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A Late Quaternary loess/palaeosol sequence at Kurtak in the Yenisey River valley, southern Siberia, has been studied magnetically. The 34 m section (340 samples) exhibits variations in magnetic susceptibility which can be correlated with oxygen isotope stages 1–7. A detailed sampling of stage 5 (a further 209 samples) permits the identification of substages 5a–e. The susceptibility variations themselves are in the opposite sense to that found in the classic sections of the Chinese Loess Plateau, but are in agreement with the 'wind-intensity' model which has been put forward to explain similar findings in loess sequences in Alaska. Published results for the susceptibility of magnetite imply volume fractions of ≈0.2 per cent in glacial stages 2 and 4, dropping to ≈0.05 per cent in stages 1, 3 and 5. These fluctuations match the aeolian flux variations observed in core V21–146 from the north Pacific. Even though the warmer intervals are characterized by lower susceptibilities, the observed frequency dependence of susceptibility indicates that new magnetic material is produced as a result of pedogenesis during interglacial and interstadial times. 相似文献
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Nathaniel W Rutter Dean RokoshMichael E Evans Edward C LittleJiri Chlachula Andrei Velichko 《Quaternary Research》2003,60(1):101-109
Loess-paleosol sequences of the last interglacial-glacial cycle are correlated from European Russia to central Siberia and the Chinese Loess Plateau. During cold periods represented by marine oxygen isotope stages (OIS) 2 and 4, loess deposition dominated in the Russian Plain and the Loess Plateau. In central Siberia, loess deposition took place also, but five to seven thin, weakly developed paleosols are identified in both stages. OIS 3, in the Chinese Loess Plateau near Yangchang, consists of a loess bed that is flanked by two weakly developed paleosols. At Kurtak, Siberia, OIS 3 is represented by two distinct, stacked paleosols with no loess bed separating the paleosols. In the Russian Plain, OIS 3 consists of a single, possibly welded paleosol, representing upper and lower stage-3 climates. Brunisols and Chernozems dominate the profiles in China and Siberia, whereas Regosols, Luvisols, and Chernozems are evident in the northern and southern Russian Plain, respectively. OIS 5 is represented in China and the Russian Plain by pedo complexes in a series of welded soils, whereas in contrast, the Kurtak site consists of six paleosols with interbedded loess. The paleosols consist largely of Brunisols and Chernozems. Although the three areas examined have different climates, geographical settings, and loess source areas, they all had similar climate changes during the last interglacial-glacial cycle. 相似文献
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Concentrations of heavy metals Zn, Mn, Cu, Fe, Ni, Cr, Pb, Cd, Hg and Co were determined in surface waters, glacier ice and plant and animal materials from three regions in Spitsbergen, Svalbard. The concentrations of these metals in two samples of surface waters and in the vascular plants from Spitsbergen were found to be lower than what is commonly found in Cental Europe. Elevated concentrations were found in old ice from the surface of a glacier. The concentrations of heavy metals in algae were lower than in vascular plants. The concentrations of metals in the samples of feathers and animal hair from Spitsbergen were higher than what is common for Central Europe. 相似文献
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Two pedogenic models for paleoclimatic records of magnetic susceptibility from Chinese and Siberian loess 总被引：3，自引：0，他引：3
The magnetic susceptibility (MS) of Chinese loess showing a general proportional relationship to pedogenic grade has been widely recognized and used for reconstruction of paleoclimate by Quaternary scientists. The in-situ pedogenic enhancement of ferrimagnetic content is normally believed to be the main reason for the increase of susceptibility in soil units. However, this pattern of high magnetic susceptibility in palaeosols, and low values in loess, are not replicated in some loess deposits. Siberian loess deposits display a completely opposite susceptibility behavior: 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. Our magnetic study of Siberian samples in this paper suggests that there are notable differences in magnetic properties between Siberian loess and developed palaeosols, not only in magnetic grain-size and concentration but also in magnetic mineralogy. This evidence is difficult to explain fully through variation in wind strength alone, but implies that the low magnetic susceptibility values in the Siberian paleosol units are a reflection, at least in part, of the alteration of the ferrimagnetic content by post-depositional processes. The Loess Plateau is a very arid area where potential evaporation is always higher than precipitation; pedogenesis occurs under dry oxidising conditions. The Siberian Kurtak region is located on the edge of the tundra where it is always wet and saturation during interglacials will lead to a reducing pedogenic environment. Ferrimagnetic minerals under this condition will be destroyed, resulting in lower magnetic susceptibility. Therefore, great care should be taken when using susceptibility values for paleoclimatic reconstruction. 相似文献
