMATIONLazareva E. 1 , Taran O. 2 , Brynskaya A. 3 , Parmon V. 2 , Zhmodik S. 1PP‐251 Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia, lazareva@igm.nsc.ru2 Boreskov Institute of Catalysis, Prospekt Lavrentieva, 5, 630090, Novosibirsk, Russia3 Institute of Cytology and Genetics SB RAS, Novosibirsk, RussiaThe oldest lithified cyanobacteria found in sediments date back to 3.6 Ga (Dobretsov,2005). Well‐preserved cyanobacteria older than 3.46 billion years were found in WesternAustralia (Brun and Lawrence, 2000). However biogenic origin of Australian stormatolites isstill being discussed (Allwood et al., 2006). Today’s cyanobacteria have been expelled toextreme habitats, such as hot springs where thermophilic communities can live. Based uponstudying of hydrotermes microbial communities, one can get information about theprocesses which occurred in early prokaryotic world and its significance for the formation ofrocks and ecosystem.There are a lot of hot springs (more than ten) within the Barguzin river basin of the BaikalRift Zone. Bacteria populations were found at all venting sites (Namsaraev et al., 2006).However carbonate agglomerates are only formed at three sites (Alla, Garga, and Gusikha)(Plyusnin at al., 2000). The largest carbonate body is formed on the Garga hot spring. TheGarga hot spring stream has Na‐SO 4 composition (TDS = 1 g/l, T=77°С, pH‐8.2). Alkaline,alkaline‐earth (Li, Rb, Sr, Cs, Ba) and anionogenic elements (Si (30‐45 ppm), Ge, Mo, W) areprevailing in the solutions.The carbonate body thickness is 3‐5 m. Cyanobacterial mat (T 54‐49°C) grows at the surface of this body. Phormidium, Mastigocladus and Oscillatoria speciesare dominate in the microbial community. The Gagra microbial mat structure was studied byscanning and transmission electron microscopy. In the thermophilic cyano‐bacterialcommunity calcite precipitates in the form of well‐faceted crystals ranging in size from 20 to40 m. Transmission electron microscopy studies showed the structure of microbial mat. Avariety of morphology of the bacteria among the cysts or spores, and rests of lysed cells isfound. Local analysis of elemental composition showed that silica is concentrated mainly in athick layer of cellular slime surrounding the bacterial cells. Monocrystals of calciumcarbonate were found in the intracellular space. Hollow nanosized calcium phosphatesphere were detected inside of the bacterium cells. The mineral formation processes in the175