【作者】 李斌；

【导师】 张虎才；

【作者基本信息】 兰州大学 ， 自然地理， 2006， 博士

【摘要】 亚洲中部干旱区是世界上最大的非地带性温带干旱区,这里不但生态环境脆弱,气候环境变化剧烈,并对全球变化和人类活动响应敏感。青藏高原东北部的柴达木盆地,正处于此干旱区的中心,控制和影响我国气候系统的西风带、东亚季风和西南季风也交汇于此处,对于区域和全球气候变化响应敏感。有证据表明,此区地面覆盖变化（植被、雪盖等）和产生的巨量粉尘不但影响着区域乃至北半球的太阳幅射平衡,而且大气粉尘还影响海洋生物生产力并进而影响大气CO₂变化,是对由于温室气体效应导致全球变暖响应最强烈的地区之一。因此对柴达木盆地古环境、古气候变化的研究将有助于加深对亚洲中部干旱区对全球变化的响应和影响的理解。深入的研究中国西部、特别是青藏高原东北缘干旱、干寒区的气候变化具有十分重要的理论价值。 为此,本论文选取柴达木盆地察尔汗湖贝壳堤剖面为研究对象,通过对此剖面分子化石、地球物理和地球化学指标的分析,结合AMS 14-C和常规14-C的年代控制,参考剖面中大量出现的贝壳化石瓣鳃类种现代的生长环境调查,重建了察尔汗盐湖晚更新世期间古环境变化的历史。本论文的主要结论和认识如下: 1、贝壳堤剖面的正构烷烃显示,在39.6-35.5kaBP间,成熟度较高,低等菌藻类和水生生物来源的烃类相对丰度较高,可能指示湖泊发育早期外源较成熟有机质的输入占有较大的贡献,湖泊早期沉积的有机质中有一定的内源菌藻类和水生生物的参与,有机质以湖泊周边发育的木本植物为主要来源。在35.5-17.1kaBP间,成熟度较低,显示出湖泊发育和晚期沉积过程中,由于环境条件的变化,周边植被由木本退化为草本,显示出以草本植物为主要来源的趋势,有机质主要为湖泊发育时期沉积形成的。姥植比从剖面底部到顶部呈逐渐减小的趋势,表明湖泊沉积过程中还原环境的加强,显示了湖泊发育晚期逐渐咸化的过程。 2、贝壳堤剖面湖相沉积还存在着特殊的含季碳长链支链烷烃类生物标志化合物。已鉴定5,5-二乙基支链烷烃、5-丁基,5-乙基支链烷烃、5-丁基,5-乙基支链烷烃系列三个（A-C）系列;其分布特征是:A、C系列为奇数碳分布,B系列为偶数碳分布。其相对丰度表现为A>B>C。A系列的高值区域对应于B、C系列的高值区域,这些特征指示它们来自同一生物源。而且根据在湖泊发育过程中A系列丰度较低,而在湖泊逐渐咸化的过程中A系列丰度增高,认为该系列化合物有可能来自更适宜湖泊咸化过程中所存在的某种菌藻类。同时,A系列主峰优势指示了湖泊早期输入的有机质成熟度较高,在湖泊晚期低成熟有机质相对富集,其主峰碳有向高碳数转移的趋势,认为A系列主峰的变化具有一定的古环境指示意义。剖面中A25/nC25变化有一定的规律,即在湖泊发育过程中A系列分布特征存在明显差异,表明这类支链烷烃的分布特征可能记录了湖泊演化的环境信息。 3、贝壳堤剖面高分辨率的物理指标和化学指标揭示了湖泊演化的历史,39.6-35.5kaBP,为湖泊的发育时期,约39.2 ka BP左右湖水达到剖面处,35.5-33.3 ka BP,湖泊较前期退缩,区内温度较高,要远远高于现代。33.3-27.1 ka BP,湖泊水位虽有波动,但相对较高,此时间为区内水热配置最佳的时期,最高湖面也出现在此期。27.1-18.1 kaBP,气候温暖,湖泊开始退缩,自18.1 ka BP开始,湖泊快速的盐化,退出剖面点所在的位置,之后再也没有扩张至剖面所代表的范围。 4、通过对瓣鳃类现生种的生长环境调查,可以确定剖面中大量出现的贝壳化石揭示了剖面所记录的湖泊沉积段温度较高,结合柴达木盆地现代的降水与温度资料,在35.5-17.5 ka BP期间,温度要比现代高出5-11℃;降均降水量增加600-800mm,与现代的环境截然不同。剖面的介形虫组合特征也表明,自38.2ka BP,湖泊开始形成,更多还原

