Calcareous algae and foraminifera of the microfaunistic horizon XIII (Visean stage) of the middle part of the central paraxial zone Dnipro-Donets Depression (Ukraine)

Visean deposits of exploration-production well 363 Yablunivs'ka contain predominantly carbonate and argillaceous rocks from the Pryluts'kyy boundary (lower Visean). This study presents limestone microfacies and foraminiferal and calcareous algal associations of the paraxial zone in the Dnipro-Donets Depression. The foraminiferal association is represented by 26 genera, whereas the algal association is composed of 24 identified species and specimens in open nomenclature representative of 31 genera, including a new species, Atractyliopsis berezovia sp. nov., and a species of calcareous algae, which is first described for Dnieper-Donets Depression, Asphaltina cordillerensis. Fossil associations of calcareous algae characterize Palaeoberesella lahuseni - Exvotarisella index - Nanopora woodi zone, which correlated with the foraminiferal Uralodiscus rotundus and Paraarchaediscus koktjubensis. Green algae are predominant within the calcareous algae from carbonate deposits of the core No 3. This predominance indicates a warm and shallow-water sedimentation platform. Many archedicids indicates that the bottom substrate is represented by soft silt. Well-developed radiant layer of archaediscida indicates to the favorable habitat conditions. From the middle part of the layer, the role of red algae, whose thally has a crusty and leaf-like shape, as well as green Koninckopora sp. and Coeloporella sp., begins to grow quantitatively. This indicates an insignificant shallowing of the sedimentation basin. Visean limestones belong to the facies of the open marine platform, zone 7 (shallow undathem). According to the results of micropaleontological analysis the boundary of XIIIl and XIIIu microfaunistic subhorizon of Dnipro-Donets Basin identified at the depth of 4435.96 m. The foraminifera and algae representation is given at the 8 paleontological plates.