【作者】 殷科；

【导师】 洪汉烈；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2013， 博士

【摘要】 在全球变化研究中,气候变化框架的构建主要基于对海洋沉积物研究的基础上。近年来,随着全球变化研究的逐步深入,陆地第四纪气候变化的研究引起了地质学家的广泛关注,而利用古土壤对气候环境信息的记录来研究全球变化问题,已成为当前地球科学研究的前缘课题。中国北方黄土高原分布的黄土-古土壤序列精确的记录了第四纪多旋回的气候环境信息,与深海同位素揭示的古气候信息十分吻合,引起了国内外古气候工作者的极大关注。中国位于典型的季风控制区,冬季风为中国南方输送了大量粉尘物质,而湿热的夏季风也对南方气候格局产生了一定的影响。中国南方第四纪研究结果显示,长江中下游地区广泛分布着更新世沉积物。作为对湿热气候的响应,土壤发育逐渐向南迁移。中国南方的风成沉积经历强烈的风化-沉积改造,掩盖了风成沉积的痕迹,严重影响了沉积物中气候及环境信息的解译。中国南方的第四纪沉积属于典型的加积型沉积,能有效揭示热带、亚热带气候条件下的同沉积成土作用。中国南方发育的第四纪沉积物主要为红土,而西北的黄土-古土壤序列具有清晰的颜色和组构,两者存在明显的区别。尽管近年来,中国南方沉积物古气候及环境的重建备受土壤学家和地质学家的关注,红土气候意义的揭示仍存在争议。长江中下游地区宣城剖面红土的氧化铁含量及有机碳同位素结果显示,红土为强烈成土作用改造的风成物质,形成时代可能与中国西北地区的黄土沉积基本一致。然而,由于红土和黄土在磁化率、氧化铁含量及有机碳同位素的变化存在着明显的差别,两者之间的相关性还不是很明确。另外,两者在成土强度方面存在着明显的差异。成土改造确实掩盖了蕴含在红土中的气候及环境演变信息,然而成土过程中会产生与当时气候环境相适应的粘土矿物。因此,南方第四纪红土形成时的气候及环境信息有效的保存在粘土矿物组分中。以往的研究主要集中在磁性地层、有机碳同位素及粒度分析等方面,而红土中的粘土矿物学研究较为缺乏。虽然沉积物中粘土矿物的组合、相对含量、结晶度等,已被广泛地应用于古气候的重建。然而,要获得更加准确的气候环境信息,必须借助特征矿物相的研究。1.4nm过渡矿物作为一种特殊的粘土矿物过渡相,通常被认为是蛭石向蒙脱石或者绿泥石向蒙脱石转变过程中的过渡矿物,在中国南方红土中广泛存在。过去由于研究方法和研究思路上的局限,很多情况下都将1.4nm粘土矿物过渡相笼统地称为绿泥石、蛭石、或蒙脱石,从而影响到对土壤物理化学性能内在因素的认识,也影响到对古土壤中粘土矿物演化、土壤发生分类、以及气候环境意义的解析。因此,本次研究将采用X射线衍射(XRD)、高分辨率透射电镜(HRTEM)、扫描电子显微镜(SEM)及电感耦合等离子体发射光谱(ICP-AES)等现代测试手段对长江中下游地区九江及宣城红土剖面不同层位中的1.4nm过渡矿物的具体种属、成因、演化、及其气候环境意义开展研究,这对粘土矿物学、土壤矿物学、乃至于全球变化研究等,均具有重要的科学价值。X射线衍射结果表明,九江及宣城剖面红土中普遍存在着1.4nm过渡矿物,在九江剖面上部黄色砂土中含量最高。1.4nm过渡矿物的1.4m衍射峰在镁饱和-甘油饱和后不发生变化,随着温度的升高1.4nm衍射峰发生有规律的变动：1.4nm→1.38nm→1.20nm,说明1.4nm过渡矿物为羟基间层蛭石。自然干燥片、镁饱和-甘油饱和片、镁饱和高温片和钾饱和高温片的X射线衍射结果显示,九江剖面上部黄色砂土中主要粘土矿物有伊利石、羟基间层蛭石、蛭石、高岭石,并含有少量伊利石-蛭石或伊利石-羟基间层蛭石及高岭石-蛭石或者羟基间层蛭石混层粘土矿物；中部均质红土中粘土矿物以伊利石、蛭石、高岭石为主,并含有少量羟基间层蛭石及伊利石-蛭石或伊利石-羟基间层蛭石混层粘土矿物、高岭石-蛭石或高岭石-羟基间层蛭石混层粘土矿物；下部网状红土中粘土矿物组成主要有高岭石、伊利石、伊利石-蛭石或伊利石-羟基间层混层粘土矿物、蛭石,并含有少量高岭石-蛭石或高岭石-羟基间层蛭石混层粘土矿物。宣城剖面上部均质红土中主要粘土矿物组成为伊利石和高岭石,含有少量蛭石、羟基间层蛭石及伊利石-蛭石或伊利石-羟基间层蛭石混层粘土矿物及微量高岭石-蛭石或者高岭石-羟基间层蛭石混层粘土矿物。下部网状红土中主要粘土矿物组分与上部均质红土基本相同,但高岭石和伊利石-蛭石或者伊利石-羟基间层蛭石混层粘土矿物含量高于上部均质红土,也含有微量高岭石-蛭石或者高岭石-羟基间层蛭石混层粘土矿物。九江及宣城剖面从下至上伊利石和蛭石含量增加,高岭石和伊利石-蛭石或者伊利石-羟基间层蛭石混层粘土矿物含量降低,也说明长江中下游地区中更新世以来气候环境有干冷化的趋势。羟基间层蛭石九江剖面上部黄色砂土含量较高,也表明九江剖面上部的黄色砂土形成的环境条件跟均质红土及网状红土有着明显的差异。高分辨透射电子显微镜下可清楚观察到伊利石-蛭石或伊利石-羟基间层蛭石混层粘土矿物及高岭石-蛭石或羟基间层蛭石混层粘土矿物,也可观察到伊利石晶层向蛭石或羟基间层蛭石及蛭石或羟基间层蛭石晶层向高岭石晶层转化的现象。上述现象表明,九江及宣城剖面红土中粘土矿物可能经历了如下的风化转变过程：伊利石→伊利石-蛭石或羟基间层蛭石混层粘土矿物→蛭石(或羟基间层蛭石)→高岭石-蛭石或羟基间层蛭石混层粘土矿物→高岭石。剖面从上往下随着风化程度的加深,加速了伊利石及蛭石或羟基间层蛭石向高岭石的演化过程,导致长江中下游地区黄色砂土、均质红土及网状红土中高岭石及伊利石-蛭石或羟基间层蛭石混层粘土矿物含量依次增加,而伊利石、蛭石或羟基间层蛭石含量逐渐降低。在扫描电子显微镜下,九江及宣城剖面红土中粘土矿物均呈片状产出,多发育不规则的、残缺的边缘,说明粘土矿物在形成过程中均经历了较强的风化作用。从黄色砂土到均质红土再到网状红土,其中的粘土矿物结晶程度依次降低,说明剖面从上至下风化作用在逐步增强,同时表明中更新世气候与晚更新世相比更为温暖潮湿。能谱分析结果表明,九江及宣城地区红土中片状粘土矿物化学成分主要为Si、Al、Fe、K、Mg、Na等元素,黄色砂土粘土矿物富K和Mg,表明伊利石和蛭石含量较高,均质红色粘土层和网状红土层中粘土矿物中Mg含量明显降低,表明中部均质红色粘土层和下部网状红土层中蛭石类矿物含量较低。均质红土及网状红土中Fe含量明显较上部黄色砂土高,红色调较为明显,表明Fe可能是以针铁矿或者赤铁矿微晶的形式吸附在粘土矿物的表面。电感耦合等离子体发射光谱测试结果表明,九江剖面上部黄色砂土层中粘土矿物的离子交换总量在45.1-67.3cmol(+)/kg之间,(Mg+Ca+Na)/Al比值在11.9～22.7之间；中部均质红土中粘土矿物的离子交换总量在85.1～116.2cmol(+)/kg之间,(Mg+Ca+Na)/Al比值在358.4～577.6之间；下部网状红土中粘土矿物的离子交换总量在在89.1～116.9cmol(+)/kg之间；(Mg+Ca+Na)/A1比值在465.9～644.2之间。宣城剖面上部均质红土中粘土矿物的离子交换总量在52.4～88.2cmol(+)/kg之间,(Mg+Ca+Na)/Al比值在193.1～406.6之间；下部网状红土中粘土矿物的离子交换总量在41.9～96.7cmol(+)/kg之间,(Mg+Ca+Na)/Al比值在260.6～413.3之间。