SIGNALS OF THE PALEOCLIMATES OF UPPER PLEISTOCENE IN THE SEDIMENTS OF LAKE BAIKAL

Abstract

The paper describes data of analysis of the uppermost (8 to 14 m) layer of bottom sediments of Lake Baikal sampled by tube corers on the top of the underwater Akademichesky Ridge at three sites separated by large distances (30 km). The cores were subjected to primary lithological description, photography on color film and X-ray fluorography. Samples taken at 10 cm intervals were analyzed for the content of water, opal silica, organic carbon, total uranium, molybdenum, and 14 other elements. Quantitative diatom analysis was done at frequency of 2-10 cm using light microscopy. Scanning electron microscopy was applied to ensure correct identification of some diatom species. Pollen grains and sponge spicules were also identified and counted. A section of one of the cores was subjected to paleomagnetic measurements and a magnetic excursion was found. The three cores perfectly correlate with each other exhibiting cyclic changes of the content of opal silica and diatom frustules. 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. The cores correlated with each perfectly correlate other in all parameters, quiet continuous sedimentation. The oceanic stages of warm climates (stages 1, 3, 5) seem to correspond to diatom-rich layers in the Baikalian cores, while the stages of global glaciation (stages 2 and 4) correspond to the beds having no diatoms. The content of diatoms, biogenic silica, and organic carbon positively correlated with U and Mo. The 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 subjected to abrupt and dramatic changes similar to those which were found by G.Bond et al. (1993) for the same time interval for North Atlantic. Typical times of appearance and disappearance of some species of diatoms are small (100-500 years). The paleoclimate record documented in sediments of the Akademichesky Ridge completely satisfies the requirements of international programs in terms of temporal resolution.