| dc.description.abstract | Clay mineralogy, element geochemistry, and Sr and Nd isotopic study of recent deep-water seafloor sediments collected in different tectonic settings around Taiwan, as well as surrounding Taiwanese river-mouth sediments and Tainan shelf edge sediments, have been investigated to know the source-to-sink of the detrital fine-grained sediments. We determine the clay mineralogy, major and trace element geochemistry along with Sr and Nd isotopes in surface sediments around offshore Taiwan, as well as the clay mineralogy in both hemipelagites and turbidites up to the top 50 cm of the deep-sea sediment cores to infer the source and transportation of detrital fine-grained sediments.
Our findings demonstrate that the clay mineral assemblages in both hemipelagites and turbidites from various provinces gradually shift between two major end-members: illite+chlorite and smectite. They are primarily sourced from Taiwan and Luzon, respectively. Besides, the presence of more smectite in river sediments sourced from the Coastal Range indicates that smectite is an additional characteristic clay mineral for sediments derived from eastern Taiwan. The high smectite content in the Hateruma forearc basin of the Ryukyu subduction system in eastern offshore Taiwan, interpreted as derived mainly from the Ryukyu Islands. The sediment cores in a bathymetric high near offshore Coastal Range, the Luzon volcanic arc, the upper-slope perched basins of the Manila accretionary wedge, and few cores in the northeastern South China Sea off southwestern Taiwan show dominantly of smectite, indicating strong influence by Kuroshio Current pathways. Whereas, the Hoping Canyon, the Nanao Basins, the Southern Longitudinal Trough off eastern Taiwan, and the Gaoping Canyon off southwestern Taiwan consist dominantly of illite and chlorite, interpreted as derived mainly from Taiwanese rivers through the river-canyon system. Our study also indicates that the clay mineral assemblage around Taiwan is mainly controlled by supply from major provenance and current transport. In most of the cores, the relative abundance of clay minerals in turbidites and hemipelagites is very comparable. As a result, we argue that the neighboring turbidites and hemipelagites of a core share common detrital sources. Besides, less smectite is found in the river-connected canyon systems, especially for coarse fraction of turbidites, indicating that the smectite brought about by the Kuroshio Current is diluted by river-fed turbidity currents.
Clay mineral indices (illite crystallinity and illite chemistry index), as well as major element indices (chemical mobility, CIX index, K2O/(Na2O + CaO) molar ratio, and weathering trend ternary diagrams), in combination with Rb, Sr, and Sr-Nd isotopic results for surface sediments around Taiwan, indicate moderate chemical weathering in the Taiwan river sediments. Also suggest that the seafloor sediments around offshore Taiwan are highly correlated to Taiwan river sediments, indicating the high influence of Taiwan-derived sediments on the bulk fraction of offshore surface sediments around Taiwan. | en_US |