【作者】 邬光剑；

【导师】 艾南山； 潘保田；

【作者基本信息】 兰州大学 ， 自然地理学， 2001， 博士

【摘要】 最近1.0Ma 以来,全球气候经过中更新世气候转型,开始进入周期为100kyr的冰期旋回。这一转型不是经典的Milankovitch 理论所能完全解释的。青藏高原的隆升作为新生代最显著的地质事件之一,对高原自身及其周边地区甚至对全球气候都有强烈的影响。祁连山作为青藏高原和中国西北干旱区的边界,明显地留下了构造隆升的烙印,该区的气候记录也受到了这两大区域的影响。这为探讨构造、气候及二者的关系提供了良好的条件。沙沟河的阶地系列是祁连山阶段性隆升和向北扩展的直接地貌证据。根据形态特征和成因分析,沙沟河五级阶地主要是构造隆升形成的,可以用阶地形成年代来确定构造隆升历史。根据古地磁、热释光、放射性14C 的测年以及黄土地层序列的对比,这五级阶地分别形成于0.83Ma、0.42Ma、0.25Ma、0.14Ma、0.01Ma。它们反映了祁连山自中更新世以来的5 次强烈隆升事件,发生时间与阶地形成时间相同。这些构造隆升事件与青藏高原其它地区的隆升有良好的对应关系。尽管高原隆升过程中的一致性显著,区域差异也是存在的。河西走廊东段的黄土堆积开始于约1.4Ma,晚于黄土高原地区,其原因可能是作为沉积基底的稳定的地形面形成较晚。这里位于夏季风的边缘区并临近腾格里沙漠,使得该区黄土具有较高的沉积速率和分辨率,有利于敏感地记录气候变化的细节。而且,这里的黄土位于沙漠?黄土边界带内,可以反映沙漠演化的特征。本文采用粒度、色度作为主要的气候指标,反映了沙沟剖面0.8Ma 以来的气候变化。根据一些年代控制点年龄和粒度年龄模型,建立了沙沟剖面的年代序列,与深海钻孔标准曲线较为吻合。砂粒含量显示,中国北方沙漠至06?0.7Ma 时开始了周期性的大规模扩张,至0.42Ma 时锯齿状的周期更为明显。粒度记录反映了各个冰期中气候逐渐变冷,至末期时成为冰盛期,沙漠范围扩张至极大。然后,突然的终止期(冰消期)使得气候快速进入间冰期。MIS16 阶段,全球冰量最大,青藏高原上发育最大规模的冰川。这两种因素的叠加,使得MIS16 阶段时沙漠极端扩张。沙沟剖面中主导周期为100kyr,与全球冰量周期吻合。地轴倾角周期(41kyr)也较为明显,但岁差周期微弱。这说明在冰期旋回尺度上,沙沟剖面的黄土堆积主要受北半球高纬地区(特别是冰盖)的控制,热带海洋的影响相对较小。频谱分析也证实了亚轨道尺度的气候事件的存在,千年尺度的气候波动贯穿于整更多还原