明显可以看出,九江剖面上部黄色砂土层中粘土矿物的(Mg+Ca+Na)/Al比值及离子交换总量低于九江及宣城剖面的均质红土及网状红土,说明Al可能以羟基离子的形式赋存在粘土矿物的层间,其活性不仅控制着粘土矿物的转化,也对粘土矿物的离子交换量影响较大。长江中下游地区黄色砂土形成于～100ka以来,对应于晚更新世,而均质红土和网状红土分别形成于400ka～100ka和800ka～400ka,为中更新世的产物。在中等风化程度、PH值介于4.5～5.0的条件下,土壤中的Al以羟基铝离子的形式进入到蛭石层间形成羟基间层蛭石,而风化作用加剧,促使伊利石和蛭石(包括羟基间层蛭石)向蒙脱石转化,最终形成高岭石。在透射电子显微镜下,伊利石-蛭石或者伊利石-羟基间层蛭石混层粘土矿物的存在即伊利石晶层向蛭石(或者羟基间层蛭石)晶层的转化现象,说明蛭石(包括羟基间层蛭石)是伊利石风化过程中的产物。因此,我们可以认为羟基铝间层蛭石的母质矿物为伊利石。在酸性的红土中,Mg、Ca、Na等离子只能以简单离子的形式存在于粘土矿物层间,而Al可在适当的酸性环境下以羟基铝离子的形式进入到蛭石中形成羟基铝间层蛭石,改变了土壤的矿物组分及离子交换量。长江中下游地区红土剖面从下至上羟基间层蛭石及伊利石含量逐渐增多,高岭石和伊利石-蛭石或伊利石-羟基间层蛭石混层粘土矿物含量逐步降低,表明长江中下游地区中更新世气候经历了从温暖潮湿向冷干的转变,与全球气候变化格局较为一致。因此,1.4nm过渡矿物羟基间层蛭石不仅能反应红土形成时期的气候环境变化,也可作为区分中更新世和晚更新世界限的特征矿物。更多还原

【Abstract】 The framework of climate change is mainly based on Marine sediments in global change research. In recent years, the quaternary climate research has attracted a great attention of geologists with the development of the global change research. However, the reasearch on global climate change using ancient soils have become a hot subject of earth science. The loess-palaeosol sequences in the Loess Plateau, northwest China, contain an excellent record of multiple-cycle change of Quaternary climate, which is quite consistent with the results revealed by deep-sea isotope and has attracted great attention of the palaeoclimatic workers at home and abroad. China is located in a typical monsoon-influenced region. The summer monsoon brings abundant moisture and heat to the continent, while the winter monsoon transports large volumes of aeolian dust to areas of east and south China. Recent studies of Quaternary sediments in south China suggest that deposits from the Pleistocene onwards cover the mid-lower reaches of the Yangtze River. In response to a warmer and wetter climate, soil development migrated progressively southwards. Aeolian deposits in south China may be subject to relatively intense syndepositional pedogenic alteration, resulting in the removal of some imprints of Aeolian provenance and consequently making it difficult todecipher the climatic and environmental information documented in the sediments. The Quaternary sediments in south China were accretionary in nature, reflecting some degree of syndepositional pedogenesis under tropical to subtropical climate conditions. Unlike the loess-palaeosol sequence with clearly defined soil layers of different colours and structures in northwest China, Quaternary sediments in south China were mainly red earth. Although in recent years the deposits have attracted the interest of many pedologists and geologists for the purpose of reconstructing palaeoenvironments and palaeoclimates in south China, interpretations of the climatic significance of the red earth are still debatable. Investigations of the Fe2O3content and organic13C composition of the Xuancheng red earth profile in the mid-lower reaches of the Yangtze River, south China suggested that the red earth in fact comprised aeolian deposits with intense pedogenic modification, which could be stratigraphically