【作者】 张丹；

【导师】 陈中原；

【作者基本信息】 华东师范大学 ， 自然地理学， 2011， 博士

【摘要】 长江流域的演化与青藏高原隆升、亚洲大河流域的起源及古气候变化等许多重大科学问题紧密相连。从“源”到“汇”的研究理念即是通过关注长江三角洲地区沉积物物源变化,进而推测长江流域演化信息。大量的实验结果和资料总结,表明沉积物中磁铁矿各种元素的丰度可以指示母岩类型,进而判断沉积物来源。为了掌握长江流域母岩类型分布,寻找有效的特征物源,从而应用于长江口晚新生代钻孔沉积物物源识别,本论文首先对现代长江上、中、下游河道不同河段的47个沉积物样品,进行了磁性矿物分选,并对其进行了磁性矿物形态电镜扫描(SEM)和化学成分的电子探针(EPMA)测试。其次,本文基于对河口区晚新生代钻孔(SG7孔,孔深336.62米)不同层位上的440个样品进行室温磁性参数测试的结果,挑选出54个强磁性层位样品进行了磁性矿物形态电镜扫描(SEM)和化学成分的电子探针(EPMA)测试,其中9个样品进行重矿物鉴定。同时结合到本研究中的还有430个样品的粒度数据、267个样品的古地磁分析、10样品的光释光测年和3个样品的u系测年结果。将长江现代河道沉积物和长江三角洲SG7孔EPMA结果进行有效指标提取、对比分析和讨论,尝试在河流汇区地层中寻找物源变化的信息及驱动力,从而为古长江流域演化过程研究展开一个新的角度抛砖引玉。长江现代河道沉积物中磁铁矿的EPMA结果表明：上游金沙江流域(石鼓段以上流域)物源贡献的磁铁矿特点是高Fe、Co,较高Cr、Mg、Al、V,低Ti、Mn、Zn；长江上游诸支流对高Ti、Cr磁铁矿贡献量较大；清江汇入Zn含量明显增高；汉江流域对高Zn磁铁矿物源也有一定贡献；大别山诸河对高Mn磁铁矿贡献量较大；鄱阳湖水系对高Ti、Al、Cr磁铁矿贡献量较大；青弋江小河流域对较高Mg丰度的磁铁矿有一定贡献；河口区本地物源贡献的是低Fe、Co,高Ti、Mg、Al、Cr的磁铁矿。表层样的EPMA分析结果还显示,长江上游产出的磁铁矿在进入江汉盆地后存在显著堆积的可能。根据磁铁矿EPMA测试结果中元素的变化情况可将SG7分为五层。Ⅰ层为上新统和下更新统底部,特征是高Ti、Mg、Mn低Cr、Zn、Al；Ⅱ层为下更新统下段,特征是高Fe,微量元素含量均为低值；Ⅲ层为下更新统中段,特征是高Ti、Mg、Mn,低Cr、Zn、Al、V；Ⅳ层为下更新统上段至上更新统,特征是所有元素都表现出强烈的波动；V层为全新统特征是低Mg、Mn、Cr,较低Al、V。长江三角洲SG7孔与长江现代河道沉积物中磁铁矿标型特征对比分析表明：长江三角洲地区上新世至早更新世初期期间沉积物中磁铁矿主要以当地白龙港富Ti玄武岩为母岩,古地形起伏较大,沉积物的来源范围狭小,主要来源于局地；早更新世早期沉积物中磁铁矿主要来自近源闽浙隆起带的沉积、变质岩性母岩,以高Fe为特征,其它元素含量均表现为低值；早更新世中期沉积物中富Mn磁铁矿颗粒的出现指示了流域至少有过一次明显扩张,反映了构造沉降作用导致沉积体系变大,本区由侵蚀区逐渐向开放的沉积体系演变,极大可能为中源大别山水系加入本区物源贡献；早更新世晚期—晚更新世磁铁矿标型特征元素波动变化指示了多次流域物源演化,其中早更新世晚期存在明显的流域扩张信息,沉积物中富Zn磁铁矿颗粒的出现极大可能指示了中远源长江中游武汉以上段物源影响到本区,反映了流域的再次扩大；全新世长江已完成全程贯通,长江三角洲地区沉积物源稳定并以上游远源贡献为主,长江流域水系演化进入成熟期。更多还原

