Knowledge Resource Center for Ecological Environment in Arid Area
| 六盘山北部寺口子组砂岩特征、成因及古环境 | |
| 其他题名 | The Features, Origin of the Sikouzi Formation and Paleoenvironment change in northern Mt. Liupanshan |
| 杨帆 | |
| 出版年 | 2017 |
| 学位类型 | 硕士 |
| 导师 | 李孝泽 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 古近纪是地球从中生代温暖气候向新近纪寒冷气候的过渡期，该期内陆古环境重建是我国新生代地质研究的前沿问题。本文选取六盘山北部中-新生界大剖面中的寺口子组砂岩地层作为研究对象。该砂岩剖面是寺口子组的正层型剖面，位于我国青藏高原东北缘六盘山北部，宁夏回族自治区固原市三营镇寺口子沟，是我国古近纪内陆古环境研究的重要剖面。尽管该套砂岩从1921年开始研究至今历史悠久，但其成因类型、形成时代及古环境等问题仍未解决。本文对该砂岩进行了比较系统的野外地质调查与室内样品分析，重点通过岩性、沉积构造、石英颗粒表面微结构特征、粒度及年代分析等方面研究，对砂岩剖面进行详细的地层划分和沉积特征定量分析，并结合前人研究基础对其成因、时代、古环境等进行探讨。初步研究结果表明：（1）通过开展系统的地层划分，并对沉积构造特征、石英颗粒表面微结构特征和粒度分布特征进行定量化研究，发现：固原寺口子组砂岩剖面真厚度为285.6m，可划分为三个沉积阶段。阶段I为河流相沉积；阶段II为砂岩主体部分，为典型风成沉积，进一步可划分出典型的风成沙丘相沉积与丘间地沉积；阶段III为湖相沉积物。（2）通过绝对测年方面的尝试，结合现有古地磁测年成果，认为固原寺口子组砂岩的形成时代为始新世-渐新世。（3）通过对比分析沙漠风成沙丘、滨岸风成沙丘沉积特征，证实本研究区寺口子组为内陆沙漠沉积。借助玫瑰花图恢复寺口子组沉积主体的古风向为盛行西风。结合古风向、气候背景及研究区域地形条件，推断砂岩主体风成沉积为中国古近纪行星风系控制下的沙漠沉积。剖面沉积相由沙漠沉积向湖相沉积的转变反映了古气候由干旱到湿润的气候演化，可能是我国新生代早期气候条件由行星风系向季风风系的转变。 |
| 英文摘要 | The Paleogene is a key period for the environment changes from the Mesozoic to the Neogene on earth, in which the warm climate type transits to the cold climate type. Reconstructing the global environment evolution of this period, it is a frontier topic faced by the study of Cenozoic geological research in china. In this paper, the author selected the Sikouzi Formation as the research object. The sandstone profile of the Sikouzi Formation, located in the northwest of Guyuan city of Ningxia Hui Autonomous Region of China, is the positive stratotype section of Sikouzi Formation and is also in the northern part of Mt. Liupanshan which at the northeastern edge of Qinghai-Tibet Plateau. This thick Cenozoic sedimentary strata is an ideal area for studying the Inland paleoenvironment in China. Despite a long history of research on sandstones of the Sikouzi Formation at Guyuan, Ningxia, since it was discovered in 1921, there are still mang controversial issues such as sedimentary characteristics, the age, cause and environment of the section. In view of this, the field geological survey and laboratory experiment are systematically carried out, in light of lithology, sedimentary structures, surface features of quartz grains and grain size distribution. Then the detailed division of sandstone profile and quantitative analysis of sedimentary characteristics are conducted. On the basis of previous studies, this paper makes a systematic study of its origin, the chronology and paleoenvironment. Preliminary results show that: (1) This paper, sedimentary characteristics of these red sandstones are systematically analyzed, based on the lithology, sedimentary structures, surface features of quartz grains and grain size distribution. This study indicates that the true thickness of sandstone section is 285.6m. The sandstones are a combination of three kind of sedimentary facies. It shows as follows：The stage I are fluvial sediments. The stage II, as the main of the sandstones, belongs to the typical eolian sandstones. Furtherly, it can be speculated that the sedimentary environment is eolian sand dunes and eolian indunes. The stage III are inferred lacustrine sedimentary preliminarily. (2) Previous studies indicate: the chronologies of described lithostratigraphic associations are constrained by magnetostratigraphic results. The timing of these red sandstones, however, has been a controversial issue. Our research made an attempt at constraint on absolute chronology, but the result is not ideal. What can be concluded is that the previous results suggest Eocene to Oligocene age. (3) Compared with these sedimentary characteristics desert dunes and coastal dunes, the sandstones of the Sikouzi Formation in Guyuan, is attributed to sediment of inland desert. By the measurement of the wind directional indicator, the regularity of the paleoprevailing wind directions and pattern of the paleowind belts are revealed. It is considered that the desert was controlled by a planetary wind system. So combined with the paleoclimate and geotectonic setting of the study area, the Paleogene aeolian dunes located in the Chinese Paleogene arid belt, which is important for understanding the climate change process before the onset of the monsoon system. Furthermore, the transition from desert facies deposition of the Sikouzi Formation to lacustrine deposition may express itself through a reorganization of the regional climate from a previous planetary-wind-dominant zonal pattern to its present monsoon-dominant regime. |
| 中文关键词 | 固原 ; 寺口子组 ; 风成砂岩 ; 古近纪 ; 沙漠沉积 |
| 英文关键词 | Guyuan the Sikouzi Formation eolian standstones Paleogene desert sediments |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287949 |
| 推荐引用方式 GB/T 7714 | 杨帆. 六盘山北部寺口子组砂岩特征、成因及古环境[D]. 中国科学院大学,2017. |
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