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| 周口店东洞洞穴沉积物的地球化学特征及其环境指示意义 | |
| 引用本文： | 王海芝,程捷.周口店东洞洞穴沉积物的地球化学特征及其环境指示意义[J].第四纪研究,2008,28(6):1090-1097. |
| 作者姓名： | 王海芝 程捷 |
| 作者单位： | 1. 北京市地质研究所,北京,100011;中国地质大学,北京,100083 2. 中国地质大学,北京,100083 |
| 摘 要： | 周口店地区的古环境变化研究多数研究集中在中更新世时期,而缺乏对早更新世时期环境变化的研究。这主要是由于缺少保存完好的早更新世沉积记录造成的。随着对20世纪80年代在周口地区发现的东洞剖面,发现这是一个保存完好的早更新世剖面,为研究早更新世时期的古环境变化特征提供了良好的研究材料。为了重建早更新世时期的古环境变化特征,利用XRF对东洞洞穴沉积物的主要元素（SiO2,Al2O3,Fe2O3和CaO）的化学组成进行了高分辨率分析,同时对沉积物中的FeO含量进行了测试。结果显示东洞剖面沉积物的主要化学组成为SiO2,占41.6%～58.9%,其次是Al2O3和Fe2O3,其含量的变化范围分别为13.69%～29.63%和5.00%～9.81%。Al2O3和Fe2O3在剖面上与SiO2含量成明显的镜像变化关系,显示出Al2O3和Fe2O3对沉积物中SiO2含量的稀释作用。另外,Fe2O3与Al2O3在剖面上具有很好的相关性,表明Fe2O3主要富集在富铝的矿物中。从元素含量在剖面的上分布看,东洞剖面的化学组成发生3次大的波动,主要表现为SiO2和FeO含量增高,而Fe2O3与Al2O3含量的减少。这3次波动分别出现在剖面的15.3～14.6m,11.0～9.9m和8.40～7.84m深度处。在3次化学组成的波动出现的同时,指示沉积物风化程度和温度变化的Si/Al（SiO2/Al2O3）和FeO/Fe2O3比值也发生了明显变化,比值增高,指示了3次大的干冷事件。另外,在剖面上部（10.00～7.84m,即第2次事件以后）SiO2/Al2O3和FeO/Fe2O3比值变高且波动频繁,表明自第2次干冷事件后沉积区的环境变得不稳定,逐渐向冷干气候转变。东洞剖面的地球化学记录（SiO2/Al2O3和FeO/Fe2O3）与泾川黄土剖面的粒度曲线具有较好的对比性,支持了东洞剖面记录的环境信息与黄土沉积记录的环境变化具有一致性。通过与泾川粒度曲线的对比发现,东洞剖面记录的3次干冷事件在时段上分别对应于黄土-古土壤序列中的L26,L15和L13。 |
| 关 键 词： | FeO/Fe2O3 SiO2/Al2O3 东洞 周口店 早更新世 古环境 |
| 收稿时间： | 2008-03-20 |
| 修稿时间： | 2008-09-16 |
GEOCHEMICAL CHARACTERISTICS OF SEDIMENTS DEPOSITED IN THE DONGDONG CAVE AND THEIR ENVIRONMENTAL IMPLICATION |
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| Wang Hai-zhi,Cheng Jie.GEOCHEMICAL CHARACTERISTICS OF SEDIMENTS DEPOSITED IN THE DONGDONG CAVE AND THEIR ENVIRONMENTAL IMPLICATION[J].Quaternary Sciences,2008,28(6):1090-1097. | |
| Authors: | Wang Hai-zhi Cheng Jie |
| Institution: | 1. Beijing Institute of Geology, Beijing 100011; 2. China University of Geoscience, Beijing 100083 |
| Abstract: | The reconstruction of paleo-environment in Zhoukoudian region of Beijing is critical not only to unraveling the underlying mechanism of environmental changes in North China,but also to understand the relationship between the environment and the human evolution.However,most previous studies concentrated on environment changes in the Middle Pleistocene,few in the Early Pleistocene,during which well-preserved sediments were rarely deposited.The studies on sediments of the Dongdong Cave in the Zhoukoudian region,which began in the 1980s,show that the deposition is well-preserved and of the age of Early Pleistocene,providing an ideal site for reconstructing the environmental changes in that time.In order to characterize the pattern of environment changes,major element compositions of the sediments（SiO2,Al2O3,Fe2O3,CaO）have been analyzed by XRF with a high-resolution.At the same time,the content of FeO is also analyzed by traditional titrimetric method.Our result shows that SiO2 is the dominant mineral of the sediments in the Dongdong Cave with a range of 41.6%～58.9%.Al2O3 and Fe2O3 are the second and third important components,ranging from 13.69% to 29.63% and 5.00% to 9.81%,respectively.The contents of Al2O3 and Fe2O3 display an obvious mirror variation with that of SiO2 along the Dongdong profile,indicating the dilution of Fe2O3 and Al2O3 to the SiO2 concentration in the sediments.Fe2O3 shows a well correlation with Al2O3,suggesting that Fe2O3 is mainly enriched in Al-enriched minerals.Three big perturbations of the elemental compositions are identified in the Dongdong profile,which are characterized by high concentration of SiO2 and FeO,and low contents of Al2O3 and Fe2O3.These three perturbations occur individually in the intervals of 15.3～14.6m,11.0～9.9m,and 8.40～7.84m.Coinciding to the perturbations of the major element concentrations,Si/Al（SiO2/Al2O3）and FeO/Fe2O3 ratios,which have close associations with degree of weathering intensity and temperature,also increase.The high ratios of SiO2/Al2O3 and FeO/Fe2O3,together with the increase of SiO2 and the decrease of Al2O3content,suggest a cold and dry environment,and three big clod and dry events occurring in the Early Pleistocene are recorded in the Dongdong sediments.In addition,the values of SiO2/Al2O3 and FeO/Fe2O3 ratios are relatively high and display high-frequent vibrations in the upper section（10.00～7.84m,after second event）.This pattern suggests that environment become more unstable,cold and dry after the second event.The chemical records（SiO2/Al2O3 and FeO/Fe2O3 ratios）of the Dongdong section display a well correlation with the grain size curve of the Jingchuan loess sequence,supporting that the chemical compositions of sediments in the Dongdong Cave are controlled by similar mechanisms to that for Chinese loess.The comparison of the elemental ratios of the Dongdong section with the grain size curve of the Jingchuan shows that the three cold and dry events individually correspond to the L 26,L 15,and L 13 in time. |
| Keywords: | FeO/Fe_2O_3 SiO_2/Al_2O_3 Dongdong Zhoukoudian Early Pleistocene paleo-environment |
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