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題 名 | Paleo-Secular Variation Records from Lacustrine Sediments of Yuan-Yang Lake, Northern Taiwan=臺灣北部鴛鴦湖沈積物的古地磁場長期變化記錄 |
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作 者 | 林華松; 李德貴; 劉平妹; | 書刊名 | 中國地質學會會刊 |
卷 期 | 38:4 1995.10[民84.10] |
頁 次 | 頁355-370 |
分類號 | 353.1 |
關鍵詞 | 古地磁學; 地磁場長期變化; 湖泊沈積物; Paleomagnetism; Secular variation; Lake sediments; |
語 文 | 英文(English) |
中文摘要 | 本研究將探討取自臺灣北部鴛鴦湖3.72公尺長湖積物岩心中所記錄的古地磁場長 期變化,總共有170岩樣被分析。本岩心共有四個可相信之碳-14定年資料,經樹輪年齡修 正後,其年代由下而上分別為取自岩心底部的3660±180年前,其上部6公分處的3840±240年 前,再往上約2.5公尺處的1590±270年前,以及取自距岩心頂部45公分處的540±100年前。 分析古地磁方向顯示,岩心之磁傾角分佈在10°至60°間,與今日該地之磁傾角比較,最大有 ±25°的改變量;而磁偏角的變化則有近60°的改變。視磁極路徑的古緯度變化大致在65°N和 85°N之間,但是在距岩心頂部110公分至150公分處發現較低之古磁緯度,似乎顯示地磁場 在大約1,500年左右可能存在一個異常事件。而視磁極曲線侷限於一相對較窄的範圍內,以 及其變化路徑最初有一小段為順時針運動,而後改變成較大路徑的逆時針運轉,暗示本岩 芯紀錄的臺灣地區最近四千年的古地磁場長期變化,可能主要受非磁偶極場控制的看法。 此外,比較本研究之古磁偏角隨時間變化型態與兵頭等(1993)整合日本地區分析自湖泊 及海洋沉積物所得之結果,發現兩地區距今最後四千年之記錄十分相似,兵頭等(l993) 也曾建議日本地區最後一萬年的地磁場長期變化主要受非磁偶極場控制,從兩地記錄之相 似性,吾人似可推論至少在距今最近這四千年間,兩地區之地磁場長期變化可能源自同一 非磁偶極場。 |
英文摘要 | This study presents a geomagnetic secular variation record analyzed from a 3.72-meter sedimentary core of Yuan-Yang Lake, northern Taiwan. A total of 170 specimens were studied. Six levels of this core were subjected to dating by the C-14 method. They were then calibrated to tree ring ages. Only four of them proved to be reliable: 3660±180 yrbp at the bottom of the core; 3840±240 yrbp at 6 cm above the bottom; 1590±270 yrbp at about 2.5 meters above the former one, and 540±100 yrbp at 45 cm below the top of this core. Stratigraphic variation of the paleomagnetic directions shows that the inclinations varied from 10° to 60° deviated about ±25° around that of present day, and the declinations scattered about 60°. Paleo-latitudes of VGP positions generally varied within the interval of 65°N and 85°N. However, a relative low latitude record was found at the depth from 110 cm to 150 cm which might imply the existence of an abnormal event (an excursion?) of the geomagnetic field at about 1,500 years ago. The VGP path was confined to a rather narrow zone and first showed a small loop of clockwise motion then changed to a larger counterclockwise loop indicating that the secular variation of the earth's magnetic field in Taiwan has dominated a non-dipole source for the last four thousand years. In addition, a comparison of the paleo-declinaiton variation patterns of this study with the stacked records studied from lake and marine sediments in Japan by Hyodo et al. (1993) show that both patterns have been very similar to each other for the last four thousand years. Hyodo et al. (1993) proposed furthermore that the paleo-secular variations of geomagnetic field in Japan for the last 12,000 years have been dominant the non-dipole feature. The similarity between the records of this study and those from Japan has led to the conclusion that the two areas have probably dominated the same non-dipole behavior for at least the last 4,000 years. |
本系統中英文摘要資訊取自各篇刊載內容。