Drilling cores from peat deposits of the Vydrinsky bog with a thickness of 4.4 m and an age of 13,100 cal. years, composed of lowland, transitional and high-moor types of peat, were studied in detail. The processes of post-sedimentary transformations of swamp sediments during early diagenesis are considered, the distribution of elements, the formation of authigenic minerals and the chemical composition of swamp waters are studied. The destruction of organic matter begins already in the upper intervals of peat at the early stages of diagenesis. Pyrograms do not have clearly defined high-temperature peaks, “rudiments” of the macromolecular structure of kerogen, which indicates a low degree of transformation of peat organic matter. A high number of organotrophic, ammonifying, nitrifying, phosphate-mobilizing microorganisms, a small number of Fe- and Mn-oxidizing microorganisms, and sulfate-reducing bacteria were revealed. The presence of organotrophic microorganisms throughout the section indicates that the biogeochemical processes of the carbon cycle cover the entire thickness of the peat deposit. A small amount of S (II) indicates a low intensity of sulfate reduction processes. Lowland peat is characterized by high contents of Si, Al, Fe, Ca, Sr, Ba, Zr, La and anomalous contents of Cu, Zn, which is a consequence of the formation of the bog under conditions of rich mineral nutrition. In the ash part of the transitional peat, a decrease in the contents of Si, Fe, Sr, Br, K Si, Ca, Ba, Cu, Zn and La is noted, which reflects the gradual weakening of the connection of the peat deposit with the underlying rocks. In the near-surface horizon of high-moor peat, there is an increase in the contents of K, Mn, Zn, Hg, Pb and As, which is associated with an increase in atmospheric dust and anthropogenic impact on the bog ecosystem in the 20th and 21st centuries. Bog waters of low-lying peat are characterized by high contents of the main ions, Al, Fe, Mn, Sr, while transitional peat is characterized by a decrease in DOC, SO42–, HCO3–, Al, Fe, Ni, Ca, Mg. The oligotrophic strata is characterized by the development of Fe oxides and hydroxides, the presence of vivianite is noted for transitional peats, and the eutrophic part of the peat deposit includes rhodochrosite and sulfides of Fe, Cu, and Zn.