A detailed study of geomagnetic excursion by sediments

回顾了布伦什正极性纪年期间的地磁漂移，发现存在23次左右的漂移，其中18次与地球其他地区的多次记录是可靠的。在23次偏移中，有20次偏移与ODP站点983的相对古强度极小值相关，这可能表明在地磁偏移期间地球磁场强度较低。布伦期大量地磁漂移的存在表明，与迄今为止所认为的古磁场图像相比，地球磁场是相当不稳定的。在贝加尔湖的Ver96-2、St. 7地核上获得了冰岛盆地偏移的记录，得到了南非和澳大利亚的虚拟地磁极（VGP）路径，形成了一个以印度为中心的逆时针圆周。这与贝加尔湖的其他VGP路径以及北大西洋和南海的其他记录是一致的，这表明冰岛盆地偏移期间的磁场是偶极子的，正如Laj等人（2006）所建议的那样。最近在MD982195地磁中心发现了两次14和6 ka的地磁偏移，这与中国北京在14和5 ka报道的两次地磁偏移具有相关性（Zhu et al., 1998）。这些偏移可以由Aggasiz冰湖的融水排放引发的1A熔体水脉冲引起的海平面快速上升和绳纹海侵期间的海平面上升引起的核幔边界的差速旋转产生。在14ka的偏移记录需要仔细研究，因为这部分受到磁化率各向异性扰动的影响。

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.