Knowledge Resource Center for Ecological Environment in Arid Area
| 青海湖一郎剑钻孔岩芯的磁性地层学与古环境记录 | |
| 其他题名 | Magnetostratigraphy and paleoenvironmental records of Yilangjian Core from Lake Qinghai |
| 符超峰 | |
| 出版年 | 2007 |
| 学位类型 | 博士 |
| 导师 | 安芷生 |
| 学位授予单位 | 中国科学院地球环境研究所 |
| 中文摘要 | 晚新生代以来青藏高原的隆升不仅导致了亚洲大陆内部强烈的构造变形,而且对周边地区的地貌格局和气候环境演化产生重大影响，长期以来一直是地球科学研究的重点和热点领域之一。青藏高原东北缘属于柴达木－祁连活动地块，是青藏高原向大陆内部扩展的前缘部位，作为高原最晚隆升的部分，这一地区构造隆升的时间对于大陆动力学以及地壳与大气圈相互作用的研究都具有重要意义。位于其内的青海湖是我国最大的内陆咸水湖，处在东亚季风、印度季风和西风激流三者的汇聚带上，湖区西接青藏高原、东临黄土高原、北靠沙漠干旱区，处于东亚季风湿润区和内陆干旱区的过渡带上，既受亚洲季风影响，又受西风环流影响，对气候环境十分敏感。是全球气候系统中各分量联系的重要枢纽。其内巨厚的沉积物记录了青藏高原隆升变形的历史及气候环境变化的信息。\n\n本文依托安芷生先生主持的国家重点基础研究发展规划项目《我国大陆季风——干旱环境系统发展过程的科学钻探研究》（批准号：2004CB720200）和国家自然科学基金重大项目青海湖项目《晚新生代青海湖高分辨率的古环境记录及其对全球变化的意义》（批准号：40599420），以青海湖一郎剑（YL）626.39m的钻孔岩芯为研究对象，通过对岩芯的岩性分析，磁性地层学研究，及粒度、磁化率、有机碳（TOC）、氮（TN）含量、碳氮比（C/N）、碳酸盐含量、色度等多项指标的实验测试和分析对比，初步重建了青海湖区上新世以来的环境演变过程以及青藏高原东北部构造隆升的历史。具体结论如下：\n\n1.依据详细的高分辨率磁性地层学研究获得了青海湖YL钻孔岩芯所记录在整个剖面中的多个磁极性转换和磁漂移事件。通过与标准极性柱（Cand and Kent，1995）的直接对比。获得了这些磁极性转换和磁漂移的具体年龄，根据沉积速率推算YL钻孔的底部年龄为5.11Ma。在磁性地层学研究的基础上，以磁极性转换事件及磁性漂移事件的发生年代为结点，分别应用线性内差法、湖泊沉积年龄模式和粒度年龄模式建立年代标尺，经过综合对比，最终获得了青海湖YL钻孔5.11Ma以来的年代标尺。\n\n2.通过对岩芯的仔细观察及岩性分析，结合详细的粒度指标的测试，将YL钻孔沉积地层沉积相划分为四个阶段，认为第一阶段（626.39－586.64m）为陆源风尘堆积相；第二阶段（586.64－393.29m）为浅湖-半深湖相堆积；第三阶段（393.29－232.16m）为浅湖相堆积。第四阶段（232.16－9.90m）为滨浅湖相堆积。\n\n3.沉积学的研究表明，典型的湖相地层开始于孔深586.64m处，对应的年代约为4.64Ma，作者认为现代意义上的青海湖形成于4.64Ma 。\n\n4.通过岩性观察，粒度、磁化率、有机碳（TOC）、氮（TN）、碳氮比（C/N）、碳酸盐含量、色度等指标的实验测试和分析对比，初步重建了5.11Ma以来青海湖流域的气候环境演变过程，认为青海湖流域～4.64Ma以前是一个干热的时期，4.64～4.42Ma，气候发生了突然的转型，由干热突变到湿冷，又由湿冷渐变到湿热；在约3.46～2.52Ma气候发生了又一次向干冷方向的波动突变后，气候变率较大，继续变干变冷，湖泊由半深过渡到浅湖，反映了内陆干旱化的急剧扩张，流域向干旱化方向发展；1.89～1.56Ma流域干旱化继续加强，水位继续下降，湖泊由浅湖演变到滨湖；1.56～0.6Ma期间湖泊至少在约1.2Ma、0.8Ma发生两次干冷化过程，水位波动较大；0.6Ma.以后气温呈周期性波动明显，0.4Ma、0.2Ma发生两次干冷化的过程。\n\n5.依据盆山沉积耦合原理，通过对YL钻孔地层沉积速率变化的详细研究，结合青藏高原多个盆地早新生代和晚新生代的变化特征分析，作者认为青海湖盆地的形成演化和青藏高原东北部的隆升变形紧密联系在一起，盆地每期的加速沉陷过程对应高原的快速隆升变形阶段，综合分析得出：青藏高原的东北部在约4.9～3.6Ma，3.4～3.0Ma，2.6～1.7Ma，1.2～1.07Ma，0.9～0.6Ma，0.2～0.1Ma发生过6期构造隆升事件，高分辨率的磁性地层学研究清楚显示出每期隆升事件强度变化的细节。4.62～4.48Ma、4.29～4.18Ma期间是第一期隆升事件发生过程事件中两起加速隆升的阶段；3.11～3.04Ma期间是第二期隆升事件发生过程中的一起加速阶段；2.15～2.14Ma、1.95～1.77Ma是第三期隆升事件发生过程中的幅度较大的两次加速阶段；0.9～0.78Ma、0.78～0.6Ma是第五期隆升事件发生过程中的两次加速隆升阶段。\n\n6.青海湖流域的环境演化过程及其所反映的我国北方内陆干旱化的过程和青藏高原的构造隆升过程有直接的对应关系。青海湖流域的环境演变过程是对青藏高原隆升生长过程的响应。大约在4.64Ma左右，该区气候环境发生由干热－湿冷的重大转型，青海湖形成，气候环境湿热。3.6～3.06Ma青藏高原的进一步隆升，阻挡了印度洋的暖湿气流向亚洲内陆的输送，驱使青海湖流域向干旱化方向发展，3.06～2.52Ma,1.89～1.56Ma,1.2Ma,0.8Ma发生了一系列干旱化进程。\n\n关键词：青藏高原东北部、青海湖、YL钻孔、磁性地层、环境演化、构造隆升 |
| 英文摘要 | Magnetostratigraphy and paleoenvironmental records \nof Yilangjian Core from Lake Qinghai \n\nFu Chaofeng (Quaternary Geology)\nDirected by: Prof. An Zhisheng (Institute of Earth Environment, CAS)\nAssociate prof. Qiang Xiaoke (Institute of Earth Environment, CAS)\n\nAbstract\nThe uplift of the Tibetan Plateau has not only resulted the intensive tectonic deformation in the inner Asian continent during the Late Cenozoic, but also has a great influence on the landform pattern, climate and environmental change around the Tibetan Plateau, which is an key issue in geoscience research. As a part of the Qaidam-Qilian active block, the northeastern Tibetan Plateau is the foreland part extending from the Tibetan Plateau to inland and