【作者】 周静；

【导师】 张平中；

【作者基本信息】 兰州大学 ， 环境科学， 2008， 硕士

【摘要】 应用生物标志化合物恢复古气候、探索古人类活动已成为古气候研究中的重要内容。生物标志化合物具有稳定、保存时限长、分布广等特点,对气候和环境有很好的指示作用。它含有反映有机质母源先质的骨架结构,可以记录古气候、古环境和古植被的演变信息,已有效运用于气溶胶、海相沉积物、湖沼沉积物、黄土和古土壤等各种环境载体中。由于其独特的地理位置和对全球变化的敏感响应,青藏高原成为全球地球科学界瞩目的焦点。本文以位于青藏高原东北部的郎木寺地区采取的一湖沼沉积物剖面为研究对象,在剖面中检出了丰富的脂类生物标志化合物。本文主要分析了正构烷烃和直链烷基-2-酮的分布特征及各项参数。正构烷烃的碳数分布范围为C₁₆～C₃₃,以中、长链组分为主,主峰碳变化较大,在C₂₁以后具有明显的奇碳优势;直链烷基-2-酮基本以C₂₃为其主峰,在C₂₁以后具有明显的奇碳优势。正构烷烃的分布特征指示了研究区植被以陆源高等植物为主。直链烷基-2-酮的分布特征与正构烷烃不具相似性,样品没有提取脂肪酸,因此,我们初步认为剖面样品中检出的直链烷基-2-酮来源于沉积物中的高等植物。文中通过对剖面总有机碳含量的分析,结合年代学建立气候序列,再结合脂类生物标志化合物的各气候代用指标,对剖面形成的气候环境进行讨论。在约11.3～7.3 cal ka BP,郎木寺地区气候整体体现为较为干冷的条件。其中,在9.6～8.6 cal ka BP,该区出现过一次短暂的沼泽化过程,气候出现较大波动,在9～8.6cal ka BP,该区有一次明显的降温事件,可能对应于以往研究中的8.8 ka BP的干冷事件。自约7.3 cal ka BP起,各项指标指示该区进入全新世最适宜期。7.3～6.5cal ka BP为初期的升温,约6.5～5.5 cal ka BP为气候最为暖湿的时期。约5.5 cal kaBP起,郎木寺地区进入一个新的阶段。气候有变干变冷的趋势,是中全新世相对较为干冷的一个阶段,这与青藏高原其它地区此时段的气候特征一致。约4.8cal ka BP,夏季风强度又回升,之后气候又转为干冷,在14 cm（约4.0 cal ka BP）处泥炭停止发育。在约5 cal ka BP出现特殊情况,该区也曾出现一次明显的降温,但正构烷烃分析结果却反映了不同的结果,我们将其归因于某一种特殊的植物。更多还原

【Abstract】 Present use of biomarkers to reconstruct paleoclimate and ancient human activities has become an important part of molecular stratigraphy.Biomarkers have the characteristics of stable compounds,long-time preservation and wide distribution, providing great information on climatic and environmental changes.They contain framework structures of parent materials,and they can record evolution of palaeoclimate,palaeovegetation and palaeoenvironment.Many types of biomarkers have been reported,such as alkanes,aromatics,alkanoic acids,alkanols,alkenones and esters.Most researches mainly focused on the category,concentration,relative abundance of biomarker compounds,and compositions of stable isotopes such as monomer carbon,hydrogen,oxygen,and nitrogen.The research areas have reached aerosols,marine sediments,lacustrine and peat sediments,loess and so on.Because of its special location and sensitive response to the global climate transformation,Tibetan Plateau has been regarded by scholars of the geoscience domain.The research area is located on the edge of the northeast Tibetan Plateau.The sampling site is in Langmusi County,with an altitude of 3559m（34°09′N,102°34′E）.This sedimentary sequence was selectively investigated by lipid molecular stratigraphy by gas chromatography-mass spectrometer（GC-MS）.A variety of molecular fossils are found in this profile,including n-alkanes,n-alkan-2-ones,pristane,phytane and so on.N-alkane and n-alkan-2-ones are concerned in our research.The n-alkanes are ranged from C₁₆～C₃₃.The n-alkan-2-ones are range from C₁₉to C₃₃,having a maximum at C₂₃or C₂₉.Higher plants are the predominant source of the n-alkane compositions.Combining the distribution of lipids and types of vegetation in and near this area,we can conclude that the source is mainly herbages.N-alkan-2-ones are from epicuticular waxes of higher plants.Based on the establishment of a reliable AMS dating,we have been able to establish climate change series of the profile using the distribution patterns of the TOC and the indexes concluding from lipids during the Holocene.The profile was formed from 11.3 to 4 cal ka BP.From the variation of those indexes,we can conclude as follow.From 11.3 to 7.3 cal ka BP,the Langmusi area was cold and arid.From 9.6 to 8.6 cal ka BP,there has been a fluctuation.Since 7.3 cal ka BP,this area became warmer,and the climate came into the optimum.Though this period,peat had been deposited,and we can devide it into three phases:from 7.3 to 6.5 cal ka BP,the climate began to become warmer;from 6.5 to 5.5 cal ka BP,the climate of this atea was warmest and most humid;since 5.5 cal ka BP,the climate became colder again,and peat cease to develop at about 4 cal ka BE During the Holocene,there were several cold events in Langmusi area.They happened in about 8.8 cal ka BP and 5 cal ka BP.It’s very special at about 5 cal ka BP.The ACL and Pαq values of n-alkane indicate that there may be many submerged and floating macrophytes in this area,but other indexes such as TOC and L/H of alkane show the cold and dry climate.We conclude that it may be attribute to a particular species of plant in this area.更多还原