Geochemistry of Early Diagenesis of Bog Deposits by the Example of the Holocene Section of the Dulikha Peat Bog (Eastern Baikal Region)

Abstract

Abstract —Two cores of the Dulikha peat bog deposits, 4.0 and 5.2 m thick, were studied in detail. The reduction type of diagenesis has been established. Decomposition of the organic matter of the bog deposits begins already in the upper intervals of the section at the earliest stages of diagenesis. Microbiological studies of the peat bog revealed numerous organotrophic, ammonifying, nitrifying, and phosphate-mobilizing microorganisms as well as Fe-Ox and Mn-Ox microorganisms and showed the almost complete absence of sulfate-reducing bacteria (except for the lower intervals of the peat section). The processes of the nitrogen, phosphorus, and carbon cycles are more active than the sulfur cycle processes. The chemical composition of the bog water changes during diagenesis. The contents of HCO3-, NH4+, PO43-, NO3- and Corg increase in the peat bog section, which is the result of the destruction of organic matter, leading to the transition of the most mobile and labile components into the bog water. The results of physicochemical modeling show that the high content of organic matter significantly changes the chemical composition of the bog water. The enrichment of the latter in Cu, Zn, Sr, Ba, As, Si, Al, and Pb indicates a diagenetic transformation of the bog deposits. A change of oxidizing conditions by reducing ones in the peat bog leads to the reduction of oxidized Fe (III) and Mn (IV) forms to mobile Fe (II) and Mn (II) forms and their subsequent migration from the solid phase of deposits into the bog water. With depth, the reduced S (II) forms become predominant in the peat, which indicates more reducing environmental conditions. The concentration of SO42- decreases in the pore water of the peat-underlying mineral deposits, which marks the beginning of sulfate reduction. This process, however, is very slow in the bog deposits because of the acid environmental conditions and the lower degree of transformation of organic matter.