利用黏土礦物及重礦物研究臺灣海峽沈積物之物源及傳輸

Abstract

臺灣海峽沈積物物源有著以化學風化輸出的中國大陸及物理風化輸出的臺灣，而臺灣海峽東側沈積物的沈積速率受臺灣河流快速輸送大量沈積物的影響，導致海峽東西兩側沈積物剖面的差異（Huh et al., 2011; Kao et al., 2008）。本研究以臺灣海峽的沈積物為研究對象，系統性探討其物源及傳輸機制，旨在了解此區域的沈積動力特徵及其與地形、水文流場的交互作用。透過對52個表層沈積樣本和13個長岩心樣本進行表層分析。黏土礦物反映了不同源區的母岩，經歷風化侵蝕過程及傳輸機制搬運至海峽沈積，使我們能夠推斷各沈積物的來源區域和貢獻比例。而重礦物因其較高的密度，具有耐磨蝕和穩定的化學特性，能在遠離母源區後仍能展現出母岩特性（Mange & Maurer, 2012）。由於重礦物比重較大的特性，重礦物本身不易受再懸浮作用影響。使用沈積物中的黏土礦物比例和重礦物組成，再結合粒徑分佈特徵，搭配水動力等因素對沈積物分佈與傳輸作出推測。 臺灣海峽的黏土礦物組成以伊萊石和綠泥石為主；高嶺石在濁水溪和淡水河出海口以及臺灣灘有較高的比例；澎湖以北至烏坵凹陷區域的樣本都有膨潤石的出現，而臺灣灘靠近澎湖地區的兩個樣本站位亦有膨潤石出現，由於廣泛遍佈在臺灣海峽西側，推測為來自澎湖玄武岩或烏坵沿線火成岩的風化輸出。重礦物以不透光礦物為主，主要為岩屑、磁鐵礦和少量海綠石。海峽東側站位的不透光重礦物佔比皆過半，西側站位點的不透光礦物佔比不到30%；海綠石主要分佈在臺灣灘站位，深色淺色有站位上的差異。透光重礦物以角閃石為主，而較能區分海峽兩岸的物源差異的綠泥石，其分佈也具有差異。 整體而言，臺灣海峽沈積物分佈與沈積特徵受海流、地形的影響。臺灣海峽北部海流強，尤其觀音凹陷區受潮汐作用影響顯著，沈積物以現代沈積為主；臺灣灘海流較弱，沈積物經歷海平面上升後的反覆輸移。綜合判斷，臺灣海峽的沈積物主要來源為所臺灣輸出，濁水溪的輸砂對雲彰隆起的貢獻尤為顯著。臺灣灘南側有著臺灣端物源輸出的可能性。此外，粒徑數據顯示，季風和潮汐驅動的高能量水動力環境有助於粗顆粒的再懸浮與搬運，而低能量水動力環境則利於沈積顆粒的沈積。

The sediments present in the Taiwan Strait are derived from both significant river systems on the Chinese mainland and smaller, steep river networks in Taiwan. The rapid transport of sediments from Taiwanese rivers plays a crucial role in determining deposition rates on the eastern side of the strait, resulting in notable differences in sediment profiles between the eastern and western regions (Huh et al., 2011; Kao et al., 2008). This study seeks to investigate the provenance and transport mechanisms of sediments within the Taiwan Strait by analyzing surface sediment and core samples, with a particular focus on sediment dynamics influenced by the interaction of hydrodynamic forces and seabed topography. The clay minerals identified, primarily Illite and Chlorite, suggest diverse source regions and the processes of weathering and erosion. Kaolinite is predominantly found near river outlets, while Smectite is concentrated in the north of Penghu and around the perimeter of the Wu-Chiu depressions, likely as a result of volcanic weathering. The distribution of heavy minerals, particularly opaque varieties such as lithic fragments and magnetite, exhibits significant variation between sampling stations in the eastern and western regions. Conversely, transparent heavy minerals, including Amphibole and Chlorite, underscore distinct provenance differences across the strait. Sediment distribution is influenced by hydrodynamic conditions and topographical features, with stronger currents in the northern strait promoting the accumulation of modern deposits, whereas weaker currents in the southern strait facilitate the reworking of sediments. Grain size analysis indicates that hydrodynamic forces driven by monsoons and tides enhance the transport of coarser particles in high-energy zones, while finer particles are more likely to settle in low-energy environments. The primary sources of sediment are attributed to rivers in Taiwan, particularly the Jhuoshuei River, which significantly contributes to deposits in the central strait. Furthermore, sediments located near the southern Taiwan shoal may also be linked to sources from Taiwan.