| The mud area off Changjiang estuary are one of the accumulative centers of Changjiang sediment since Holocene epoch, the main container pollutant materials from human activities, and the hypoxia zone. So it is very significant for the research of the material flux and Land-Ocean Interactions in the Coastal Zone(LOICZ) in the East China Sea.The piston core sediments, collected at station Chjk01(122°45.035′E, 30°50.00′N; water depth, 28m) and E4(122°37.311′E, 31°00.325′N; water depth, 21m) in the mud area off the Changjiang estuary, were taken for geochemical and sedimentological analysis. The piston cores Chjk01 and E4 are respectively 366cm and 144cm long. Based on the analyzing results with 210Pb dating data, high resolution of the sediment grain-size are studied. This paper analyzed the characteristic and regularity of grain-size variation and expounded its influential factors.The 210Pb dating of the two cores showed that the mean sedimentation rate of the core Chjk01 and E4 were 2.8 cm/a and 3.5 cm/a, respectively, in corresponding to the sedimentation duration of 132 a (1873～2005 a) for core Chjk01 and 41 a (1962～2003 a) for core E4.The two core sediments, belonging to the muddy deposition body with silt as the main part. are mostly consists of silt(66.5%～69.8%), and clay in minor portion(27.7%～30.1%) with small amount of sand(2.5%～3.4%). At the stratum, the content of sand and clay varies in an opposite way, while the content of silt remains quite stable.Variation of the grain-size parameters in sediment core Chjk01 illustrated clearly a three-phasic changes since 1873: 1) The grain size became gradually coarser and coarser since 1873 to 1957 with increasing mean size, sand content and standard deviation and decreasing clay content; 2) The grain size became finer in 1957～1981 with decreased mean size, sand content and standard deviation, and decreased clay content. The finest part is the sediment in 1971～1981; 3) The grain size became coarser again in 1981～2005 with fluctuated increased mean size and sand content, with no obvious trends. Variation of the grain-size characteristics of core E4 during 1962～2003 was in agreement with that of core Chjk01 in general.There was a negative correlation between the organic carbon content and grain-size variation in the sediments of the piston core E4 during 1966～1981a and 1988～2003a, and the organic carbon content was essentially influenced by the grain-size change in the two periods. Moreover, the inorganic carbon content was positively correlated with grain-size variation in general.The phase characteristics of the grain-size variations in the Yangtze River mouth mud area since 1873, was generally in accordance with the phase evolvement of the location of the Yangtze River trunk stream, and the sediment diversion ratio of the main branch channel. The variations of water and sediment discharge at Datong Station and the Asian monsoon show little effect on the features of the grain-size variations. The variations of the distance between the trunk stream of the Yangtze River and the Chjk01 and E4, was the main controlling factor influencing the changes of relative content between the fine and coarse sediments in the mud area, and concealed the influence of other factors.The mud area off the Changjiang estuary belongs to the sedimentary province of pro-delta among the sub-aqueous Changjiang Delta. There is obvious difference in deposition process among the mud area off the Changjiang estuary and the coastal mud area off Fujian and Zhejiang. The evolvement of the location of the Yangtze River trunk stream was the main controller factor for the variation of grain-size in the mud area off the Changjing estuary, moreover, the other mud area was the results of re-deposition of the re-suspended material, driven by the East Asian monsoon, from the sediments of the Changjiang, and its grain-size variation was mainly controlled by the East Asian monsoon.
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