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1.
《Boreas: An International Journal of Quaternary Research》2018,47(3):954-966
A loess‐palaeosol succession from the last glacial cycle was palaeomagnetically studied in the Rivne abandoned brickyard (western Ukraine). Two samples of undisturbed loess from the same depth of parallel sections display steep negative inclinations. These reversed directions in the loess dated at c. 18 ka may possibly be correlated with the Hilina Pali palaeomagnetic excursion. This is the first occurrence of the Hilina Pali in a loess sediment. Unfortunately, the loess with negative inclination does not form any continuous layer that could be suitable for studies of detailed features of geomagnetic field inversion. Another six samples from an illuvial horizon of the Holocene soil also showed negative inclinations and strongly deviated declinations. This part of the section does not represent, however, any palaeomagnetic excursion. The anomalous magnetization in maghemite‐ and titanomagnetite‐rich sediment results most probably from self‐reversal remagnetization. A new insight into palaeomagnetic excursions noted in loess, especially in its parts affected by pedogenic processes, is recommended. 相似文献
2.
环县剖面的古地磁研究结果表明，在第一层古土壤S1的上部和下部分别存在两个地磁场异常。通过剖面磁化率曲线与深海沉积物氧同位素曲线的对比，建立了地磁场变化的时间序列。S1上部记录的地磁场异常，年龄与挪威-格陵兰海及大西洋中发现的地磁异常年龄相当。S1下部的地磁异常，以磁偏角方向强烈摆动，偶极磁场强度明显下降为特征，其年龄与报道的布莱克事件的年龄相当，也与索马里海和地中海所记录的大幅度偶极磁场减弱相吻合，但与西宁剖面的记录不同的是，环县剖面记录的地磁场从没有达到完全的倒转，VGP曲线表现为围绕采样点旋转的经过南半球低纬地区的大环。这些特征表明，在偶极磁场减弱期，具有强烈区域性的非偶极磁场的变化可能对地磁场起着重要的作用。 相似文献
3.
本文以欧亚黄土中记录的布容一松山极性倒转界线为例,简要回顾近年来对黄土中 古地磁极性界线地层学解释的讨论。研究表明,由于在记录古地磁极性转换时存在不同程度 的“错位”,黄土中所测的极性界线的年代地层意义存在很大的不确定性。就中国黄土而言,第 ８层黄土（Ｌ８）中下部或第８层古土壤（Ｓ８）顶部测得的布容－松山界线系“错位”的产物,该层位 的年龄应老于 ０．７９ＭａＢ．Ｐ。对黄土中测得的Ｃｏｂｂ Ｍｏｕｎｔａｉｎ极性事件界线进行地层学解释, 推论蓝田猿人化石层位的年龄１．２ＭａＢ．Ｐ。 相似文献
4.
洛川黄土地层定年的一个模式及其初步应用 总被引：13，自引：0，他引：13
选择黄土中２～１６μｍ的颗粒作为沉积速率相对稳定的大气粉尘沉降组分，根据黄土粒度变化与沉积速率变化的相关性，设计了以下的年代学模型:Ｔｍ＝Ｔ１＋（Ｔ２－Ｔ１）（∑ｍｉ＝１ＣｉＨｉ）/（∑ｎｉ＝１ＣｉＨｉ）以黄土地层中根据热释光和古地磁极性倒转点获得的绝对年代作为时间控制点，利用上面的模式对洛川第四纪黄土地层的年代进行了计算，结果表明该模式可以用于黄土高原中部黄土地层的精细定年。 相似文献
5.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》1999,24(9):785-792
Previous work has demonstrated that magnetic properties and sediment particle size of Chinese loess deposits provide information on past behaviour of Chinese summer and winter monsoons, respectively (Heller and Evans, 1995; Derbyshire et al, 1997). It has been suggested that the East Asian winter monsoon system in particular is teleconnected on earth orbital and sub-orbital timescales to climatic states and events in high northern latitudes, especially northern hemisphere ice volume and Heinrich events, (Porter and An, 1995; Chen et al., 1997). However, the majority of this research has been performed around the central part of the Chinese Loess Plateau where the rate of dust accumulation is relatively low, thus limiting the potential resolution of palaeoclimatic records. Here we present a high resolution (5mm / ~20 yr interval) magnetic susceptibility record from an thick loess deposit located at Caoxian in the north-western part of the Loess Plateau. The record spans the “Lateglacial” (last glacial / interglacial transition) and when placed on a palaeomagnetic chronology shows a relationship with the GISP2 proxy air temperature record from Greenland (Grootes et al., 1993; Meese et al., 1994; Stuiver et al 1995). The results demonstrate that several Lateglacial climatic fluctuations previously reported in the North Atlantic region and in Europe are also recorded in China. In addition, the apparent absence of a signal corresponding to the Bølling Interstadial in China during the early deglaciation suggests that, at certain times, the apparent North Atlantic — Asian monsoon teleconnection may have collapsed. The demonstrated ability of the loess deposits to resolve sub-millennial scale climate variations points to their potential as a previously unexplored archive for very high-resolution studies of terrestrial climate. 相似文献
6.
