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 IMAGES III- IPHIS Cruise in 1997. A total of 281 samples taken from this core were subjected to AF demagnetization to analyze their characteristic remanent magnetization.

The results indicated a reversed event at depth of between 21.7 and 23.8 meters. It was identified as the Blake Event, and has an age interval of about 130 ka. Another short reversed event was found near the bottom of the core. This was tentatively described as an excursion that occurred at about 150-160 ka. These assignments were in very close agreement with the results of oxygen isotope analysis. Consequently, the core under study was determined to be presenting a record of perhaps the last 160 ka probably. And the sedimentation 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 latter excursion was estimated to be of about 75 ka in age, based on comparing the results of this study to the intensity record made by Valet and Meynadier (1993). However, the former one might well be a recent excursion, under 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 sediments. Of course, this question will require further study.

Finally, the paleo-longitude variation pattern shows that the VGPs seemed to drift eastward at a record rate of over 4 meters in depth. This departs from observations of the present-day geomagnetic field that indicate the magnetic pole is drifting westward. The significance of this discrepancy warrants further study too.

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