Knowledge Resource Center for Ecological Environment in Arid Area
| 渤海湾地区末次冰期古环境 | |
| 旺罗 | |
| 出版年 | 2000 |
| 学位类型 | 博士 |
| 导师 | 刘东生 |
| 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 | 中国黄土-古土壤序列是古气候变化和古环境演化的重要陆相记录。沿海地区的黄土堆积为冰期北方干旱化问题研究提供了可利用的材料。本文以渤海沿岸黄土沉积为研究对象，在地层划分对比和定年的基础上，结合粒度、磁化率以及渤海沿岸黄土中特有的海相有孔虫化石的变化特征，探讨末次冰期渤海地区的古环境变化。以热释光和~(14)C测年为基础，结合磁化率、粒度的变化和生物地层学研究，作者对渤海沿岸蓬莱林格庄、长岛王沟阳坡、长岛王沟阴坡、砣矶岛后口呼砣矶岛井儿等5个黄土剖面进行综合分析发现渤海沿岸黄土地层都保存不太完整，一些剖面中缺失氧同位素2阶段沉积的黄土，并且同一时期沉积的黄土厚度有巨大的差异。尽管黄土高原的黄土和渤海沿岸的黄土具有不同的物质来源，但粒度和磁化率的变化同样具有较好的相关关系，渤海地区黄土磁化率和粒度的变化特征记录了该区末次冰期的气候变化。渤海沿岸黄土的沉积速率与黄土高原沙漠边界的黄土堆积速率差不多，粗颗粒组分的含量也较高，说明本区冰期时干旱化已达到一定的程度，使该区能够产生足够的粉尘，并在风的搬运下堆积形成黄土。但是，根据粗颗粒（>60μm）在空间上的变化和磁化率的变化显示冰期时陆架可能并未达到沙漠化的程度。这些粗颗粒一般只能以跃移的形式被搬运，即很难被风吹扬至高空而以悬移的形式输送，在没有植被的沙漠内部，以跃移运动的粗砂可作远距离的搬运，但其一旦离开沙漠，在地表植被的作用下，将很快沉积下来。渤海沿岸的黄土是近源堆积的产物，因此粗颗粒含量较高是必然的，但粗颗粒的含量在各剖面中具有巨大的差异，显示从北到南迅速递减的规律，比同一时期可能处在沙漠中的榆林到吴堡地区递减的速率快3倍多。此外，本区冰期时黄土的磁化率比黄土高原沙漠边界处的黄土磁化率灵敏性高，具有频繁的波动，而磁化率的变化只有在一定的温湿条件下才能显现出来。说明渤海地区末次冰期时比黄土高原沙漠边界边同一时期的植被发育程度高，气候也相对湿润。从138个样品中鉴定出46属，71种。黄土中含有大量的海相有孔虫化石，说明时宜海沿岸的黄土沉积与海平面的变化有着密切的关系，即只有海平面下降，陆架暴露后海相沉积物成为物源，在风的搬运下堆积形成富含有孔虫化石的黄土。但是本次研究发现并非所有冰期沉积形成的黄土中都含相对丰度较高的有孔虫化石，通过进一步的分析，认为这种差别是由于海平面下降时，河流输砂量不同造成的。因为河流输砂量直接影响海相沉积物中有孔虫化石的含量。冰期黄土中有孔虫化石的这种差别，说明同样是海平面下降，但不同时期海平面下降时可能具有巨大的差别。另外，氧同位素4阶段沉积的黄土中有孔虫化石丰度也具有频率的波动，并且与磁化率、频率磁化率具有很好的相关关系，通过化石分异度和均衡度的进一步分析认为这种频繁的化石丰度变化可能主要是溶蚀作用造成的。化石的丰度和磁化率的变化都与降水量有直接的关系，而降水量主要是受夏季风控制，因此说明东亚夏季风可能也具有迅速而频繁的变化。渤海沿岸地区间冰期古土壤中含有一定量的砾石，此外，氧同位素3阶段和末次间冰期高海平面时期发育的古土壤层也含有海相有孔虫化石，说明渤海沿岸地区的粉尘堆积主要发生在冰期，而间冰期时期主要是在黄土母质上妈育古土壤和水流搬运堆积形成次生黄土的时期。也就是说，渤海地区的干旱化可能仅发生在冰期。 |
| 英文摘要 | The loess-paleosol sequence in China is one of the best archives for studying paleoenvironmental and paleoclimatic processes. The loess deposits in the coast of the Bohai Sea are suitable for the study of aridification in the northern China during glacial periods (fig.2-1). In this paper, stratigraphy was correlated by using magnetic susceptibility, grain size, and thermoluminence (TL) and accelerater mass spectrometer (AMS) ~(14)C ages. Based on the loess records, an interpretation has been made for paleoenvironmental changes on the coast of the Bohai Sea during the last glacials. The results of magnetic susceptibility, grain size, biostratigraphy, TL and ~(14)C dating, suggest that the loess-paleosol sequence in the coast of the Bohai Sea is discontinuous. The loess deposits correlated with the marine δ~(18)O stage 2 are usually absent in some profiles. Also, the thickness of the loess deposits in the same period varied significantly in different sections. In the coast of the Bohai Sea, the higher magnetic susceptibility corresponds to the finer grain size, consistent with the results of the Loess Plateau. It is indicated that the changes in magnetic susceptibility and grain size may record the paleoclimatic fluctuations of the last glacial. Although the loess deposits during the last glacial have been slightly altered by slope runoff, they have still remained main characters as the representative loess deposits of the Loess Plateau. During the last glacial, the less accumulation rate in the coast of the Bohai Sea is similar to that of the desert-loess transition zone in the northwestern Loess Plateau, and the all section contain high concentrations of sand (>60μm), indicate that the aridification in the Bohai Sea occurred during the glacial. But the changes in sand content of loess deposits along a north-south transect of the Bohai Sea and the changes of magnetic susceptibility implicate that desertification might not occur in the shelf of the Bohai Sea during the last glacial. The frequent fluctuations of summer monsoon during the marine δ~(18)O stage 4 are demonstrated by magnetic susceptibility, frequency-dependent susceptibility and the abundance of foraminifera. 46 genera, 71 species of foraminifera were identified from 138 loess samples. Almost all of the foraminifera are present in the last glacial loess, but the distribution patterns of foraminifera show significant temporal changes. The results of magnetic susceptibility, grain size and XRD indicate that not only sea-level changes had influences on foraminifera abundance, but also variations in sediment flux by rivers when sea-level drops might control the abundance of foraminifera. In addition, the diversity and exquitability of the foraminifera suggest that the frequent fluctuations of foraminifera fossil abundance during the marine δ~(18)O stages could be partly attributed to leaching. In summary, the changes in foraminifera of abundance related to the paleoclimatic variations, and the aridification extends to the coast of the eastern China during the last glacial. |
| 中文关键词 | 渤海 ; 黄土 ; 末次冰期 ; 有孔虫 ; 古环境 |
| 英文关键词 | the Bohai Sea loess the last glacial foraminifera paleoenvironment |
| 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/2XILL650/286246 |
| 推荐引用方式 GB/T 7714 | 旺罗. 渤海湾地区末次冰期古环境[D]. 中国科学院地质与地球物理研究所,2000. |
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