【作者】 黄传琴；

【导师】 谭文峰； 邵明安；

【作者基本信息】 中国科学院研究生院(教育部水土保持与生态环境研究中心) ， 土壤学， 2011， 博士

【摘要】 黄土高原完整的黄土-古土壤序列作为第四纪古环境三大支柱记录之一,储存了2.5Ma B.P.以来丰厚的地学-生物学信息，它记录了黄土高原乃至整个欧亚大陆第四纪多旋回的生物气候环境变迁，为研究古气候和古环境变化提供了很好的研究材料。粘粒矿物作为土壤的重要组成成分，它的形成与转化受温度、湿度等环境条件的影响。因此，矿物组成特征可指示土壤演化过程与成壤环境。本研究以武功、洛川、安塞全新世黄土-古土壤以及武功第五层古土壤为研究对象，采用X-射线衍射（X-raydiffraction）、X-射线荧光光谱法（X-ray fluorescence）、选择性溶提等技术研究了不同土壤层次的矿物学特征，结合14C加速器质谱法测年、粒度组成、CaCO₃以及磁化率分析，探讨全新世黄土-古土壤和第五层古土壤中的矿物风化与成壤过程，揭示地质时期古气候与成壤环境的时空特征，取得的主要结果有：1.武功全新世黄土剖面的土层（上覆黄土层/L0，0-50cm；均一古土壤层/S0，50-150cm；古土壤与马兰黄土层之间的过渡黄土层/LT，，150-200cm）明显可辨。根据¹⁴C测年结果进行插值计算，L0、S0、LT土层的更迭说明了黄土高原南缘全新世0-3,100yrB.P.、3,100-8,500yr B.P.、8,500-11,500yr B.P.期间气候干冷-暖湿-干冷变化的“三阶段”模式。武功全新世黄土-古土壤剖面的CaCO3含量、粒度组成、磁化率均与成壤作用呈相应的周期变化。相对下伏马兰黄土层（L₁，200cm以下）及上覆黄土层（L0），全新世古土壤（S0）CaCO₃的强烈淋溶、粘粒的富集、磁化率的增强，说明该层土壤的成壤发育作用增强。根据武功全新世古土壤层CaCO₃的淋溶量、迁移深度及磁化率推算，全新世中期S0发育时的年均降水量高达800mm以上。该区全新世中期气候类型相当于现今亚热带北缘（秦岭南坡）土壤发育的气候条件。2.黄土高原南缘武功全新世黄土粘土矿物的组成特征分析结果表明，全剖面粘土矿物组成相似，以伊利石为主，绿泥石、蛭石次之，含有少量高岭石与蒙脱石等。古土壤S0中存在少量的层间羟基物矿物（hydroxy-interlayered minerals，HIM），这意味着全新世中期黄土高原南缘以森林为主的古土壤环境。柠檬酸钠溶液80oC连续处理结果HIM主要由层间羟基物蒙脱石（hydroxy-interlayered smectite，HIS）和层间羟基物蛭石（hydroxy-interlayered vermiculite，HIV）组成，并提出了古土壤中硅酸盐矿物的形成与转化过程及HIM形成的可能途径。3.黄土高原南缘武功全新世古土壤层（S0）中的伊利石结构特征指数相对较高，但全剖面（L₀、S₀、L₁）伊利石的半高宽（half height width，HHW）、积分宽度（integralbreadth，IB）、化学指数（illite chemistry index，ICI）分别在0.25-0.30o2θ、0.4-0.6o2θ、0.25-0.40之间变化，表明土壤形成于物理风化较强的环境中，矿物化学风化较弱。富含CaCO₃的风尘物质的连续沉积抑制了矿物的风化演化，减弱了古土壤的成壤发育强度，主要的矿物风化过程是伊利石的脱钾作用和绿泥石的风化。因此，黄土高原地质时期的古气候及成壤环境条件，比黄土-古土壤层中的矿物风化及成壤特征所反映的气候更为暖湿。4.黄土高原自北向南的安塞、洛川和武功全新世黄土-古土壤(¹⁴C测年：23860±90-0yr B.P./晚更新世晚期至今)剖面中的层状硅酸盐矿物以伊利石为主，绿泥石、蛭石次之，含有少量高岭石与蒙脱石等，其矿物及元素组成相似，并且各剖面之间的矿物与元素组成也相似。沿气候梯度，自北（安塞剖面）向南（武功剖面），古土壤层中蛭石含量逐渐增加、高岭石和蒙脱石略有减少，同时伴有粘粒的富集、碳酸盐强烈的淋溶以及磁化率的增强。安塞全新世剖面的层状硅酸盐粘土矿物组成一致且含量稳定，与剖面中高砂粒含量、稳定的CaCO₃含量以及极低的磁化率一致，风尘沉积后经历的矿物风化、成壤作用弱，这说明黄土高原北部11,500yr B.P.以来气候及成壤环境稳定，全新世中期并没有受到东南亚暖湿季风气候的影响。黄土高原黄土-古土壤中的矿物学组成特征确切地记录了地质时期成壤环境的时空变化。黄土高原全新世期间的气候变化存在地区差异，典型的全新世气候变化的“三阶段”模式在区域上并不具有普适性。5.黄土高原南缘武功第五层复合古土壤（S₅）每一层古土壤层(S_5-1、S_5-2、S_5-3)的CaCO3在成壤前期完全淋失，在古土壤底部形成了30-50cm厚的CaCO3结核层。S5-1土层中的粘粒含量和磁化率均明显高于S_5-2和S_5-3土层，说明S5-1土层经历了更为强烈的物理、生物化学风化，其成土作用较S_5-2和S5-3土层的强烈。S5的粘粒/粉粒比值较高，小于0.002mm的粘粒含量高出下伏黄土层（L₆）约60-100%。粒度结果表明，S5的粘化作用较全新世古土壤（S0）的强。各古土壤层中部磁化率在120-310SI(10-8m³kg^-1)范围内波动，远比S0的磁化率(190-220SI/10^-8m3kg^-1)高。可以推断S5古土壤代表了比全新世中期更为暖湿的气候条件。武功S5复合古土壤成壤过程中CaCO₃完全淋失、粘化作用强烈、磁化率增强，都说明S5在暖湿的气候条件下经历了强烈的成壤作用。但是，粘土矿物的分析表明，S5的粘粒矿物组成相似，S_5-1、S_5-2和S_5-3的粘土矿物均以伊利石为主，并含有不同数量的绿泥石、蛭石、高岭石与蒙脱石等。S5并没有表现出比其上覆黄土层（L₅）和下伏黄土层（L₆）更为强烈的矿物风化，这与粒度组成、CaCO₃及磁化率的分析结果矛盾。这可能是因为每层复合古土壤层底部坚硬、致密的CaCO₃淀积层和粘化层对下渗水的滞留作用，阻碍了上伏土层中碱土金属元素和硅的淋移，抑制了矿物的风化转化。更多还原

【Abstract】 The complete set of “loess-paleosol” sequences on the Loess Plateau, China, as one ofthe three records for paleoenvirenment during the Quaternary period, record the biologic,climatic and environmental changes of the Loess Plateau, even of the Eurasian since2.5Ma B.P.. Soils derived from the Loess Plateau of China are regionally important andexpression of the soil properties along the soil profile may be directly related to climatechanges. Clay minerals are derived from weathering of parent material and/or precipitatedfrom the soil solution. They reflect successive stages of mineralogical evolution dependingon the various environmental conditions that have prevailed during soil formation.Therefore, this study focused on the mineralogy in the Holocene loess-paleosol in theWugong, Luochuan and Ansai sections and the fifth paleosol （S₅） in the Wugong section,together with the specific properties （e.g. grain size, carbonate content and magneticsusceptibility）、¹⁴C dating by the accelerator mass spectrometry method （AMS） and fieldobservations to access the clay mineral transformation, in relation to the pedogenesis andthe regional climate changes. The main results are as follows:1) The main stratigraphic subdivisions of the Holocene loess-paleosol in the Wugongsection clearly identified in the field were confirmed by analytical data with single-weldedpaleosol S0（8,500-3,100year B.P.） and a cover loess L0（3,100–0year B.P.） and atransitional loess （L_T）（11,500–8,500year B.P.）