【作者】 隋玉柱；

【导师】 李吉均；

【作者基本信息】 兰州大学 ， 自然地理学， 2007， 博士

【摘要】 过去气候变化研究是今后气候动态预测的基础，变化指标和时间标尺的构建又是古气候研究的关键。作为第四纪古环境三大支柱记录之一的黄土在过去全球变化研究中占据着非常重要的地位。针对黄土研究中出现的问题，本文制定的技术路线是：（1）在确认黄土也是土壤的前提下，通过国内外黄土土壤学系列研究成果的综合，构建黄土成壤模式；（2）通过土壤微形态学研究确定宁夏彭阳剖面各层古土壤的发育强度，并以此作为评价标准；（3）进行粒度、磁化率、化学成分、色度、CaCO₃、烧失量等多项指标的测试，并建立集定性、定量指标于一体的综合指标—土壤发育指数；（4）比较研究土壤发育指数及其它指标能否反映古土壤的发育强度；（5）以黄土成壤模式为依托，探讨各指标在反映成壤强度方面的差异性、矛盾性及其可能的原因，并筛选较优定量指标；（6）利用较优指标建立定年模型；（7）结合年代序列、成壤强度探讨黄土高原西北部重大气候事件及820ka气候变化。取得的主要新认识如下：1．黄土成壤模式主要由母质的特异性（母质分布在上、下两个方向），成壤、沉积的同步性，成壤的双向性（上、下）、速成性，土壤性状的均一性、叠加性、矛盾性（钙积与粘化同层），成壤强度的特异性和成壤速率地表最大等要素构成。2．运用本文初次建立的土壤指数定年模式证实，宁夏境内具有松山期的黄土层，B／M界线位于彭阳县城阳乡杨塬103m深的黄土中，其黄土年龄为0—828ka B.P.，这在既往研究中尚未报道。3．与其它剖面相比，彭阳剖面粒度总体上要比东部的洛川、西安，甚至西部的兰州、新疆东湾要粗；CaCO₃平均含量不仅高于黄土高原中部，也高于高原西部，反映出本剖面富含碳酸盐的六盘山近源沉积起到了很重要的作用；易溶元素含量在剖面10m处快速升高，淀积特征明显，反映出黄土受现代淋溶成土作用影响较大，黄土直立、疏松、多孔特性和高温与多雨组合的气候特点，使得元素淋溶、淀积的强度和深度超出了传统的认识和判断；烧失量与其它指标相比，不仅能区分冰期、间冰期；而且能够区分出次一级的冰阶、间冰阶，有较高的分辨率；土壤发育指数、红度能够反映土壤强度差异，是反映气候波动的较好指标；然而，磁化率不能反映古土壤S₈的存在，且S₇的磁化率在全剖面中最高，这与大多剖面S₅磁化率最高的特点不一致。4．在彭阳剖面成壤较弱的黄土层发现了黏粒胶膜，这在以往研究中很少报道，并且用传统土壤学难以解释，因为黄土成壤较弱，在碱性环境中难以形成胶膜。然而，此种“矛盾现象”恰能进一步证实上覆发育较强的土层已经产生了显著的粘粒移动，且迂出了土体，并在黄土中淀积。5．500ka B.P.前后，本剖面出现了研究序列成壤最强的层段—S₅。经综合对比后确认，S₅发育时北亚热带可能波及到黄土高原西北部的六盘山北段，这又把前人研究的此时北亚热带向北推进了200km。土壤发育指数、红度、烧失量、CaCO₃形态和含量整体上反映出本区有逐渐变干的趋势。800ka B.P.以来，六盘山地区发生了796-792，766-756，730-722，510-504，350-336，100-88ka B.P.六次比较强的沙漠扩张。更多还原

【Abstract】 Along with the warming and drying of modem climate, the evolution of arid and semiarid regions has become the focus in the research on climatic changes around the world. Studies of climatic variability in the past are essential for evaluating its evolution. Knowledge of the timing and extent of the growth and retreat of deserts is important for the prediction of future global changes and for understanding their mechanisms. Thick sequences of interstratified loess and paleosols from the Chinese Loess Plateau provide one of the most complete and most sensitive terrestrial records of environmental change for the past 2.5million years.In the past climatic change research, the extraction and establishment of indexes are extremely important. In this paper, an attempt is made to integrate various physical and chemical proxies into a representative paleoclimate index, and verify mutually information from different proxies. The Pengyang section of the northwest Chinese Loess Plateau has been studied and a soil development index has been set up. Correspondingly, the paleoclimatic change patterns of this arid-semiarid region spanning the past 800,000 years have been developed.The soil-forming mode of loess is mainly composed of the particularity of parent materials, synchronization of soil-forming and sediment, bi-directional weatherings, uniform and ambivalent properties and so on.The defined B/M boundary is located in loess L8, in good agreement with that of the central loess plateau. Taking B/M boundary at 780 ka B. P., the average sedimentary rate in the Brunhes Chron is 13.21 cm.ka^-1, therewith, the age of the section bottom is extrapolated to～828 ka B. P.Compared with other loess section, the particle-size distribution of Pengyang section was coarser than that of luochuan, Xian, Lanzhou and Xinjiang Dongwan section. This is not surprising, given the closer proximity of Pengyang to the Asian inland dust sources; The average content of calcium carbonateis of Pengyang section is not only higher than that of central loess plateau, but also higher the west of Chinese Loess Plateau, which reflected Pengyang loess had been deposited by near Liupanshan’s substances that contained more calcium carbonateis; The content of diffluent element of 10m depth in the section increased fast, which indicated that the modern eluviation and the leaching depth of loess may be stronger than our guess; The soil growth index can reflect the intensity of soil forming and the climatic changes; The "abrupt chang" of glacial and interglacial period was caused by strong soil-forming processes that enlarged the discrepancy of granularity between loess and paleosol. However, the magnetic susceptibility nearly cannot reflect the existence of S₈ and the magnetic susceptibility of S₇ is highest in the whole section, which is inconsistent with other studies that S₅ has the highest magnetic susceptibility.Thin-section examination shows that the micro-texture of the soil layers is divided into both cementing texture in S₇, S₅ and S₁, and granular texture in all others. These paleosols exhibit both a Bt horizon and an argillic horizon with aped structure defined by slickensided clay skins and deeply penetrating sand-filled cracks and are similar to the most ancient known soil of well-drained forest ecosystems and S₅ （subtropical paleosol） of the Xian sequences. Because aeolian grains contain much calcium, pedogenesis must have been prolonged. Based on these facts together with the difference in particlesize distribution within loess, we prefer to consider the S₇, S₅ and S₁ （720-667ka, 513-412ka and 114-73 ka B. P.） as a kind of semitropical spectacle. Certainly, this needs be further validated.The integrative analysis revealed that Qinling Mountains and Liupan Mountains were all in subtropics climate in 500,000 year before present, the soil growth index, red degree, the shape and the content of calcium carbonateis reflected that the climate of Liupan region had the dry tendency. The soil growth index has particular effects on reflecting climatic changes due to its generational mechanism. The paleoclimatic change patterns of arid-semiarid region spanning the past 800,000 years reveal that the desert expansion and approach in China happened in about 796-792, 766-756, 730-722, 510-504, 350-336, 100-88ka B. P..更多还原