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The origin of the Tertiary ‘red clay’ underlying the Pleistocene loess in the Chinese Loess Plateau remains controversial, although several lines of evidence have suggested a wind‐blown origin. This study examines the particle‐size parameters of the late Miocene and Pliocene ‘red clay’ by comparing it with those of the late Pleistocene loess. The particle‐size distribution of a total of 15 339 loess and 6394 ‘red clay’ samples taken from 12 loess sections along a north–south transect and two ‘red clay’ sequences at Lingtai and Jingchuan was systematically analysed. The median grain size, skewness and kurtosis of the late Pleistocene loess all show a systematic southward change and are principally influenced by distance from source region. The spatial and temporal differentiation of dust deposits is expressed in a skewness–kurtosis–median grain size ternary diagram, from which the distance to the source region can be inferred. The particle‐size characteristics of the Tertiary ‘red clay’ sediments are very similar to those of the palaeosols within the late Pleistocene loess deposits, suggesting an aeolian origin for the ‘red clay’. Based on the comparison of ‘red clay’ and loess in the ternary diagrams, it is inferred that the source–sink distance was greater in the Neogene than in the last and penultimate interglacials, and that the dust source region in north‐western China underwent a progressive expansion during the period from at least 7·0 Ma to the present. 相似文献
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Palaeoclimatic interpretation of the Red Clay in the Chinese Loess Plateau is particularly important for understanding of the East Asian monsoon evolution from Pliocene to the Quaternary. In this study, a N-S transect involving five loess-Red Clay sections across the Loess Plateau was selected for detailed investigation with analyses of grain size and major element geochemistry, in order to address the spatial pattern. Results indicate that the Red Clay contains large amount of coarse (<6?, i.e. >16 μm) fraction and shows a prominent N-S decreasing gradient much similar to that of the overlying loess, suggesting that the dust transport was dominantly by low-level northerly/northwesterly winds. Compared with overlying loess, the Red Clay is markedly fine and rather constant through all the sections, implying a distant and steady dust-source area about 200 km further north during most of the Pliocene time. Pedogenic leaching intensities inferred from geochemical data display a clear decreasing trend from south to north both for the Red Clay and the loess, suggesting that the modern spatial pattern of the East Asian monsoon regime has been maintained at least for the past 5 Ma. The N-S spatial gradient, however, might be smaller during the Pliocene than the Quaternary period. Temporally, two short periods of climatic deterioration implied by marked grain-size coarsening and low weathering intensity occurred at 5.3 and 3.5 Ma, respectively, which divide the Pliocene into two major stages. The 5.3-3.5 Ma stage is characterized by a steady state climate through the entire region, consistent with other records. In the 3.5-2.7 Ma stage, the Red Clay in the Jingbian section shows a noticeable coarsening in grain size than the previous stage, indicating some southward extension of the deserts, in agreement with mass accumulation rate record in the north Pacific. But the eolian dust deposition remained relatively stable in major part of the Loess Plateau until 2.7 Ma. The Red Clay deposition was then terminated by massive and coarse loess deposition in the entire region, suggesting dramatic intensification of the winter monsoon in response to the onset of extensive glaciation of Northern Hemisphere. 相似文献
