Magnetic observation of ODP Site 152-919 in the Irminger Basin, North Atlantic

Component natural remanent magnetizations derived from u-channel and 1-qcm discrete samples from ODP Site 919 (Irminger Basin) indicate the existence of four intervals of negative inclinations in the upper Brunhes Chronozone. According to the age model based on planktic oxygen isotope data, these “excursional” intervals occur in sediments deposited during the following time intervals: 32-34 ka, 39-41 ka, 180-188 ka and 205-225 ka. These time intervals correspond to polarity excursions detected elsewhere, known as Mono Lake, Laschamp, Iceland Basin and Pringle Falls. The isotope-based age model is supported by the normalized remanence (paleointensity) record that can be correlated to other calibrated paleointensity records for the 0–500 ka interval, such as that from ODP Site 983. For the intervals associated with the Mono Lake and Laschamp excursions, virtual geomagnetic poles (VGPs) reach equatorial latitudes and mid-southerly latitudes, respectively. For intervals associated with the Iceland Basin and Pringle Falls excursions, repeated excursions of VGPs to high southerly latitudes indicate rapid directional swings rather than a single short-lived polarity reversal. The directional instability associated with polarity excursions is not often recorded, probably due to smoothing of the sedimentary record by the process of detrital remanence (DRM) acquisition.对取自大洋钻探计划（Ocean Drilling Program, ODP）919站位（伊尔明厄海盆）的u-channel样品与1-qcm离散样品的分量天然剩余磁化强度进行分析后发现，布容正向磁性带（Brunhes Chronozone）上部存在四个负倾角区间。基于浮游氧同位素数据构建的年代模型显示，这些极性漂移区间赋存于以下时段沉积的沉积物中：32~34 ka、39~41 ka、180~188 ka及205~225 ka。上述时段分别对应于全球其他区域已被识别的极性漂移（polarity excursions）事件，即莫诺湖（Mono Lake）漂移、拉斯尚普（Laschamp）漂移、冰岛海盆（Iceland Basin）漂移与普林格尔福尔斯（Pringle Falls）漂移。该基于同位素的年代模型得到了归一化剩余磁化（古强度）记录的佐证，该记录可与0~500 ka时段内其他已校准的古强度记录（如大洋钻探计划983站位的记录）进行对比。对应莫诺湖与拉斯尚普漂移的时段内，虚拟地磁极（virtual geomagnetic poles, VGPs）分别抵达赤道纬度与南中纬度。对应冰岛海盆与普林格尔福尔斯漂移的时段内，虚拟地磁极多次向高南纬度漂移，这表明地磁方向存在快速摆动，而非单次短暂的极性反转。与极性漂移相关的地磁方向不稳定性记录较为罕见，这大概率是由于碎屑剩余磁化（detrital remanence, DRM）的获取过程对沉积记录起到了平滑作用所致。