CLAY MINERALS AND PALEOCLIMATIC SIGNALS IN THE HOLOCENE-PLEISTOCENE SEDIMENTS OF LAKE BAIKAL

Abstract

The deep-water sediments of Lake Baikal retain an uninterrupted record of the climatic and environmental variations of continental Asia in the Late Cenozoic (Baikal drilling project). The paleoclimatic record is based on the rhythmic variability of the content of biogenic silica and diatoms depending on warming/cooling cycles. The biogenic silica accounts for up to 40-60% of sediments during interglacial stages and less than 3-5% during glacial ones. Biogenic paleomarkers characterize lake productivity, but they bear no direct information on weathering conditions in a watershed basin. Such information is included in the terrigenous component, mainly clay minerals. Their composition, structure, and crystallochemical parameters mainly depend on hydrolysis conditions in the weathered rock profile of the watershade. Because of the low salinity of the Lake Baikal waters, postsedimentary alterations of clay minerals are insignificant and can be excluded. However, previous attempts to use clay minerals as paleoclimatic markers yielded significantly inconsistent results. Researchers engaged in paleoclimatic reconstructions have lost interest to these minerals because of the methodical difficulties encountered during analysis of complex multicomponent sediments and the absence of sharp differences in clay mineral assemblages. The present paper demonstrates that the application of special techniques for analysis of terrigenous components of sediments seems to be highly informative for deciphering paleosignals.