【作者】 陈传飞；

【导师】 方小敏；

【作者基本信息】 兰州大学 ， 第四纪地质学， 2009， 硕士

【摘要】 地球环境系统发生重大变革的新生代是距离人类最近的时期,它后期的演化直接促成了生物界最高级类型-人类的诞生。因此,我们非常关注与人类社会休戚相关的过去地球环境系统的演化。与此同时,由于人类在工业化过程中促使温室气体浓度的显著增加,使全球地表平均温度近百年来（1906-2005年）升高了0.74℃,预计到21世纪末仍将上升1.1-6.4℃,对全球自然生态系统产生了重要影响,对人类社会的生存和发展带来严重挑战。全球气候变化及其不利影响已成为全人类共同关心的问题。因此,预测未来气候变化进而提出应对策略乃是关乎人类社会未来生存的最有效方法,类似现今如此高浓度的CO₂所带来的气候环境剧烈变化可以从新生代早期的高浓度温室气体和温室效应过程中找到参考。因此,“以古论今”为更好的理解现代和未来气候变化提供依据是地球科学界对过去气候变化研究的另一个重要原因。来自深海的氧同位素曲线清楚记录了新生代以来全球持续变冷过程和多次冰盖扩张事件。不仅如此,新生代以来亚洲大陆发生了显著构造运动与气候变化:青藏高原的隆升、亚洲内陆干旱化和亚洲季风的形成等,这些构造和气候之间内在的联系与未来的发展演化更是关乎我国可持续发展战略的重大议题。那么,亚洲内陆生态环境和气候是如何变化的?如何响应全球气候系统、青藏高原构造和东亚气候环境格局以及与上述因素之间（全球气候变化、青藏高原隆起、西北内陆干旱化、东亚季风的演化）如何联系?要解决上述问题,不仅需要精准的海洋记录作为全球气候变化的背景,更需要亚洲大陆上具有准确年代的、不同位置上的、跨度时间长久的气候代用指标的记录进行比对综合研究。位于青藏高原东北缘的西宁盆地地处我国三大自然地理区的交界处,也是我国黄土高原的西部边缘,对气候、环境的变迁十分敏感。同时,由于新生代以来青藏高原的构造隆起,西宁盆地沉积了巨厚的堆积物,比较完整地记录了高原东北部的变形隆升、源区风化剥蚀历史和气候环境变化过程,是研究高原构造隆升和气候环境变化相互作用过程与机制的理想地区。西宁盆地的磁性地层年代学研究获取了该盆地的52.5～17.0Ma的古地磁年代,为开展古气候研究奠定了年代基础。而在各种自然因素中,植物对于生态环境变化的反应尤为敏锐,孢粉植被自然成为陆相地层中环境与气候变化最直接和敏感的记录者。为此,本文通过对西宁盆地谢家剖面孢粉样品的分析,获取了一条我国大陆新生代较为详细的孢粉记录,并在此基础上进行了古生态环境演化的分析,得到以下结论:1.孢粉记录揭示出西宁盆地新生代古生态环境在33Ma发生重大转变,前后分为两个大的演化阶段。52.5～33Ma为第一个阶段,包括组合带Ⅰ-Ⅴ:整体上表现为麻黄、白刺与喜热分子的高含量带,呈现出一种亚热带干旱灌丛-稀疏森林植被景观。33～17Ma为第二阶段,包括组合带Ⅵ-Ⅷ:表现为草本和喜温成分高含量,植被景观转变成一种温带森林-草原类型。2.孢粉记录最为显著的变化是从33Ma开始,喜热分子百分含量显明降低,草本植物含量明显增加。该结果与全球温度变化具有良好的对应关系,说明全球背景下的大降温可能是导致西宁盆地植被演化的主要原因。3.通过对西北内陆地区新生代孢粉植物群的深入研究揭示出:古近纪时期整个西北内陆地区处于行星风系控制之下,植被面貌为亚热带灌丛-稀树森林,气候干燥炎热。新近纪时期植被面貌发生转变,以温带草原-森林为主,气候干旱温凉。同时,孢粉植物群记录也表明我国西北内陆地区自新生代以来就处于干旱环境区;新近纪开始我国古气候环境格局发生转变,西北内陆地区由行星干旱区转变为内陆干旱区,并持续变干变冷。这一结果指示了我国环境格局在23Ma左右的古近纪/新近纪之交发生转变。4.西宁盆地针叶林在52.5～37Ma之间含量很低,37Ma开始大量出现（主要指云杉）,同期孢粉组合并伴生有喜温、喜热分子以及草本植物。结合新生代全球温度曲线与现代针叶林（云杉）生态特征,可以认为:1)当云杉在孢粉组合中出现时,要充分考虑组合中其它孢粉植物的生态习性,以此确定孢粉组合所代表的气候特征。2)西宁盆地针叶林高含量带指示了山地的存在。3)云杉、冷杉等暗针叶林分子大量出现不仅指示低温环境,同时也必需一定的有效水分使之生长。4)云杉属植物现代分布特征及其生态习性是长期适应气候变化的结果。5.在谢家剖面车头沟组最底部（约23Ma）发现了木化石群,通过对该化石群同层位孢粉组合特征与有机组分分析的结果进行比对,推测木化石为云杉属植物,且当时云杉林能够生长在西宁盆地。对应于Mi-1降温事件,说明在海洋中发现的该事件在亚洲内陆同样表现明显。6.孢粉记录揭示在37～33Ma和26～22Ma之间西宁盆地附近存在高海拔山地,孢粉结果为恢复青藏高原东北缘古海拔与阶段性隆升提供了依据。更多还原

