Last 160 Ka paleomagnetic directional secular variation record from core MD972151, southwestern South China Sea

This study presents the directional paleomagnetic secular variation pattern of core MD972151 taken from the southwestern South China Sea during the IM AGES III - IPHIS Cruise in 1997. A total of 281 samples taken from this; co re were subjected to AF demagnetization to analyze their characteristic rem anent magnetization. The results indicated a reversed event at depth of between 21.7 and 23.8 me ters. It was identified as the Blake Event, and has an age interval of abou t 130 ka. Another short reversed event was found near the bottom of the cor e. This was tentatively described as an excursion that occurred at about 15 0-160 ka. These assignments were in very close agreement with the results o f oxygen isotope analysis. Consequently, the core under study was determine d to be presenting a record of perhaps the last 160 ka probably. And the se dimentation rate can thus be estimated to be of about 17-18 cm/ky. In addition to the reversed events, two excursions were also observed, one at the core top to 3.7 meters, and the other at 15.3-15.5 m in depth. The l atter excursion was estimated to be of about 75 ka in age, based on compari ng the results of this study to the intensity record made by Valet and Meyn adier (1993). However, the former one might well be a recent excursion, und er 20 ka in age, because comparison with oxygen isotope data ruled out the possibility of being the 'Laschamp Event'. Another possible cause for this abnormal event might be that it was due to deposition process of the sedime nts. Of course, this question will require further study. Finally, the paleo-longitude variation pattern shows that the VGPs seemed t o drift eastward at a record rate of over 4 meters in depth. This departs f rom observations of the present-day geomagnetic field that indicate the mag netic pole is drifting westward. The significance of this discrepancy warra nts further study too.