Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

The chemical composition of bottom sediments and pore waters of organic-mineral sediments (sapropel) of Lake Kotokel (Eastern Baikal region) based on long drilling cores, 14.5 and 16.5 m. A reduction type of diagenesis has been established, during which destruction of organic matter occurs, transformation of the chemical composition of pore waters and the formation of authigenic minerals. Already in the uppermost intervals of sapropels, organic matter is subject to deep transformation processes and differs significantly in composition from that of bioproducers (plankton). The main role in diagenetic transformations of organic matter belongs to different physiological groups of microorganisms, primarily heterotrophic, amonifying and sulfate-reducing bacteria. During diagenesis, there is a change in the basic chemical composition of pore waters (HCO₃^–, SO₄^2–, Cl^–, Ca²⁺, Mg²⁺, K⁺, Na⁺), a redistribution of trace elements (Fe, Mn, Sr, Ba, Pb, As, Co, Ni) and an increase concentrations of HCO₃^–, NH₄⁺, PO₄^3–, and Si, which is a consequence of the destruction of organic matter. In the process of bacterial sulfate reduction in pore waters, the concentration of SO₄^2– decreases along the depth of the section, and in the sediment the proportion of reduced forms of sulfur increases and the isotopic composition of δ³⁴S changes. Transformation of the chemical composition of pore waters and the activity of microorganisms leads to the formation of authigenic pyrite, rhodochrosite, and barite.