ISOTOPIC COMPOSITION OF URANIUM AND THORI UM IN THE ORGANIC FRACTION OF BOTTOM SEDIMENTS OF LAKE BAIKAL

The isotopic composition of uranium and thorium in bottom sediments en riched in autochthonous humified organic matter was studied. The U-234 /U-238, Th-230/U-234, and other isotope ratios were shown to regularly change through the bottom-sediment column and form separate fields fo r the water of Lake Baikal, organic phase of bottom sediments, and dia toms in the U-234-U-238-Th-230 activity triangle. This places the isot opic composition of uranium and thorium in with other geochemical mark ers of climatic conditions that contribute to the growth of biologic p roductivity of Lake Baikal.