Mineralogical indicators of Holocene climate in sediments of the high-mountain Lake Sagan-Nur (East Sayan Mountains)

We present the first results of study of bottom sediments taken from the high-mountain freshwater Lake Sagan-Nur of glacial origin which is located on the Oka plateau (East Sayan Mountains). Comprehensive investigations of the mineral composition of Lake Sagan-Nur sediments accumulated during the last ~8600 cal. years were carried out. The research methods include X-ray diffractometry (XRD), infrared spectroscopy, laser grain size analysis, SiO2bio determination, AMS and 210Pb dating. The mineral composition of the bottom sediments is dominated by layered silicates, quartz and plagioclase; and also, the X-ray amorphous component consisting of biogenic silica and organic matter is constantly present. The method of mathematical modeling of XRD profiles was used for correct identification of the layered silicates. It was found that the clay mineral assemblage was stable comprising muscovite, chlorite, illite, mixed-layer illite-smectite and chlorite-smectite, kaolinite. At the same time, the quantitative ratios of these minerals and their structural characteristics were modified significantly in response to paleoenvironmental changes in the region. This feature reveals the potential of a number of phyllosilicates (illite, mixed-layer minerals) as indicators of paleoclimate in sedimentary sections of freshwater basins. The study of sediment composition and, especially, the precision mineralogical-crystallochemical analysis of layered silicates allowed us to reconstruct the paleolandscapes and climatic conditions of sediment accumulation for different Holocene sub-stages.