Provenance of late Pleistocene loess in central and eastern Europe: isotopic evidence for dominant local sediment sources
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Abstract Loess profiles along the Danube River provide a record of long-term Quaternary dust (loess) deposition in central-eastern Europe. Here, Sr–Nd isotopic data from four loess-palaeosol profiles (47 samples) spanning the last two-glacial-interglacial cycles are presented. The isotopic compositions generated by this study are compared with bedrock and sedimentary samples from Europe and North Africa to decipher the sources of sediment. The results demonstrate that over the last 300 ka the alluvial plains of the Danube (which are themselves sourced from surrounding mountain belts) are a local source of material and consequently sediment experiences aeolian transport over relatively short distances. The results dispute the commonly held assumption that the Sahara was a sediment contributor to loess in central-eastern Europe as North African contributions are not needed to explain loess signatures. Consequently, the findings suggest a suppressed southerly wind direction and dominance of the westerly and north-westerly wind systems over the entirety of the record.Keywords:
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Abstract The loess deposits in the southern part of the South Island represent at least four major periods of accumulation. The deposits include the present soil and three well-defined paleosols separating individual loess members. A fourth poorly defined paleosol within the uppermost loess member is considered to represent a minor period of soil formation. The name Stewarts Claim Formation is proposed for the loess deposits of the region. The formation comprises four members: Yellow loess member (the youngest); Brown A loess member; Brown B loess member; and Brown C loess member (the oldest). The distribution pattern and morphology of the loess deposits is described. It is considered that in most localities, paleosols do not have a complete paleo-solum. The break between a paleosol and the overlying loess of the succeeding deposit is marked by a sharp boundary, in many places associated with a discontinuous stone line. The morphology of paleosols is comparable to that of the lower part of the solum or sub-solum horizons in present day soils developed on loess, particularly the yellow-grey earths. Thus it is considered that a period of “pedosphere stripping” has decapitated the soil prior to the deposition of the succeeding loess layer. Wood fragments at the base of the second youngest loess member immediately above the second major paleosol give a radiocarbon date (NZ1457) of 21 500 ± 1100 years B.P. The loess deposits are considered to span the period from the Waimean Glacial Stage to the present day and are correlated with advances and retreats of the ice during the Pleistocene.
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From observing in field, the author has found the third paleosol in Xi'an region that developed in middle pleistocene, consists of 3 paleosol layers and 2 loess beds, which is different from S\-3 of Lanzhou profile and of Baicaoyuan profile. In Xian region, Shuangzhucun section lies to the southern of Xi'an city and Duanjiapo section lies to the eastern of Xi'an city. Firstly, stratigraphic structure was studied, from top to bottom the structure units are S\-\{3-1\}, L\-\{x-1\}, S\-\{3-2\}, L\-\{x-2\}, S\-\{3-3\}, L\-\{x-3\}. Secondly, the samples gathered from Shuangzhucun section (or Duanjiapo section ) was analyzed in laboratory; magnetic susceptibility, TOC and granulometric composition were studied, and the results are as following:\;(1) The maximum magnetic susceptibility value (296 SI) of S\-3 in Shuangzhucun section and the average value are all more than those of S\-0, S\-1 in other sections, for example, Qishan profile and Fufeng profile. The results show that the soil developing of the third paleosol in this area is stronger than that in others. On the curve of magnetic susceptibility of S\-3, there are 3 peak values corresponding to paleosols and 2 valley values corresponding to loess beds. In the meantime, the fact that the magnetic susceptibility value of the loess(141 SI) is far more than Malan loess shows that the loess layer between paleosols isn't pure loess parent material in Duanjiapo section; the magnetic susceptibility values of the top paleosol and the bottom paleosol appear two peaks, and the middle paleosol is not same as these.\;(2) From the result of TOC analyzing to Shuangzhucun section, it is found that the contents of TOC of paleosol and loess are all lower (0.8%), but it still appears clearly peak and valley alternating: the peak of wave corresponds to paleosol(0.5%) and the valley corresponds to loess (0\^5%).\;(3) Analyzing to granulometric composition of S\-3 from Shuangzhucun loess section shows that the composition of paleosol is distinctively differentiated from that of loess layers. Every group of grain size, \%M\-d\% and \%S\-o\% appear distinctively changed in loess layer, and these changes are corresponding to quickly accumulation of loess at that time.\;According to the characters of stratigraphic structure, magnetic susceptibility, TOC and granulometric composition described above, as well as ancient temperature and rainfall that is recovered based on the curve of magnetic susceptibility, the period of time (330~272 ka B.P.) when the third paleosol formed may be divided into 6 stages of warm humid and cold arid climatic changes. The 6 stages show 3 climatic cycles: cycle I, include L\-\{x-3\}, S\-\{3-3\}; cycle Ⅱ, include L\-\{x-2\}, S\-\{3-2\}; cycle Ⅲ, L\-\{x-1\}, S\-\{3-1\}. The climatic character was cold and arid when L\-\{x-3\}, L\-\{x-2\}, L\-\{x-1\} were accumulating; when S\-\{3-3\}, the climate was subtropic warm humid; S\-\{3-2\}, the semi humid climate of warm temperate zone; and S\-\{3-1\}, the humid climate of warm temperate zone.
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Abstract Loess accumulation and paleosol formation are important Quaternary geoarchives in northern Iran. Two loess-paleosol sequences at Mobarakabad and Aghband were examined using soil morphology and micromorphology, mineralogy, magnetic susceptibility (MS), free Fe oxides and calcium carbonate equivalent. The loess-paleosol sequences provide a record of changes in paleo-rainfall in the northern Iran. Micromorphological and MS differences between the loess and paleosols in the sections reflect changes in climate. The different behaviors of magnetic susceptibility between Aghband and Mobar-akabad loess are mainly produced by their different pedogenic environments, topography and climatic conditions. As a result, the MS at the Mobarakabad section is much higher than at Aghband. Paleoeco-logical reconstructions coupled with magnetic depletion in paleosols at Mobarakabad suggest a wetter climate dominating during the formation of the paleosols.
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In this paper,the chemical weathering intensity and the element migration features of the LC loess-paleosol profile in the Zhouyuan region are studied in detail after analyzing the elements and their variation with XRF.Research results show that CIA value and Rb/Sr and Na/K ratios were obviously different in paleosol and loess layers.The CIA value and Rb/Sr ratio were high in paleosol layer(S0) but low in loess layer(L0),while Na/K ratio was lower in paleosol than in loess,revealing that chemical weathering of paleosol(S0) was more intensive than that of loess(L0).The chemical weathering difference between paleosol(S0) and loess(L0) was mainly caused by the distinction of climate conditions.The stronger chemical weathering in paleosol reflects that the climate was warm and humid with high eluviation during the paleosol formation.A relative enrichment of Si,K and Fe occurred during the loess formation,while Ca,Na,Mg and Ti were migrated and leached during the chemical weathering process.The migration capability of elements was in an order of Ca Na Mg Ti Al Si K Fe.Through the research of the activities of elements in the LC profile,it was found that Holocene loess in the LC profile experienced the primary process of chemical weathering characterized by leaching of Ca and Na,or just reached the secondary process characterized by leaching of K.
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