HR: 0830h
AN: GP41B-0050    [PDF]
TI: Environmental magnetic records of core sediments for the past 100 ka from Erhai Lake in China and Sogwipo Maar in Korea
AU: * Fukuoka, M
EM: s020112d@mbox.nagoya-u.ac.jp
AF: Department of Earth Environmental Science, Graduate School of Environmental Studies, Nagoya university, Furo-cho, Chikusa-ku, Nagoya, 464-8601 Japan
AU: Hayashida, A
EM: ahay@doshisha.ac.jp
AF: Science and Engineering Research Institute, Doshisha.University, Kyo-Tanabe, Kyoto, 610-0321 Japan
AU: Yasuda, Y
EM: yangtze@nichibun.ac.jp
AF: The International Research Center for Japanese Studies, -2 Oeyama-cho, Goryo, Nishikyo-ku, Kyoto, 610-1192 Japan
AB: In order to detect high-resolution records of environmental changes in East Asia, we made environmental magnetic study of core sediments from Sogwipo Maar in Cheju Island, Korea (9.4 m long), and Erhai Lake in Yunnan Province, China (10.0 m and 42.6 m). Measurements of initial susceptibility (k), natural remanent magnetization (NRM), anhysteretic remanent magnetization (ARM) and isothermal remanent magnetization (IRM) were made by pass-through method using u-channel samples from both cores. Results of AMS radiocarbon dating suggest that the Sogwipo core is dated from 5 ka to 30 ka, and that the upper 16 m of the Erhai core is dated from 2 ka to 30 ka. Variation of NRM intensity of both cores, when normalized by ARM and IRM, showed similarity with paleointensity stack Sint-800 between 15 ka and 100 ka. Variation of magnetic concentration parameters of the Sogwipo core was consistent with lithological changes. In particular, magnetic minerals in the upper part seem to be diluted by increased biogenic productivity after 15 ka. The topmost part of the Erhai core showed rapid downcore decrease of magnetic concentration associated with increase of magnetic grain size, suggesting reductive environment before 3 ka. Negative correlation between magnetic concentration and magnetic grain size may indicate a gradual change in degree of the reductive diagenesis. In both cores, significant increases of ARM susceptibility were observed at several horizons, which can be correlated to interstadial periods of the Dansgarrd-Oeschger cycles. The increase of ARM susceptibility suggests that input of fine magnetic minerals were enhanced under increased precipitation due to activity of the Monsoon activity during the warm periods.
DE: 1512 Environmental magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting