Ediakarské mikrobiality z okolí Nového Knína (tepelsko-barrandienská oblast). (Czech)

Ediacaran microbialites from theTown of Nový Knín surroundings (Teplá-Barrandian Unit). (English)

Laminated siliciclastics from the middle part of the Štěchovice Group (Teplá-Barrandian Unit, Czech Republic) contain various arrays of thin ridges, wrinkles, shallow grooves, low warts and other types of the sedimentary surface marks. The analogy with similar textures in younger strata as well as the observation of modern coastal ecosystems showed that they are primary products of an interaction of firm, cohesive cyanobacterial mats with not yet lithified sediment. Microbially induced sedimentary structures (MISS) reflect the morphology of various cyanobacterial communities, which influenced clastic sedimentation from the Archean Era to recent. Reticulate, pustular, wrinkled, and sinuous patterns have been distinguished. Most frequent types of observed textures are closely similar to wrinkled skin pattern of an old elephant and it is therefore referred to as EPS, an elephant skin structure. Modern examples of biofilms and thick, elastic microbial mats occur exclusively in a marine shallow water environment. Prokaryotic microorganism, embedded in a viscous, sticky extracellular substance, took part in trapping of fine detrital particles, in solidification of the substrate and in a preservation of sedimentological features such as ripple-marks and Ediacaran metazoans. Microbialites have been collected from outcrops in ca 500 m long profile of the Štěchovice Group along the Kocába Creek near the town of Nový Knín. Textures are preserved as casts and moulds in rhythmically alternating greywackes and siltstones. One new type of the microbially generated texture is illustrated. Sinusoids are regularly distributed and regularly oriented on a sedimentary surface. A modern analogue of a cyanobacterial biofilm was found at the Slapy Dam. MISS brings new information on sedimentary environment at the late Czech Proterozoic. Microbial mats are formed mostly of photoautotrophic microbes and are therefore confined to insolated shallow coastal facies. The studied samples were deposited not deeper than in a storm-dominated subtidal zone. [ABSTRACT FROM AUTHOR]

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