[A-CG33_28PM1] Environmental changes in the Japanese Alps region

[ACG33-01] Diatom analysis on the late Pleistocene Takano Formation, Nagano, Japan

*Koichi NAGAYASU¹, Hiromi OTANI², Fujio KUMON³ (1.Interdisciplinary Graduate School of Science and Technology, Shinshu University, 2.Faculty of Science, Shinshu University, 3.Department of Environmental Sciences, Faculty of Science, Shinshu University)

Diatom analysis has been performed at a 0.5 m interval for a sediment core of 53.88 m length from the late Pleistocene Takano Formation. According to the age-model proposed by Tawara et al. (2006), this core can covers from 170 ka to 40 ka in age and analysis interval correspond to about 1500 years.From 170 ka to 140 ka, benthoic diatoms such as Achnanthes spp. and Staurosira spp. are dominant, and diatom abundance is very low (lower than 1.0×10⁸valves/g). After 140 ka, planktonic diatoms such as Cyclotella radiosa, Aulacoseira ambigua, Cyclotella stelligera, Aulacoseira alpigena are dominant. From 140 ka to 130 ka, C. radiosa is dominant, and diatom abundance is low (1.6 - 6.9×10⁸ valves/g). From 130 ka to 115 ka, Aul. alpigena is dominant, and diatom abundance is high (over 10×10⁸ valves/g). From 115 ka to 100 ka, C. stelligera is dominant, and diatom abundance varies largely (0.1 - 38.2×10⁸ valves/g). From 100 ka to 70 ka, C. radiosa is dominant, and diatom abundance is abundant, between 3.2×10⁸ valves/g and 56×10⁸ valves/g. From 70 ka to 40 ka, C. radiosa and Aul. alpigena are dominant, and diatom abundance is low, fluctuating a little between 0.9×10⁸ valves/g and 20×10⁸ valves/g. These results are compared with the diatoms analysis of the sediment cores from Lake Biwa. After 140 ka, planktonic diatoms are dominant in the Takano Formation, and the diatom assemblage changes synchronously between Takano Formation and Lake Biwa.