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Chinese Science Bulletin

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Springer-Verlag

Clay minerals in surface sediments of the Pearl River

drainage basin and their contribution to the South

China Sea

LIU ZhiFei1, Christophe COLIN2, HUANG Wei1, CHEN Zhong3, Alain TRENTESAUX4 & CHEN JianFang5

1

State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;

2

Laboratoire IDES, UMR 8148 CNRS, Universit de Paris XI, Orsay 91405, France;

3

South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;

4

UMR PBDS 8110 CNRS/USTL, FR 1818, Universit de Lille I, Villeneuve d'Ascq 59655, France;

5

Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China

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

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

GEOLOGY

erosion occurred in the Pearl River drainage basin.

clay minerals, surface sediments, provenance, East Asian monsoon, Pearl River drainage basin

tology and oxygen isotope stratigraphy in the past[5], but

The East Asian monsoon is a significant component of

the global climate system[1]. Following the successful also in sedimentology and sedimentary geochemistry[6,7].

study on deep-sea sedimentary records of the South

Asian monsoon evolution in the Arabian Sea[2], the Received September 27, 2006; accepted January 23, 2007

doi: 10.1007/s11434-007-0161-9

South China Sea is becoming an international oceanic

Corresponding author (email: abphuc@r.postjobfree.com)

location for the study on the East Asian monsoon evolu- Supported by the National Natural Science Foundation of China (Grant Nos.

40331002, 40621063 and 40506014), the Fok Ying Tung Education Foundation

tion[3]. Specially, the Ocean Drilling Program (ODP) (Grant No. 101018), the Doctoral Program of Higher Education (Grant No.

Leg 184[4], which was carried out successfully in the 200********), the Excellent Young Teachers Program and the Program for New

Century Excellent Talents in University of the Ministry of Education of China (Grant

South China Sea in 1999, has impelled the study on the No. NCET-04-0372), and the Laboratory of Marginal Sea Geology Grant of the

East Asian monsoon evolution not only in micropaleon- Chinese Academy of Sciences (Grant No. BYH03A08)

www.scichina.com www.springerlink.com Chinese Science Bulletin April 2007 vol. 52 no. 8 1101-1111

Among them, clay minerals can be used to track oceanic South China Sea, especially on the northern slope. But

current variations and to reveal contemporaneous paleo- clay mineral investigations in surface sediments were

climatic changes prevailing in continental source ar- previously carried out only for a few locations in the

eas[8,9], and therefore have played a significant role in Pearl River drainage basin[22,23], and the clay mineral

the study of the East Asian monsoon evolution in the assemblages in the whole drainage basin are still poorly

South China Sea[7,10 13].

known. This study is an investigation of clay mineralogy

for 38 surface argillaceous sediments collected along the

The significance of clay mineral assemblages in the

Pearl River drainage basin in March 2004 and 12 bottom

study of the East Asian monsoon evolution requires a

surface sediments collected in the Lingdingyang of the

detailed knowledge of distribution of clay minerals and

estuary and in the northern margin of the South China

investigation of their provenance. Hence, clay minera-

Sea in July 1999 and July 2000, respectively. We present

logical characteristics of modern sediments in major

the results to reveal clay mineral assemblage characters

rivers surrounding the South China Sea and surface

and to evaluate sources of clay minerals in the northern

sediments on the sea bottom are the keys to study varia-

South China Sea.

tions in the clay mineral assemblages occurring in the

geological past. Provenances of terrigenous matter in the

1 Materials and methods

South China Sea are complicated because they involve

two markedly different geological regions: the Asian

Surface sediments, in the Pearl River drainage basin,

continent and Taiwan in the north and the volcanic arcs

were collected along three main channels: the East River,

in the south and east. A few clay mineral provinces in

the North River, and the West River (Figure 1, Table 1).

