Microfossils in carbonaceous cherts from Barrandian Neoproterozoic (Blovice Formation, Czech Republic)


Authors: Vavrdová M

Published in: Bulletin of Geosciences, volume 75, issue 3; pages: 351 - 360;

Keywords: Neoproterozoic, Blovice Formation, stromatolites, silicified microbiota, palaeoecology,

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Silicified organic-walled microfossils occur abundantly in dark carbonaceous cherts of Neoproterozoic age (Kralupy-Zbraslav Group, Teplá-Barrandian Unit). Investigated localities of siliceous lenses, which outcrop mostly in the lower part of the Bohemian Neoproterozoic succession, yielded rare planktonic acritarchs, large agglomerations of coccoidal cyanobacteria, filamentous microbial mats, degraded trichomes of algal and/or cyanobacterial origin, colonial forms and vase-shaped bodies. Three successive 'generations' have been distinguished among recovered associations, based on dominating mat-forming (Gunflintia - Eomicrocoleus - Siphonophycus) and planktic (Huroniospora - Leiosphaeridia - Buedingiisphaeridium) microfossils. Stromatolitic biosedimentary textures and structures have been ascertained in algal laminites from the Stříbro-Plasy metamorphic belt, Main volcanic belt and Nepomuky-Příbram belt. Recently, stromatolitic textures have been recognized in the northern part of the Barrandian Neoproterozoic basin, in area between Prague, Kralupy and Slaný. Recovered organic remains indicate primary chemogenous, most probably carbonate nature of silicites and silicified sediments. Together with additional geochemical, mineralogical, and sedimentological evidence, recovered microfossils enabled to recognize the following sedimentary biofacies in the Bohemian Late Proterozoic coastal sequences: subtidal limestones with oolitic and algal intraclasts, restricted basins with organic sludge, tidally influenced facies of stromatolitic build-ups, volcanoclastic sequences and supratidal evaporitic algal marshes.