【作者】 杨桂芳；

【导师】 殷鸿福； 李长安；

【作者基本信息】 中国地质大学 ， 第四纪地质学， 2003， 博士

【摘要】 中国黄土是最丰富的第四纪时期地质环境演化的信息库。它记录了240万年以来中国大陆的古气候、新构造运动、古地理等多方面的变化过程和重大地质事件；同时，它也记录了与全球古气候、古环境演化进程同步发展的全过程。因此，中国黄土成为记录全球变化的最佳地质信息标志，在时间和空间上都为全球变化研究者提供了非常难得而又十分有益的条件。所以，国内外的研究者，在黄土高原对中国黄土做了大量的工作，使中国黄土研究的深度不断提高，不断获得新的认识。研究黄土高原地区过去气候环境演化，仍需要以研究不同地点的沉积记录为基础，以便通过不同方法，从中提取有关环境变化的信息，进行综合指标的分析，为区域对比和环境演化研究提供重要依据。鉴于此，遴选典型的黄土剖面是首要的工作。剖面应能完整地反映第四纪不同时期的黄土堆积，应选择在露头比较完整、地貌部位确切的地点，以便观察到黄土堆积的岩性连续变化情况，并采集样品进行多元分析。晚更新世以来的气候演化包含有最后一个冰期，一直受到众多学者的重视。在不同时间尺度的古气候研究中，30ka BP以来的古气候是一个重要的时段，因三万年以来地球经历了一次从冷到暖完整的气候旋回，并且包括几次重大的气候突变事件，如三次H事件、新仙女木事件、末次盛冰期等，对全球气候变化产生了深刻的影响。而以往的研究重点多为早更新世—晚更新世的气候演化，其分辨率至多达到千年级，无法从中提取更短尺度的气候变化信息，而且以三万年来作为研究时段的还比较少见。本文所研究的剖面底部年龄大约为三万年，包括了末次冰盛期、冰消期和冰后期，是距离现今最近、变化最剧烈的一次气候变化。对其进行高分辨率研究，找出其中的短尺度气候变化对研究未来气候具有重要意义。其次，在气候信息的提取上，利用有机碳稳定同位素作为环境代用指标前人研究较少，因此这也算是一种尝试。本文研究区域地处黄土高原西缘，我国三大自然区的交接地带，并且靠近青藏高原，对气候变化反应敏感，是研究东亚季风变化的理想地区，故这一特殊地理位置的黄土—古土壤能够敏感地记录下第四纪气候旋回的更替和全球气候变化的各种脉动。因而，开展黄土记录研究在恢复第四纪气候变化历史方面有着特殊而重要的意义。红咀寺剖面位于兰州以西新寺乡，是一套晚更新世—全新世湖相沉积。剖面发育连续、完整，底界年龄三万年左右，中间夹有多层泥炭，为高分辨率测年提供了基础，是研究三万年以来气候演化非常难得的比较完整的黄土剖面。本文通过对兰州红咀寺进行高精度、高密度采样，运用14C测年和热释光测年，根据有机碳同位素、碳酸钙含量、碳酸盐碳、氧同位素、粒度特征数据，并对各气候代用指标进行R/S分析，结果表明，有机碳同位素和碳酸盐氧同位素的Hurst指数几乎完全相同，且分维值和现代年平均温度的分维值1.25十分接近，这表明有机碳同位素和碳酸盐氧同位素主要受温度的影响，而碳酸钙含量、碳酸盐碳同位素分维值与年均降水量接近，指示了<WP=7>降水量的变化。而中值粒径的分维值为1.22，介于年均温度和年平均降水量之间，说明该指标不仅受气候因素影响，还受季风强度等因素影响，同时包含了温度和降水两方面的信息，使其在指示气候意义方面有一定局限。同时，各气候代用指标的Hurst指数均大于0.5，表明该区气候持续变冷变干，这与吴敬禄等人的综合研究得出的结论相一致。之后，又通过功率谱分析和小波分析等技术手段，对兰州地区晚更新世—全新世气候演变周期规律性进行了初步探讨，认为兰州地区古环境演变存在不同时间尺度的演化规律，既有如万年尺度和千年尺度的气候变化，又存在几百年的小尺度波动。在这些周期波动中，千年尺度的周期性较强。根据分析结果，我们就可以将兰州地区古环境划分出不同尺度的演变周期。最后，结合兰州地区综合气候曲线和不同地区气候记录，将研究区三万年以来的古气候演化划分为以下三个阶段，每个阶段中又可细化为若干个小阶段。Ⅰ.末次冰盛期以前（20ka BP以前）的古环境演化30ka BP~27.5ka BP，综合特征表明该阶段气候偏冷，初始时降水量极少，之后气候逐渐向湿润方向转变，总体是偏冷偏湿的气候条件；27.5ka BP~27.0ka BP，该阶段气候比较湿润，温度也逐渐上升；27.0ka BP~25.0ka BP，一种偏温偏干的气候；25.0ka BP~23.2ka BP，总体上气候偏冷偏湿；23.2ka BP~22.0ka BP，一个相对较温暖的时期；22.0ka BP~20.0ka BP，此阶段降水较多，是一个相对湿润偏温凉的时期。Ⅱ.20ka BP-全新世古环境演化从红咀寺碳综合气候曲线上可以看到，这一时期碳酸盐碳同位素明显高于平均值，指示气候较干；在CaCO3含量曲线上，在20.0ka BP左右有一个明显的高值，此后其值略偏正。这说明在末次冰盛期时，虽然本地区靠近青藏高原，但气候仍然干冷，反映了此时的青藏高原可能具有独特的大气环流和动力学机制。而处于兰州气候变化的敏感地带，在某种程度上受其影响，形成了该区独特的气候特征。大约20.0～18.0ka BP，是一个相对温和的时期，气候干旱；18.0~16.2ka BP，温度降低，降水减少，对应末次盛冰期；16.2~15.0ka BP，气候?更多还原

