【作者】 张文翔；

【导师】 张虎才；

【作者基本信息】 兰州大学 ， 自然地理学， 2009， 博士

【摘要】 青藏高原东北部的柴达木盆地处于亚洲中部干旱区，同时也是世界上最大的非地带性温带干旱区的中心。由于其特殊的地理位置一处于西风带、东亚季风和西南季风的交汇处，它对于区域和全球气候变化具有较高的响应。因此，对柴达木盆地古气候、环境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及反馈机制的理解。进一步深入的、系统的研究我国西部，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意义。本论文所选取的柴达木盆地察尔汗湖贝壳堤，是到目前为止在柴达木盆地发现的惟一大型贝壳堤，其完整的地质记录、大量的生物化石为研究的可信度提供了良好的保证。通过对柴达木盆地察尔汗古湖贝壳堤沉积物中可溶与残留（酸不溶）组分中常、微量元素及其稀土元素、元素对的分析，并结合可溶与残留组分中元素相关性对比，讨论了贝壳堤剖面元素地球化学指标和沉积环境之间的关系，并根据根据柴达木盆地贝壳梁剖面的化学元素及生物、物理化学指标，在精确测年的前提下，重建了43．5～22．4cal．ka B．P．(39．7～17．5ka B．P．¹⁴C年代)柴达木盆地察尔汗古湖高湖面期间古气候与环境演变过程。根据上述研究本论文得出以下主要结论与认识：1．通过对比分析得出，可溶组分与残留组分中所含的元素在环境响应模式上并不完全相同，可溶组分中的元素及其元素对可以作为湖泊和流域古气候演化的代用指标；残留组分中的元素及元素对与原岩及其风化程度紧密相关，更多地是记录了物源区的环境特征。2．由于可溶组分与残留组分中元素在环境响应模式上的差异，故在前处理、研究区域演化时应将二者分开，这样有助于避免在解译环境信号时产生偏差。3．贝壳堤剖面沉积物中各元素指标揭示了晚更新世43．5～22．4cal．ka B．P．(39．7～17．5ka B．P．¹⁴C年代)期间，柴达木盆地察尔汗古湖高湖面从淡水到半咸水-咸水-盐湖转变以及区域古气候与环境演变的过程：43．5～39．8cal．ka B．P．期间，为湖泊高湖面形成期。随着流域降雨增多，湖区的水面扩张，湖泊盐度较低，物源区风化强度增强，气候温湿，但是气候不太稳定，波动较为剧烈；39．8～37．8cal．kaB．P．，当时已经形成淡水至微咸水湖泊；约37．8～31．7cal．ka B．P．为湖泊发育的壮年期，此时段降水量较大，风化强度大，大量的风化物由物源区向湖泊输送物质，湖区水位迅速上升，由于温度适宜，水热条件配备好，形成高湖面鼎盛时期；约31．7～27．0cal．ka B．P．为环境的转变时期，降雨较少，湖泊的盐度加大，物源区风化强度变弱，水动力能下降且入湖水量减少，使得湖泊水位开始降低，气候也由暖湿向温干变化；约27．0～22．4 cal．ka B．P．为湖泊发育的晚期，由于此时降雨较少，湖区的水面强烈收缩，湖泊盐度进一步升高，加上物源区受到环境的影响，风化强度微弱，致使向湖泊输送的物质量衰减，气候表现为凉干的特征；晚期由于环境急剧恶化，湖水快速蒸发，形成盐壳，至此高湖面演化史结束。4．柴达木盆地贝壳堤剖面揭示的青藏高原东北部晚更新世中晚期高湖面及其演化过程，且其结果可与腾格里沙漠等进行对比，揭示了当时区域性气候环境、特别是水文循环过程的与现代相比发生了根本性的转变与调整，是大范围跨地域气候环境变化的表现，为我们更好的理解晚更新世气候变化的过程及特点，进而探讨气候变化的机理及其对人类和生物界的影响提供资料。5．研究结果表明，对于同一类沉积物，如湖泊沉积物而言，其元素含量、组分变化及特征参数的差异，反映了沉积环境的差异；在同一参考标准下，利用同一分析方法，对不同地区同一类型沉积物做进一步深入、系统的分析，对于探讨不同地区气候环境差异及区域分异、进而探讨气候变化特点以及全球响应模式具有十分重要的意义。更多还原

