台灣海峽東側沉積物之來源及其傳輸途徑

Sources and transport of sediments in the eastern Taiwan Strait

張嫚珊(Man-Shan Chang)

指導教授 ： 蘇志杰

國立臺灣大學/理學院/海洋研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00781

摘要

本研究利用ORI-790之7管箱型岩心及ORⅢ-1166之23個表層沉積物，分析其粒徑分布、超量210Pb活度剖面及X光攝影結果，加上連續變頻聲納對於砂波的探測資料，期望能了解台灣海峽沉積物之來源及傳輸途徑。
粒徑分析結果顯示，台灣海峽沉積物中的粗、細顆粒物質分別代表著不同的來源。台灣近岸的粗砂，為台灣輸出的現代沉積物；有別於近岸粗顆粒沉積物，海峽中的細砂則是受到潮流作用侵蝕澎湖水道後搬運至彰雲沙脊的老沉積物，而後此細砂沉積物再經由潮流作用持續往北傳輸，與泥質沉積物混合；至於以往被認為是由中國沿岸流攜帶而來的泥質沉積物，則可能部分源自於台灣西部河川的輸出。
比較過量Pb-210及Cs-137所計算出之沉積速率，可知台灣海峽沉積物深受混合作用的影響。而位於澎湖水道及彰雲沙脊地區存在許多大型砂波，亦說明此地流速強烈、易造成沉積物之再懸浮與混合作用。另外由ORI-790 BC5岩心之X光影像可看出具有交錯層理構造，推論此地主要是受到潮流往復作用的影響，造成沉積物混合強烈。
綜合言之，台灣海峽屬淺海陸棚區，潮流在此扮演著侵蝕與搬運沉積物的角色；以沉積動力的角度觀之，台灣海峽沉積物屬現代潮流沉積系統的一部份。而台灣海峽沉積物應包含來自台灣西部河川所輸出的現代沉積物，藉由海流作用向北傳輸，並與老的潮流沉積物混合、沉積所形成。

關鍵字

台灣海峽 ； 粒徑分析 ； Pb-210 ； 殘餘沉積物 ； 潮流沉積物

並列摘要

In this study, 7 box cores and 23 surface sediment samples were collected by using ORI-790 and ORIII-1166 cruises in the Taiwan Strait. Grain size analysis, in conjunction with 210Pbex, and X-ray radiographs results have been used to identify the sources, transportations and deposition of the sediments.
The grain size result shows the sediments in the Taiwan Strait may classify into three different types. For coarse sand sediments in the nearshore area of Taiwan are modern sediments exports from the rivers in the western Taiwan. The fine sand sediments in the central Taiwan Strait are the aged sediments which influenced by tidal current in the Taiwan Strait and deposited in the Changyun Ridge. Afterwards, these fine sand sediments will transport northward and mix with mud sediments. For the mud sediments located at the Kuanyin Depression which were considered from mainland China may reconsidered as the products of the western Taiwan rivers.
Comparing the sedimentation rates which calculated from the excess Pb-210 and Cs-137 profiles, the sedimentation processes in the Taiwan Strait are highly influenced by the resuspension and mixing processes. This inference is also supported by the existing of large to very large sand waves occur on the Changyun Ridge and the Penghu Channel regions. In core ORI-790 BC5, we may see the development of the cross-bedding in the X-radiographic image. It suggests that the mixing process in the Taiwan Strait are mainly caused by the tidal currents.
In summary, with the erosion and movement of the sediments influenced by tidal currents, the Taiwan Strait may be considered as a modern tidal deposition system. The sediments in the central Taiwan Strait are composed by the coarse sediments from the Changyun Ridge and the fine sediments from western Taiwan.

並列關鍵字

Taiwan Strait ； grain size analysis ； Pb-210 ； relict sediment ； tidal current sediment

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