Abstract:
By comparing the compositions of glacial and interglacial intervals of the Late Pliocene, Pleistocene, and Holocene from different parts of Lake Baikal, we demonstrate the use of the Baikal clay mineral associations as indicators of past changes of environment and climate. The methodical part of this work discusses the optimal sample preparation techniques and develops the previously suggested method for structural modeling of X-ray diffraction patterns as the most suitable for studying the Baikal sediments. The clay mineral associations in the Selenga delta area and at the Akademichesky Ridge are very similar, thus indicating a minor influence of local sediment sources on their formation. The similarities revealed by this comparison indicate uniformity of the Baikal catchment basin in terms of the processes of erosion, weathering, and supply of sediments. Despite the conditions of continuous hemipelagic sedimentation at the sites where deep drilling took place, both drill cores reveal a strong relation between the composition of clay mineral associations and paleoclimatic conditions. Intervals if glacial sediments during both the Late Pleistocene and the Late Pliocene are similar and are characterized by dramatic enrichment in well-crystallized mica (muscovite) and plagioclase, indicating intensification of physical weathering under cold climatic conditions. Interglacial intervals are enriched in fine illite, which suggests that it is a secondary mineral, the product of chemical weathering. In addition, the content of smectite layers in mixe layer illite-smectite increases during interglacials, which is also likely to imply a warmer and more humid climate. The lower interval of the BDP-96 core with the age over 4.5 Ma is characterized by an anomalous composition: high content of illite-smectite with a high concentration of smectite component, the presence of chlorite-smectite, and low contents of illite and muscovite. This specific mineral association has formed under climatic conditions much warmer than at present.