Study of the Polarity Transition Record of the Upper Olduvai Event from Wulochi Sedimentary Sequence of the Coastal Range, Eastern Taiwan

Abstract

This study presents the preliminary results of the upper Olduvai transition record analyzed from the Wulochi sedimentary sequence of the Coastal Range, eastern Taiwan. Variations of both the declination and paleolatitudes of VGP reveal an antisymmetric characteristic about the mid-point of the transition. However, variation of the VGP latitudes shows that the first half record is a three stage 'stop and go' pattern similar to that of the same event reported from Po river, Italy, by Tric et al. (1990) while the second half fluctuated more. The later part might also indicate that secular variation of the earth's magnetic field was still dominant during this transition. For the longitudes of the VGP path, they are found to be largely confined to a belt from meridian 200¢X to 250¢X centered around 230¢X which is about 40¢X west of the American continents. This result is dissimilar to many other paths which passed through them. However, the Coastal Range has undergone a clockwise rotation of about 30¢X during Plio-Pleistocene (Lee, 1989; Lee et al., 1990; 1991); the discrepancy might result from this clockwise rotation event. After the correction of the rotation angle, it is found that the VGP path is much closer to the American continents. In addition, VGP path seems to show a far-field phenomenon and magnetite is identified to be the major magnetic mineral contained in our samples.

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