11:45 AM - 12:00 PM
[SGL19-05] A geomagnetic excursion detected at the lower Matuyama reversed polarity chronozone in a marine Pleistocene sequence distributed in the southernmost Boso Peninsula
Keywords:Matuyama reversed chron, geomagnetic excursion, marine isotopic stratigraphy, Boso Peninsula
In this study, we collected a total of 133 mini-core samples (2.5 cm in diameter) from 44 stratigraphic horizons of siltstone beds at intervals of 10 cm to 1 m in thickness, from a 30-m interval lower than the Feni normal polarity subchronozone in the marine sequence exposed along the stream flowing beside the Komatsji-temple in Minamiboso City, where the magnetostratigraphy was described by Konishi and Okada (2020).
In the paleomagnetic measurements, we used a hybrid demagnetization technique that combines a thermal demagnetization at 250°C and progressive AF demagnetization, which is effective for this sequence by Konishi and Okada (2020). The average declination calculated from the results is about 16°E. The latitude and longitude of the VGP were calculated from the declination and declination obtained by removing the effect of structural rotation using this value. As a result, it was confirmed that there are two consecutive sections where the VGP latitude ranges from -45° to +45° with a decrease in RPI, which can be judged as geomagnetic excursions. According to a tentative age model using oxygen isotope curves obtained from the stratigraphic level, the ages of the two excursions detected are calculated to be approximately 2.173 Ma and 2.176 Ma, respectively. Since no geomagnetic excursions have been reported near these ages, the two consecutive excursions detected in this study are considered discoveries.
Referece: Konishi and Okada (2020) https://doi.org/10.1186/s40645-020-00352-0
In the paleomagnetic measurements, we used a hybrid demagnetization technique that combines a thermal demagnetization at 250°C and progressive AF demagnetization, which is effective for this sequence by Konishi and Okada (2020). The average declination calculated from the results is about 16°E. The latitude and longitude of the VGP were calculated from the declination and declination obtained by removing the effect of structural rotation using this value. As a result, it was confirmed that there are two consecutive sections where the VGP latitude ranges from -45° to +45° with a decrease in RPI, which can be judged as geomagnetic excursions. According to a tentative age model using oxygen isotope curves obtained from the stratigraphic level, the ages of the two excursions detected are calculated to be approximately 2.173 Ma and 2.176 Ma, respectively. Since no geomagnetic excursions have been reported near these ages, the two consecutive excursions detected in this study are considered discoveries.
Referece: Konishi and Okada (2020) https://doi.org/10.1186/s40645-020-00352-0