陕西段家坡黄土剖面中布容／松山古地磁界线附近铱异常的发现及其启示 总被引：3，自引：0，他引：3
利用高灵敏度放射化学中子活化分析方法,对我国陕西段家坡黄土剖面早－中更新统（约０．７３Ｍａ）沉积界线附近铱和其它元素的丰度进行了测定。结果表明,在布容／松山（Ｂ／Ｍ）古地磁界线附近铱的含量明显增大,最大值为４６．３ｐｇ／ｇ。相对于整个剖面的平均背景值（约１５ｐｇ／ｇ）大约富集了３倍。用地壳元素钪进行标准化之后,铱异常十分明显,而其它元素在界线附近则没有变化。黄土剖面上铱异常的赋存层位与西南太平洋钻 相似文献
7.
Edward Derbyshire Armelle Billard Brigitte Van Vliet-Lanoë Jean-Pierre Lautridou Mauro Cremaschi Cnr 《第四纪科学杂志》1988,3(2):147-169
In 1985, a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western Europe was initiated jointly by laboratories in Leicester, Meudon, Caen, Milan, Cardiff and Southampton, involving a limited amount of comparative work on the loess from types sites in the Loess Plateau of central China. Preliminary results include the following: (1) Experimental procedures in particle size analysis, clay sample preparation and microscopy have been standardised in all cooperating groups; distinctive fabrics indicative of depositional mechanisms have been recognised. (2) Comparison of aeolian, colluvial and alluvial silt by laser-scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re-deposited by slope processes and flowing water. (3) The variability in the anisotropy of the limon à doublet facies has been assessed by image analysis of scanning electron microscopy (SEM) and optical microscopy. Strong anisotropy has also been measured in thin section imagery of loess from Normandy and Poland as the product of freezing and thawing. This is confirmed by scanning electron microscopy and by experimental freezing of some silts. (4) The clay fabric and mineralogy in western European loess differ from those in Chinese loess, especially in the case of semi-arid deposits. (5) Distribution of CaCO3, using thin sections and SEM analysis, has been determined for loess from Normandy and the Rhǒne valley in France and for some Chinese loess, At Saint Vallier, zones of CaCO3 concentration occur masking much of the original (loess) sedimentary skeleton which is a locally reworked loessic silt with some laminations. Despite considerable scatter, the palaeomagnetic results indicate a reversed polarity throughout, placing the whole Saint Vallier sequence in the Matuyama chron. These preliminary results suggest the existence of two different palaeoenvironments: one typified by central China, with arid glacials and humid interglacials; and the other represented by western Europe, with generally high humidities. There was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern Italy than in western littoral Europe. 相似文献
8.
东秦岭南洛河上游黄土地层年代的初步研究 及其在旧石器考古中的意义* 总被引：8，自引：1，他引：7
近年来,在东秦岭南洛河流域发现了大批旧石器地点,该区域被认为是中国南北方旧石器工业的交汇和过渡地带。但是,早期人类在这一带的活动时间和环境背景尚不清楚。由于第四纪黄土的定年方法相对成熟,旧石器遗址的黄土堆积可为解决这些问题提供重要证据。对洛南盆地上白川和刘湾两个遗址的黄土剖面进行土壤地层和磁性地层研究以及光释光年龄和磁化率测定结果显示,该地区的黄土堆积可能从110万年前就已经开始,地层有明显的黄土-古土壤旋回,指示了气候和环境在冰期-间冰期时间尺度的变化。黄土地层下部出土的石制品表明,至少在约80万年前后人类就在这一带活动并制作工具。石制品两面加工技术被广泛采用,大量制作精美的手斧和薄刃斧等Acheulian工业类型工具的发现,显示洛南盆地的旧石器工业可能已经突破了"莫氏线(Movius Line)"的框架。 相似文献
9.
10.
