【作者】 白艳；

【导师】 方小敏；

【作者基本信息】 兰州大学 ， 第四纪地质， 2006， 博士

【摘要】 季风环流的起源和发展、中国西北和中亚地区的荒漠化与干旱化以及黄土高原植被演化与水土流失等一系列相关的重大科学问题一直为科学界和社会所瞩目,与我国西北地区的发展和人们的生活息息相关。黄土高原上厚层、连续的黄土—红粘土风成堆积序列详细地记录了东亚季风演化过程和源区变化过程。近年来,大量的无机指标在季风气候演化研究方面取得了显著成果,而有机生态环境方面的研究非常欠缺,不利于我国干旱-季风气候环境系统形成演化的深入研究,尤其难以给我国西北生态环境建设和恢复提供更多准确的过去生态环境变化的信息。 生物标志化合物在海相、湖相和泥炭等载体的全球环境变化研究已经发挥了重要作用,但至今尚未建立起公认的黄土地区古气候有机质组成特征和替代指标,黄土地层中还没有开展系统、完整的有机地化研究,第三纪红粘土至今无人问津。为此,本文首先对我国温带不同气候区的现代土壤中的生物标志化合物特征与现代气候环境的关系进行了系统研究,然后以此为基础初步开展了朝那红粘土-黄土剖面生物标志化合物记录的植被和生态系统环境变化研究,以期为上述科学问题提供新的有机地化证据。 初步取得的研究成果如下: 1、除了在我国土壤中检测到正构烷烃、正构烷基-2-酮和长链脂肪酸等土壤中常用的生标化合物外,本文首次在土壤中报道了具有奇碳优势的正烷基-3-酮和十一种含季碳的支链烷烃化合物(BAQCs),包括2,2-二甲基烷烃、3,3-、5,5-、6,6-和7,7-二乙基烷烃、3-乙基-3-甲基烷烃、5-乙基-5-甲基烷烃、5-丁基-5-乙基烷烃、6-丁基-6-乙基烷烃、3,3,ω3,ω3-和5,5,ω5,ω5-四乙基烷烃。较低碳数和较高碳数BAQCs的相对丰度在不同的气候区和不同的地层中协变,说明其源生物(可能为原核生物)在现代和古土壤中普遍存在,而且能够响应环境变化而呈现不同的分布模式。 2、在我国温带现代土壤中,正构烷烃、正构烷基-2-酮、正烷基-3-酮和BAQCs更多还原

【Abstract】 Topics of the formation and development of Asian monsoon, drying of Asian inland, and vegetation evolution and soil erosion on the Loess Plateau have been more and more gain scientific and social attention. The thick and continuous loess-red clay sequence on the Chinese Loess Plateau records in detail the evolution of Asian monsoon and its related dust provenance variation. Application of numerous inorganic proxies to this sequence has contributed to considerable progresses in monsoonal evolution. However, less organic proxies are involved.Biomarkers have be used as proxy for the re-construction of paleoenvironments and paleoclimate in the study of marine sediments, lake and peat deposits. However, the biomarker record so far obtained from CLP only spans narrow time, and the detailed information on the red clay has not been reported to our knowledge. This thesis systemically investigated molecule characteristics of Chinese modern soils collected from tempetate zones in response to modern environmental changes. Based on this, loess-red clay samples collected from complete Chaona section spanning the last 8.1 Ma are analyzed to discuss in details the vegetation and biological evolutions with these molecule varied with monsoon climate on the Loess Plateau. The results provide strong organic geochemical evidence for the scientific topics above. Following conclusions are obtained:1. Besides n-alkane, n-alkan-2-ones and n-fatty acid, eleven pseudohomologous families of branched alkanes with quaternary substituted carbon atoms （BAQCs）, 2,2-DMAs, 7,7-, 6,6-, 5,5-, and 3,3-DEAs, 3-E-3-MAs, 5-E-5MAs, 5-B-5-EAs, 6-B-6-EAs, 3,3, ω3, ω3-TEAs, and 5,5,ω5, ω5-TEAs, as well as hitherto unreported n-alkan-3-ones, were observed in Chinese modern soil samples and loess-red clay samples from the Chaona section. The relative abundances of LMW (C₁₈-C₂₂) and HMW （C28-C33） BAQCs seem to covary with climate zones and change s with age in loess-red clay samples, suggesting that the source organisms of BAQCs, present in soils, can express different lipid distributions in response to environmental constraints.2. Their distribution and CPI(h> and C15-21/C22-35 ratios changes with climate zones, their lower molecular weight components（Ci5-C2i） dominate in southeast China, while the higher molecular weight ones （C23-C33） dominate in cold, arid northwest China. The distributions of ?-Alkan-2-ones, n-alkan-3-ones and 5,5-DEAs exhibit strong regional variations, correlated with the spatial distributions of climate and vegetation.This study is the first biomarker record from complete Chaona section （8.1Ma）. Significant fluctuations were observed in the patterns of ?-alkanes and w-alkan-2-ones, as well as several biomarker ratios, which are related to changes in lithology/paleoclimate. These records revealed the important environment changes at about 5.48, 3.6 and 2.6Ma, characterized by the occurrence of deciduous trees and the enhanced degradation and diagenesis of organic matter associated with enhanced precipitation between 8.1-2.95Ma, and the onset of the Asian monsoon and aridification between -7.28-5.48Ma;4 4an intensification of Asian summer monsoon between the warmest period ⁵.48-3.54Ma, characterized by increases of woody plant, enhanced microbial activity and the highest soil humidity;and an intensified Asian winter monsoon with a dry and cool climate at 3.6Ma, resulting in continued aridity in China and occurrence of grassy vegetables grasses with increasing intensification and fluctuation since 2.6Ma over CLP. They support the similar evolution of the Asian Monsoon revealed by inorganic indices, which were in broadly consistent with those given by some other inorganic proxies.4. This work evaluated the potential of using different biomarker indices and as proxies for the environmental change, which could reveal the source organisms, microbial degradation and diagenesis of organic matter in response to evolution of the Monsoon. With analyse of other biomarkers, we could reveal the more comprehensive history of evolution of the Monsoon.更多还原