correlated with the loess deposits in northwest China. However, the correlation between the red earth and the loess deposits was not clear, as the differences in the multiple cyclic changes in magnetic susceptibility, Fe2O3content and organic13C composition were very small. Moreover, there was a major pedogenic discrepancy in the soil-forming periods between the two materials. Pedogenic alteration indeed removed some imprints indicating the environmental and climatic conditions. However, this process would also have produced clay minerals corresponding to the conditions of weathering or hydrolysis of the materials. Hence, evidence for environmental and climatic conditions is probably preserved in the clay fraction of the sediments.Previous studies have mainly focused on magnetic strata, organic carbon isotope and grain size analysis, etc., and the clay mineralogy of red earth is rarely lack. Although the asseblage, relative content and crystallinity of clay minerals in sediments have been widely used in the reconstruction of the paleoclimate. However, the characteristic mineral phases must be used to obtain more accurate climate information. As a special intergrade clay mineral,1.4-nm Spacing intergrade mineral, widely existing in red earth of southern China, is usually considered as a intergrade mineral transforming from vermiculite to montmorillonite or chlorite to montmorillonite. Due to the limited methods and ideas in the past,1.4-nm Spacing intergrade minteral was mistaken as chlorite, vermiculite or smectite, which would influence the understanding the internal factors of physical and chemical properties of soil,also the clay mineral evolution in the ancient soil, as well as soil classification and its climate significance. Therefore, specific species, Genesis, evolution, and climate environment of1.4nm intergrade minteral from different soil layers of Jiujiang and Xuancheng section are investigated using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High resolution transmission electron microscope (HRTEM), Scanning electron microscope (sem) and Inductively coupled plasma emission spectrum (ICP-AES), which is of great importance to clay mineralogy, soil mineralogy, and even the global change research and so on.The XRD patterns of the clay fractions show that1.4-nm Spacing intergrade minteral is widely distributed in Jiujiang and Xuancheng red earth section, with the highest levels in yellow sandy soil of Jiujiang section. The1.4nm peak of1.4-nm Spacing intergrade minteral did not expand after Mg saturation and glycerol solvation, and the1.4nm peak shifted to1.38nm and afterwards1.20nm with temperature, indicating that1.4-nm Spacing intergrade minteral is hydroxy-interlayered vermiculite (HIV). The XRD patterns of Air-dried, Mg-saturated and glycerol solvated, Mg-saturated and heated and K-saturated and heated samples show that the clay mineral assemblages of yellow sandy soil were mainly illite, HIV and kaolinite, with minor illite-vermiculie or illite-HIV and kaolinite-vermiculite or kaolinite-HIV mixed-layer