【Abstract】 The continuous Chinese paleosol-loess sequences, which are traditionally regarded as good records of paleoclimatic changes, provided insights into past long-term climatic changes thus are widely used to indicate paleoclmatic conditions and paleoenvironmental evolution. With the development of paleoclimate and paleoenvironment to higher resolution, study of loess provides important evidences for the global climatic evolution, abrupt oscillations, climatic change regularities on millennial, centennial scale. So many scientists devote themselves to the research of climatic unstability, in order to clarify the dynamic mechanism and provide useful information for the prediction of climatic evolution and calamity.However, the research into paleoclimatic evolution must based on different sections in different areas. Then, we can distill useful environmental information by combining analysis of integrated indicators. As a result, the efforts to study past high-resolution climatic varibilities are challenged on ideal sections. In the study of different temporal scales, the researchers pay no attention to paleoenvironmental evolution since 30 ka BP. By contrast, they are willing to throw themselves into early-late Pleistocene or even the whole Quaternary. We know, to the survival and development of Human being, of important is the period since 30ka BP in the course of which many high-frequency and rapid climatic oscillations occurred including three Heinrich events, Younger Dryas event, and the last glacial maximum. The area studied (103°00′N, 36°00′E) is in the center of Gansu Province at 1600 to 2450 m altitude. Mean annual temperature in study area is 5-9℃. Precipitation averages approximately 300 mm per year, about 75% of which falls between June and September. The low precipitation and arid climate have led to sparse vegetation and bad entironment. Hongzuisi section is located on the second terrace of secondary tributary of the Yellow River. It is characterized by a series of lacustrine peat and clay layer. The sedimentation is successive and stable. It is an ideal section for the study on the climate change in the past 30 ka of Lanzhou area. The Hongzuisi section was 17.74 m thick. 902 samples of organic carbon isotope, CaCO3 content, granularity were collected at 2 cm intervals. In some special part, the samples were collected at 1 cm intervals. We tested the organic carbon isotope in Finnigan MAT251 mass spectrometer. Results were reported relative to the V-PDB standard. Measure precision of organic carbon isotope during the study was less than 0.2‰. We calculated CaCO3 content based on the volume of CO2 which was produced from interaction between samples and standard acid.<WP=11>Analytical precision was <2%. In order to testify the validity of result, we also test the carbonate carbon isotope, oxygen isotope together with granularity. Chronological data were obtained by 14C dating of 5 samples from 2.4, 3.05, 3.95, 6.75 and 9.75 m in Hongzuisi section respectively. We use R/S anslysis, functional spectral analysis and wavelet analysis to infer the persistency and periodicity of paleoenvironment in Hongzuisi section since about 30 ka. As a part and parcel of nonlinear theory, the rescaled range analysis (R/S analysis), proposed by Harold E. Hurst in 1965, play an important role in paleoclimatic evolution. In this paper, the rescaled range analysis was used to analyze the pale climatic evolution of Hongzuisi section in Lanzhou area on the basis of the materials of organic carbon isotope, CaCO3 content, granularity, carbonate carbon isotope and oxygen isotope. According to R/S analysis, the feature of organic carbon isotope and carbonate oxygen isotope can indicate temperature change, the CaCO3 content and carbonate carbon isotope can show the precipitation in some degree. While the granularity represent the synthetical information. The result also indicates that this method is very useful to study the durative of climatic change. Based on the results, we can conclude that the trend of paleocl更多还原