MINERAL COMPOSITION AND FORMATION CONDITIONS OF BOTTOM SEDIMENTS OF THE SMALL LAKES IF THE UKOK PLATEAU (ALTAI)<a href="#FN1"><sup>1</sup></a>

Abstract

Numerous modern lakes appeared in the intermountain basins and on the high-elevation plateaus of Altai within the immediate distribution of glaciation in the Neo-Pleistocene. There is little known about the geochemical processes of autigenic mineral formation in lake systems under conditions of nival sedimentogenesis. The study of cores of bottom sediments of 8 high-altitude lakes of Altai showed that the waters of the lakes are fresh bicarbonate with variations in the cationic composition of Ca–Na. The bottom sediments of lakes are characterized by different ratios of mineral detrital material, autigenic minerals (calcite, gypsum, pyrite, illite) and mortmass of plant residues. In the bottom sediments of lakes located within the same basin (Bertek or Tarkhatinskaya), the absolute concentrations of elements differ within one standard deviation, with the exception of significant variations in the contents of individual elements (Mo, U, Li, Be). The enrichment of bottom sediments of lakes (Argamdzhi, Teply Klyuch, Krasnoe) with these elements is associated with the presence of ore concentrations (Mo, U, Li, Be) in the local catchment areas of a single lake. The mineral associations of the sediments of the studied lakes differ from each other in the composition of autigenic minerals, and from rocks, soils of catchment areas in the composition of layered silicates. In the composition of fine-scaled, tangled fibrous aggregates of the bottom sediment illite, the amount of iron is 2-4 times greater than in the composition of lamellar aggregates of micas, chlorites from rocks, soils of catchment areas. Cryogenic processes have determined the crystallization of gypsum nodules in the lakes Argamdzhi and Small Tarkhatinskoye; and calcite aggregates in Zerlyukol-Nur and Large Tarkhatinskoye in significant volumes for lakes with fresh water composition.