南京地区下蜀黄土磁性地层年代与古环境变化 总被引：2，自引：0，他引：2
通过对南京江北泰山新村下蜀土剖面所采的144个样品和南京江南燕子矶下蜀土剖面所采的467个样品所进行的古地磁测年、磁化率测量和粒度测定,建立了南京地区下蜀黄土地层220kaB.P.以来较精细的时间标尺;在此工作基础上,将南京下蜀黄土堆积所记录的环境信息同北方经典黄土、深海沉积氧同位素记录进行了对比,发现燕子矶剖面磁化率曲线能够与深海沉积氧同位素曲线1—7阶段进行良好的对比,两者之间的细节变化具有一致性,其中S0表现为高值,可与氧同位素曲线阶段1对比,为一高温期;L1可以划分为两层黄土(L1LL1、L1LL2)和一层弱发育的古土壤(L1SS1),L1LL1和L1LL2可与阶段2和4对比,L1SS1可与阶段3对比;S1古土壤层由3个古土壤亚层(S1SS1、S1SS2、S1SS3)和2个弱成土亚层(S1LL1、S1LL2)叠置而成,磁化率曲线具有明显的三峰夹两谷形式,正好可与氧同位素阶段5对比,表明这一时期的古气候特点是在湿热的背景下有两次干冷波动,其中S1SS1、S1SS2、S1SS3分别对应于5a、5c、5e,S1LL1、S1LL2对应于5b、5d;L2黄土磁化率曲线整体呈谷形,但中下部有一次峰,下部磁化率偏高,与阶段6的曲线特征相吻合;S2古土壤层未见底,目前获得的磁化率曲线特征可与7a和7b对比。以上研究结果确立了江南风尘堆积的古气候全球变化意义。 相似文献
11.
黄土高原陆面过程试验研究(LOPEX)有关科学问题 总被引：28，自引：7，他引：21
主要讨论了黄土高原陆面过程野外科学试验研究项目的有关科学技术问题。首先从科学和现实角度说明了开展黄土高原陆面过程试验研究（LOPEX）的意义,并从黄土高原陆面过程野外观测和特征分析、黄土高原陆面水分过程特征及其对生态生理过程的影响、黄土高原陆面过程参数化研究等3个方面介绍了该科学试验研究项目的主要研究内容和重点要解决的科学问题,而且还初步探讨了黄土高原陆面过程试验研究的技术难点以及解决这些技术难点的主要科学技术思路。 相似文献
12.
DECOUPLED SUMMER AND WINTER MONSOON IN NORTHEAST TIBET AND NORTHWEST LOESS PLATEAU DURING THE LAST INTERGLACIATIONtheNationalKeyProjectforBasicResearchonTibetPlateau (G19980 4 80 0 )andtheNationalNaturalSci
encesFoundationofChina (No.4 990 相似文献
13.
地质科学研究要以人为本,从可持续发展出发,开拓地质多样性,有所为有所不为.中国黄土研究经历了发现研究、比较研究和目的研究3个层次阶段,今后需要加强目的研究.中国已有条件从黄土所保存的各种信息,以揭示新生代以来全球干旱化的机制、规律和人类活动影响为目的,从区域性走向全球性研究,提出黄土"地质生态系统”研究的概念.基础研究方面,讨论了1)黄土序列连续性和间断性的间断平衡(PUNCTUATED EQUILIBRIUM)问题;2)黄土全球分布形成机制一元论问题;3)黄土地貌形态与地壳运动表现问题.应用研究方面,讨论了1)健康与黄土区域地球化学与地质生理学(GEOPHYSIOLOGY)问题;2)建设城乡与黄土地质生态结构问题;3)农业与黄土区域生态系统管理评价(REGIONAL ECOSYSTEM ASSESMENT).认为在黄土研究中会遇到社会和技术发展方面的挑战,但关键是科学工作者自己的挑战. 相似文献
14.
Loess is mainly distributed in arid and semiarid areas of the world, and water is essential and precious in the loess areas. Water is also an important factor inducing various geohazards and soil erosion in the loess areas. The thematic issue of Environmental Earth Sciences was edited to reflect the latest research on water and water-related themes in the loess areas of the world, especially on the Chinese Loess Plateau. This editorial introduced the background and initiative of editing this thematic issue, and it also introduced briefly the water environment projects currently underway on the Chinese Loess Plateau such as the grain for green project, the huge land creation project, and the sponge city project. The papers included in the thematic issue were also introduced to give readers a general understanding of their main research points. Finally, some suggestions to boost further water environment research in the loess areas were put forward. All the papers included in the thematic issue will scientifically support the sustainable socio-economic development in the loess areas of the world. 相似文献
15.
