【作者】 齐红艳；

【导师】 范德江；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2008， 硕士

【摘要】 利用X射线成像技术、紫外分光技术、X射线衍射矿物物相分析技术、ICP—AES(MS)元素分析技术,对横跨长江水下三角洲不同亚环境的浅层沉积层序进行了研究,并系统解剖了长江三角洲前缘的无扰动浅层沉积物柱样高分辨率粒度、生物硅、矿物组成、常量元素、微量元素以及稀土元素记录,揭示了三角洲前缘沉积与长江入海水沙、海洋环境的响应关系,分析了夏秋、冬春两个时段的沉积特征。这是该区首次尝试进行年际和季节性时间尺度的高分辨沉积记录研究,证实可以实现精确的季节性和年代级的高分辨记录。研究表明:长江水下三角洲沉积物总体上以粉砂质黏土为主,近岸粒度细,向外,粒度逐渐变粗。浅层层序中以发育块状构造、水平层理、生物扰动等构造为特征,并且具有空间上的分带性,从三角洲前缘到前三角洲及过渡带再到正常浅海,生物扰动指数呈低-高-低变化。长江三角洲前缘浅层沉积层序与长江入海泥沙、三角洲环境的季节性波动有着良好的响应关系。夏秋季时输沙多,海洋能量相对较弱,初级生产力高,形成的沉积物偏细、生物硅含量高;而冬春时期,河流输沙少,海洋能量相对较强,初级生产力低,形成的沉积物偏粗、生物硅含量低。这正是进行季节性沉积层序识别的依据所在。夏秋季沉积层主要矿物为石英、长石、云母与黏土矿物,次要矿物为方解石和白云石,具有明显的长江型物源性质。元素组成上表现为:常量元素中Al2O3> TFe>CaO> K2O>MgO>Na2O>Ti2O3,占所有元素组成的34%,其中Al2O3含量为16.02%,CaO和Na2O含量分别为4.31%和1.17%。所分析的六种微量重金属元素含量Zn>Cr>Cu>Pb>As>Cd,平均含量总值为291.85×10-6。稀土元素总量平均为219×10-6,轻稀土元素含量是重稀土元素含量的4.34倍。较之冬春季沉积层,夏秋季沉积层中Al2O3和重金属元素含量偏高、CaO与Na2O含量偏低。冬春季沉积层主要矿物仍然为石英、长石、云母与黏土矿物,次要矿物为方解石和白云石,也具有明显长江型物源性质。其元素组成表现为:常量元素中Al2O3> TFe>CaO> K2O>MgO>Na2O>Ti2O3,亦占所有元素组成的34%,其中Al2O3含量为15.34%,CaO和Na2O含量分别为4.63%和1.43%。Zn、Cr、Cu、Pb、As、Cd的平均含量之和为265.42×10-6。稀土元素总量平均216×10-6,轻重稀土元素含量之比约为4.4。较之夏秋季沉积层,冬春沉积层元素组成表现为Al2O3低、CaO与Na2O高,重金属元素含量低。另外,沉积层序厚度与长江入海泥沙通量有很好的正相关关系。在研究时段1992~2005年间,年沉积厚度为1.1~3.6cm。最大沉积厚度发生于1998年,为3.6cm,对应的长江年输沙量4.01亿t;最小沉积厚度发生于2004年,为1.1cm,对应的长江年输沙量仅1.47亿t。更多还原

【Abstract】 With the use of X-photograph method、ultraviolet Spectrophotometry、X-ray diffration、ICP-AES(MS) analysis method, surficial sedimentary sequences of different sub-environments in the subaqueous Yangtze River Delta are studied. And undisturbed surficial sediment sample records are then analyzed, including high resolution records of grain size、BSi content、mineral and elements composition, which show a good response of delta front sedimentation to the Changjiang material flux and ocean environment. Based on the above records, characters of sedimentation in both summer-autumn and winter-spring are analyzed respectively. This is the first study about the sediment records on the scale of a year or even seasons in this area.The results show that sediments in the subaquous Yangtze River Delta are mainly silt clay. From the coast to the seaside, the grain size is gradually coarser. Surficial sequences are charactered by block structures, horizontal laminations and bioturbation strauctures. And the distribution of the bioturbation structure is largely spatial different in the Subaqueous Yangtze River Delta. From the delta front to prodelta and transitional zone to shelf environment, the bioturbation index is varied as low-high-low.This kind of response is the key point according to which sequences that deposit in different seasons can be identified.The delta front surficial sequence gives a good response to the seasonal variations of Changjiang sediment flux and delta environment. In summer and autumn, large sediment flux, weak ocean energy and high primary production result to finer sediment and high content of BSi in the sequence. While in winter and spring, when the sediment flux decreased, the ocean energy becomes stronger and the primary production gets to low, there will be croaser sediment and low content of BSi which deposit to the sequence. Mineral composition of the Sediment in summer and autumn is very near to those come from Yangtze River, in which major minerals are quartz, feldspar and clay minerals while calcite and dolomite appear as minor minerals. In the sediment, Al2O3> TFe>CaO> K2O>MgO>Na2O>Ti2O3,they constitute 34% of all. The content of Al2O3 in the sediment is16.02%, while the contents of CaO and Na2O about 4.31% and 1.17% respectively. Total content of the six heavy metal elements which are studied is 291.85×10-6, in which Zn>Cr>Cu>Pb>As>Cd. Total Ree is about 219×10-6, in which light Ree weight as 4.34 times as heavy ones. Compared with winter and spring, sediment in summer and autumn is high in Al2O3 and heavy metals, low in CaO and Na2O.Mineral composition of the Sediment in winter and spring is also near to those come from Yangtze River, and in which major minerals are quartz, feldspar and clay minerals while calcite and dolomite appear as minor minerals too. Similar to summer and autumn ones, in the winter and spring sediment, Al2O3> TFe>CaO> K2O>MgO>Na2O>Ti2O3,and they constitute about 34% of all. However, the content of Al2O3 in the sediment is15.34%, and the contents of CaO and Na2O are 4.63% and 1.34% respectively. Total content of Zn, Cr, Cu, Pb, As and Cd tend to be 265.42×10-6, Total Ree has no difference which weight about 219×10-6, and the content of light Ree is about 3.4 times higher than heavy ones. Compared with summer and autumn, sediment in winter and spring shows low contents of Al2O3 and heavy metals, but high CaO and Na2O.There is a good positive correlativity between the thickness of sediment sequence and the sediment flux of Changjiang. During1992~2005, which period that is researched, the annual deposite thickness ranges from 1.1cm to 3.6 cm. And the maximum thickness—3.6cm is deposited in 1998 when the sediment flux of Changjiang is 401 milion tons, while the minimum—1.1cm happens in 2004 when the sediment flux is only about 147 million tons.更多还原