Reconstruction of the Holocene climate based on a carbonate sedimentary record from shallow saline Lake Verkhnee Beloe (western Transbaikalia)

We present results of mineralogical and crystallochemical studies of the Holocene carbonate sediments of a small saline lake localized in the Borgoi dry-steppe region, western Transbaikalia. Mg-calcites with a varying Mg content are predominant in the assemblage of endogenic carbonate minerals from bottom sediments. Mathematical modeling of the XRD spectra of carbonates permitted us to identify excess-Ca dolomites, which are an indicator of a shallow (playa) lake. The studies showed that the lacustrine Mg-calcites do not form a continuous series from low- to high-Mg varieties. We discuss the cause of this phenomenon and also consider the existing viewpoints of the structure of low-temperature Mg-calcites and excess-Ca dolomites and their formation conditions in lacustrine sediments. Juxtaposing the carbonate record with the data of lithological analysis, determined stable isotopes (δ¹⁸O and δ¹³C), and distribution of some geochemical indicators of climatic changes, we reconstructed the intricate evolution of Lake Verkhnee Beloe, which was controlled by the regional climate since the postglacial period till the present day.     

Detailed Holocene climate record from the carbonate section of saline Lake Tsagan-Tyrm (West Baikal area)

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.     

Climatic signals in the Holocene carbonate sedimentary record of Namshi-Nur lake,West Baikal region

A new high-resolution Holocene climate record of the Western Baikal region from the evaporite sediments of one of the small saline lakes with the carbonate type of sedimentation are obtained on the basis of detailed mineralogical and crystallochemical studies of chemogenic carbonates. All carbonate phases occurring in the sediment are identified by decomposition of complex XRD-profiles of carbonates into individual peaks using the Pearson VII function, and the quantitative relationships between them are determined. Mg-calcites provide the major paleoclimatic information. The carbonate record contains data on the stratigraphic distribution of Mg-calcites, in which the number and ratio between the phases of different magnesium contents are determined by the past values of the Mg/Ca ratio, salinity, and total alkalinity of lake water that vary according to climatic cycles and fluctuations of the lake level. The high potential of the approach proposed for paleoclimatic reconstructions is demonstrated.