HR: 0830h
AN: GP31D-0772    [PDF]
TI: Geomagnetic Excursions of the Late Brunhes Chron Detected in a Piston Core Sample (MD012421) from the Western North Pacific off Kashima
AU: * Hayashida, A
EM: ahay@doshisha.ac.jp
AF: Science and Engineering Research Institute, Doshisha University, Kyo-Tanabe, Kyoto, 610-0321 Japan
AU: Oda, H
EM: hirokuni-oda@aist.go.jp
AF: Geological Survey of Japan, AIST Tsukuba Central 7, Tsukuba, 305-8567 Japan
AB: Several records of geomagnetic excursions of the Brunhes chron have been reported from Japan, including a pioneering work in Lake Biwa. It is difficult, however, to investigate detailed features and possible correlation of these reported excursion records at present, mainly because of unresolved issues about chronology and reliability of the older paleomagnetic records. In order to clarify the nature of such geomagnetic excursions, we have made paleomagnetic study of a giant piston core MD012421 obtained during the IMAGES cruise in the western North Pacific off Kashima. Oxygen isotope study along with AMS radiocarbon dating and tephrostratigraphy established high-resolution chronology of this core, covering the time interval from oxygen isotope stage 6 to the present with an average sedimentation rate about 30 cm/ka. We obtained u-channel samples from the entire sequence and subjected them to pass-through measurements of natural remanent magnetization and stepwise alternating field demagnetizations. We also measured anisotropy of low-field magnetic susceptibility (AMS) of discrete cubic samples to investigate sedimentary fabrics. Although the AMS data suggest that the sediments were partly deformed during core recovery, this core provides a high-resolution paleomagnetic record for the last 140 kyrs. Anomalous paleomagnetic directions occur at two horizons between MI events 5.4 and 5.5, yielding VGP paths which are consistent with the Blake excursion reported from Chinese loess-paleosol and volcanic sequences. On the other hand, no significant fluctuations of the paleomagnetic directions correlative to the Mono Lake and/or Laschamp excursions are observed, while the interval around 40 ka is characterized by low paleomagnetic intensity. This result suggests that these phenomena may have caused no anomalous geomagnetic field direction around the Japanese Islands, while the occurrence might be associated with minima of the main dipole field intensity.
DE: 1513 Geomagnetic excursions
DE: 1518 Magnetic fabrics and anisotropy
DE: 1520 Magnetostratigraphy
DE: 1521 Paleointensity
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting