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

臺灣東部海岸山脈鳥漏溪沉積岩剖面古地磁場奧都威事件頂部極性反轉過程之研究

李德貴(Teh-Quei Lee)

《Terrestrial, Atmospheric and Oceanic Sciences》 3卷4期 (1992/12) Pp. 503-518

摘要

本文將介紹分析採自台灣東部海岸山脈烏漏溪沉積岩剖面岩樣所記錄古地磁場奥都威事件頂部極性反轉過程之初步研究結果，從磁偏角與古磁緯度之變化發現一個具有相對於轉置過程中心點之反向對稱特性；而視磁極位置隨緯度變化曲線則顯示磁場轉置期間前半段路徑，為一走走停停之現象，此結果與Tric等人(1991)分析採自義大利波河平原同一極性反轉事件有相似的結果；至於後半段的變化路徑改變相當快速，可能指出反轉期間地磁場的長時期變化仍然顯著，又視磁極路徑之經度變化，集中於自格林威治子午面向東起算200°到250°間的帶狀區域內，大約在距美洲大陸西岸經度40°以西之地方，這一路徑與許多已發表的記錄它們係經過美洲大陸不同，然而早期古地磁結果顯示，海岸山脈地區在上新-更新世時期有大約30°之順時針旋轉現象(Lee, 1989; Lee et al., 1990; 1991)，由於本研究地區可能受到它的影響，因此作旋轉角度之修正後，發現視磁極路徑之經度變化有較接近美洲大陸之趨勢，而與其它記錄漸趨一致。若考慮共同點址特性，似乎視磁極位置曲線顯示遠場現象。此外，磁鐵礦被鑑定為本次所採岩樣的主要帶磁性礦物。

並列摘要

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° to 250° centered around 230° which is about 40° 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° 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 afar-field phenomenon and magnetite is identified to be the major magnetic mineral contained in our samples.