Knowledge Resource Center for Ecological Environment in Arid Area
| 晚中新世以来中国北方风成沉积的磁性地层学和沉积学研究 | |
| 杨石岭 | |
| 出版年 | 2001 |
| 学位类型 | 博士 |
| 导师 | 丁仲礼 |
| 学位授予单位 | 中国科学院地质与地球物理研究所 |
| 中文摘要 | 本论文对泾川和灵台两个厚度较大的红粘土序列进行了磁性地层学和沉积学研究。古地磁研究表明，泾川剖面的底界年龄为8．O Ma，这比灵台剖面的底界年龄老1．O Ma。以往的研究(Ding et a1., 1999a)将灵台红粘土序列从顶到底划分为五套地层。野外观察表明，泾川红粘土序列从顶到底可以分为六套地层。根据灵台和泾川剖面的磁化率和颜色记录，泾川红粘土序列上部的五套地层总体上可同灵台红粘土序列的五套地层对比。泾川、灵台、西峰和蓝田红粘土剖面的地层对比结果表明，灵台红粘土序列相对较为完整和连续，可以作为中国北方晚第三纪红粘土的标准剖面。黄土和现代尘暴沉积的粒度分布均呈现为单峰态。黄土高原S2以上南北向大断面的沉积学研究表明，黄土的中值粒径、偏度和峰度在时间和空间上的沉积分异较为显著。这种分异特点在中值粒径、偏度和峰度的三角图中可以清晰地反映出来。灵台和泾川红粘土序列的粒度分布亦呈单峰态，其粒度分布特征与黄土中古土壤的粒度分布特征类似。灵台和泾川黄土-红粘土序列在中值粒径、偏度和峰度三角图中的投影特征表明，黄土-古土壤-红粘土应是同一种沉积动力搬运和分异的产物。以上沉积学特征表明，这两个红粘土序列是风成沉积。由此，黄土高原风成沉积的下界至少可追溯至8.0 Ma前后。一些地质记录表明，末次冰盛期时中国北方沙漠的分布范围同现代基本一致(Sun J. et a1.，1998)。通过对末次冰盛期时南北向黄土大断面粒度参数的系统分析，初步建立了“粉尘沉积的粒度参数—沉积区距源区最小距离”的半定量模型。根据这个模型推测，泾川和灵台红粘土堆积时期其距源区的最小距离约为600 km，即红粘土的主要源区可能在现代的巴丹吉林沙漠及其以西地区。这个距离远远大于黄土堆积时沉积区距源区的距离。灵台黄土-红粘土序列的游离铁／全铁值变化表明，晚中新世以来东亚夏季风经历了非线性的演化历史。约4.1-4.8 Ma间为黄土高原地区7．0 Ma以来东亚夏季风最为强盛的时期。该气候事件的出现可能同全球温度背景较高及全球冰量较小有着动力学上的联系。 |
| 英文摘要 | The past two decades have witnessed an unprecedented growth of interest in the palaeoenvironmental significance of the Pleistocene loess deposits in northern China. However, it is only several years ago that the Tertiary red clay sequence underlying Pleistocene loess attracted much attention. One of the major advances in recent studies of eolian deposits on the Loess Plateau is the verification of the eolian origin for the Tertiary red clay sediments. The evidence of the eolian origin for the red clay is mainly from geochemical and sedimentological studies. However, sedimentological studies of the red clay deposits are still few compared with those of the overlying loess sediments. To date, the red clay sections located near Xifeng, Baoji, Lantian, Jiaxian, and Lingtai have been studied, with an emphasis on magnetostratigraphy. These sections have a basal age ranging from ～4.3 Ma to ～7.0 Ma. The thickness of the sections varies significantly, depending perhaps on the development of local geomorphological conditions and the drainage system. Although the stratigraphy of the red clay sections has been recorded in some detail, correlation of the red clay sequences has not yet been undertaken. Geological records (Sun J. et al., 1998) have shown that during glacial periods of the Quaternary the deserts in northem China were greatly expanded compared with modern desert distribution. During interglacial periods, desert areas contracted and retreated mostly to northwestern China because of the increase in inland penetration of monsoonal precipitation. According to pedogenic characteristics of the red clay deposits, the climatic conditions of the Loess Plateau is warmer and wetter generally in the Neogene than in the late Pleistocene. Panicle analyses show that grain size distribution of the red clay sequence is similar to that of the paleosols in the Pleistocene loess record, thus implying a relatively remote provenance of the red clay materials. However, the quantitative or semiquantitative estimates of the distance from the source region to the Loess Plateau during the red clay development remains to be investigated. In this study, magnetostratigraphic and sedimentological studies are conducted at two thick red clay sequences-Jingchuan and Lingtai section. The objectives of these studies are focused on further sedimentological evidence for the eolian origin of the red clay, correlation of red clay sequences, provenance of the red clay, and the palaeoclimate reconstruction in the Neogene. Paleomagnetic studies show that the Jingchuan red clay has a basal age of 8.0 Ma, which is 1 million years older than the previously studied Lingtai section. The Lingtai red clay sequence was divided into five units on the basis of pedogenica