【Abstract】 Qaidam Basin, situated at the northeastern Tibetan Plateau, is in the central part ofthe arid Asia, which is the biggest non-zonal arid area in temperate zone on the earth,and is the conjunction area among the Westerly jet, southeastern Asia Monsoon andsouthwestern Asia Monsoon that influence the climate of China. Therefore, it is verysensitive to the regional and global changes. Detailed researches can promote ourunderstandings of the climate change in the central Asia to the global changes and themechanisms behind these changes. The study on the climate change history in thearid-cold area of the northeastern Tibetan Plateau is of great theoretical and appliedimportance.Shell Bar is the only one which has been discovered at Qaidam Basin so far, it hasan important significance. In the stratigraphy there are four layers containing largeamount fossil shells of Corbicula fluminea m（u|¨）ller and Corbicula lorgillierti philippi,with both taxa often kept together and standing in situ. Based on the spatial distributionpattern of the shell bar, sedimentary characteristics of the deposits, assemblages ofmicrofossils such as Ostracods, the appearance of fossil shell Corbicula and pollen ofPediastrum, all of them only could survive under certain water depth, it could beconcluded that the shell bar section is a continuously deposited sequence under thewater condition and possibly one of the most suitable geological records of thepaleoclimate change history. Based on the analytical results of the elements of the acidsoluble （AS） and residual （AR） fractions of the Shell Bar section and the correlationsbetween the related elements and their ratios, the geochemical fractionations inpaleolake deposits and their sedimentary environmental significance were studied.According to the results, the paleoenvironment change history between 43.5 cal ka B. P.and 22.4 cal ka B. P. (39.7～17.5 ka B. P. ¹⁴C) was reconstructed.1. According to the correlations between the elements （major, trace and rare earthelements） in AS and AR, which are been seen as the climatic proxies, indicated that thelacustrine deposition have different material sources, experienced varying geochemicalprocedures and the different response in the evolution pattern of environment. The AS fractions of the sediments have been utilized as a sensitive geochemical andenvironmental indicator in lake area, and AR fractions were always bearing thegeochemical characteristics of source area and information of weathering processes.2. It is not only necessary, but should separate AS fractions from the AR fractionswhen elements was used to study the paleoclimate and environmental evolution historyrecorded in the lacustrine deposits, especially during the high resolution paleoclimateand lake level reconstruction. In this way, we could not only avoid interfering amongvarious proxies and drawing misleading conclusions, but also improve ourunderstanding on natural processes and reliability of the information about materialsources, climate changes in the catchment and lake areas.3. Based on the sediment proxies of geochemical and other results of the section,the environmental change history was reconstructed between 43.9 cal. ka BP and 22.4cal. ka BP. During 43.9～43.5 cal ka BP, the paleolake has been formed and reached thestudy section. From 43.5 to 39.9 cal. ka BP, it is the development of the paleolake andindicated a reductive sedimentary environment, with the precipitation of the catchmentincreasing, the scope of paleolake had been expanding, the climate became warm-humidalong with the paleolake level increased and had strong chemical weathering of sourcearea. From 39.9 to 31.9 cal. ka BP, it is reveal a reductive sedimentary environment, theclimate during this period was the warmest and the paleolake reached it fully developedperiod because of the abundant precipitation and strong chemical weathering. From 31.9to 27.0 cal. ka BP, it was the transitional period of the environment recorded by theShell bar section, all proxies implied strong decrease of the lake level even thetemperature was high, it means that the climate shifted from humid-worm to warm-drythat resulted in an oxidative sedimentary environment. During the period between 27.0and 22.4 cal. ka BP, it is indicated an abrupt temperature decrease and strong lake levelfluctuations during the period, showing that the climate changed from a warm-dry into acold-dry condition. Further temperature decrease and a sudden lowering of lake levelsand shrank of the water body related to the strong evaporation resulted in the formationof the salt layer in the top of the section. Till then, the paleolake retreated quickly alongwith the further climate deterioration, the high paleolake level evolution history ended and never recovered again.4. According to the regional correlations between elevated high Qaidam Basinand lower Tengger desert, it shows a similar evolution patter. The study results from theseparated geological evidences prove that palaolake in such different areas not onlyposses a similar evolution pattern but also started synchronously, imply the climatechange resulted from the regional changes which links to global changes, providing newdata for understanding the mechanisms of the climate change. All of these can help usbetter to understand the climate change and the characteristics of the process duringLate Pleistocene. Thereby, we can explore the mechanism of climate change and itsimpact on human beings and the biosphere.5. This study suggested that the variations of elements contents, the ratiosbetween different components and their indices revealed the changes of the sedimentaryenvironments. A comprehensive test and detailed analyses on the same kind of deposits,such as lacustrine deposits using a similar technique with the same standard, is crucialto explore the regional climate changes and their responding to the global changes.更多还原