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| 黄河上游全新世特大洪水及其沉积特征 | |
| 引用本文： | 杨晓燕,夏正楷,崔之久.黄河上游全新世特大洪水及其沉积特征[J].第四纪研究,2005,25(1):80-85. |
| 作者姓名： | 杨晓燕 夏正楷 崔之久 |
| 作者单位： | 1. 中国科学院地质与地球物理研究所,北京,100029;北京大学环境学院,北京,100871 2. 北京大学环境学院,北京,100871 |
| 基金项目： | 国家自然科学基金;国家自然科学基金;高等学校博士学科点专项科研项目 |
| 摘 要： | 黄河上游官亭盆地的黄河二级阶地面上沉积了厚约2m左右的平流沉积物,每次洪水形成1个由红色粘 土水平层和黑灰色粘土水平层组成的洪水单元。对研究剖面洪水沉积层的磁化率测量区分出了14个洪水单元, 代表了14次特大洪水的发生;利用盆地内的考古资料,将古洪水频繁发生的时期定为3700～2800aB.P.。粒度分 析表明官亭盆地平流沉积的沉积物几乎全部由粒径小于4φ的悬移物质组成,其分选系数>2,偏度<0,峰态中等。 与黄河中游进行比较,官亭盆地的平流沉积粒级更小,偏度更小且呈负偏。 |
| 关 键 词： | 黄河上游 官亭盆地 平流沉积 全新世特大洪水 沉积特征 |
| 文章编号： | 1001-7410(2005)01-80-06 |
| 收稿时间： | 2004-10-11 |
| 修稿时间： | 2004年10月11 |
HOLOCENE EXTREME FLOODS AND ITS SEDIMENTARY CHARACTERISTIC IN THE UPPER REACHES OF THE YELLOW RIVER |
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| Yang Xiaoyan,XIA Zhengkai,Cui Zhijiu.HOLOCENE EXTREME FLOODS AND ITS SEDIMENTARY CHARACTERISTIC IN THE UPPER REACHES OF THE YELLOW RIVER[J].Quaternary Sciences,2005,25(1):80-85. | |
| Authors: | Yang Xiaoyan XIA Zhengkai Cui Zhijiu |
| Institution: | 1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029; 2. College of Environmental Sciences, Peking University, Beijing 100871 |
| Abstract: | Over the past two decades, analysis of slackwater sediments has become a widely accepted tool in palaeoflood research. This paper reports a period of enhanced palaeoflood activity during Holocene that recorded in a suit of overbank slackwater sediments found on the second terrace of the upper reaches of the Yellow River at the Guanting basin, and the sedimentary characteristic of slackwater deposits. Since each flood units in slackwater sediments occur as couplets, we used a portable Bartington susceptibility meter to discern the number of couplets as the organic rich deposits cause a magnetic susceptibility variation. 14C dating samples collected from archaeological sites relative to palaeofloods determine the timing of the period, and grain size analysis was undertaken to examine the sedimentary characteristic of slackwater deposits. There are abrupt changes in color, grain size, and sedimentary type between the slackwater deposits and the underlaid floodplain sediments. Floodplain sediment is uniform brownish-yellow fine silt-sand, significant different froM Slakcwater sediments that alternate between red clayed-silt and grayish-black silty-clay with horizontal bedding. The curve of magnetic susceptibility for slackwater sediments has 14 fluctuations. The wave crests correspond to the grayish-black layers due to organic matter, while the wave troughs correspond to the brownish-red layers. 14 fluctuations imply at least 14 extreme floods because the profile only records the floods whose backwaters are capable of overtopping previously existing slackwater sediments. Two samples of wood recovered from two late Qijia refuse pits immediately under slackwater sediments at the Lajia Site, which yielded two radiocarbon ages of 3 678±75aB.P.(cal.) and 3 875±70aB.P.(cal.) suggest the start of slackwater deposits. In the upper of the slackwater sediments, an organic matter sample was sampled from the ruins of the Xindian culture buried in the slackwater sediment, Lamafeng Site, including fragments of Xindian potteries and bones in a large amount of ashes. 14C dating of ashes produced an age of 2 775±50aB.P.(cal.). And settlements of the mid-late Xindian sites have been found on top of the slackwater sediment. Radiocarbon dating of a single piece of animal bone in a securely stratified archaeological context at one of these settlement sites provided a radiocarbon date of 2 685±50aB.P.(cal.) and provides an upper age limit for the end of slackwater deposits, although it is acceptable that there could be a prolonged hiatus between the date provided by the animal bone and the final deposition of the sediments. Thus we inferred that there was an enhanced extreme flood activities during ca. 3 800～3 700aB.P. The grain size analysis reveals that the slackwater deposits are almost composed of suspended loads. The average grain diameter is ca.6, the sorting coefficient is less than 2 and the coefficient of skewness is less than zero. Compared with the sedimentary characteristics of slackwater deposits in the middle reaches of the Yellow River, the average grain diameter and the coefficient of skewness are smaller in the upper reaches. |
| Keywords: | the upper reaches of the Yellow River Guanting Basin slackwater deposits Holocene extreme flood sedimentary characteristic |
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