Differences in glacial and interglacial clay mineral associations of Baikal sediments from BDP-93-2 and BDP-96 cores

By comparing the compositions of glacial and interglacial intervals of the Late Pliocene, Pleistocene, and Holocene from different parts of Lake Baika l, we demonstrate the use of the Baikal clay mineral associations as indica tors of past changes of environment and climate. The methodical part of thi s work discusses the optimal sample preparation techniques and develops the previously suggested method for structural modeling of X-ray diffraction p atterns as the most suitable for studying the Baikal sediments, The clay mi neral associations in the Selenga delta area and at the Akademichesky Ridge are very similar, thus indicating a minor influence of local sediment sour ces on their formation. The similarities revealed by this comparison indica te uniformity of the Baikal catchment basin in terms of the processes of er osion, 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 cond itions. 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 intensif ication of physical weathering under cold climatic conditions, Interglacial intervals are enriched in fine illite, which suggests that it is a seconda ry mineral, the product of chemical weathering. In addition, the content of smectite layers in mire layer illite-smectite increases during interglacia ls, 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 character ized by an anomalous composition: high content of illite-smectite with a hi gh 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.