This study presents the directional paleomagnetic secular variationpattern of core MD972151 taken from the southwestern South China Seaduring the IMAGES Ⅲ-IPHIS Cruise in 1997.A total of 281 samplestaken from this core were subjected to AF demagnetization to analyze theircharacteristic remanent magnetization.The results indicated a reversed event at depth of between 21.7 and23.8 meters.It was identified as the Blake Event,and has an age interval ofabout 130ka.Another short reversed event was found near the bottom ofthe core.This was tentatively described as an excursion that occurred atabout 150-160ka.These assignments were in very close agreement with theresults of oxygen isotope analysis.Consequently,the core under study wasdetermined to be presenting a record of perhaps the last 160ka probably.And the sedimentation rate can thus be estimated to be of about 17-18cm/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 15.3-15.5m in depth.Thelatter excursion was estimated to be of about 75ka in age,based on comparingthe results of this study to the intensity record made by Valet andMeynadier(1993).However,the former one might well be a recent excursion, under 20ka in age,because comparison with oxygen isotope dataruled out the possibility of being the'Laschamp Event'.Another possiblecause for this abnormal event might be that it was due to deposition processof the sediments.Of course,this question will require further study.Finally,the paleo-longitude variation pattern shows that the VGPsseemed to drift eastward at a record rate of over 4 meters in depth.Thisdeparts 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.
關聯:
Terrestrial, Atmospheric and Oceanic Sciences, 10卷(1), p.239-254
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