A geomagnetic excursion during the late Matuyama Chron, the Osaka Group, southwest Japan

• Published in: Earth and planetary science letters 1995-12, Vol.136 (3), p.511-524
• Main Authors: Takatsugi, Kaori O., Hyodo, Masayuki
• Format: Article
• Language: English
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/0012-821X(95)00175-C

Duplicate records of a geomagnetic excursion during the late Matuyama Chron were obtained from sediments gathered at the Takatsuki and Izumi sites in southwest Japan. The excursion is dominated by westerly declinations with shallow inclinations, and was found just above the volcanic ash known as the Azuki Tuff, in a marine clay layer of the Osaka Group. The excursion occurred at about 0.85 Ma, a recently revised age for the Azuki Tuff. By extrapolating constant sedimentation rates for the Holocene marine clay dated by the radiocarbon method, the duration of the excursion is estimated at about 240 yr, with a range of 200–500 yr if we consider possible fluctuations in sedimentation rates. The Kamikatsura excursion previously reported around this time from the Osaka Group data is estimated to be a few tens of thousands of years older than the excursion reported in this study, based on correlations of changes in sea level recorded in the sediments of the Osaka Group and the oxygen isotope record of deep-sea cores. These two excursions in Japan, together with short normal events reported in the Southern Ocean, North America and China, suggest that during the period from 0.87-0.84 Ma the geomagnetic field may have been unstable, and excursions or short reversals may have occurred regionally and sporadically over the earth.