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1.
中国黄土-古土壤系列的磁学性质,如磁化率等被广泛用于古气候和古环境研究,这必须建立在对黄土-古土壤的剩磁的性质和获得剩磁的机制以及古土壤磁性增强的原因有深入了解的基础之上。作者通过对洛川和吉县剖面马兰黄土和离石黄土的磁学性质的深入研究,对黄土与古土壤磁学性质差异的各种表现,对它们剩磁的性质,对古土壤磁性增强的原因以及磁性变化对古气候、古环境研究的意义进行了讨论,并对利用某些磁学性质建立的黄土-古土壤形成的时间模式提出了质疑。 相似文献
2.
Elena I. Virina Friedrich Heller Stanislav S. Faustov Nathalia S. Bolikhovskaya Robert V. Krasnenkov Tatyana Gendler Ernie A. Hailwood Jozeph Hus 《第四纪科学杂志》2000,15(5):487-499
Until now, palaeoclimatic reconstructions for the major stages in the development of the Quaternary loess–palaeosol sequence on the Russian Plain have been based on pedological, palynological and faunal (vertebrates and molluscs) analyses. In order to demonstrate the palaeoclimatic influence on the magnetic properties of this sequence, the magnetic susceptibility signature of the Strelitsa type section in the Upper Don basin is compared with a detailed landscape – climate reconstruction of loess and soil from palynological data. Large amplitude fluctuations of palaeoclimate and palaeoenvironment are reflected clearly in the lithology and in the rock magnetic properties, which usually are enhanced in wet and warm interglacial periods, but stay at low levels during cold glacial epochs. Palynological climate zonation, however, is sometimes in conflict with the pedologic–magnetic record. Strong climate fluctuations, as indicated by changing pollen assemblages, are not always paralleled by corresponding changes in lithology and/or rock magnetic properties. Alternatively, light coloured illuvial horizons with low magnetic signal sometimes appear to have formed during early stages of interglacials, and the top parts of some palaeosols apparently formed during glacial stages. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
3.
《Quaternary International》1999,53(1):93-102
The in situ pedogenic enhancement of ferrimagnetic content provides the well-established patterns of magnetic susceptibility variation within mid- to low-latitude loess deposits such as those of China and Central Europe. However, this pattern of high magnetic susceptibility in palaeosols, and lower values in unweathered loess, is not replicated in the higher-latitude loess deposits of Alaska and Siberia. In these localities the relationship is inverted, with high values in loess, and low values in palaeosols. This inverse relationship has been explained by the idea that magnetic susceptibility is reflecting the magnitude of an aeolian ferrimagnetic component of consistent mineralogy, the grain size of which is related to average wind velocity. However, the results of the magnetic study presented in this paper suggest that there are differences in magnetic properties between Alaskan loess and palaeosols, not only in magnetic grain size and concentration but also in magnetic mineralogy. This complicates the simple hypothesis of a `wind velocity’ signal by introducing an additional factor into the climatic signal. In contrast to the enhancement of susceptibility observed in palaeosols of the Loess Plateau, China, we suggest that the low magnetic susceptibility values in the Alaskan palaeosol units are a reflection, at least in part, of the alteration of the ferrimagnetic content by post-depositional processes associated with waterlogging (i.e. gleying) of the soils. 相似文献
4.
Geochemical and isotopic studies of aeolian sediments in China 总被引：5，自引：0，他引：5
The Sr and Nd isotopic, rare earth element (REE) and major element compositions, together with mineral and grain‐size proportions, are reported for aeolian loess deposits and desert sands from several Chinese localities. The study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments, and to constrain the provenance of Chinese loess. Samples include loesses from the Tarim and Junggar basins and desert sands from the Taklimakan desert in north‐west China, loess from the Ordos area and desert sands from the Tengger and Mu‐us deserts in north‐central China, as well as loess and desert sands from the Naiman area, north‐east China. REE distributions show minimal variation among the Chinese loess deposits, whereas those for the desert sands show regional variations. New isotopic data document a latitudinal variation in Sr and Nd isotopic features for the loesses and desert sands. The Naiman and Junggar loesses have distinctly lower 87Sr/86Sr ratios and higher εNd(0) values than the loesses from the Tarim Basin, the Ordos area and the Loess Plateau. Among the desert sands, the Naiman samples have higher εNd(0) values than the Taklimakan, Tengger and Mu‐us samples. Isotopic data suggest that loesses of the Loess Plateau were supplied from the Tarim Basin loesses and Taklimakan Desert sand, and that the Naiman loesses were supplied from the Junggar Basin loesses. The latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the Tianshan and west Kunlun Mountains, which are possible sources for the loesses and desert sands. These inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over East Asia. 相似文献
5.
