Distribution of recent clay minerals as a possible indicator of sediment sources in the North Basin of Lake Baikal

Analyses of clay minerals have been performed on recent and ancient (age <9 00 years) sediments of the west-east trending Zavorotnyi transect in the No rth Basin of Lake Baikal (southeastern Siberia). The aim was to study clay minerals to identify the characteristics of the eastern and western sedimen ts and to relate them to catchment areas or to sedimentation mechanisms. Ap art from illite, which is the most abundant mineral along the transect, the clay mineralogy changes distinctly between the eastern and western sedimen ts. The western clayey sediments are characterized by high chlorite content s, low smectite and kaolinite contents, and a general good crystallinity of all clay minerals. The eastern clayey sediments have lower chlorite conten ts, higher smectite and kaolinite contents, and poorer crystallinity of the clay minerals. We suggest that differences in the geological background an d morphology of the catchment areas lead to these differences between the e astern and western surface elements as a result of different weathering and transport mechanisms prior to sedimentation. The smectite content and illi te-chlorite ratio are possible indicators for differentiating between the w estern and eastern predominant sediments. From this interpretation it follo ws that western catchment areas supplied the turbidites accumulated in the center of the Zavorotnyi transect. The great variability in distribution of clay minerals over a few hundred years, most pronounced in the smectite co ntent and illite-chlorite ratio, indicates significant changes in the facto rs controlling sedimentation in the North Basin. This must be taken into ac count when using the distribution of clay minerals in Baikal sediments for paleoreconstructions.