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JIRI CHLACHULA YURII B. SERIKOV 《Boreas: An International Journal of Quaternary Research》2011,40(1):146-160
Chlachula, J. & Serikov, Y. B. 2010: Last glacial ecology and geoarchaeology of the Central Trans‐Ural area: the Sosva River Upper Palaeolithic Complex, western Siberia. Boreas, 10.1111/j.1502‐3885.2010.00166.x. ISSN 0300‐9483. Quaternary and geoarchaeology studies from the eastern limits of the Ural Mountains provide multiple lines of evidence of the Palaeolithic peopling of this geographically marginal and still poorly explored territory of western Siberia following the mid‐last glacial (MIS 3) warming. A complex of investigated open‐air localities in the Sosva River basin (the north‐central Trans‐Ural area) at the periphery of the western Siberian Plain, distinguished by very high concentrations of Pleistocene megafaunal remains previously regarded as ‘mammoth cemeteries’, indicate, in conjunction with the associated diagnostic ivory/bone and stone industry, open occupation sites during the Last Glacial (MIS 2). Fossil faunal remains, dominated by mammoth (98%) together with bird and fish species, indicate various methods of exploitation of the Late Pleistocene natural resources and successful behavioural adaptation to the last glacial sub‐polar tundra‐steppe environment. The taphonomy and composition of the well‐preserved skeletal remains from the main occupation sites suggest both active hunting and anthropogenic ‘scavenging’ practices. The contextual geology and the cultural and biotic multi‐proxy records from the Trans‐Ural Upper Palaeolithic Complex provide new insights into the timing and palaeoecological conditions of the Pleistocene human occupation of north‐central Asia. 相似文献
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中国与西伯利亚黄土磁化率古气候记录-氧化和还原条件下的两种成土模式分析 总被引：8，自引：0，他引：8
近20多年来随着中国黄土深入研究, 揭示了中国黄土地层磁化率与成土古气候温湿程度基本成正比例关系, 黄土地层磁化率也因此成为一个重要的古气候参考指标在第四纪古气候研究中, 不仅在黄土堆积物而且也在湖相和海相沉积物中广泛应用. 但是中国黄土地层磁化率与古土壤成壤强度(古气候温湿程度)呈正比的模式却不是到处都适用, 黄土高原的周边地区就有不少例外的报道. 而西伯利亚和阿拉斯加黄土则显示出另一极端的情形, 一个完全相反的磁化率特点: 在气候干冷期的黄土层获高值, 而在气候温湿期的古土壤层获低值. 过去的研究一直认为, 其磁化率主要是反映古风力大小的变化, 与成土作用基本无关. 磁学测量研究发现, 西伯利亚黄土和古土壤的差别, 不仅有颗粒从大到小的变化, 而且还有矿物组分变化: 如磁赤铁矿从多到少, 最后完全消失并取而代之出现了完全不同热磁行为的另一种矿物. 这种矿物相变现象难以用单纯的风力强弱来解释. 说明中国黄土和西伯利亚黄土可能存在两种不同的机制模式: 中国黄土高原大部分处于蒸发量大于降雨量的干旱氧化环境, 适当的水分或降雨有利于细小的磁铁矿和磁赤铁矿的形成, 使得磁化率与古气候呈正比. 而西伯利亚以及相应的高纬度地区, 地理上属苔原或苔缘地区, 湿润是该区域基本特点. 间冰期更加温湿的气候使其湿润增加以致过剩, 导致地表成土环境向还原方向移动. 它使得喜氧化的强磁性矿物磁赤铁矿和磁铁矿渐趋不稳定, 并逐渐转化形成适合其还原环境的弱磁性矿物如褐铁矿或其他铁的硫化物. 间冰期气候越潮湿, 还原程度也越高, 强磁性矿物就被损耗得越多. 正是这种高纬度的成土作用可能是导致其古土壤磁化率比黄土更低的主导因素之一. 相似文献
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JIRI CHLACHULA ROB A. KEMP CATHERINE A. JESSEN ADRIAN P. PALMER PHILLIP S. TOMS 《Boreas: An International Journal of Quaternary Research》2004,33(2):164-180
Two high-resolution loess-palaeosol sections from the Ob Loess Plateau (Iskitim) and the Minusinsk Basin (Kurtak 33) provide new detailed information on the last interglacial climate variations and landscape development in the parkland-steppe zone of southern Siberia. The complete last interglacial sensu lato (130-74 ka BP) records of the two sites, documented by magnetic susceptibility, grain-size, CaCO 3 and organic carbon content as proxy climatic data, and supplemented by thin-section studies, indicate several short warm and very cold intervals correlated with OIS 5e-5a. A strongly continental warm climate culminated around the peak of the last interglacial sensu stricto (OIS 5e) and cooler conditions occurred during the following interstadial stages (OIS 5c and 5a), corresponding to shifts in palaeolandscape development with gradual replacement of parkland-steppe and mixed southern taiga by boreal forest. During stadial stages (OIS 5d and 5b), the palaeolandscape was transformed into a cold arid periglacial tundra-steppe. Evidence for a major cooling in Siberia during OIS 5d, corroborating the palaeolimnological record from Lake Baikal, is provided by deep frost-wedge casts distorting the OIS 5e chernozemic palaeosol, suggesting formation of permafrost shortly after the last interglacial climatic optimum. The pedosedimentary record, reflecting the effects of syndepositional pedogenic processes, attests to a dynamic climate pulsation during the last interglacial stage. 相似文献
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JIRI CHLACHULA NIKOLAI I. DROZDOV NIKOLAI D. OVODOV 《Boreas: An International Journal of Quaternary Research》2003,32(3):506-520
Multidisciplinary Quaternary investigations in the Minusinsk Basin in the upper Yenisei River region and other southern Siberian continental depressions have produced evidence of prehistoric peopling pre‐dating the last glacial stage (>100 ka BP). Abundant ‘pebble tools’ and bone artefacts exposed from eroded alluvia of the Yenisei River terraces indicate repeated occupation of this territory since the Middle Pleistocene. A new stage of expansion of the early human occupation habitat occurred around the last interglacial (OIS 5e) by a Middle Palaeolithic (Neanderthaloid?) population characterized by a core and flake stone industry and open‐air occupation sites. The key camp/kill‐processing site at Ust‘‐Izhul’, dated to c. 125 ka BP and documenting complex behavioural activities, is so far the most complete in situ pre‐Late Palaeolithic site found in Siberia. This unique record provides new insights into the timing and the palaeoenvironmental conditions of the Pleistocene colonization of north‐central Asia. 相似文献
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