characteristics (Ding et al., 1999a). The Jingchuan red clay sequence, however, can be lithologically divided into six units according to field observations. The upper five units of the Jingchuan red clay can generally correlate well with the five units of the Lingtai red clay. Comparison of magnetic susceptibility and color reflectance records of four red clay sections suggests that the Lingtai red clay sequence can be the type-section of the Neogene red clay deposits in northern China. Pleistocene loess and modem dust deposits have a unimodal grain-size distribution. The red clay sediments at Jingchuan and Lingtai also have a unimodal grain-size distribution especially similar to the paleosols in the Pleistocene loess record. Sedimentological studies of a north-south transect of loess deposits above S2 on the Loess Plateau show that loess deposits had distinct temporal and spatial sedimentary differentiation. The characteristics of such sedimentary differentiation can be well presented in a triangular diagram of normalized median grain size, normalized skewness, and normalized kurtosis. The triangular diagrams of the red clay-loess sequence at Lingtai and Jingchuan indicate that loess-paleosol-red clay may be transported and sorted by the same agent wind, thus extending the eolian record in the Loess Plateau from 2.6 Ma back to about 8.0 Ma. It has been recognized that during the last glacial maximum (LGM) the deserts in northern China had a distribution similar to the present, whereas during the Holocene Optimum the deserts retreated to the area west of the Helan Mountains. Advance-retreat cycles of the deserts will lead to changes in the distance of the Loess Plateau to the dust source regions, thereby controlling changes in grain size of the loess deposited in a specific site. To observe spatial changes in sedimentological characteristics of loess during the last glacial-interglacial cycle, the texture of loess was measured along the north-south transect of the Loess Plateau. Since the southern margin of the Mu Us desert during the LGM is already known, several models of grain size parameters versus the minimum distance from the source region to depositional areas were developed. According to these semiquantitative models, the minimum distance from the source region to Lingtai and Jingchuan areas is about 600 km during the Neogene. Therefore the estimated provenance of the Tertiary red clay deposits is the areas now occupied by the Badain Jaran desert and arid regions west of it. The ratio of the free iron to total iron concentration attests to being a good proxy indicator for the summer monsoon evolution. The Lingtai Fe_20_3 ratio record shows high values over three time intervals: 4.8-4.1 Ma, 3.4-2.6 Ma, and during the interglacial periods of the past 0.5 Ma. The increase in summer monsoon intensity over the three intervals also coincides with the well-developed soil characteristics. It is therefore concluded that the East-Asia summer monsoon has experienced a non-linear evolution since the late Miocene. In general, the East Asia summer monsoon was stronger in Neogene than in Quaternary and the strongest East Asia summer monsoon may occur between 4.1 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene. |
| 中文关键词 | 黄土 ; 红粘土 ; 风成沉积 ; 粒度 ; 游离铁／全铁值 |
| 英文关键词 | loess red clay eolian deposits grain size the ratio of the free iron to total iron concentration |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/286267 |
| 推荐引用方式 GB/T 7714 | 杨石岭. 晚中新世以来中国北方风成沉积的磁性地层学和沉积学研究[D]. 中国科学院地质与地球物理研究所,2001. |
| 条目包含的文件 | 条目无相关文件。 | |||||
| 个性服务 |
| 推荐该条目 |
| 保存到收藏夹 |
| 导出为Endnote文件 |
| 谷歌学术 |
| 谷歌学术中相似的文章 |
| [杨石岭]的文章 |
| 百度学术 |
| 百度学术中相似的文章 |
| [杨石岭]的文章 |
| 必应学术 |
| 必应学术中相似的文章 |
| [杨石岭]的文章 |
| 相关权益政策 |
| 暂无数据 |
| 收藏/分享 |
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。
