Age of long sediment cores from Lake Baikal

The most important issue in the dating of the long Baikal core (600 m) is whether the segment between the base of C3An.2n and the top of C3Bn (267.67–375.48 m) is distorted. Changes in γ-ray intensity (H. Tsukahara et al., personal communication), which reflects the structure of the cores, indicate that this part is different from the rest (strictly speaking, the upper and lower shifting points seem to be at around 262 m and 362 m, respectively, from the fluctuation). To investigate this difference, we carried out spectral analyses of the upper section of the core (163–261 m), and of the middle (263–361 m) and lower (363–673 m) parts. Prevailing periods for each part are different, particularly in the middle one. There is a distinct common prevailing period of around 4.5–4.9 m in the upper and lower parts, whereas a period of 18 m prevails in the middle part, suggesting that the structure of the middle is different from the upper and lower parts of the core.