the South China Sea divided by the surface distribution

Knowing that the river water level falls greatly from

suggest that illite and chlorite derive mainly from the

December to March, and that muddy channel deposits

Asian continent and Taiwan to the north, whereas smec-

are a close proxy for the components of suspended par-

tite and kaolinite come mainly from the Sunda shelf and

ticles in river water, we sampled argillaceous sediments

the Indonesian arcs to the south[14]. The less investigated directly from shallow water river beds or from river beds

clay mineral assemblage in major rivers surrounding the with water depth 50%) in sediments of water depth 2092 m)[12] are included in the discussion of

the Lingdingyan in the Pearl River estuary[17], Liu et the provenance of clay minerals deposited on the north-

al.[7,12] concluded that clay minerals at ODP Site 1146, ern slope of the South China Sea.

very close to Sites 1144 and 1145, derive mainly from Clay minerals were identified by X-ray diffraction

Taiwan and the Yangtze River. This conclusion was con- (XRD) on oriented mounts of clay-sized particles (0.50, indicating a strong hydrolysis.

Illite crystallinity varies between 0.24 and 0.42 2 . West River. Accordingly, smectite is very rare in the

East River and North River and the average content is

For the Lingdingyang sediments in the estuary, simi-

lar to the Pearl River sediments, the clay mineral assem- generally less than the semi-quantitative calculation er-

blages consist mainly of kaolinite, chlorite, and illite ror (2%). No significant differences exist for chlorite

(Table 1, Nos. 39 47). Their average contents are 40%, and illite contents in the whole Pearl River drainage ba-

28% and 26%, respectively. Smectite slightly increases sin (Figure 3).

with an average of 6%. Only few samples can reach However, through the Lingdingyang on the northern

17%. The illite chemistry index varies between 0.44 and margin of the South China Sea, kaolinite decreases on

0.56, and the illite crystallinity is between 0.16 and average from 40% to 33%, and smectite increases from

0.20 2 . 6% to 16% (Figure 3). Through the northern margin to

The samples from the northern margin of the South the three ODP sites on the northern slope of the South

China Sea (Table 1, Nos. 48 50) were compared to the China Sea, kaolinite decreases continuously to 7% and,

clay mineral assemblage of the Pearl River and Ling- inversely, smectite increases to 35%. At the same time,

dingyang sediments. In these samples, kaolinite de- illite also increases to about 40% (Table 2). The distri-

Average clay mineral assemblages of various sections in the Pearl River drainage basin and the northern South China Seaa)

Table 2

Illite chemistry index Illite crystallinity ( 2 )

Region Sample number Chlorite Illite Smectite Kaolinite East River 4 30 15 1 54 0.69 0.30

Northern North River 6 21 28 1 50 0.60 0.28

Southern North River 6 24 27 3 46 0.56 0.30

Eastern West River 7 33 22 2 43 0.67 0.30

Middle West River 8 24 29 3 44 0.63 0.33

Western West River 4 22 32 6 40 0.55 0.28

Southwestern West River 3 20 33 4 43 0.59 0.28

Lingdingyang 9 28 26 6 40 0.51 0.19

Northern margin 3 25 26 16 33 0.46 0.17

Holocene at ODP Site 114*-*-**-**-**-**

Holocene at ODP Site 114*-**-**-**-** 7

Holocene at ODP Site 114*-*-**-**-** 9 0.40 0.22

a) Clay mineral data of ODP Site 1144 are from ref. [16], those of Site 1145 from ref. [23], and those of Site 1146 from ref. [12].

1106 LIU ZhiFei et al. Chinese Science Bulletin April 2007 vol. 52 no. 8 1101-1111

Figure 3 Distribution of average clay mineral assemblages of various sections in the Pearl River drainage basin and the northern South China Sea.

bution of clay minerals in the northern South China Sea

presents a significant regional difference. Globally, clay

mineral segregation exists in the marine environment[32].

For instance, kaolinite particles are relatively large and

smectite particles, have usually a smaller diameter. This

observation explains why kaolinite may decrease and

smectite may increase gradually form river beds to

ocean bottom[32]. However, for clay particles

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