【Abstract】 The evolution of the Yangtze River is closely linked with many important scientific issues, such as the Qinhai-Tibet Plateau uplift, the origin of large river basins in Asia and the paleoclimate change. The theory of "source" to "sink" is by tracking down the sediment provenance of the Yangtze Delta back to the evolution of Yangtze River Basin. Numerous experimental results from previous studies have proved that the elemental composition of magnetite in sediments can be used as a proxy for the mother rock types, and further to indicate the sediment provenance.To get the knowledge of the rock type distribution of the Yangtze River catchment, and look for the effective diagnostic source are the first step to apply for the Late Cenozoic core in the Yangzte Delta. Thus, firstly, this paper identified 47 samples by magnetic mineral collected from different locations in the middle and lower reaches of the modern Yangtze River, and measured the magnetic mineral form of scanning electron microscopy (SEM) and chemical composition of the electron probe (EPMA) test.Secondly, based on the results of the chemical composition of the electron probe (EPMA) test on the 440 samples from different sediment layers in the Late Cenozoic sediment core (SG7,336.62m long) in the Yangtze estuary, this paper picked up 54 samples with strong magnetic properties for the measurements of magnetic mineral form of scanning electron microscopy (SEM) and chemical composition of the electron probe (EPMA) test. Among of them,9 samples were tested for heavy mineral compositons. Meanwhile, other materials incorporated into the present study are 430 samples of particle size,267 samples of paleomagnetic analysis,10 samples of optical dating and 3 samples of U-series dating.Through the comparison analysis between the modem sediments of the Yangtze River of EPMA results in SG7. the present study is trying to reveal the provenance evolution of the Yangtze River and the related driving forces, which will also provide a new insight into the evolution of the Yangtze River drainage basin.The EPMA results on the modern sediments of the Yangtze River showed that: the dominant contribution of magnetite source in upper Jinsha River (basin above Shek Kwu Section) is characterized by high Fe. Co, high Cr, Mg. Al, V, low Ti, Mn. Zn; various tributaries of the Yangtze River also contributed a lot of magnetite with high Ti. Cr: the increasing Zn were significantly derived from Qingjiang River: Hanjiang River also have some contributions to the sediment source with high-Zn magnetite; Rivers from Dabie Mountain provide a lot of large iron ore with high-Mn magnetic; Rivers from Poyang Lake Basin largely contributes sediments with high-Ti, Al and Cr; Qingyi River Basin has contributed sediments with high Mg magnetite; the local provenance from the estuary contributes the local source by the low-Fe, Co, high-Ti, Mg, Al, Cr magnetite. EPMA analysis of surface samples also showed that output of magnetite from the upper Yangtze River basin are more likely to accumulate when it is discharged into the Jianghan basin.The elemental compostion of magnetite in SG7 can be divided into five sections according to EPMA results. Section I (Pliocene-the bottom of Early Pleistocene) is characterized by high Ti, Mg, Mn low-Cr, Zn, Al; SectionⅡ(the lower part of the Early Pleistocene) is featured with high in Fe, and low in trace element contents; Section III is the next middle Pleistocene, characterized by high Ti, Mg, Mn, low-Cr, Zn, Al, V; Section IV (the upper part of Early Pleistocene-late Pleistocene) is characterized by the strong elemental fluctuations; Section V (the Holocene) is characterized by low Mg, Mn, Cr, and even lower Al, V.Typomorphic characteristics of magnetite from sediments of the SG7 core in the Yangtze Delta and modern river sediments of Yangtze River show that:From the Pliocene to the beginning of Pleistocene, magnetite in sediments of Yangtze River Delta region mainly come from Bailonggang Ti-rich basalt rock. Ancient topography is undulating, and sediments from a narrow range of local. Magnetite of Early Lower Pleistocene sediments mainly from proximal sedimentary rock and metamorphic rocks of Fujian and Zhejiang Uplift.It is characterized by high Fe. the content of other elements is low.Middle Lower Pleistocene sediments have a large number of Mn-rich magnetite particles. It indicates that the basin occurred at least once a significant expansion Event. It reflects the area become to an open depositional system under the tectonic subsidence movement.The sediments may come from the Dabie Mountains. Zn-rich magnetite particles appear in the Late Lower Pleistocene sediments. It indicates the sediments reach to this area most likely come from the Middle Yangtze River Region before Wuhan at this time. The basin expanded once again.The Yangtze River has been completed throughout at Holocene.Holocene sediments of the Yangtze River Delta comes from distal upper reaches steadily.The Evolution of Yangtze River water system gets into the mature period.更多还原