【Abstract】 The Cenozoic era with great changes of the environmental system is the most important period for our humanity for the birth of a human. We are very concerned about the evolution of the Earth’s systems. Moreover, the concentrations of greenhouse gas increase significantly as a result of the industrialization process. The global surface temperature has already increased 0.74℃over the past century, and will be expected to increase 1.1-6.4℃at the end of the 21st century, which has made a severeimpact on the world natural ecosystems and brought a serious challenge to human’s survival and development of society. Global climate change and its adverse impacts have become a common concern of humankind. Therefore, to predict the future climate change and put forward the responding strategy is the most effective way which is related to the survival of the human society future. Such a high concentration of CO₂ similar to the present that brought about by dramatic changes in climate and environment could find the reference from the early Cenozoic high concentration of greenhouse gases and the process of greenhouse effect. Therefore, "to the ancient theory of this", to provide a basis for a better understanding of modern and future climate change on Earth is the major reason for the geoscientific community research on over the past climate change. Deep-sea oxygen isotope data sets have a clear record of the Cenozoic global cooling progress interrupted by a series of transient ice sheet expansion events.During the same time, the significant tectonic movement and climate change have taken place in the Asian continent: the uplift of Tibet Plateau, the drying of Asian inland and the formation of Asian monsoon, etc. The intrinsic link between tectonic and climate and its future development are related to the major issues of China’s sustainable development strategy. Then, how did the Asian inland environment and climate change? and how the Tibet Plateau tectonic and the climate and environment pattern in East Asia was responded to the global climate system, as well as what’s the connection between these factors （global climate change, the uplift of Tibet Plateau, the drying of northwest inland, the evolution East Asian monsoon）? To resolve these problems requires not only the accurate marine record as the background of global climate change, but also a comprehensive study on the Asian continent with the exact age, different position, the long-term proxy records of climate.Xining Basin is located in the northeastern of Tibet Plateau where is the junction of the three major geographical areas of China, and also the western edge of China’s Loess Plateau. This location is very sensitive to changes of climate and environment. At the same time, because of the tectonic uplift of the Tibet Plateau since the Cenozoic, thick sedimental deposits have accumulated in Xining Basin, a relatively complete record of the deformation and uplift of the northeastern of the plateau, denudation of weathering history of the source region, and the environment and climate change, is ideal to examine the course of interaction and mechanism between the uplift of plateau and climate changes.The Magnetostratigraphy geochronology of Xining Basin obtained the 52.5Ma～17Ma palaeomagnetic age, and laid a foundation for the paleoclimate research. For the variety natural proxies of climate changes, plants are particularly sensitive to the ecological environment changes, palynological flora becomes the most direct and sensitive records of the environment and climate change in continental history.This paper is based on the analysis of palynology samples from the Xiejia section of the Xining Basin, and obtained a relatively detailed pollen record of our continent. With that, the evolution of paleoecological environment has been discussed. Main conclusions are summarized as following:1. The palynological records of Xiejia section display the Cenozoic ecological environment in Xining Basin had a major change at 33Ma. Two major stages and eight pollen assemblage zones can be divided before and after the change. 52～33Ma is the first phase, including the combinations with I - V: the overall performance for Ephedripites, Nitrariadites and thermophilic elements with high content, showing a sub-tropical arid shrubs-savanna forest vegetation in the landscape. 33～17Ma is the second phase, including the combinations with VI - VIII: herb and temperate elements performance for the high content, vegetation landscape is a temperate forest-grassland type.2. Palynological records suggest that the most significant change in performance is that thermophilic elements content are obviously lower, with the beginning of a marked increase of herb plants from the onset of 33Ma. Palynological record of Xining Basin has a good matching to the Cenozoic global temperature curve, which shows that the temperature might be the main reason for the vegetation evolution in Xining Basin, the large-scale expansion of the Antarctic ice sheet led to global cooling, resulting the ecological environment change in Xining Basin. 3. Further study of palynofloras in northwest inland reveals that: it was controlled by the planetary wind system through the Paleogene period with the landscape of sub-tropical shrub- savanna forests, dry and hot climate. The landscape changed during the Neogene period, becoming temperate grassland-forest, with warm cool climate. At the same time, Palynoflora record also shows that the northwest inland of China was a arid region through the Cenozoic period.The pattern of China’s paleoclimate and environment have changed since Neogene. Northwest inland was translating from the planetary arid region into an inland arid region, continuing drying and cooling. This result further indicates that the pattern of China’s environment change at about 23Ma when the Paleogene turned to Neogene.4. The conifers in the Xining Basin had a low percentages during 52～37 Ma and became aboundant at.37Ma. Combining with the Cenozoic global temperature curve and the ecological characteristics of modern conifers（ mainly Picea） , we can considere that:1) When the Picea and Abies appear in the palynological assemblages, it should also take the ecological habits of other pollen types as well into account in order to determine the assemblages on behalf of the climate types. 2) The appearance of high conifers content in Xining Basin indicates the existence of a mountain. 3) The occurrence of a large number of Picea, Abies and other dark conifers not only implies a low temperature and cold climate, but also shows a rich water condition.4)The modern distribution and ecological habits of Picea are the result from the adapting to climate change in a long time.5. The original burial fossil woods are excavated at the bottom of the Chetougou formation （about 23 Ma） in Xiejia section. Together with the analysis of pollen and the organic components at the same layer, we presumed that the fossil woods are Picea, that is, the spruce forest could grow in the Xining Basin at that time. Corresponding to the Mi-1 cooling event found in ocean records.6. Palynological records reveal that a high altitude mountains existed in Xining Basin during 37～33Ma and 26～22Ma. It si a much more powerful material for the restoration of palaeo-elevation and deformation and uplift of northeastern of Tibet Plateau.更多还原