为了解黄土三轴剪切过程中的微观变化,采用PFC3D建立黄土三轴试验模型,模拟围压分别为0、50、150、300 kPa的三轴剪切试验,并与室内试验进行对比分析。分析结果表明：PFC3D能够较好地模拟出不同围压下从开始到破坏到残余变形整个过程中应力-应变的变化规律,且位移场及接触应力场的变化规律与室内三轴试验宏观现象较一致;发现弹性模量、泊松比及峰值强度与数值模型中微观参数有着密切的联系,如法向刚度kn控制试样宏观弹性模量,kn /ks值控制泊松比,摩擦系数控制峰值强度;通过体应变-轴向应变曲线发现,随着围压的增加应变能增大,试样呈现出由体积膨胀到体积减缩的变化规律。其研究结果为进一步探究黄土的应力-应变性状及抗剪强度特性提供参考。 相似文献
16.
为研究原状马兰黄土的渗透各向异性,以延安削山造地重大工程开挖所揭露的完整黄土剖面中的马兰黄土层为研究对象,采用室内变水头渗透试验获取不同埋深不同渗流时长原状黄土垂直向和水平向的渗透系数,并对试验前后黄土试样垂直向和水平向SEM（scanning electron microscope）电镜扫描结果进行分析,从微观结构上揭示原状马兰黄土结构各向异性的原因。结果表明：原状黄土垂直向和水平向饱和渗透系数具有显著各向异性,且垂直向和水平向渗透系数都随渗流时间的持续而减小,各向异性渗透性能在时间尺度上具有某种衰减关系;同时,原状黄土各向异渗透性能随埋深的增大而逐渐减弱;土颗粒结构的接触、排列方式是导致黄土原生各向异性的根本原因,也是导致渗流初始阶段渗透系数各向异性的原因,而渗流作用产生的次生结构各向异性则使渗透系数各向异性在时间尺度上表现得更为明显。 相似文献
17.
Guo Jianyang 《岩土力学》1985,6(1):1-9
The paper presents the results of the laboratory research about the shear strength and the structural strength of loess at Gubaizui. Gubaizui loess behaves like creep, and its long time shear strength is lower than its peak value(cq) during direct shear tests, the ratio between these value is about 0.51~0.75(when normal stress σ=0.1~0.5MPa). It is found that the structural strength of Gubaizui loess is very high, from the compression curves(one-dimensional consolidation test) it is obtained that strength is about 0.85~2.38MPa. 相似文献
18.
宇宙成因核素10Be示踪古地磁场的研究在海洋和冰芯研究中得到了广泛应用,然而受黄土来源及沉降过程的复杂性制约,运用中国黄土10Be示踪古地磁场变化的研究直到近年来才取得突破进展.综述了黄土10Be的研究现状并指出将其应用于地磁场示踪研究存在的关键问题,重点介绍了为分离黄土10Be浓度记录所包含的气候因素和地磁场影响因素而建立的LGM分离方法、剩磁矫顽力估算模型方法和"平均值概念"方法.各种创新数理方法的建立基本解决了黄土10Be示踪古地磁场的科学难题,使黄土10Be示踪古地磁场变化研究成为可能. 相似文献
19.
黄土有机质稳定碳同位素研究进展 总被引：8，自引：0，他引：8
有关黄土高原历史时期原生植被类型的研究不仅具有重要的理论意义,也具有现实的指导意义。土壤有机质稳定碳同位素（δ13Corg）是区域植被中C4/C3植物相对丰度的灵敏指示器,对黄土有机质稳定碳同位素的研究可以部分地重建过去的植被类型变化历史,并可探讨与此有关的气候、环境问题。已有的研究结果表明：黄土高原古土壤发育阶段δ13Corg偏正于黄土沉积阶段,表明随气候由冷干向暖湿转变黄土高原C4植物相对丰度上升,然而在C4植物相对丰度上升的主要驱动因素上仍存在夏季风和温度两种观点。相应的在空间上,C4植物的相对丰度无论冰期还是间冰期都是由黄土高原东南向西北递减。而基于黄土δ13Corg的研究认为黄土高原历史时期一直以草原为主,不存在大面积的森林。尽管已有的研究对黄土有机质稳定碳同位素分布和变化的一般性规律取得了共识,但在研究中还存在一些问题,在黄土δ13Corg变化机制上还存在争议,值得进一步研究。 相似文献