A detailed study of geomagnetic excursion by sediments

点击翻译按钮获取中文摘要

Geomagnetic excursions during the Brunhes normal polarity Chron were reviewed and it was found that about 23 excursions exist and that 18 of them can be reliable with multiple records from other parts of the globe. Out of 23 excursions, 20 excursions can be correlated with the relative paleointensity minima of ODP Site 983, which may indicate that intensity of the Earth's magnetic field is low during geomagnetic excursions. The existence of large number of geomagnetic excursions during the Brunhes suggest that the Earth's magnetic field is rather unstable compared with the picture of the paleomagnetic field believed until now. A record of Iceland Basin excursion was obtained from Core Ver96-2, St. 7 in Lake Baikal, which gives Virtual Geomagnetic Pole (VGP) path on south Africa and Australia forming a counter clockwise circle around India. This is consistent with the other VGP paths from Lake Baikal and other records from North Atlantic and South China Sea, which suggests that the magnetic field during Iceland Basin excursion was dipoler as Laj et al. (2006) suggested. Two recent geomagnetic excursions were found from Core MD982195 at 14 and 6 ka, which can be correlated with the two excursions reported from Beijing, China at 14 and 5 ka (Zhu et al., 1998). These excursions can be generated by a differential rotation at the Core-Mantle boundary caused by a rapid rise in sea level due to melt water pulse 1A triggered by melt water discharge from Glacial Lake Aggasiz and by a sea level rise during Jomon transgression. The record of an excursion at 14 ka need careful investigation, because this part is affected by a disturbance seen in the anisotropy of magnetic susceptibility.