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Understanding loess sedimentation rates is crucial for constraining past atmospheric dust dynamics, regional climatic change and local depositional environments. However, the derivation of loess sedimentation rates is complicated by the lack of available methods for independent calculation; this limits interpretation of the environmental changes revealed by the loess record. In particular, while the Quaternary/Neogene Chinese loess and Red Clay sequences have the potential to provide detailed records of past sedimentation and climate change, there is great uncertainty concerning: (i) the influences on sediment grain‐size and accumulation; and (ii) their relationship through time and across the depositional region. This uncertainty has led to the widespread use of assumptions concerning the relationship between sedimentation rate and grain‐size in order to derive age models and climate reconstructions. To address this uncertainty, detailed independent age models, based on optically stimulated luminescence dating, undertaken at 10 to 40 cm intervals at five sections across the Loess Plateau in China, have been used to calculate sedimentation rates and make comparisons with grain‐size changes over the late Pleistocene and Holocene. The results demonstrate that sedimentation rates are site specific, extremely variable over millennial timescales and that this variation is often not reflected in grain‐size changes. In the central part of the Loess Plateau, the relationship between grain‐size and sedimentation rate appears most complex, suggesting an interplay between local conditions at source and sink and a changing emplacement mechanism. This observation further undermines the common use of loess sedimentation age models that rely on a derived relationship between grain‐size and sedimentation rate from a type section. The results also highlight the difficulty in assigning specific environmental causes to sedimentation rate changes and, to a lesser extent, grain‐size shifts. 相似文献
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Baotian Pan Qingyu Guan Hongshan Gao Dongsheng Guan Fenliang Liu Zongmeng Li Huai Su 《Boreas: An International Journal of Quaternary Research》2014,43(1):121-131
The grain size of the loess‐like sediment in the Jinsha River Valley is essentially similar to that of typical loess, and it differs from that of the fluvial sediment in the Jinsha River area. We conclude that the loess‐like sediment is of aeolian origin, as is the loess of the Chinese Loess Plateau. The geochemical characteristics of the loess‐like sediment are similar to those of dammed lake and fluvial sediments in the same area, which is significantly different from those of the typical loess in NW China. The geochemical characteristics show that the loess‐like sediment originated from proximal materials. Combined with the grain‐size distribution pattern of the aeolian deposits, we suggest that the loess‐like sediment of the Jinsha River Valley originated from the dammed lake and fluvial sediments that accumulated in the valley. The local mountain‐valley wind circulation (especially the valley wind in winter and spring) provided the transport force for the loess‐like sediment. The presentation of the loess‐like sediment may indicate the appearance of the grassland and forest steppe and the beginning of the dry‐hot valley phenomenon. 相似文献
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Variations in magnetostratigraphy, pedostratigraphy, grain size and magnetic susceptibility of the loess deposits near Beijing have been studied at two sections. The sections are about 400 km east of the main loess deposits in China, have a maximum thickness of 100 m and extend back to 1.1 Ma. The sequence consists of 14 loess–palaeosol couplets (S0‐S14), which correlate well with sequences in the Loess Plateau. Susceptibility records from the sites near Beijing are comparable to the Xifeng, Luochuan and Baoji sections located in the middle part of the Loess Plateau; however, the down‐core variations in the grain size in the Upper Lishi Formation exhibit some differences. The median grain size increases by about 25–30 µm from L4 to L2, with the sandy grains (>63 µm) increasing from 10–20 wt% to 40–50 wt% . This implies that the depositional environment of the dust sources in the Beijing loess section is different in some aspects from the Loess Plateau. The Beijing loess may have had a different dust source than the Loess Plateau. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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对黄土高原西部秦安地区晚新近纪甘肃群中的一套黄土-古土壤序列以20cm间距采集的310个蜗牛化石样品进行了系统的研究。结果表明,黄土层与古土壤层中的蜗牛化石全部为陆生种类,以Gastrocopta,Pupilla,Vallonia,Metodontia,Cathaica和Punctum等占优势,与黄土高原第四纪黄土-古土壤序列中蜗牛化石的种属组成基本一致,这表明研究剖面是一套陆生成因的地层,与黄土高原第四纪黄土-古土壤序列有着相似的沉积环境。上述结果为提取古环境信息从生物学角度提供了证据。 相似文献
