长江中下游地区第四纪红土沉积特征与成因机制研究

发布时间：2017-12-30 20:31

本文关键词：长江中下游地区第四纪红土沉积特征与成因机制研究　出处：《华东师范大学》2017年博士论文　论文类型：学位论文

【摘要】：中国南方广泛分布的第四纪红土被认为是重建第四纪古气候演化历史的重要载体,因此越来越受到学界重视。本文选择中国南方长江中下游地区的安徽宣城剖面(XC)、江西九江剖面(JJ)、江西南昌剖面(NC)、江西新余剖面(XY)、湖南长沙剖面(CS)、浙江汤溪剖面(TX)等6个典型红土剖面为研究对象,并基于电子自旋共振测年法(ESR)建立了时间标尺。通过对红土的粒度、石英颗粒表面形态等方面的分析,探讨了剖面记录的第四纪红土沉积与物源特征,进一步结合地球化学、环境磁学等分析,对研究区第四纪红土的形成机制进行了探讨。本文的研究认识有助于更好地理解中国东部晚第四纪古气候、古环境演变历史。论文取得的主要认识如下:(1)长江中下游典型第四纪红土的形成年代基于湖南长沙(CS)、江西南昌(NC)以及江西新余(XY)三个剖面的ESR测年,并结合前人研究成果,认为长江中下游地区网纹红土开始沉积的时间为～1.0-1.2Ma B.P.、结束于～0.4Ma B.P.,而后均质红土层以及黄棕色土层开始发育形成。(2)第四纪红土的沉积动力特征利用新疆西风区黄土、黄土高原黄土、江苏下蜀黄土、长江河漫滩沉积物等典型的风成沉积物与水成沉积物的粒度特征为训练样本,建立了 Fisher线性判别函数。以此为基础,对研究剖面的第四纪红土进行了沉积动力判别分析。结果显示,长江中下游地区第四纪红土中均质红土层与黄棕色土层样品全部被判定为风成沉积;网纹红土层上部样品大多被判定为风成沉积,网纹红土层下部样品有较大部分被判定为水成沉积,网纹红土样品被判定为水成沉积的比例随着纬度的减小而增加。长江中下游地区第四纪红土的粒度特征表明,无论样品被判别为何中沉积,其平均粒径都较黄土高原黄土以及下蜀黄土细,而样品中的石英颗粒粒度特征表明造成第四纪红土粒度更细的原因不仅仅是风化作用,其原始物质来源本身也较黄土高原黄土与下蜀黄土细。样品的C-M图显示第四纪红土样品的平均传输动能较黄土以及河漫滩沉积小,这表明了该区域内第四纪红土的主要搬运动力仍然是风力。被判定为水成沉积的网纹红土样品中含有较多的100 μm组分,其最大传输动能与河漫滩沉积相当,这将该类网纹红土与典型的黄土高原黄土、下蜀黄土等风尘沉积相区别。长江中下游地区网纹红土中分离出来的石英颗粒的显微照片表明,无论样品被判别分析判定为何种沉积,石英颗粒样品中往往都混合着磨圆度好与磨圆度差的石英颗粒。由此推测长江中下游地区的网纹红土是一种近源风尘与远源风尘沉积的混合物,不同时期,不同位置远源于近源组分的比例不同。(3)第四纪红土的地球化学特征利用X荧光光谱仪、ICP-MS等仪器对中国东部第四纪红土的地球化学特征进行了常、微量元素、稀土元素分析。第四纪红土总体表现为高化学风化指数(CIA)值和低盐基淋溶系数(ba)值,表明其遭受了强烈的化学风化作用。对于同一红土剖面内部,网纹红土层的CIA值都较其上的均质红土或者黄棕色土高,而ba值则低,说明网纹红土比均质红土层与黄棕色土层的风化程度高。JJ、CS剖面表现出强风化网纹红土层的Si02/Al203值小于其上风化相对较弱的黄棕色土以及均质红土,而Si02/Al203值的地球化学行为趋向于随风化程度的增加而增大。长江中下游第四纪红土剖面的δCe表现为网纹红土的轻微负异常,而均质红层与黄棕色土层为轻微正异常。强风化的网纹红土层轻稀土与重稀土的比值∑L/HREE小于相对弱风化的均质红土层或者黄棕色土层,而稀土元素的地球化学特征表明,δCe与∑L/HREE值趋向于随风化程度的增加而增大。JJ、NC剖面稀土元素的聚类分析、Ti02/Al203与K20/A1203的散点图都表明,网纹红土层的下部、网纹红土层上部以及均质红土或者黄棕色土层的地球化学组成差异较大。这些特征表明,第四纪红土的物质来源具有不稳定性,不同时期,主要物质来源不同。(4)第四纪红土的环境磁学特征第四纪红土剖面的磁学特征表明,网纹红土层的磁化率相对于风化较弱的黄棕色土层以及均质红土层显著降低。相同气候区内的风化壳红土的磁学特征表明,网纹红土中磁化率降低可能并不仅仅是风化过程中强磁性矿物转变为弱磁性的赤铁矿等反铁磁性矿物造成的。在JJ、NC两个第四纪红土剖面中,网纹红土上部与其上的均质红土层以及黄棕色土层的主要磁性矿物类型、磁性矿物粒径都没有本质的区别,但是磁化率却显著减小了,这说明了网纹红土磁化率降低也不仅仅是网纹红土层细粒磁性矿物减少造成的。第四纪红土物质来源差异很可能是造成网纹红土层磁化率降低的主要原因。(5)第四纪红土的成因机制综合以上分析,在剥离风化因素的影响后,本文认为网纹红土很可能是一种远源与近源的混合物。远源物质由东亚冬季风从亚洲内陆地区搬运来。近源物质主要来自于附近水成沉积物释放的粉尘,由夏季风或者局地风场搬运而来。由于近源物质被风力搬运的距离短,其被风力改造也相对较弱,保留了大部分水动力沉积的特征。早期第四纪红土的物质来源以近源堆积为主。随着冬季风的逐渐加强以及河流的下切侵蚀,第四纪红土中近源物质的含量逐渐减少而远源物质逐渐增加,直到0.4MaB.P.均质红土以及黄棕色土(下蜀黄土)开始出现,第四纪红土转变为远源堆积为主。不同时期其主要物质来源不同,造成第四纪红土剖面内各层位粒度特征、地球化学与环境磁学差异。也由于近源物质的影响,造成不同区域内第四纪红土粒度、地球化学环境磁学特征的差异。
[Abstract]:Quaternary red clay widely distributed in South China is considered as an important carrier of reconstruction of Quaternary paleoclimate evolution history, so more and more academic attention. In this paper Chinese Southern Yangtze River region of Anhui Xuancheng section (XC), Jiangxi Jiujiang section (JJ), Jiangxi Nanchang section (NC), Jiangxi Xinyu (section XY) Hunan, Changsha profile (CS), Zhejiang Tangxi section (TX) of 6 typical laterite profile as the research object, and based on the electron spin resonance (ESR) dating method is established. Through the time scale size of laterite, analysis of Shi Yingke particle morphology, discusses the sedimentary provenance and Quaternary red clay the characteristics of profile records, combining with geochemical analysis, environmental magnetism, formation mechanism of Quaternary red clay were discussed. The study contributes to a better understanding of the ancient climate in the east of the late Quaternary ancient Chinese. The environmental evolution history. The main ideas are as follows: (1) the formation of the Yangtze River in Hunan based on the typical Quaternary Red Changsha (CS), Jiangxi Nanchang (NC) and Jiangxi Xinyu (XY) the three section of the ESR dating, combined