clays. The clay mineral assemblages of homogeneous red earth were dominated by illite, vermiculite and kaolinite, with minor HIV, illite-vermiculie or illite-HIV and kaolinite-vermiculite or kaolinite-HIV mixed-layer clays. The clay mineral assemblages of net-like red earth were composed of kaolinite, illite, illite-vermiculie and vermiculite, with kaolinite-vermiculite or kaolinite-HIV mixed-layer clays. The clay mineral assemblages of homogeneous red earth in Xuncheng section were dominated by illite and kaolinite, with minor HIV, illite-vermiculie or illite-HIV and trace kaolinite-vermiculite or kaolinite-HIV mixed-layer clays. Net-like red earth had the same clay assemblages with homogeneous red earth, but contained more kaolinite and illite-vermiculie or illite-HIV mixed-layer clays. The increase of illite and vermiculte and the decrease of kaolinite and illite-vermiculie or illite-HIV mixed-layer clays occurred from the bottom up along the two sections, indicating that since middle pleistocene the climate advanced toward cold and dry in the mid-lower reaches of the Yangtze river. The relatively high content of HIV in Jiujiang yellow sandy soil suggests that yellow sandy soil apparently experienced a different pedogenic process with homogeneous red earth and net-like red earth.Under HRTEM, illite-vermiculite or illite-HIV mixed-layer minerals and kaolinite-vermiculite or kaolinite-HIV mixed-layer minerals can be clearly observed. Meanwhile, lattice fringe image presented the transformation of illite layers to vermiculite or HIV layers, and also showed the transformation of vermiculite or HIV layers to kaolinite layers. These observations show that the weathering sequence of clay mineral of Jiujiang and Xuancheng red earth section may be as this:illite→illite-vermiculite or illite-HIV mixed-layer minerals→vermiculite (HIV)→kaolinite-vermiculite or kaolinite-HIV mixed-layer minerals→kaolinite. An increased weathering trend towards the bottom of section, the transformation of illite and vermiculite or HIV to kaolinite was accelerated, causing the downward increase of illite-vermiculite or illite-HIV mixed-layer minerals and the downward decrease of illite and vermiculite or HIV.Under the observation of SEM, the clay minerals in the Jiujiang and Xuancheng section occurred as flakiness shape with irregular and fragmentary edges, indicating the clays have undergone intensive weathering during its formation. The crystallization of clay minerals exhibited a decreased tendency from the yellow sandy soils to homogenous red earth and to net-like red earth, suggesting the weathering of the section enhanced downwards, meanwhile showing the climate in mid-Pleistocene was warmer and wetter than that in late Pleistocene. The EDS showed that the chemical composition of the flakiness shape clays in the red earth of the Jiujiang and Xuancheng section were mainly composed of Si, Al, Fe, K, Mg and Na, with enrichment of K and Mg in the yellow sandy soils. These results with more enrichment of K and Mg might mean the higher content of