Geochemistry and Mineralogy of Organic-Mineral Bottom Sediment of Small Lakes in the Middle Mountains of the Russian Altai: A Case Study of the Chibitka Lake System

The article introduces the first geochemical and mineralogical data regarding the organicmineral bottom sediment in the small middle mountain lakes (Chibitka Lake system, Russian Altai). The lacustrine sediments are sapropel and mineral silt, which are formed in the nival type of lithogenesis (cryolithogenesis). Sapropel is categorized into three types based on ash content (A, %): organic-mineral (42–46), mineral-organic (66), and mineralized (81) and primarily belongs to the silicon class and macrophytic species. The bottom sediment geochemistry is impacted by cryolithogenesis processes, reflecting the composition of the soil-forming substrate and the soils within the catchment area. Based on an initial assessment of heavy metals (mg/kg) – Cd (0.044–0.159), Pb (7–34), Hg (0.047–0.197), trace elements (mg/kg) – Cu (26–71), Mn (0.03–0.04), Cr (56–83), Co (7–13), Ni (34–52), technogenic 137Cs (32–154 Bq/kg) and the total effective specific activity of natural radionuclides (Ac – 5.5–14.8 Bq/kg), sapropels belong to the first class of suitability in accordance with GOST (the Russian interstate system of technical standards). The presence of authigenic low-Mg calcite, gypsum, and halite has been identified in the bottom sediment of freshwater Lake Biryuzovoe. The formation of these minerals is a result of various factors influenced by the cryolithogenesis, such as shallow depth, ice thickness, cryogenic concentration, and HCO3 – Ca water composition with a high SO4 content.