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Maarten A. Prins Hongbo Zheng Kay Beets Simon Troelstra Patrick Bacon Ilse Kamerling Wouter Wester Martin Konert Xiangtong Huang Wang Ke Jef Vandenberghe 《第四纪科学杂志》2009,24(1):75-84
The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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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
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东北平原东部天恒山钻孔的粒度特征及其对地层划分的指示 总被引：2，自引：2，他引：0
东北平原东部荒山剖面是我国东北地区的第四纪典型剖面,但针对该剖面的地层划分和成因的研究尚存在不同看法,对其开展详细的粒度特征研究有望对该剖面的地层划分和地层成因提供进一步的认识。通过天恒山（THS）钻孔对该区地层进行高分辨率的粒度特征研究,并与黄土高原典型黄土进行对比。研究结果显示哈尔滨组地层平均粒径、中值粒径以及粒级百分含量等大幅度波动,呈现黄土-古土壤地层旋回变化特征,黄土层粒度粗,古土壤层粒度细,与黄土高原典型第四纪黄土的粒度特征一致。荒山组地层则呈现小幅度波动,沉积动力较稳定。哈尔滨组和荒山组的粒度频率分布、C-M图及粒度参数（平均粒径、标准偏差、偏度、峰度）等特征均存在显著差别,指示二者的沉积动力过程明显不同。基于以上粒度特征,结合沉积相特征和已有划分方法,THS钻孔中-晚更新世地层自上而下可划分为哈尔滨组和荒山组,并将哈尔滨组地层判定为风成堆积,将荒山组地层判定为河湖相沉积。 相似文献
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Late Quaternary loess deposition in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland and its palaeoclimatic implications 
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下载免费PDF全文 Honghua Lu Yidi Xu Ying Niu Zhen Wang Hui Wang Junxiang Zhao Weiguo Zhang Xiangmin Zheng 《Boreas: An International Journal of Quaternary Research》2016,45(2):304-321
The piedmont aeolian sediment in Central Asia is has been widely used for Quaternary palaeoclimatic reconstructions. Here we present detailed sedimentological and rock magnetic investigations on 188 samples from the ~9.4‐m‐thick Urumqi River section (URS) in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland. Optically stimulated luminescence (OSL) dating constrains the time‐span of the URS loess sedimentation from c. 28 to c. 6.8 ka. This chronology implies that the onset of the URS loess sedimentation is approximately synchronous with the Shangwangfeng Glaciation (MIS 2) in the headwaters of the Urumqi River. Analyses of sediment grain size and rock magnetic parameters indicate that sediment grain‐size composition controls magnetic properties of the URS loess, i.e. the wind intensity model, distinct from the pedogenic model interpreting the variations in magnetic properties of the loess in the Chinese Loess Plateau (CLP). Overall, the variations in sediment grain size and magnetic properties throughout the URS indicate that the present study area was dominated by a climate of strengthened wind associated with gradually intensified aridity during the latest Pleistocene. In contrast, the intensity of aridity and coldness during the early Holocene gradually became relatively weakened. 相似文献
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GERILYN S. SOREGHAN REW M. MOSES MICHAEL J. SOREGHAN MICHAEL A. HAMILTON† C. MARK FANNING‡ PAUL K. LINK§ 《Sedimentology》2007,54(3):701-719
The Late Palaeozoic configuration of Pangaea contributed to a palaeoclimatic extreme that was characterized by both icehouse and monsoonal conditions. This study uses sedimentological, geochemical, and provenance data from silty facies of the Earp and equivalent Supai Formations (Arizona, New Mexico) to shed light on atmospheric circulation and glacial–interglacial climate change in westernmost equatorial Pangaea. Five silt‐rich facies comprise both loessite and marine and fluvially reworked loessite. An initial aeolian origin for the silt is indicated by the remarkably invariant grain size and the laterally continuous, sheet‐like geometry of beds. The silt‐rich facies occur in