Clay minerals have played a significant role in the study of the East Asian monsoon evolution in the South China Sea by being able to track oceanic current variations and to reveal contemporaneous pa- leoclimatic changes prevailing in continental source areas.As one of the most important rivers input- ting terrigenous matters to the northern South China Sea,the Pearl River was not previously paid at- tention to from the viewpoint of clay mineralogy.This paper presents a detailed study on clay minerals in surface sediments collected from the Pearl River drainage basin(including all three main channels, various branches,and the Lingdingyang in the estuary)by using the X-ray diffraction(XRD)method. The results indicate that the clay mineral assemblage consists dominantly of kaolinite(35%-65%), lesser abundance of chlorite(20%-35%)and illite(12%-42%),and very scare smectite occurrences (generally<5%).Their respective distribution does not present any obvious difference throughout the Pearl River drainage basin.However,downstream the Pearl River to the northern South China Sea,the clay mineral assemblage varies significantly:kaolinite decreases gradually,smectite and illite increase gradually.Additionally,illite chemistry index steps down and illite crystallinity steps up.These varia- tions indicate the contribution of major kaolinite,lesser illite and chlorite,and very scarce smectite to the northern South China Sea from the Pearl River drainage basin.The maximum contribution of clay minerals from the Pearl River is 72%to the northern margin and only 15%to the northern slope of the South China Sea.In both glacials and interglacials,kaolinite indicates that the ability of mechanical erosion occurred in the Pearl River drainage basin.
LIU ZhiFeiChristophe COLINHUANG WeiCHEN ZhongAlain TRENTESAUXCHEN JianFang
The sediment macro-distribution patterns and their evolutionary characteristics in the South China Sea (SCS) are discussed based on a quantification of the sediment mass from the beginning of seafloor spreading in the Oligocene to the Present. Above the pre-Oligocene base, the total sediment mass for the whole SCS is estimated to be 1.44×1016 t, with the highest average accumulation rate of ～22 g·cm-2·ka-1 in the Oligocene. Having no large abyssal fans but fast accumulation in sedimentary basins on the continental shelf and slope, the SCS shows quite different sedimentary characters not only from the open ocean but also from small backarc basins along the marginal West Pacific, apparently controlled by the coupling between local tectonics and global climate changes.
