DISTRIBUTION OF BRYOZOANS IN VARIOUS FACIES OF EMSIAN SALAIR FORMATIONS
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Abstract (English):

The article analyzes the facial dissimilarity of bryozoans of the Emsian Stage near the town of Gyr’evsk. The bryozoans associations have been found in all types of facies, except the sand-mudstone one. In the littoral facies (bioclastic limestones with subordinate sand-mud-siltstones rock) the bryozoans are represented by the orders of Trepostomida, Fenestellida, Cryptostomida, Cystoporida, but treposomides predominate (63 % of the total number of species). After the littoral facies turn into the facies of the open lagoon (mudstones with subordinate limestones), only trepostomides are represented in the Emsian section, near the boundary, forming the Briozoan interbeds. Briozoan interbeds consist of the fragments of Neotrematopora salairiensis colonies. The restoration of species and genus diversity in new facies occurs relatively quickly. In comparison with trepostomides, representatives of other orders appear with a large time-lag. Under the conditions of an open lagoon, bryozoans are characterized mainly by branched bifoliate colonies. In the slope facies (bedded limestones), characterized by greater depths and low hydrodynamics, fennestellids dominate (58 % of the total number of species). Trepostomides and cystoporides in these facies are represented by species with thick-branched and massive branched colonies. When the facies of bedded limestones change to sandy-mudstones (the beginning of the regression), the fenestellids also form Briozoan interbeds near the boundary. In the lateral rows of the facies of a single stratigraphic unit, several facial associations of bryozoans are often found. The species of bryozoans characteristic of this stratigraphic level are present in all associations. The unity of the Emsian complex of bryozoans is expressed in the gradual change of their associations upwards the section (three Briozoanbiostratigraphic Zones have been identified).



Keywords:
bryozoa, Emsian Stage, Salair, associations, littoral facies, open lagoon facies, slope facies
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