repetitive facies associations (1–20 m scale) that form mixed continental‐marine (loess, marine‐reworked loess), shallow‐marine, and continental (loess, palaeosol) ‘sequences’. Facies repetitions of both mixed continental‐marine and shallow‐marine sequences reflect a linked glacioeustatic–glacioclimatic control, whereas the continental (loess–palaeosol) couplets reflect a primary glacial–interglacial climatic cyclicity linked to glacioeustasy. Stratigraphic interpretations suggest that aeolian silt flux maximized during glacial to incipient interglacial stages (lowstand to early transgression), and decreased significantly or ceased during interglacials (highstand to early falling stage). Detrital‐zircon geochronological data indicate a transition from dominantly north‐easterly winds during the Middle Pennsylvanian to north‐westerly and south‐easterly winds by the Early Permian, which trend is inferred to reflect the onset of monsoonal circulation in western Pangaea. Relative grain‐size data support the detrital‐zircon data, and exhibit a significant decrease from the Sedona arch/Central Arizona shelf (north) to the Pedregosa basin (south) sections. Whole‐rock geochemical data suggest a relatively unweathered source for the silt in the north, and detrital‐zircon data indicate significant silt was derived from the local basement. These large piles of silt(stone) preserve valuable information for reconstructing both long‐term evolution in atmospheric circulation and short‐term fluctuations in glacial–interglacial climate. Many such indicators for long have been applied to ‘recent’ (Plio‐Pleistocene) loess, but are equally applicable to ‘deep‐time’ strata. 相似文献
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《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
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WANGXi－sheng ReidarLφVLIE 《地学前缘》2002,9(1):73-84
近二十年来中国黄土环境磁学的研究基本上是沿着两条主线进行的 ,即磁性地层学和古气候研究两个方面。对早先确定的典型黄土剖面的磁性地层研究表明风成黄土的堆积开始于Matuyama的下界 ,约 2 .6Ma。而近年来对黄土古土壤序列之下的红粘土的进一步研究显示风成堆积的开始比原先认为的要早的多 ,至少可追溯到约 7Ma。尽管目前在古土壤磁化率的增强机制和磁化率如何记录古气候变化等问题上还没有达成广泛的一致 ,而黄土古土壤系列磁化率与深海氧同位素的良好对比可证实中国黄土确是记录全球气候变化非常理想的信息载体。近年来许多学者尝试性提出的其它古气候替代性指标 ,如全岩粒度、稳定同位素组成、FeD/FeT指标、Rb/Sr比值和CaCO3 含量等必将为重建古季风变化和古气候提供重要信息。 相似文献
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There is agreement that ultrafine maghemite grains (<100 nm) are responsible for the magnetic enhancement of Chinese loess. Recent studies show that grain size distribution of ultrafine pedogenic maghemite grains within the aeolian sequences on the central Chinese Loess Plateau deposited in the last 8 Ma is consistent. However, whether the observed grain size distribution of ultrafine pedogenic maghemite grains can be observed in the western Chinese Loess Plateau and modern soils is not entirely clear. Here we find that young surface soil samples across the Chinese Loess Plateau and early Neogene loessic soils from the western Chinese Loess Plateau also show consistent grain size distribution with that of ultrafine pedogenic maghemite grains on the central Chinese Loess Plateau. The fact that young surface soil samples show apparent magnetic enhancement suggests that the ultrafine pedogenic maghemite grains derive from oxidation of ultrafine magnetite grains. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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He Xiubin Tian Junliang Tang Keli Sun Jianzhong John A Matthews 《Journal of Asian Earth Sciences》2004,22(5):455
Micromorphology, heavy minerals, pollen and soil properties were examined in a typical Holocene loess profile in the north of the Loess Plateau, consisting of a palaeosol (locally known as the Ansai palaeosol) underlain by the Malan loess and overlain by modern loess. The palaeosol consists of an upper humus-rich (AB) horizon over a clay-rich (Bt) horizon. The humus-rich horizon is intensely weathered, contains precipitated calcitic material derived from the overlying modern loess, and has both high pollen content and diversity. Clay coatings in the clay-rich horizon indicate formation by eluviation–illuviation of clay. Pedogenetic characteristics and pollen analysis imply that the vegetation during the time of most intensive soil development is likely to have been a warm-temperate forest. A complex interpretation of the loess–palaeosol sequence recognizes several development stages. The phase of soil development, maximum and minimum limiting ages for which are ca. 8800 and 4400 14C years BP, involved continuing but reduced loess deposition, and successive Holocene bio-climatic environment overprinted new features on the palaeosol. 相似文献