the latest uplift part of the plateau. The uplifting time of this region is helpful to the understanding of the continental dynamics and the interactivity between lithosphere and aerosphere. Lake Qinghai, situated in a semi-arid area, lies at the confluence of the East Asian monsoon, the moisture of which is derived from low-latitude oceans; the cold, dry polar airflow from the Siberian high pressure system; and the Westerly Jet Stream. To the east lies the Loess Plateau, while to the northwest is a vast desert region. The tectonic evolution of this region is intimately associated with the growth of the Tibetan Plateau. Previous studies have revealed that Lake Qinghai possesses a long, continuous sedimentary record that dates at least back to the Pliocene. Because of its unique geographic location, the lake is very sensitive to environmental change and is an outstanding site for obtaining high-resolution records of late Cenozoic continental environmental history. The Lake Qinghai record will address fundamental questions about the environment effect of recent uplift of the Tibetan Plateau, as well as questions about regional tectonics and the evolution of sedimentary basins in this area.\nThis dissertation is supported by the National Basic Research Program of China——《Coupled Evolution of the Monsoon-arid Environment System of China: a Continental Drilling Approach》(Authorized No.: 2004CB720200), and by National Natural Science Foundation of China——《Scientific Drilling at Lake Qinghai, Northeastern Tibetan Plateau: High-resolution Paleoenvironmental Archives and Global Change》 (Authorized No.: 40599420) which is supervised by Professor An Zhisheng. Here a 626.39m long core from Yilangjian (YL) area in the southern Lake Qinghai is selected for the understanding of the climate and evolution history of this area. Based on the lithological and magnetostratigraphical results and various climatic proxies such as grain-size index, magnetic-susceptibility, organic carbon, nitrogen, the ratio of carbon to nitrogen, carbonate content, chroma, we try to reconstruct the history of environmental variation and uplifting history of the northeastern Tibetan Plateau since the Pliocene. The preliminary conclusions are just as follows:\n1. Detailed palemagnetic measurements indicate that the bottom paleomagnetic age from the YL drilling core of Lake Qinghai is 5.11 Ma .\n2. In accordance with the investigation of the lithology and the analysis of the grain-size index, YL drilling stratigraphic-sediment can be categorized into four depositing stages: the first stage is from 626.39m to 586.64m in depth and the sediment is aeolian originated; the second stage (586.64-393.29m) the shallow or semi-deep lacustrine sediment; the third stage (393.29-232.16m) the shallow deposit; the last stage (232.16-9.90m) the littoral sediment.\n3. The study into the stratigraphy of YL drilling core indicates that the typical lacustrine deposit starts at the depth of 586.64m, and the paleomagnetic age at this depth is 4.64Ma .Therefore, it is inferred that, in modern meanings, Lake Qinghai may come into being at 4.64Ma .\n4．