The Geochemical Features of Microbial Carbonates of the Abalak and Georgian Formations in Western Siberia

Abstract—The geochemical and lithological features of bacterial–algal structures from the top of the Abalak and Georgia Formations in the central part of Western Siberia were studied in order to determine the specific conditions of their formation. The authors compared the element composition of these microbial carbonates with the secondary carbonate rocks of the Abalak and Georgia formations. According to the results of X-ray fluorescence analysis, differences were identified in the contents of MnO, Cr, V, Ni, Cu, and Zn in two types of carbonates. The higher content of MnO in bacterial–algal structures were explained by the ability of bacteria to sorb Mn on the surface of their cells. This process requires oxygen, which suggests the presence of a natural aerobic environment for the development of bacteria during the period of sediment accumulation. According to the results of the study of microbial carbonates under a scanning electron microscope, it was revealed that Mn, for the most part, is concentrated in carbonate minerals, in particular in kutnohorite. The increased content of biophilic elements such as Ni, Cu, Zn, V in microbial carbonates, is probably associated with the transformation of humic organic matter, that was accumulated in shallow water environments and was actively recycled by microbial organisms. Minerals with the high Ba concentration were also found in isolated bacterial–algal structures. According to the authors, such single barium mineralization could be caused by the point effect of both near-surface and deep-seated barium-containing solutions and are not associated with an increased content of manganese in the studied deposits.