The Olkhon region of the Western Pribaikalie is highly attractive for geologists due to the presence of diverse metamorphic complexes and highly complicated combinations of folded structures in this region. The Olkhon region is located within the area of the Pribaikalsky National Park of Russia. At abundant outcrops in the subject area, various geological aspects resulting from the Early Palaeozoic collision system can be studied in detail. By its parameters, the subject area can be considered a «geodynamic proving ground». In recent years, abundant aerospace materials on the area have been accumulated, and long-term field studies resulted in many discoveries and findings which encourage critical revision of the initial conceptions. The material available allows compilation of a new package of geological maps in hard and electronic versions.

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We present results of a complex study of evaporite sediments from one of the small saline lakes with carbonate sedimentation in the Ol’khon area and substantiate their high significance for paleoclimatic reconstructions. The mineral composition of the bottom sediments was studied by XRD analysis, IR spectroscopy, scanning electron microscopy, elemental analysis (SR-XFA), etc. By decomposition of the complex XRD profiles of carbonate minerals into individual peaks by Pearson VII function, we identified carbonate phases in each sample and determined their proportions. A high-resolution carbonate record has been obtained for the first time for the lacustrine sediments. It bears the information about the stratigraphic distribution of Mg-calcites (a continuous series of structurally disordered low- to high-Mg calcites, up to Ca-dolomites), in which the amount and proportions of phases with different Mg contents are controlled by Mg/Ca, salinity, and total alkalinity of the lake water changing depending on the climatic cycles and lake level fluctuations. Comparison of the carbonate record for the Holocene section dated by the radiocarbon (14C) method with results of lithological, diatom, and palynological analyses, data on stable isotopes (δ18O and δ13C), and the distribution of some geochemical indicators of climatic changes permitted the reconstruction of the intricate evolution of the Lake Tsagan-Tyrm basin, which was controlled by the regional climate from the Atlantic period to the present time. The directed change in various characteristics of essentially carbonate sediments evidences that the Ol’khon regional climate has become more arid in recent 6.5 kyr. Moreover, drastic frequent changes of climate and, correspondingly, the Lake Tsagan-Tyrm water level in different periods of its existence have been revealed. The widespread saline and brackish lakes in southern East Siberia, Mongolia, and North China and the highly informative (in terms of paleoclimate and paleolimnology) carbonate sediments might help to recognize the general tendencies of paleoclimate changes and local fluctuations in Central Asia.