【Abstract】 The arid central Asia is the biggest non-zonal aid area in temperate zone on earth. The area has not only a fragile eco-environmental system with a changeable climate, but also is sensitive to the human induced global changes. Basin, which is situated at the northeastern Tibetan Plateau, is in the central part of this arid area, and is the conjunction area among the Westerly jet, southeastern Asia Monsoon and Southwestern Asia Monsoon that influence the climate of China and therefore, it is very sensitive to the regional and global changes, at the same time, the study results already show that the land surface changes in the area and huge amount of dust inputs into the atmospheric system not only influences isolation equilibrium and the marine life productivity, further influence the content of atmospheric CO2, the area is one of the most sensitive area that strongly response to human induced global warming. Detailed researches can promote our understandings of the climate change in the central Asia to the global changes and the mechanisms behind these changes. The study on the climate change history in the arid-cold area of the northeastern Tibetan Plateau is of great theoretical and applied importance.For these reasons, this thesis concentrate our attention on the Shell Bar section at the southeastern Cha’erhan salt lake, Qaidam Basin, based on the detailed discussions of the dating and chronology establishment, through analyses on the biomarkers of the organic matters, sedimentological characteristics and geochemical analyses, with the reference of the eco-climatic backgrounds of the living cubicula, ostrucod assemblages in the samples, the climate-environmental change history is reconstructed and the main results can be summarize as follows:1. the alkanes of the Shell Bar section show that between 39.6ka BP and 35.5kaBP, the maturity of the organic matter is high, the alkenes originated from the bacterial and alga, and water living creature are abundant, which implies that the main organic matters in this part of the section comes from the old materials with a high maturity organisms, and together with some lake organic matters. It indicates a main material input into the lake from the outside. Between 35.5 and 17.1kaBP, the maturity of the organic mater is low, implying that the degrading of the vegetations in the surrounding area of the lake that dominated by the grasses and the organism in the sediments originated mainly from lake itself. The Pr/Ph ratio is reduced from the lower part of the section to the upper part, which shows the reduction in the lake system increased and the saltification of the lake water in the later of the lake evolution history.2. from samples of the shell bar section, the branched aliphatic alkenes with quaternary substituted carbon atom (BAQCs) is identificated. It includes 5,5-diethylakanes of series A, 6,6-diethylakanes of series B and 5-butyl, 5-ethylakanes of series C;among them, A and C are the odd carbon number distribution pattern while B is of even carbon number distribution pattern and their abundant is A>B>C. The high value district of the series A corresponds to the high value of the B and C, indicating they share a similar source. Because the abundant of a series is lower in the earlier of the palaolake evolution than the late period, it can deduced that these three series originated most likely from kinds of bacteria and/or alga living in thewarm mesohaline waters. This is of great importance to the palaoenvironmental reconstruction because such kind of bacteria and alga are extremely sensitive to the environments. At the same time, A25/nC25 ratios change systematically in the section and possibly bearing the environmental information of the lake evolution process.3.the sedimentary and geochemical indices of the samples from the Shell Bar section show the palaolake evolution processes, that are from 39.6 to 35.5ka BP is the period of lake formation, from 35.5-33.3ka BP the lake level was high and stable, temperature in the area was more warm-humid than that of today. The lake level reached it maximum between 33.3 and 27.1ka BP, both temperature and precipitation were higher than today. The living creatures were blooming and the spices are abundant. Between 27.1 and 18.1ka BP, the climate was still warm, but the lake level started to lowering, most likely is because of the reduction of the precipitation amount and the deterioration of the environments. Start from 18.1ka BP, the lake retreated abruptly with a very strong increase of the evaporation, resulted in the salt formation. Then the lake shrank further and never reached the level again.4. Based on the existence of the fossil cubicula and their living climate backgrounds, it can be deduced that between 35.5 and 17.5 ka BP the paleoclimate recorded by the Shell Bar section from the Cha’erhan was 5- 11°C higher and the precipitation was 600-800mm more than that of today, it means that the climate was completely different from that of today. The ostracod assemblages reveal that salt degree was higher in earliest stage of the lake formation and then reduced very much along with the fresh water input. The lake level increased continuously along with the increase of the water input amount from both the precipitation and river water from the surrounding mountains.5.Based on the regional correlations between elevated high Qaidam Basin and lower Tengger desert, it show a similar evolution patter because in both areas the palaolake level started to increase and lake areas started to advance. The climate reconstructed in both areas show that it was warm and humid between 35 and 21ka BP, with a substantial increase of the temperature and precipitation, especially precipitation, and resulted in high lake levels in both areas. The study results from the separated geological evidences prove that palaolake in such different areas not only posses a similar evolution pattern but also started synchronously, imply the climate change resulted from the regional changes which links to global changes, providing new data for understanding the mechanisms of the climate change.更多还原