. They presented a pretty classic picture asa complete episode of the Holocene climate change, corresponding to a glacial-interglacialclimatic fluctuation on the southernmost Loess Plateau. The intensive decalcification,enrichment of clay content and increasing of magnetic susceptibility in the paleosol （S₀,50-150cm） signified the strong pedogenesis with respect to the Malan loess. Thecalculated from the magnetic susceptibility and the depth and the total amount of carbonateleaching suggested that the average annual precipitation during the mid-Holocene was up to800mm. And the climate type in this period was analogous with the modern climateconditions in the northern subtropical zone （the southern slope of Qingling Mountains） forthe formation of Udic Luvisols （Brown Soil）.2) Mineralogy of the Holocene loess-paleosol in the Wugong section on thesouthernmost Loess Plateau suggested that clay mineralogical compositions were similar inthe stratums with the illite in the majority throughout the profile. The changes of thephyllosilicate minerals were consistent with the soil genetic horizons and with thevariations in CaCO₃content, particle size distribution, and magnetic susceptibility. Arelatively high vermiculite content and the presence of hydroxyl-interlayered mineral （HIM）occurred in the most weathered palaeosol （S₀）. According to the XRD analysis before andafter sodium citrate extraction, the HIM in the paleosol was mainly composed of thehydroxy-interlayered smectite （HIS） and the hydroxy-interlayered vermiculite （HIV）. Thehydroxyl-interlayers common present in Alfisol of southern China, occurred in the paleosolsignified the dominant forest landscape palaeoecology and the acidic paleosol environmentduring the mid-Holocene. The contradiction between the type clay minerals present and themeasured alkaline soil pH values in the palaeosol could be understood by therecalcification caused by the post-pedogenic leaching from the overlying loess. A mostlikely explanation for the occurrence of HIM and transformation of phyllosilicate mineralsin the paleosol stratum derived from loess was suggested.3) The relatively high values of half height width （HHW） and integral breath （IB） andthe relatively low values of chemical index of illite （ICI） represent relatively low illitecrystallinity and intensive weathering and pedogenesis in the Holocene paleosol （S0） withrespect to the overlying and underlying loess. However, the values of HHW, IB and ICIshowed no significant variations throughout the profile ranging from0.25to0.30（o2θ）,0.4to0.6（o2θ） and0.25to0.40（o2θ） throughout the profile, respectively, whichimplied a weak chemical weathering. The successive adding of eolian sediments withabundant CaCO₃restrained the intensity of mineral weathering and pedogennesis.Generally, the depotassication of illite and the degradation of chlorite were the majormineral transformation processes that occurred with soil-formation of the Holocenepalaeosol on the southernmost Loess Plateau and the pedogenic strength did not reachedthe level of Udic Luvisols （Brown Soil）. Due to the special pedogenesis pattern, the palaeoclimate would be warmer and wetter than the climate that was derived from themineral weathering and soil evolution characteristics in paleosol.4) Analysis of the Holocene loess-paleosol at Ansai, Luochuan and Wugong in anorth-south transect and in geological age from the late Epipleistocene （0-23860±90yearB.P.） suggested