J.C. Bidegain Y. Rico A. Bartel M.A.E. Chaparro S. Jurado 《Quaternary International》2009,209(1-2):175
Quaternary loess sequences of Argentina, with interbedded loess and buried soils (palaeosols), provide terrestrial records of past climates and environmental conditions. Study of rock magnetic parameters measured over a large area of the Pampean loess seems to indicate that the existing magnetoclimatological models cannot adequately account for the complexities of the Pampean loess.The Chinese loess has been considered as typical, where magnetic properties are largely controlled by pedogenesis. On the other hand, the Siberian loess is an alternative magnetoclimatological model in which palaeosols appear as magnetic lows and the intercalated loess as magnetic highs. Argentine loess is apparently closer to the Siberian model. However, considering the data obtained in Argentina, the situation seems to be more complicated. The higest magnetic values (SIRM and susceptibiliy values) in silty and sandy loess indicate a more efficient entrainment of dense iron oxides particles during stormy dry (glacial) intervals.The parent material shows the highest susceptibility values (>100 × 10−8 m3/kg) while the waterlogged horizons show the lowest ones (below 20 × 10−8 m3/kg). Pedogenesis resulting in the development of BC and B soil horizons of palaeosols in the parent loess produced decreases in susceptibility values and increases in the F factor. This phenomenon occurs at some degree of humidity in which the process of gleying caused the total depletion of both susceptibility and frequency factor. The magnentic data allows consideration of the relevance of major cycles (arid/humid) separated by discontinuities as the main factor favoring one particular behavior of the magnetic parameters. The B horizons of palaeosols developed during an arid cycle will not show a notable difference in the magnetic records from the parent material. In contrast, during humid climate condition the pristine loess can be progresively obliterated by pedogensis through to the extreme situation of gleying. 相似文献
6.
中国黄土和阿拉斯加黄土磁化率气候记录的两种模式探讨 总被引：45，自引：16，他引：29
在中国和中欧黄土-古土壤研究中发现的磁化率与成壤作用(或古气候温湿程度)的正相关性已被第四纪科学家广泛认识,并应用于古气候研究中.成壤过程形成的亚铁磁性矿物被认为是古土壤磁化率增加的主要原因;然而,这一模式并不一定适用于其他黄土沉积地区,如阿拉斯加和西伯利亚黄土沉积显示了一个完全相反的磁化率行为,即在黄土层获高磁化率值而在古土壤层获低磁化率.这种相反的关系过去被解释为磁化率反映的是与风动力吹来的亚铁磁性矿物的含量,即与风速或风力大小有关.本研究发现阿拉斯加黄土与古土壤的磁性矿物性质有明显差异,不仅仅是粒径的大小,还有磁性矿物的种类即矿物相的差别.这一证据很难单纯以风力强度的大小来解释,意味着阿拉斯加古土壤的低磁化率至少部分是在成壤过程中亚铁磁性矿物发生改变(如溶解)而造成,表明阿拉斯加黄土和中国黄土的磁化率与古气候记录可能存在两种模式,即氧化和还原条件下的成土模式.黄土磁化率在不同的气候(温度湿度)条件下有着不同的对应关系:在低降水量、高蒸发量的干旱氧化成壤条件下,利于亚铁磁性矿物的生成,其磁化率与古气候的关系呈正相关,如中国和中亚黄土;在高纬高湿的还原成壤条件下,亚铁磁性矿物会被破坏被分解,其磁化率与古气候呈负相关关系,如阿拉斯加黄土.如果成壤条件在氧化和还原之间来回变换,那么就很难找到两者之间的联系.因此,将磁化率应用于古气候的重建时要加倍的小心. 相似文献
7.