with the previous research, that the downstream areas of long river laterite deposition the time is 1.0-1.2Ma ~ B.P., B.P. ~ 0.4Ma in the end, then the homogeneous red and yellow brown layer which begins to develop. (2) dynamic sedimentary characteristics of Quaternary red clay loess in Xinjiang by the westerly wind area, the Loess Plateau, the Xiashu loess in Jiangsu, Yangtze River floodplain sediments and typical aeolian sediment granularity characteristic and water sediment the training samples to establish Fisher linear discriminant function. On this basis, the research of Quaternary red clay profile was used to analyze the sedimentary dynamics. The results showed that fourth of the Yangtze River Region Ji in laterite homogeneous laterite layer and yellow brown layer samples are judged as aeolian deposits; reticulate red clay upper layer samples are mostly judged as aeolian deposits, laterite sample has a lower layer is judged to be most sediments, reticulate red clay samples were determined as the proportion of sediments increases with decreasing latitude. The grain size characteristics of the Yangtze River area of Quaternary red clay, both samples were deposited in distinguishing why, the average particle size is in the Loess Plateau and Xiashu loess and fine granularity characteristics of quartz grains in the sample showed that the cause of Quaternary red clay fine granularity is not only the weathering, the original source material itself is the Loess Plateau loess and Xiashu loess samples. The fine C-M figure shows that the average kinetic energy of Quaternary red clay samples of loess and floodplain sediment transmission is small, which shows in the region The main handling power is still the wind. The Quaternary red clay was judged to be 100 m group containing more water deposited in a sample of Plinthitic red earth, the maximum transmission of kinetic energy and floodplain sediment, this will be the typical laterite and loess of the Loess Plateau, distinguish Xiashu loess. The wind dust deposition. Micrographs the quartz particles separated from the lower reaches of the Yangtze River in the laterite showed that both samples were discriminant analysis to determine what kind of deposit, quartz particles in the sample are often mixed with good roundness and rounded quartz grains. Thus the poor area of the lower reaches of the river long Plinthitic red earth is a near and far away from the source of the dust source aeolian sediment mixture, different period, different position comes from near source component ratio. (3) the geochemical characteristics of Quaternary red clay by X fluorescence spectrometry, ICP-MS and other instruments on the eastern fourth China Ji The geochemical characteristics of laterite are often, trace elements, rare earth elements analysis. The overall performance of the Quaternary red clay high chemical weathering index (CIA) value and low base leaching coefficient (BA) value, that it has suffered strong chemical weathering. The same clay profile, the reticulate red clay layer CIA value is the homogeneous red or yellow brown soil is high, and the Ba value is lower than that of homogeneous laterite, clay layer and yellow brown soil weathering degree of high.JJ, CS profile showed strong weathering Plinthitic red earth layer of the Si02/Al203 value is less than the weathered relatively weak yellow brown soil and homogeneous laterite geochemical behaviors. The Si02/Al203 value increases with increasing trend in weathering degree. The lower reaches of the Yangtze River Delta Ce quaternary laterite profile showed