that the mineralogy were similar over the Loess Plateau, China. However,in detail, there were significant temporal and spatial variations in analytical results ofpedogenesis and mineralogy of the profiles in the three sections along the climate gradient.Mineral weathering and pedogenesis resulted in a vital increase of vermiculite in paleosolof Wugong section with more clayey, intensive decalcification and increasing of magneticsusceptibility. The subtle decrease of kaolinite and smectite in paleosol southward resultedfrom the resilication by strong plant/clay interaction and leaching of soil base ions withlush vegetation and increasing precipitation during the mid-Holocene. The pedogeneticcyclicity and mineral weathering were progressively weakened with the trendingsouth-north across the Loess Plateau signified the weaker climate fluctuation since11,500years and the decreased influence of summer monsoon on pedogenesis and mineralweathering intensity northward. In general Holocene loess in Ansai section preserved inthick eolian deposits was found to be relatively homogeneous as far as grain size and claymineralogy. There was no significantly variation in phyllosilicate composition with depthwhich coincided with more coarse grains and constant CaCO₃content signified the leastweathering and pedogenesis under stable and dry climate and pedogenic environment overthe last11,500years. The mineralogical composition in loess-paleosol across the CLPrecords precise temporal and spatial variability of the palaeoenvironment. The traditionalscheme of the Holocene climatic change is not a unique phenomenon across the LoessPlateau.5) The fifth paleosol （S₅） is a complex paleosol essentially composed of threewell-developed reddish soil pedons (S_5-1, S_5-2, S_5-3). The carbonate of each paleosol pedonswas absolutely leached from the paleosol during the early stage of soil formation underintensive eluviation condition, and deposited beneath the pedons of30-50cm in thicknesswhich can easily be recognized as stratigraphic markers between each pedons. The claycontent and magnetic susceptibility in the S5-1pedon were absolutely higher than those inthe S_5-2and S_5-3pedons which signified more intensive physical and biochemical weathering and pedogenesis in the S_5-1with respect to the S_5-2and S_5-3pedons. The clay/siltratio was higher in the S5than those in the overlying and underlying loess （L5and L6） andclay content in the S5was60-100%higher than those in the L5and L6. Particle sizedistribution illustrated that the intensified clayification in situ after deposition in the S5than that in the Holocene paleosol （S₀）. It was possible that the S5with clay content higherthan that in yellow-brown earth is belong to the soil type formed in the subtropical zone.Magnetic susceptibility in the S5varied from120to310SI(10^-8m³kg^-1)was well abovethe turnout of the S0, signified intensive pedogenesis under much warmer and wetterclimatic condition than that during the mid-Holocene.Nevertheless, the results of mineralogy analysis showed the similar composition ofphyllosilicate minerals throughout the complex paleosol (S_5-1, S_5-2, S_5-3). Mineralweathering processes in the S5were depotassication and hydration of primary minerals anddegradation of chlorite. The S5did not shown more intensive mineral weathering than theL5and L6which was incompatible with the results of CaCO₃content, particle sizedistribution and magnetic susceptibility. One of the possible reasons was that the trappingaffection of harder and denser of CaCO₃illuvial horizon and argillic horizon in eachpaleosol pedons on the water percolation which listened for the loss of alkali and alkalineearth elements and restrained the transformation of soil mineral.更多还原