南京下蜀土的岩石磁学特征 总被引：5，自引：0，他引：5
对南京附近的下蜀土进行了岩石磁学测定，通过磁化率各向异性测量研究了它的沉积磁性组构特征，下蜀土的各异向性很不明显，各向异性废Ｐ小于水成岩的Ｐ值（＞１．０２），且与困面理度Ｆ高度相关，与磁线理度Ｌ相关不明显，这种特征与中国中部风成黄土极相似。对新生圩剖面进行的磁化率测量发现用化率曲线上有７个旋回的波峰、波谷变化，这与剖面中的古土壤－黄土系列相一致，说明下蜀土的剖面磁化率同样可以作为地层划分与对比，反映古气候冷暧变化的物理参数。对典型下蜀土样品进行的低温磁化率测量揭示出古土壤和黄土的成颗粒的构成不同，古土壤以超顺磁质为主，黄土以顺磁质为主。细小磁颗粒在古土壤中的积聚可能与古土壤的发育及古气候的暧湿程度有关。 相似文献
8.
《Quaternary International》1999,53(1):103-110
The magnetic enhancement of paleosol is observed in the Chinese loess. The origin of this magnetic enhancement is still very uncertain. It is, however, a key problem in correctly understanding the paleoclimatic significance of changes of magnetic susceptibility and in transferring the magnetic signals to paleoclimatic parameters. Two main models have been proposed to explain the mechanism of magnetic enhancement in paleosols: a depositional model and a pedogenic model. Together with composition and concentration, grain size distribution of magnetic minerals also plays an important role to the magnetic enhancement of paleosols. Systematic susceptibility measurements were carried out on the samples of the upper part (S0 to top of L2) of three loess sections from Jixian, Xifeng, and Xining, along an east–west transect in the loess plateau, China. The samples with the highest value of magnetic susceptibility in S1 and the lowest value in L2 of each section were selected as the representatives. These representatives were separated into different grain size fractions based on Stokes’ law for coarse grains and by centrifuge for fine grains. Measurements of magnetic susceptibility and mass have been carried out on these fractions. Results show that for the loesses magnetic susceptibility changes little in the fractions with different grain size and for the paleosols it increases with decreasing grain size. The magnitude of changes is bigger in the east (Jixian and Xifeng) than that in the west (Xining). The fraction with the finest particle size in paleosols does not show very high magnetic susceptibility values. A new approach is used to estimate the contribution of each fraction to total magnetic susceptibility. The contribution comes mainly from coarse grains (>10 μm) for loess samples. It reaches about 90%. The main contribution comes, however, from the particles with medium size (10–0.2 μm). The very fine grained particle (<0.3 μm), which is considered to be with the pedogenic origin, contributes little to the bulk magnetic susceptibility, no more than 3% because of their very little amount. This approach provides a sounder basis for the study of the origin of the magnetic susceptibility enhancement in paleosols and of the paleoclimatic significance of magnetic susceptibility of loess and paleosols. 相似文献
9.
不同地区非饱和黄土动力结构性研究 总被引：3，自引：0，他引：3
对兰州、洛川、杨凌地区黄土在不同含水率与不同应力状态下进行动扭剪三轴试验,测定了黄土的动剪应力-应变关系曲线;同时,依据Hardin-Drnevich双曲线模型,改进了基于动剪应力考虑的土结构性定量化参数,并应用该参数对三地区非饱和黄土的动力结构性进行了分析。结果表明,三地区非饱和黄土的动力结构性参数随动剪应变的增大先降低,而后保持在一个稳定的水平;含水率与固结应力对黄土的动力结构性影响显著,在相同的固结应力条件下,含水率越低,黄土的动力结构性参数越大,在相同的含水率条件下,固结应力越小,黄土的动力结构性参数越大;在相同的条件下,杨凌地区黄土的动力结构性最强,洛川地区黄土次之,兰州地区黄土最弱,即黄土的动力结构性在地理空间分布上存在从西北向东南方向增强的规律。 相似文献
10.
兰州九洲台黄土沉积年代的综合研究 总被引：10，自引：1，他引：10
据上、下粉砂层在剖面上出现的位置、黄土-古土壤地层层序、14C、热释光（TL）和裂变径迹年龄以及古地磁测量结果,兰州九洲台黄土仅仅是距今140-150万年以来才沉积而成的,因而距今220-240万年以来形成的结论不能成立. 相似文献
11.
12.
G. S. Lodha K. J. S. Sawhney H. Razdan D. P. Agrawal N. Juyal 《Journal of Earth System Science》1987,96(2):135-145
Major and trace element concentrations of a few representative loess profiles in Kashmir valley are studied using EDXRF spectroscopy.
