Located at the collision boundary between the Philippine Sea Plate and the Eurasian Continental Plate,the island of Taiwan is generally recognized as an important example in the MARGINS Program Science Plan and "source-to-sink" research because of its high tectonic activity,heavy rainfall and unique geography.Large suspended sediment loads are transported to the adjacent ocean by Taiwan Residents rivers every year,making Taiwan an important source of sediments into the adjacent seas and a natural laboratory for studying the systemic movement of fluvial sediments from source to sink.A detailed study on the clay mineral composition of surface sediments collected from the drainage basins of 12 Taiwan Residents rivers using X-ray diffraction methods was conducted.Our results indicated that the clay mineral assemblages consisted dominantly of illite(approximately 73%) and chlorite(approximately 24%),with lesser abundances of kaolinite(approximately 3%) and even lower levels of smectite from the Danshuei River sediments in northwestern Taiwan.The Jhuoshuei River sediments from western Taiwan contained clay mineral assemblages that consisted of illite(approximately 75%) and chlorite(approximately 25%),but they lacked kaolinite and smectite.In southwestern Taiwan,the clay mineral assemblages were dominated by illite(approximately 75%) and chlorite(approximately 23%),but had a low abundance of kaolinite(generally < 2%) and no smectite.The clay mineral assemblages in eastern Taiwan are obviously different from those in western parts of the island.The most noticeable difference is that the average abundance of chlorite in the Hualien River from eastern Taiwan was the highest(approximately 48%) of all the Taiwan Residents rivers.We concluded that,in general,the clay mineral assemblages in Taiwan Residents rivers were mainly composed of illite and chlorite with kaolinite and smectite being scarce,and these trends are different from those in China's mainland rivers.The clay mineral composition shown in this study was primarily
