Biogeochemical Features of Holocene Sediments in Oligotrophic Bogs of the Baraba Forest Steppe

— The paper presents data on the geochemical processes of postsedimentation transformations of boggy deposits at early diagenesis and the redistribution of chemical elements, including biogenic ones, in the Holocene sections of peat bogs in the Baraba forest-steppe in southern West Siberia. The contents of Fe, Mn, Pb, Hg, Sb, Cd, Cu, and Zn were found out to increase in the upper layers of the peat, whereas the S, N, Ca, and Sr concentrations increase in the middle parts of the peat profiles. The distribution character of various physiological groups of microorganisms in the peat profiles of Ubinskoe and Sherstobitovo peatlands lead to the conclusion that the nitrogen and carbon cycles are more active than that of sulfur. The activity of microorganisms leads to a decrease in pH and Eh in the vertical sections of the peatlands. The high values of NH_4^ + , NO_3^ - , TOC, and the chemical oxygen demand in the bog waters of Ubinskoe and Sherstobitovo bogs indicate that active biochemical decomposition and oxidation of organic matter proceed in these bogs. According to their predominant ions, the waters of the bogs belong to the hydrocarbonate class of the calcium group and are characterized by elevated concentrations of Al, Fe, Cu, and Zn, which is caused by the acid composition of the waters. The low pH values of the bog waters and the oxidizing environment facilitated the development of goethite–hydrogoethite mineralization in the upper horizon of peat profiles. The formation of hematite and anhydrite in the middle parts of the peat profiles was probably caused by paleofires. The authigenic minerals formed in the process of early diagenesis are, first of all, pyrite and less often siderite, calcite, and kaolinite. Under reducing conditions, nanoparticles of native Ni and Ni–Cr intermetallic compounds can be formed, and amorphous silica can be deposited at the dissolution of aluminosilicate minerals from the upper peat horizons.