Principal component analysis for pattern recognition has been employed to study association between elemental concentration
variations in various horizons. The present study reveals that elements related to clay illuviation (K, Rb, Fe, Ti, Mn) and
plant activity (Cu, Zn) are generally higher in B horizon of the palaeosols whereas Ca and Sr have a high concentration in
the loess layers. Such an elemental concentration variation provides us with an objective index for identification and confirmation
of palaeosols. There is further a close association in the movement of (i) K, Rb, (ii) Fe, Ti, Mn, (iii) Cu, Zn and (iv) Ca,
Sr. These clusters of elements are also present in modern soils, suggesting that the soil characteristics in palaeosols have
been preserved. Concentration of iron and titanium is also observed to be higher in loess profiles on Pir Panjal mountain
flank which is dominated by basic rocks, compared to profiles on Himalayan flank, suggesting that the loess in Kashmir might
have been derived from the nearby rocks in a localized way. 相似文献
13.
《Quaternary Science Reviews》2002,21(7):811-817
Five lateral sand–loess–palaeosol continua occur within the last glacial sediments of the central Loess Plateau of China along a 500 km north to south climatic gradient. The continua shift southward or northward in concert with desert expansion or contraction, respectively. Lateral lithofacies (desert sand to loess) variations are evident at the north end of the gradient and follow Walther's Law of the correlation of facies. Lateral pedofacies (loess to palaeosol) variations are present near the south end of the gradient, where the climate was warmer and wetter. The lateral stratigraphic changes from sand to loess or loess to soil are driven by variations in the rate of sedimentation along a climatic gradient.Vertical stratigraphic profiles at the north end of the gradient reveal alternating sand and loess beds. In contrast, alternating loess and palaeosols occur within the same stratigraphic interval in the southern Loess Plateau, where dust accretion rates were lower. However, in high resolution studies of climate change vertical profiles of alternating loess and palaeosols (especially weak palaeosols) may not reflect regional or global climate change. Alternating loess and weak palaeosols may reflect local variations in the balance between the rates of dust accretion and pedogenesis. Local fluctuations in either of these rates could result in the presence of time equivalent loess and palaeosols at high resolutions. Thus, some of the high resolution loess-palaeosol alternations may reflect local climatic variation rather than global or hemispherical climate change. 相似文献
14.
E.M. Rutledge M.J. Guccione H.W. Markewich D.A. Wysocki L.B. Ward 《Engineering Geology》1996,45(1-4):167-183
Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although “double submergence” was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of “loessification” which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under “Kansan” till. Stratigraphy indicates the Marianna is the older of the five loesses.
Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed * Corresponding author. by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses. 相似文献
15.
最直观、最直接的古气候记录莫过于陆相黄土地层,它由许多黄土和古土壤层叠覆而成,详细地记录了第四纪以来的古气候变化。黄土高原中部黄土和古土壤的风化和发育程度可以用磁学参数,如磁化率等来描述。本文作者对甘肃西峰剖面约13万年以来的黄土地层做了详细采样,测量其磁滞回线各参数,频率磁化率、低场和高场磁化率、温度磁化率、磁组构等参数。研究表明,黄土与古土壤中的磁性矿物组分相似而且稳定。磁铁矿、赤铁矿和磁赤铁矿(主要是磁铁矿)的含量及其颗粒大小决定了它们的磁学特征。黄土和古土壤的磁学性质差别主要受成土过程中形成细小磁铁矿的影响。 相似文献
16.
《Earth》2006,74(3-4):309-316
Loesses form wide belts in front of previously glaciated areas. Their thicknesses may be considerable, changing in Eurasia from maximally a few metres in the west to a hundred metres or more in the east. The Eastern (particularly Chinese) loesses are mostly unrelated to glaciations. The periglacial loesses from China and elsewhere predominantly date from the last Pleistocene glaciation: relatively few comparable occurrences are known from earlier Quaternary glaciations. As it is difficult to imagine that the conditions in front of the land-ice masses during the earlier glaciations differed fundamentally from those of the last one, considerable quantities of loess must have disappeared. This disappearance, which is commonly ascribed to fluvial and eolian erosion, is not easily explained as equivalent deposits that may have the older loesses as a source, are practically absent. A possible explanation might be that loess is recycled during successive glaciations. Some loess disappears during interglacials by erosion, but this quantity is more than compensated by the formation of new silt particles. The implication would be that the loess deposits increase in volume for each new glaciation. 相似文献
17.