illite and vermiculite. The element Mg presented a lower value in the homogenous red earth and net-like red eath, indicating a lower content of vermiculiteic minerals in these soils. However, the homogenous red earth and net-like red earth were richer in Fe and showed distinctly red hues, suggesting Fe might occur as goethite and/or hematite microcrystalline minerals adsorbed onto the surface of the clay minerals.The ICP-AES results showed that total extracted cations of clay minerals in Jiujiang yellow sandy soils ranged from45.1to67.3cmol (+)/kg, and the (Mg+Ca+Na)/Al raios ranged from11.9to22.7; total extracted cations of homogeneous red earth ranged from85.1to116.2cmol (+)/kg, and the (Mg+Ca+Na)/Al raios ranged from358.4to577.6; total extracted cations of net-like red earth ranged from89.1to116.9cmol(+)/kg, and the (Mg+Ca+Na)/Al raios ranged from465.9to644.2. Total extracted cations of clay minerals in Xuancheng homogeneous red earth ranged from52.4to88.2cmol (+)/kg, and the (Mg+Ca+Na)/Al raios ranged from193.1-406.6; Total extracted cations of clay minerals in Xuancheng net-like red earth ranged from41.9to96.7cmol (+)/kg. It is clear that the (Mg+Ca+Na)/Al raios and total extracted cations of Jiujiang yellow sandy soils were smaller than those of homogeneous and net-like red earth from Jiujiang and Xuancheng, suggesting that The Al cations are adsorbed as hydroxyl ions in the interlayer of clay minerals. The activity of hydroxyl-Al not only controlled the transformation of clay minerals, also influenced their total extracted cations.The yellow sandy soils of Jiujiang in the lower reaches of Yangtze River formed since100ka, corresponding to late-pleistocene. However, homogeneous and net-like red earth formed during the period of400ka to100ka and the period of800ka to400ka, which were the product of mid-pleistocene. Al was adsorbed in the interlayer region of vermiculite as hydroxyl-Al, resulting in the formation of HIV. Illite and vermiculite or HIV might transform into smectite wih weathering, and kaolinite formed as weathering proceeded. The occurrence of illite-vermiculite or illite-HIV mixed-layer minerals and the transformation of illite to vermiculite or HIV indicated that vermiculite or HIV was the weathering product of illite. Therefore, HIV may have an illite precursor. Since Mg, Ca, Na occurred to be simple ions in the interlayer of clay minerals from acid red earth, whereas Al entered in the interlayer of vermiculite in the form of hydroxyl-Al, altering mineral composition and icon exchange capacity. A gradual crease of HIV and illite and a gradual decrease of illite-vermculite or illite-HIV mixed-layer minerals suggest that a gradual climate change from warm and humid to cool and dry in the mid-lower reaches of Yangtze River region since mid-pleistocene, in good agreement with global climate change. Thus, not only HIV can reveal the climate change during the forming period of red earth, but also can be used as a characteristic mineral to define the boundary of Middle Pleistocene and Late Pleistocene.更多还原