Presenter: Wen-Shu Koo
Date: 2017/03/30
Abstract
The Taiwan Shoal in the southern Taiwan Strait exhibits a lobe-shaped shallow water area, with a depth less than around 40 m and an area approximately of 13,000 km 2 . The Shoal consists of relict sediments remnant from deltaic deposits during the last glacial period and associated with the paleo-Jiulong River. We collected seafloor sediments in and around the Taiwan Shoal to study the sediment characteristics and provenance of the Shoal as well as Taiwanese river sediments to characterize sediment sourced from southern Taiwan and sediments collected from the Deep South China Sea are also studied to understand their provenance. Our results help to understand possible sediment delivery pathways in a source-to- sink context from the southern Taiwan Strait to the northern South China Sea. The method of X-ray diffraction is used to identify mineral compositions for muds and mineral compositions are examined under polarized microscope for sands. Zircon grains are separated from heavy minerals for U-Pb dating in order to understand the sediment source terranes. Sediments of the Taiwan Shoal are mostly tawny-colored, medium to coarse-grained sands with abundant shell fragments and shallow-water benthic foraminifera. Sediments to the south of the Taiwan Shoal and in the outer shelf consist of dark brown-colored and fine-grained sands with rare shell fragments. Siliciclastic compositions of the Taiwan Shoal sediments are mostly quartz. Slate fragments are found to occur near Taiwan and outer shelf, especially in the Penghu Channel area. Clay minerals from the Penghu Channels and south of the Taiwan Shoal are dominated by illite and chlorite. The sediment colors and mineral species are very different for the sediments of the Taiwan Shoal and outer shelf, revealing that these two areas featuring different oceanographic processes and sediment provenance. Zircon U-Pb dating reveals that sediments in Taiwan Shoal are mostly sourced from Jiulong River in the Fujian province; the sediments in the outer shelf, the Penghu Channel and the northern South China Sea receive more inputs from southwestern Taiwanese rivers, however.