【作者】 陈晓辉；

【导师】 杨作升；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2007， 硕士

【摘要】 长江口泥质区是末次冰消期高海面以来的长江入海物质沉积中心和“物质汇”之一,也是长江人类活动排放入海污染物的重要捕集区,该区域存在长江口贫氧区。本区沉积学的研究对认识东海物质通量和陆海相互作用有重要意义。通过沉积学和地球化学的方法和210Pb测年数据,对取自长江口泥质区的重力柱状样E4(122°37.311′E、31°00.325′N,水深21m,样长144cm)和振动柱状样Chjk01(122°45.035′E、30°50.00′N,水深28m,样长366cm)进行了高分辨率的粒度分析,阐述了其特征和变化规律,分析了其影响因素。两柱状样210Pb测年表明,长江口泥质区Chjk01与E4柱状样的沉积年代分别为132年(1873～2005年)和41年(1962～2003年),平均沉积速率分别为2.8cm/a与3.5cm/a。两柱状样地层中粉砂的含量为66.5%～69.8%,粘土含量为27.7%～30.1%,砂含量为2.5%～3.4%,属于以粉沙为主的泥质沉积。两柱状样地层中粉砂含量基本不变,砂与粘土含量则呈此消彼长。季节性尺度的高分辨率沉积物粒度变化显示,Chjk01孔沉积物粒度自1873年以来呈三段式变化:1)1873～1957年间的84年中,粒度稳定地逐渐变粗,砂含量增加,粘土含量减少,分选变差;2)1957～1981年间的24年中,粒度明显变细,粘土含量增加,砂含量减少,分选变好,1971～1981年间粒度最细;3)1981～2005年间的24年中,粒度总体变粗,砂含量波动式增大,但变化趋势不明显。E4孔在1962～2003年间的41年中,沉积粒度特征与Chjk01孔基本一致。E4柱状样沉积物中有机碳含量在1966～1981年段和1988～2003年段与沉积物粒度变化存在负相关,有机碳含量在此两段时间内主要受粒度变化影响;而无机碳含量总体与沉积物粒度变化呈正相关。1873年以来的132年期间长江口泥质区粒度变化的阶段性特征,主要与同时期长江水沙入海主泓通道的位置以及主汊道的分沙比阶段性演变相对应,而对长江大通站水沙变化和东亚季风强度变化不敏感,主泓入海位置与两孔位置距离的变化,是影响泥质区粗、细粒级含量相对变化的主控因素,掩盖了其他因素的影响。长江口泥质区属长江水下三角洲前三角洲区,沉积过程与浙闽沿岸的长江泥质区有明显区别。前者沉积物粒度变化主要受长江入海主泓位置变化控制,后者是东亚冬季风驱动下浙闽沿岸流输送的长江再悬浮物质的沉积体,其粒度变化受到东亚冬季风强度的控制。更多还原

【Abstract】 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.更多还原