[SEM18-P09] Verification of reducitive chemical demagnetization effect on the sedimentary rocks from the Kokumoto Formation, Kazusa Group, Boso Peninsula
Keywords:Reductive chemical demagnetization, chemical remanent magnetization, Matuyama-Brunhes boundary, Chiba composite section
In this study, RCD was performed on 4 samples collected between the Byk-E and Byk-A key tephra beds, in which the directional polarity reversal corresponding to the M-B boundary was confirmed in Okada et al. (2017). For RCD, an etchant solution whose pH was adjusted with sodium bicarbonate in a 5 % ascorbic acid aqueous solution was used. Thermomagnetic measurements in air were carried out on samples for both of subjected and not subjected to RCD and the sample not subjected to RCD. RCD s were performed by dropping a solution onto two samples out of four samples and immersing the remaining two samples in a solution. Then, thermomagnetic measurements were carried out again on samples for both of subjected and not subjected to RCD. In all the samples not subjected to RCD, the saturation magnetizations which showed gradual decreasing with increasing temperature rose greatly at around 400 ℃. On the other hand, in samples subjected to RCD, it was observed that the increase in saturation magnetization at around 400 ℃ was suppressed. These results suggest that minerals related to thermal alteration is eluted by RCD, and dripping is better than dipping as a method of RCD.