Mineral composition and geochemical features of organomineral deposits of the tract of Lake Peschanoe in the southern part of the Amur-Zeya interfluve

Research subject. The article presents the results of a comprehensive study of a column of organomineral deposits (750 cm) in the tract of Lake Peschanoe (Amur Region, between the Amur and Zeya rivers).Material and methods. In the studied section, the composition of organomineral deposits were examined based on radiocarbon dating and palynological analysis.Results. According to radiocarbon dating, the sedimentation began over 4 thousand calendar years. Specific features of the accumulation and distribution of rock-forming oxides and microelements along the organomineral sedimentary profile were established. The mineral composition is dominated by quartz, feldspars, amphiboles, pyrite, garnet and biotite. The highest values of the scattering coefficient in the thickness of the deposits are typical of Hg (8.0), Tl (6.7), La (5.3), below – Zr, Rb and Li (4.7, 4.4 and 4.1, respectively).Conclusions. The study of the geochemical characteristics of organomineral deposits allowed us to identify the industrial period of sedimentation, which was characterized by an increase in the concentrations of Hg, Cd, Pb and Sn. The background contents of elements in the organomineral deposits of the Lake Peschanoe tract can be used as a regional background for deposits in the transboundary territory of the Upper and Middle Amur and its tributaries. The calculated geochemical coefficients indicate the freshwater content of the basin and the alternation of stagnant and oxidizing environments during sedimentation. The increased Ca/Sr values are associated with a change in the climatic regime towards cooling, which occurred during the last 4 thousand years in this area: 4300–4100, 2400–2100, 500–230 years ago.