slight negative anomalies and homogeneous laterite, red and yellow brown soil layer for the slight positive anomalies of strong weathering. The reticulate red clay layer LREE and hree ratio of sigma L/HREE lower than that of the homogeneous clay layer is relatively weakly weathered or yellow brown soil, and the geochemical characteristics of rare earth elements Ce and L/HREE show that the delta sigma value tends to increase with the increasing of the weathering degree of.JJ cluster analysis of NC profile of rare earth elements, plot Ti02/Al203 and K20/A1203 have shown that lower reticulate red clay layer, the upper layer and the reticulate red clay homogeneous red soil or yellow brown soil geochemical composition differences. These characteristics suggest that the material source of Quaternary red earth is unstable, different period, different source material. (4) showed that the magnetic characteristics of environmental magnetic characteristics of Quaternary quaternary laterite profile laterite, magnetization reticulated red soil layer rate compared to weathering weak yellow brown soil and red soil layer decreased significantly. The homogeneous laterite in the same climate zone Show that the magnetic characteristics, may not be the transformation process of strong magnetic minerals weathering weak magnetic hematite, anti ferromagnetic minerals caused the reduction of vermicular red earth in magnetic susceptibility. In JJ NC, the two section of Quaternary Red Earth in laterite layer and the upper part of the homogeneous red soil and yellow brown soil is the main type of magnetic minerals the particle size, magnetic minerals are not essentially different, but the magnetization rate decreased significantly, indicating that the reticulate red clay is not only reduce the susceptibility of the reticulate red clay layer of fine magnetic mineral decrease. The Quaternary red clay material source of difference might be mainly caused by the reticulate red clay layer magnetic susceptibility (5) causes reduced. The mechanism of Quaternary red earth based on the above analysis, the influence factors of the weathering peeling, the laterite is likely to be a mixture of a distant source and near source. The source material from far east Asia winter monsoon from the inland areas of Asia. Handling the near source material from dust emission in the vicinity of hydatogen sediment, by summer monsoon or local wind field due to transport. Because the near source material is carried by wind short distance, the wind transformation is relatively weak, retains the characteristics of most of the water power source material deposition. The source of early Quaternary red clay accumulation. With the gradual strengthening of the winter monsoon and the river erosion, the content of near source material in Quaternary red clay decreases gradually and far source material gradually increased, until the 0.4MaB.P. in yellow brown soil and red soil homogeneous (Xiashu loess) began to appear, into a distant source of Quaternary red clay deposits the main source of material. In different periods of different grain size characteristics of each layer of Quaternary laterite profile by, geochemistry and environmental magnetism differences. Also due to the influence of near source material, cause The difference between the granularity of the Quaternary Red Soil in the same region and the geochemical characteristics of the geochemical environment.

【学位授予单位】：华东师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P534.63;P512.2

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