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標題: | 南沖繩海槽MD012403岩芯碎屑沉積物:源區與古海洋變遷 Detrital Sediments of Core MD012403 in Southern Okinawa Trough : Implications for Provenance and Paleoceanographic Changes |
作者: | Wen-Hsin Lee 李文心 |
指導教授: | 魏國彥 |
關鍵字: | 沖繩海槽,黑潮,黏土礦物,粒徑分析,主要元素分析, Okinawa Trough,Kuroshio,clay minerals,grain size analysis,major elements, |
出版年 : | 2008 |
學位: | 碩士 |
摘要: | 國際古海洋全球變遷計畫(IMAGES)於2001年在西太平洋鑽取了一系列的深洋岩芯,期望可解析晚第四紀以來千年尺度的古海洋環境變化。沖繩海槽位處黑潮主流流經的地理樞紐,本研究利用取自南沖繩海槽MD012403岩芯的碎屑沉積物的粒徑分佈、黏土礦物及主要元素的組成,探討三萬年來黑潮流徑的變遷,以及沉積物供應來源變化。MD012403岩芯位於沖繩海槽的西南端 (25° 03.90' N,123° 16.94' E),沉積物以陸源碎屑物為主,海源生物殼體次之;相對於其他深洋岩芯而言,本岩芯擁有較高的沉積速率(每千年50-500 cm)。
MD012403岩芯細粒沉積物的粒徑中值在20-32.6 ka時為7.3-7.8 Φ,較10.1-20 ka為細;10.1 ka以後,沉積物有變粗並伴隨著淘選度變差的趨勢,這樣的粒徑變化與可淘選粉砂(sortable silt)含量的增高指示著黑潮在此時進入了沖繩海槽。 台灣北部沉積物黏土礦物的Chlorite / Kaolinite值(>5)遠遠高於東海陸棚(<2),本研究中岩芯沉積物在0-12 ka的Chlorite / Kaolinite值(2-6)高於12-21 ka的Chlorite / Kaolinite值(0.5),推論12-21 ka東海陸棚為南沖繩海槽沉積物主要供應來源。 台灣沉積物與東海陸棚物質在主要元素K2O/TiO2比值上也有明顯差距,台灣沉積物的K2O/TiO2會高於東海陸棚的值,本研究中K2O/TiO2值(4.5)在12-21 ka遠遠低於0-12 ka及21-32.6 ka時的6-6.5,和黏土礦物變化趨勢一致,在12-21 ka時,東海陸棚物質輸入遠大於台灣東北部的貢獻。 High sedimentation rates (50-500cm/kyr) in the South Okinawa Trough (SOT) provide high resolution records for reconstructing millennial or centennial paleo-environment changes. This research analyzes the grain size distribution , clay mineral assemblage and major elements of the IMAGE Core MD012403 retrieved from the Southern Okinawa Trough. The medians of grain size in MD012403 varied from 7.3 Φ to 7.8 Φ during 32.6 ka-20 ka and showed a coarsening trend during 21 ka-10.1 ka. After 10.1 ka, the grain sizes increased to 6.6-7.1 Φ were more stable in association with poor sorting. High content of sortable silt also occurred at this period, indicating the intensity of Kuroshio current was enhanced. The average chlorite / kaolinite ratio of detrital sediments from Taiwan (5.0) is much higher than that from the East China Sea Continental (ECS) Shelf (<2.0). The ratio of chlorite / kaolinite in Core MD012403 shows high values (2-6) during 0 ka-12 ka and maintains low (0.5) between 12 ka-21 ka. This suggests that the ECS may be the major sedimentary provenance during 12 ka-21 ka. Concentrations of MnO、CaO、MgO、ΣFe2O3 in sediment increase with depth but Na2O displays an opposite trend. Aoki and Oinuma(1974) documented that the sediments come from East China Shelf have a significantly low K/Ti ratio. In this study, the ratios of K/Ti drop down during 12 ka-21 ka indicating sources of sediments were mainly from ECS shelf. This interpretation is consistent with evidence also supports the inference derived from clay mineral assemblage. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/27316 |
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顯示於系所單位: | 地質科學系 |
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