大别山北麓竹竿河黄土—古土壤样品的磁组构特征显示,研究剖面0～1480cm层段的平均Pj、F值小于1.02,而底部Pj、F大于1.02。F—L、Pj—q组合关系图反映磁化率椭球体为压扁状,磁面理较磁线理发育。磁化率椭球体主轴方位显示0～1480cm层段样品的椭球体轴向分布分散,长轴的倾角大于60°,短轴的倾角小于15°,而底部的分布聚集,长轴的倾角一般小于10°,短轴的倾角大于80°,上述特征综合揭示了0～1480cm层段属于典型风成沉积而底部属于典型水成沉积。磁化率椭球体最大主轴的偏角暗示风成沉积的主导风向为NW—SE方向,而水成沉积的古流向为SW—NE方向,与现代竹竿河水系的方向基本一致。磁化率各向异性最大轴方向的优选方向可能与大别山抬升等构造运动有关。 相似文献
18.
以填土厚约80 m的吕梁机场黄土高填方试验段为研究对象,开展不同性状黄土的室内变形时效性试验,并建立了反映其变形时效性的修正Burgers模型（M-B模型）,将其引入到有限差分法软件FLAC3D中,开展了填土在不同压实度、含水率控制标准和不同地基处理方案下高填方的工后沉降规律敏感性分析。基于原位监测结果进行数值反演和预测分析,进一步探究室内试验得到的变形时效性参数与高填方概化层参数之间的差异。结果表明：深厚黄土地基上的高填方工程,其原地基的处理是控制工后总沉降的首要因素,在设计填料的压实度时,其含水率的控制也是影响工后沉降的重要因素;经反演分析得到,概化层变形参数比室内大1～4倍,预测得到深厚黄土地基上的高填方沉降稳定的时间需3～4 a,建议竣工后1.5～2.0 a开展基础设施建设。 相似文献
19.
J. Šajgalik 《GeoJournal》1991,24(2):165-174
The Slovak Carpathians in Pleistocene presented a very articulate territory, so that loesses, as well as loess-like deposits could occur here with various lithofacial types.Based on a complex evaluation of a great number of loess samples of the Danubian lowland and their analysis by methods of mathematical statistics, it was possible to create a realistic model of the base soil. For the statistical processing we picked 4 selective sets of the Danubian lowland hilly country, where each set can be considered as a homogeneous engineering geological type.By comparing the loess properties of the Danubian lowland with the loesses of other European countries (mainly USSR), it can be stated that the studied loesses are not so dangerous from the sagging standpoint. The increase of the oedometric modulus with the depth was shown. Similar relationships were derived also for the parametres of shear strength.The regional characteristics of the loess mechanical properties will serve well in the initial phases of investigation, planning and designing, but also in more exact geoo technical calculations. 相似文献
20.
Grain‐size data from different climatic zones across the Chinese Loess Plateau show that the loess generally contains an ultrafine component, which has a consistent modal grain size of ca 0·37 μm and a variable proportion of 4 to 10%. The variation of the ultrafine component through a loess section is characterized by a high proportion and fine grain size in palaeosols, and by a low proportion and coarse grain size in loess layers. Its proportional content in a stratum roughly increases from north‐west to south‐east across the Loess Plateau. Quantitative X‐ray diffraction analysis indicates that the ultrafine component is composed mainly of clay minerals (ca 70%), which are mostly illite (ca 80%), and with significant amounts of kaolinite (ca 8%) and chlorite (ca 2%). The temporal and spatial variations of the ultrafine component, and the degree of illite crystallinity, suggest that this component in aeolian sediments is linked closely to the process of pedogenesis. Weakly altered loess on the north‐western margin of the Loess Plateau contains considerable amounts of detrital clay minerals derived from the aeolian source areas. Results from a loess section with a basal age of 7·6 Ma in the central Loess Plateau show that the ultrafine component increased from 7·6 to 5 Ma, and progressively decreased thereafter. This trend was punctuated by two abrupt changes at 2·6 and 0·6 Ma. These variations reflect to a considerable extent the history of pedogenesis during the Late Cenozoic. 相似文献