臺灣海峽表層沈積物中黏土礦物分布之研究

Abstract

海洋沈積物中黏土礦物（伊來石、綠泥石、高嶺石、膨潤石）的分布與陸地上的母岩性質和搬運的機制有很大的關係。因此黏土礦物常被當成天然的沈積物來源指標。本研究依照美國地質調查所（USGS）所公布的黏土礦物分析方法，使用X光繞射法（X-Ray Diffraction; XRD鑑定黏土礦物種類並進行半定量的分析工作。 本研究結果顯示，臺灣海峽表層沈積物的黏土礦物組成以伊來石和綠泥石為主。海峽西側高嶺石含量比東側高，反映來自中國大陸現代沈積物中的黏土礦物組成與來自台灣本島的黏土礦物組成不同。膨潤石含量在澎湖群島西側海域最高，表現出澎湖群島火成岩的母岩特性。綠泥石含量向彰雲沙脊增加，可能顯示受潮流影響使細顆粒沈積物在沙脊上堆積。 颱風過後，臺灣沿岸的高嶺石含量增加，反應颱風造成對地層侵蝕作用的加劇，使陸上的沈積物輸出量增加。 臺灣海峽表層沈積物的來源主要為中國大陸沿岸和臺灣西部河川。過往認為泥質沈積物都是中國大陸河川或中國沿岸流的供應，實際上臺灣本島也會輸出細顆粒的沈積物，特別是在颱風之後。從沈積動力的角度來看，表層沈積物中黏土礦物的分布在海峽中間呈混合情形，顯示海峽內受到潮流作用的影響。

The distribution of clay minerals in marine sediment are related to the nature of the parent rocks and the mechanism of transportation on land. Clay minerals are often used to indicate the source of sediment. In this study, the analysis of clay minerals is based on the method which published by the U.S. Geological Survey (USGS). The clay minerals in surface the sediment of Taiwan Strait are mainly composed of illite and chlorite. The amount of kaolinite in western Taiwan Strait is higher than eastern. It shows that the composition of modern sediments from the mainland China is different from Taiwan. The highest amount of smectite is located off west Penghu Islands and highly related to its parent rock. The amount of chlorite increase alone the Changyun ridge, and it may be related to the effect of tidal current that carried fine-grain sediments and settled on the ridge. The increase of kaolinite off western Taiwan coastal area indicates the influence of typhoon induced flooding that eroded the Tertiary strata which devastated during the 921 Earthquake. We suggest that the rivers in western Taiwan and southeastern China are the major sources of surface sediment in Taiwan Strait. In the past, it regards that muddy sediments may be delivered from the rivers of mainland China and transported by China Coastal Water. Our results indicate the fine-grained sediments can be provided by rivers in western Taiwan, especially after the typhoon. In term of sediment dynamics, the distribution of clay minerals in the surface sediment on Changyun Ridge is highly influenced by tidal currents in the Taiwan Strait.