The climate change process in Lake Qinghai region has been preliminarily reconstructed from 5.11 Ma, according to investigation of lithology, grain-size index, magnetic-susceptibility, TOC, TN, C/N, carbonate content and chroma. Climate before 4.64 Ma was warm and dry, while it changed abruptly between 4.64-4.42 Ma, from warm and dry to humid and cool, in succession, to humid and warm. The climate became dry and cool again during 3.46-2.52 Ma, after that, cooler and drier, the variation was bigger than before. The lake became shallower, indicating abrupt speading and expanded drought in inland; Drought became more serious between 1.89-1.56Ma, while lake level kept a drawdown continuously, the lake became shallower. Between 1.56-0.6 Ma, there were at least two dry and cold situations, the big fluctuations could be seen in the lake level. After 0.6 Ma, temperature fluctuated periodically, and two more dry and cool situations occured in 0.4 Ma and 0.2 Ma .\n5. We conclude that the evolution of Qinghai Lake basin is closely correlated with the uplift of the Northeastern Tibetan plateau, based on the principle of basin-mountain coupling and the research of stratum sedimentation rate in YL core and combined with the analysis of the features of avariations of the basins in the Tibetan Plateau in early Pliocene and late Pliocene. We claim that, when the Tibetan Plateau uplifted, the lake basin went down. After the comprehensive analysis, the conclusions come as follows: 6 tectonic uplift events are identified: they occurred at 4.9-3.6Ma, 3.4-3.0Ma, 2.6-1.7Ma, 1.2-1.07Ma, 0.9-0.6Ma, and 0.2-0.1Ma respectively. High-resolution magnetostratigraphy can help us come to see intensity variation of uplift event in detail: 4.62-4.48Ma, 4.29-4.18Ma accelerated the uplift stages in the first moment event; 3.11-3.04Ma the second moment event; 2.15-2.14Ma, 1.95-1.77Ma the third moment event; 0.9-0.78Ma, 0.78-0.6Ma the fifth moment event.\n6. The climate change process in Qinghai Lake drainage area and its implication on the inland drying process are directly corresponded to the uplift of Tibetan plateau. The climate change process in Lake Qinghai is respondent to the uplift of the Tibetan plateau. About 4.64 Ma, climate had been changed greatly from dry and warm to humid and cool, then humid and warm, Lake Qinghai came into being at this stage. The Tibetan Plateau experienced further uplift between 3.6-3.06Ma, which blocked the passage of the humid air current from the Indian Ocean to the Asian inland, and drived this drainage area to dry. As a result, in 3.06-2.52Ma, 1.89Ma-1.56Ma, 1.2Ma, 0.8Ma, a series of droughts happened in this area.\n\nKey word: Northeastern margin of the Tibetan Plateau, Lake Qinghai, YL core, Magnetostratigraphy, Environment evolution, Tectonic uplift |
| 中文关键词 | 青藏高原东北部 ; 青海湖 ; YL钻孔 ; 磁性地层 ; 环境演化 ; 构造隆升 |
| 英文关键词 | Northeastern margin of the Tibetan Plateau Lake Qinghai YL core Magnetostratigraphy Environment evolution Tectonic uplift |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 第四纪地质学 |
| 来源机构 | 中国科学院地球环境研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/286545 |
| 推荐引用方式 GB/T 7714 | 符超峰. 青海湖一郎剑钻孔岩芯的磁性地层学与古环境记录[D]. 中国科学院地球环境研究所,2007. |
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