Microfacies and foraminifers of the Tulian horizon (the Visean substage, Lower Carboniferous) of the southeast of the East European platform and the Southern Urals

The article presents the characteristics of microfacies and foraminiferal complexes of the Tulian horizon of the Visean substage in sections of the Preduralskaya-106 and Oktyabrskaya-106 boreholes in the Eastern part of the Volga-Ural region and the Sikaza 2 section of the western slope of the Southern Urals. The age of the deposits corresponds to the foraminiferal zone Endothyranopsis compressa – Paraarchaediscus koktjubensis of Russia. Based on the study of the microstructures of carbonate rocks, six microfacies (MF) are distinguished, differing in component composition and textures. Limestones are mainly fine-grained polybioclastic packstones. The main components (grains) are the remains of tubular algae, foraminifers, echinoderms (mainly crinoids), ostracods, brachiopods, rarely bryozoans, as well as calcispheres, peloids and intraclasts. The deposits were formed in the conditions of an open shallow shelf of the ramp type with different hydrodynamics. An analysis of the distribution of microfacies in sections and the relationship of foraminifer complexes with them is given.