【Abstract】 After the mid-Pleistocene transition (MPT) that occurred about 1.0Ma ago, global climate began the 100kyr glacial cycles. The classical Milankovitch theory is inadequate to explain the genesis of MPT and the strong 100kyr-cycle in climate records satisfactorily. The uplift of the Qinghai-Tibetan (Q-T) Plateau is the most significant geological event in the Cenozoic. High and huge plateau in middle-low latitude not only changed environment of itself and adjacent regions but also had a global significance. The Q-T Plateau was called as “the Driver and Amplifier”. Correlation between uplift and climate is one of the kernel topics for Quaternary research. Qilian Mountains, as the boundary between Q-T Plateau and northwest arid region of China, has experienced strong uplift process and left clear evidences. This provides a convenience to discuss tectonic uplifts, climatic changes, and their relations. Terrace series of Shagou river, which flow northward into Tengger desert, is the direct proof for the uplift and northward expansion of Qilian Mountains. From characteristic analysis, it can be concluded that the five major terraces of Shagou river are mainly tectonic genesis, though the climate still played a role. Based on paleomagnetic dating, Thermoluminescence dating, radio carbon dating and loess-paleosol sequence matching, the ages of five major terraces are primarily determined at about 0.83Ma, 0.42Ma, 0.25Ma, 0.14Ma and 0.01Ma, respectively. The tectonic uplift events that reflected by these terraces occurred at the same time and have well parallels with the Q-T Plateau. Though the coincidence is significant, regional difference of tectonic also exists. Based on paleomagnetic dating, loess deposited in eastern Gansu (Hexi) Corridor might begin at 1.4Ma. This was late than that in the Loess Plateau. The possible cause is the stable substrate formed late than those in the Loess Plateau. Shagou loess section is situated in the marginal region of summer monsoon and Tengger desert. High dust deposit rate favors the resolution of climatic changes. Shagou section also lies in the desert-loess transition belt, thus it record could also reflect desert evolution that reflected by sand (>63μm) content. Chronology of this section was established based on some age control points and grain size age model. The result coincides well with those standard deep-sea cores. Shagou section recorded the climatic changes over the past 0.83Ma and the bottom of it is loess layer L9. Grain size and color were chosen for main climatic proxies. Chinese northern desert periodically expanded obviously since 0.6?0.7Ma, and the saw-tooth shaped characteristic became more typical since 0.42Ma. Grain size became coarser during every glacial, and reached the coarsest at glacial maximums. Then, an abrupt and rapid termination (deglaciation) ended the glacial and turned climate into interglacial. During MIS16, the combination effect of maximum global ice volume and maximum glaciation on the Q-T Plateau caused the desert to expand extremely. Spectral analysis indicates that the 100kyr periodicity, which is the same as the global ice volume cycle and the eccentricity, dominates the whole record, both in grain size and color a*. Tilt (or obliquity, 41kyr) cycle is also obvious, while the procession periodicity is weak. The results suggest that in glacial cycle time scale, loess deposit of Shagou section were mainly controlled by high latitude in North Hemisphere, such as ice sheet. Millennial scale variations, which were proved by spectral analysis, also punctuated the whole record over the past 0.8Ma. Climate changes over the last glacial cycle were well recorded in Shagou section. A pause occurred during the penultimate termination (deglaciation), like those in other region over the world. But the TII was abrupt and rapid. The record suggested that the Eemian was rather stable because of being lack of variations in MIS 5e substage. Interstadials (IS) and Cold event (C) in North Atlantic could be found in Shagou section, both in grain size record and in stratigraphy. Thus, the changes in North Atlantic could influence East Asian Monsoon system via westerlies and Siberian High even in interglacial. The last glacial could be divided into three stage according to marine isotope curve, and the millennial variation was superimposed on the global ice volume changes. Differences exist between westerlier region and monsoon region, event in inner monsoon region. From northwest to southeast, the Dansgaard-Oeschger (D-O) cycles reflected by grain size record in loess deposit became weak, while the effect of summer monsoon became strong. Thus, the intense variation in tropicalPacific Ocean could also impact loess record by counteracting the climatic signal transported from high latitude. From Shagou record, it may suggest that influence of North Atlantic was distinct during interglacial, while that of tropical oceans was obvious during glacial. Being close to glaciers and high altitude, Menyuan loess section may be the optimal candidate for reflection of glacial evolution. But the special characteristics of analysis results are beyond our understanding at now. In a certain time scale, tectonic uplift and climatic change are tightly in correlated. The coupling evolutions of glacier, loess and desert are not only controlled by the same global background but also by the amplifying effect of Q-T Plateau. The Plateau affected the westerlier and East Asian monsoon via its dynamic and thermal effects when it reached to threshold altitudes. The tectonic uplifts, which reflected by Shagou river terraces, had the parallels in climatic changes recorded in Shagou loess section. These coupling relation are named as tectonic-climatic events. It is clearly that the uplifts occurred in 0.83Ma is corresponded to desert significant expansion and periodically variation from 0.64Ma to present, the mid-Pleistocene transition and the setup of Chinese climate pattern. The 0.42Ma uplift is corresponded to the beginning of more typical saw-tooth characteristics in the climate record, and 0.14Ma uplift is corresponded to the extreme drought in northern China since the last glacial, respectively. Whether the uplift at 0.25Ma is related to the Mid-Brunhes climatic event needs more works. Though the Q-T Plateau has important role in climatic change, other factors, such as solar insolation and sea-land configuration, could affect climate obviously.更多还原