SIGNALS OF THE PALEOCLIMATES OF UPPER PLE ISTOCENE IN THE SEDIMENTS OF LAKE-BAIKAL

The paper describes data of analysis of the uppermost (8 to 14 m) laye r of bottom sediments of Lake Baikal sampled by tube corers on the top of the underwater Akademichesky Ridge at three sites separated by lar ge distances (30 km). The cores were subjected to primary lithological description, photography on color film and X-ray fluorography. Sample s taken at 10 cm intervals were analyzed for the content of water, opa l silica, organic carbon, total uranium, molybdenum, and 14 other elem ents. Quantitative diatom analysis was done at frequency of 2-10 cm us ing light microscopy. Scanning electron microscopy was applied to ensu re correct identification of some diatom species. Pollen grains and sp onge spicules were also identified and counted. A section of one of th e cores was subjected to paleomagnetic measurements and a magnetic exc ursion was found. The three cores perfectly correlate with each other exhibiting cyclic changes of the content of opal silica and diatom fru stules. A new method of thorium-uranium dating was applied to data on the activities of uranium series isotopes obtained by Egdington et al. (1994) and showed that the age of one of core is ca. 100,000 years. T he cores correlated with each perfectly correlate other in all paramet ers, quiet continuous sedimentation. The oceanic stages of warm climat es (stages 1, 3, 5) seem to correspond to diatom-rich layers in the Ba ikalian cores, while the stages of global glaciation (stages 2 and 4) correspond to the beds having no diatoms. The content of diatoms, biog enic silica, and organic carbon positively correlated with U and Mo. T he profile of the content of diatoms taken at a 2-cm frequency for one of the cores suggests that the paleoclimates of East Siberia were sub jected to abrupt and dramatic changes similar to which were found by G . Bond et al. (1993) for the same time interval for North Atlantic. Ty pical times of appearance and disappearance of some species off diatom s are small (100-500 years). The paleoclimate record documented in sed iments of the Akademichesky Ridge completely satisfies the requirement s of international programs in terms of temporal resolution.