【作者】 易治宇；

【导师】 孙东怀；

【作者基本信息】 兰州大学 ， 自然地理学， 2008， 硕士

【摘要】 通过系统的野外地质调查,在塔里木盆地西部、塔克拉玛干沙漠腹地选择了地层连续稳定、出露良好的新生代剖面—塔格山剖面进行了野外地层测量、岩性描述及样品采集。用超导磁力仪和磁化率仪作了系统的磁性地层研究,获得了该剖面的磁性地层年代和磁化率记录。以古地磁极性界线年代作为控制点,以沉积速率线性内插,计算了剖面各个位置的年龄,从而获得了该剖面的年代标尺;确定了塔里木盆地海相结束、大规模沙丘开始发育及大砾石层形成的时代,从而对第三纪新特提斯海塔里木古海湾的演化、塔克拉玛干沙漠形成的年代及青藏高原的隆起提出了新的见解。通过古气候记录和沉积相的分析,揭示了塔里木盆地晚新生代干旱化的历史;在此基础上,本文进一步讨论了塔里木盆地干旱化与特提斯海演化及青藏高原隆升的关系。本文得出了以下结论:1.用热退磁方法和超导磁力仪对塔格山剖面非海相部分进行系统的磁性地层研究表明,该剖面磁性地层主要由Matuyama负极性时、Gauss正极性时、Gilbert负极性时上部组成,Matuyama负极性时的特征是有三个正极性亚时,Gauss的特征是中下部有两个负极性亚时,Gibert时上部出现较大段的负极性段,塔格山剖面陆相底界年龄为4.2Ma,顶部年龄为0.8Ma。2.剖面磁性地层研究显示,冲积平原相与海相的界限位于Gilbert负极性时上部,年龄大约为4.2Ma,它标志着塔里木盆地西部残留海的演化于4.2Ma结束,塔里木古海湾最迟在4.2Ma退出。3.塔格山剖面砾石层首次出现的年代为3.0Ma,标志着青藏高原晚新生代以来强烈隆升的时代为3.0Ma。4.大规模风尘堆积开始发育的时代约为3.4Ma,它标志着晚新生代亚洲内陆进一步干旱化的开始,塔克拉玛干沙漠在3.4Ma就已经形成,同时可能意味着青藏高原在此时达到了一定的高度。更多还原

【Abstract】 On the systematic geological survey, Mazatagh section, a consecutive and well-outercropping section of cenozoic in central Tatim basin was chose for investigation on stratigraphy, paleomagnetism and paleoclimatology. Thermal demagnetizer and cryogenic magnetometer were used to systematically measure the magnetic remanence from room temperature up to 650°C with 50°C step in order to dertimime magnetostratigraphy of the section. Meanwhile, magnetic susceptibility was measured as a proxy of paleoclimate for the section. Magnetic polarity boundary ages are used as the controlling points, while using the linear-interpolated accumulation rate for building up the time scale of the section. Consequently the bottom age of continental facies, the age of eolian accumulation in large scale and the age of large gravel bed were estimated. On that basis, we get some new understanding about the evolution of the Tarim gulf, the age of the Taklimakan desert as well as the uplift of Qinghai-Tibet Plateau in Cenozoic .On the analysis of paleoclimate records, the drought history of Cenozoic in Tarim basin was revealed. The following points mark the main conclusions of this thesis:1. On a systematic thermal demagnetization and remanence measurement using a cryogenic magnetometer, Magnetostratigraphy of Mazatagh section was produced for the Cenozoic continental strata, which shows a consistent polarity structure. Magnetostratigraphy of the section consists of reversed Chron of Matuyama, normal polarity Chron of Gauss and reversed Chron of upper Gilbert. Chron Matuyama is characterized by a long reversed polarity with three normal subchrons, Chron Gauss is characterized by a long normal polarity with two reversed subchrons at lower part of the Chron.and Chron Gilbert can be determined by a long reversed polarity at the top of the Chron. The bottom age of the continental facies is 4.2Ma and the top age of the section is 0.8Ma.2. Magnetostratigraphic study of the section shows the boundary between alluvial plain facies and marine facies lies in revised Chron of Gilbert, the age is estimated to be 4.2Ma. It suggests that the evolution of semienclosed sea in western Tarim ended at 4.2Ma, and the regression of Tethys occoured at 4.2Ma.3. The time when the gravel bed appeared for the first time is about 3.0Ma, and it may suggest the quick uplift of Qinghai-Tibet Plateau in Cenozoic.4. The initiation of large scale accumulation of eolian material is estimated to be 3.4Ma, which is a symbol of a further drying occurred in Late Cenozoic in inland of northwest area, and also a symbol of the appearance of the Taklimakan desert, meanwhile, it may suggests that Qinghai-Tibet plateau had reached a significant height at that time.更多还原