Sediment Source Variations and Environmental Changes of the Southern South China Sea
Date Issued
2006
Date
2006
Author(s)
Cheng, Chien-Liang
DOI
zh-TW
Abstract
The East Asian Monsoon (EAM) is an importment force of climate system in the
world and controls the precipitation and wind in the east Asia. The South China Sea
(SCS) is the largest marginal basin in the western Pacific which has high
sedimentation rate and well-preserved carbonate fraction, and is located in the main
route of EAM. Thus, it records very important climatic changes of the EAM.
The materials in this study were from the sediments of the Cores MD012390
(8°32.57’N, 113°24.56’E) and MD012391 (6°38.112’N, 110°20.94’E), collected near
the eastern slope of the Sunda shelf in the southern South China Sea by the giant
piston cores of IMAGES. Sampling intervals for analyses were about 20 centermeters
in the Cores MD012390 and MD012391 which had the total 217 and 212 samples,
respectively. The clay mineral (<2μm) analysis was carried out by the X-ray powder
diffraction (XRD) and the major element composition of bulk sediments was done by
the X-ray fluorescence (XRF). The aims are to reconstruct the weathering condition,
to explore the climatic changes and to understand the sediment provenance of the last
300 ka in this region.
Clay mineral analyses of both cores indicate that the major components are illite
with subordinate chlorite, kaolinite and minor smectite. The smectite content
increases during the MIS 2, 4 and 6 in the Core MD012390, but didn’t in the Core
VI
MD012391. The clay mineral distributions in surface sediment of sea bottom of the
southern SCS suggest that the sediments from the Indonesia arc provided high content
of smectite. However, it was trapped in the Sunda shelf during the interglacial periods.
Therefore, the clay mineral assemblages of the Core MD012390 suggest that the
Borneo may be the major source for the sediments during the interglacial period, but
had kaolinite and smectite from Sunda shelf during the glacial period. On the other
hand, the Mekong River may be the major sediment sources for the Core MD012391.
For eliminating the biogenic effect on the bulk compositions of sediment, we
subtract the CaO which contributed from carbonate firstly and recalculate the major
element contents. Then normalize them with TiO2 to examine their variations during
glacial-interglacial cycles. The normalized rations of SiO2 and Al2O3 increase during
the MIS1, 3, 5, and 7, but decrease during the MIS 2, 4 and 6. These two elements are
predominantly derived from the continent and their abundance could be controlled by
chemical weathering on land. Therefore, the higher ratios of them suggest that the
MIS 1, 3, 5 and 7 may have higher precipitation in summer to supply the higher
weathered sediments to the cores.
Subjects
南海
黏土礦物
主要元素
South China Sea
clay minerals
major elements
SDGs
Type
thesis