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Grain size and magnetic susceptibility measurements on samples from a typical loess–palaeosol sequence on the central Chinese Loess Plateau are used to reconstruct the Pleistocene East Asian monsoon climate. The coarse‐grained fraction, i.e. the weight percentage > 30 μm of the bulk grain‐size distribution, is used as a sensitive proxy index of the East Asia winter monsoon strength. On the basis of an absolute time‐scale, time‐series variations of this proxy show that winter monsoon strengths varied on millennial time‐scales during the periods 145–165, 240–280, 320–350, 390–440, 600–640, 860–890, 900–930 and 1330–1400 kyr BP. The wavelength of these climatic oscillations varied between 1.89 and 4.0 kyr, as is shown by spectral analysis using the multitaper method. Although numerical simulation experiments show that high frequencies also can arise from measurement errors in the grain‐size analysis, the frequencies prove to be sufficiently stable when the spectral analysis is repeated with a different number of tapers. For the time being, we do not correlate these climatic oscillations with palaeoclimatic records in the North Atlantic deep‐sea sediments because both time‐scales need to be further improved. Our data, however, certainly demonstrate that millennial‐scale East Asian winter monsoon variations in the last 1.4 million years can be detected from terrestrial loess records. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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川西高原甘孜黄土的成因 总被引：10，自引：1，他引：9
本文通过对甘孜满地黄土的粒度组分、石英砂的表面结构以及其它地质现象的综合研究,对甘孜黄土的成因进行了探讨。在黄土的概率累计曲线上,跃进组分和悬移组分反映明显,并以悬移组分为主。悬移组分粒径小于2φ~3φ,并以粉砂(4φ~8φ)为主,占悬移总体的94%~99%;对甘孜黄土进行扫描电镜观察表明,石英砂大部分为块状颗粒,少量(10%)呈纺锤形。采用矩阵法计算甘孜黄土的粒度参数:黄土的平均粒径(d50)为5.057φ~5.883φ,明显大于古土壤(6.120φ~6.549φ).古土壤的标准偏差(σφ)为1.513~1.973,大于黄土(1.205~1.778);黄土和古土壤的偏度系数(SKφ)为-0.088~0.248,显示为正偏或近于对称。黄土和古土壤的尖度系数(Kφ)分别为0.123~1.702、0.023~0.059,前者峰形窄,后者峰形较宽。对甘孜黄土扫描电镜观察表明,石英砂大部分为方形或长方形颗粒,少量(10%)呈纺锤形。石英砂有密集的翻卷片、蛇曲脊、圆麻坑,这些结构反映了风成特征。另方面,少量石英砂显示冰川作用结构,例如大大小小的贝壳状断口、平行擦痕等。在甘孜西面、德格以南的金沙江东岸川藏公路980km路碑处,三阶地上部的黄土层中,发现3条冰楔。此外,甘孜黄土中孢粉稀少。根据上述特征推断,甘孜黄土应为冰缘风成黄土。 相似文献
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A micromorphologically based pedosedimentary reconstruction of a 40‐m loess–palaeosol sequence from the western part of the Chinese Loess Plateau provides a sensitive proxy record of changing processes and associated environmental conditions in this region between ca. 150 000 and 10 000 yr BP. Depth functions of more traditional climate proxies, such as magnetic susceptibility, calcium carbonate content and median grain size, support the broad pattern of environmental changes inferred from the micromorphology, although the bulk properties sometimes lag behind or are out of phase with each other and do not match all the fluctuations in the micromorphological record. The reasons for the disparities are probably complex, although they partly reflect differences in response rates and sensitivities of proxies to different climate parameters, as well as genuine out‐of‐phase changes in strength of monsoonal climate controls. This work illustrates the sensitivity of micromorphology in detecting past environmental changes within rapidly aggrading landscapes, and emphasises the need to understand more fully the local and regional significance of bulk proxies currently used in global correlations with marine‐ and ice‐core records. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献