【作者】 鲁新川；

【导师】 宋春晖；

【作者基本信息】 兰州大学 ， 古生物学与地层学， 2007， 硕士

【摘要】 近来全球变暖、冰盖大面积消减、海平面升高等一系列现象为世人所关注，这种现象归因于全球环境问题并影响着每一位地球人。因此全球环境变化是每个人关心的问题，也一直是众多学者研究的焦点问题。作为对全球气候有着重要影响的青藏高原首先被国际学者关注。享有“世界屋脊”之称的青藏高原，如一高大屏障横亘在中纬度的大气层中。高原隆起不仅对高原及其毗邻地区，甚至对北半球、乃至全球的气候与环境都产生了深刻的影响。临夏盆地是以一条深大断裂为界紧接青藏高原东北缘的新生代前陆盆地，同时位于我国三大自然地带的交汇处以及处于季风三角区的顶点部位。因此，临夏盆地的地层序列忠实地记录了新生代以来区域构造、气候变化以及干旱化环境的演化历史，是研究青藏高原隆升和新生代气候环境演化的理想地区。本文通过对沉积环境和沉积相分析，揭示临夏盆地14-4.4Ma属封闭古湖稳定、连续的细粒沉积物，因此该沉积物是完整记录该时段区域气候变化的良好载体。在此基础上，通过高密度采样和元素分析，建立了临夏盆地14-4.4Ma时段稳定湖相沉积物地化元素随时间变化的高分辨率序列。通过沉积物元素与深海氧同位素曲线的对比，得出CaO／Sr变化是能够较敏感的反映流域气候变化可作为气候变化的替代性指标。通过临夏盆地稳定湖相沉积物元素含量变化序列的分析，并结合孢粉、碳酸钙、氯离子和风成砂等研究资料，揭示了8 Ma、6.2 Ma存在两次重大气候转型事件，即8 Ma气候干旱化转型，可能代表了亚洲内陆干旱化的开始：6.2 Ma气候变化代表了气候干旱化的加剧。通过对临夏盆地毛沟剖面14-4.4 Ma湖相沉积物化学元素研究表明：钛、铝、铁、硅、钾、镁、磷、铷、钙、钠对气候环境变化有一定的指示作用。在一定条件下稳定湖泊沉积物的TiO₂、Al₂O₃、TFeO、SiO₂、P和Rb含量与湿润气候成正相关，CaO、Na₂O和CaO／MgO、CaO／Sr比值与干旱气候成正比。CaO／Sr能作为指示气候冷暖干湿的替代性气候指标，CaO／Sr比值高反应气候干冷，其值低代表气候热湿。从CaO／Sr变化特征和北大西洋深海氧同位素变化阶段性耦合分析，亚洲冬季风可能形成于12Ma以前，其演化大致经历了3个阶段，12-8.0 Ma为古冬季风形成阶段。8.0-6.2 Ma为古冬季风阶段。6.2-4.4Ma为古冬季风向现代冬季风演化阶段。北大西洋深海氧同位素变化比临夏盆地沉积记录的CaO／Sr变化存在滞后性，这种滞后性可能说明高原隆升导致了北极冰盖的增加。以反应化学风化强度的Rb／Sr作为夏季风的替代性指标，其变化特征与南海ODP1148氧同位素变化阶段性耦合分析，认为夏季风经历了：14-12.6Ma段古夏季风稳定期、12.6-10Ma段古夏季风盛行期、10-7.8Ma古夏季风减弱期、7.8-6.2Ma古夏季风向现代夏季风过渡期以及6.2-4.4Ma现代夏季风形成期。临夏盆地沉积记录的14-4.4Ma高原构造隆升过程与气候干旱化过程及东亚季风的演化阶段的一致性，表明青藏高原的晚新生代的大幅隆升可能是该区古气候变化和气候干旱化转型的驱动机制。更多还原

【Abstract】 Tibetan Plateau, which has often been called the "Roof of the World", forms a barrier in the stratosphere. Tibetan Plateau Uplift is believed to have made great affects on the environment of its vicinity. Linxia basin, which is a Cenozoic foreland basin, borders on Northeast of Tibetan Plateau with a fault zone. It is not only in the cross area of three main geographic zone but also in monsoon triangle zone. Strata series should be a good record of the history of region tectonic, climate changing and arid environment development and Linxia basin would be an ideal area to study Tibetan Plateau Uplift and evolution of Cenozoic climate-environment.Linxia basin has deposited, steady, continuous lacustrine sediments in 14-4.4Ma by analyzing the sedimentary environment and facies, so it perfectly recorded the location environmental changes. With the high-resolution sampling and elements analyzing, upbuild a high-resolution variety sequence of steady lake sedimentary elements. Comparing to the deep sea oxygen isotope curve, we draw a conclusion that changes of the CaO/Sr ratio can sensitively reflect the palaeoclimate change, and act as a proxy of palaeoclimate change.High resolution analyzing results of the elements contents in long time scale of stable lake, accompanied with the results of pollen spore, calcium carbonate, chlorine ion, and aeolian sands etc. reveal that there are grant climate transform events at 8Ma and 6.2Ma respectively. Of them, climate transform event at 8Ma may represent the start of the desertification of asian interior and the one at 6.2Ma indicates the enhance of the desertification.The results of study on the lacustrine sedimentary chemical elements in Linxia basin between 14 and 4.4Ma, show that the environmental change can be indicated by the elements Ti, Al, Fe, Si, P, Rb, Ca, Na. The stable lacustrine sedimentary elements, TiO₂,Al₂O₃,TFeO,SiO₂,P₂O₅ and Rb, their contents positive correlating to the humid climate, CaO,Na₂O,CaO/MgO,and CaO/Sr direct proportion to the aridity climate. CaO/Sr ratio can act as a proxy of cool and aridity climate, and it directly proportions cool and aridity climate.The results of study on the change of CaO/Sr ratio which is staggered coupling with the north atlantic deep sea oxygen isotope curve, and the sedimentary records in Linxia basin in 14-4.4Ma, we consider that the asian winter monsoon was formed before 12Ma. And its’development experienced three phases: 12-8.0Ma as the forming phase of ancient winter monsoon, 8.0-6.2Ma as the phase of ancient winter monsoon, 6.2-4.4Ma was the time during which ancient winter monsoon evolved to modern winter monsoon. Through the contrast CaO/Sr curve with the north atlantic deep sea oxygen isotope curve, we can find the phenomena that the oxygen isotope changes always lag the changes of CaO/Sr, which may reveal that the Tibetan Plateau Uplift leads to augment of the arctic ice sheet. The results of study on the change of Rb/Sr ratio which is staggered coupling with the south ocean oxygen isotope curve, and the sedimentary records in Linxia basin in 14-4.4Ma, we consider that ancient summer monsoon experienced : 14-12.6Ma as the stable form stage of ancient summer monsoon , 12.6-10Ma as the prevailing stage of ancient summer monsoon, 10-7.8Ma as the declining stage of ancient summer monsoon, ancient summer monsoon transiting into modern summer monsoon in 7.8-6.2Ma,and 6.2-4.4Ma as the evolution stage of modern summer monsoon.The coupling relationship between Tibetan Plateau Uplift course, the desertification of Asian interior and the course of the East Asian monsoon development reveals that Plateau Uplift in late Cenozoic may force the palaeoclimate changes and the formation and development of Asian winter monsoon in Linxia basin between 14 and 4.4Ma.更多还原