Тrophic structures and the specifcs of paleocoenosis of the Middle-Upper Carboniferous skeletal mounds on the Shchuger River (Northern Urals)

Abstract

Research subject. Organogenic structures such as the Moscowian-Kasimovian skeletal mounds from the Verkhnie vorota section on the Shchuger River (Northern Urals). Materials and methods. The lithological-paleoecological analysis of biohermal limestones and the determination of their fauna in thin sections (60 samples) and polished slabs (10 samples) taken in outcrops 39 on the Shchuger River, 89 m thick. Results. It is revealed that the Middle-Upper Carboniferous skeletal mounds were characterized by a three-level food chain at three stages of their development. Cyanobacteria, calcimicrobes and green algae were the suppliers of organic matter. Their further consumers were bryozoans, brachiopods, fusulinids, small foraminifera and bacteria. Omnivores and predators were absent. It is found that, heterotrophs were the most common organisms at the stabilization stage, while autotrophs were typical of the colonization stage. The paleocenoses of the Kasimovian skeletal mound had a more extensive composition. Here, each developmental stage was represented by two types of paleocenosis, compared to the Moscowian mound. Conclusions. It is found that the main external abiotic factors that controlled the development of the biocenosis in the sites under study were the hydrodynamic regime and sea level fluctuations. An important internal factor was the development of bio-induced cement on the skeletons of organisms, which contributed to the formation of solid frameworks of buildings. Another internal factor was the widespread occurrence of Anchicodiaceae algae, which caused a decrease in the biodiversity of other groups of organisms. The data obtained allowed us to conclude that a shallow sea basin with a good aeration and low hydrodynamic regime existed in this area in the MiddleLate Carboniferous. A decrease in the basin area in the Late Carboniferous was manifested by a reduction in not only algal taxa, but also the biodiversity of the entire ecosystem.