Abstract
The brine and long drilling core (4.8 m) of bottom sediments of the hypersaline Lake Maloe Yarovoe were studied. For the first time, the detailed chemical composition of pore waters and microbial diversity of bottom sediments were studied along the section. A complex mineral composition of sediments was revealed, reflecting the evolution of salinity and changes in sedimentation conditions in the Holocene Epoch. In the upper horizons, the mineral composition of the sediment is dominated by halite, quartz, and plagioclase, while in the chemical composition, Na and terrigenous elements (Si, Al, Fe, K) are associated with greater salinity and a high level of lake waters, while in the lower intervals, an increase in gypsum, calcite, magnesite, as well as Ca, Mg, Sr, U, Stot, S (VI) is noted, which indicates a drop in salinity and the level of lake waters in the past. Authigenic minerals (pyrite, hydrotroilite, siderite, ankerite) are formed in reducing environmental conditions, in the process of bacterial sulfate reduction. Distribution of biogenic elements along the section is stratified: maximum TOC (up to 3.2%) and TN (up to 0.52%) in the upper sediment layers is associated with accumulation of OM of planktonic genesis, and a decrease with depth reflects destruction of OM during diagenesis and changes in the bioproductivity of the lake. In pore waters, in comparison with brine, an increase in the average contents of ions SO42−,PO43−,Ca2+ and dissolved elements – Si, Al, Fe, Mn, Mo – is noted. A trend is observed for a decrease in Cl– concentrations with depth and an increase HCO3−,Ca2+,Sr2+, and Mn2+ in pore waters, which indicates some decrease in the salinity of lake waters and more intense processes of carbonate sedimentation. Cyanobacterial mats play an important role in the biogeochemical cycles of the lake, they accumulate Zn, S and Mg in their composition, and their microbial communities (Pseudomonadota, Cyanobacteriota, Rhodothermota) create unique conditions for the formation of zinc sulfides, copper carbonates, as well as sulfides and intermetallics of noble metals (Ag–Au). Microbial processes play a key role in the formation of authigenic minerals and the destruction of organic matter during diagenesis.