Comparison of textural features of loess and reworked loess in Yili area, Xinjiang.
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Yili area is located in the west of Xinjiang and is an intermountane basin of Tianshan, in which the loess is widespread. Only a few studies were carried out during past decades. For this reason, there are different opinions on the origin of loess. The results of grain size analysis of loess and reworked loess show that the textural features of both are same on one side and different on the other side. Firstly, the composition of grain size of loess is similar to that of the reworked loess, but the sand particles of loess is higher and the clay particles is lower than that of reworked loess. Secondly, the frequency curve of loess and reworked loess occures to be positive normal distribution. The mode of both locates in the range of 15-30μm, but the percentages are different. The amount of loess is less than 20 %, while the maxmum percentage of reworked loess reaches 50 %. Thirdly, the sorting of loess is better than that of the reworked loess, even though both are poor sorting deposits. The skewness of loess ranges from 0. 13 to 0. 43 and most of them is lower than 0. 3. Comparied with the loess, the skewness of reworked loess is higher and the mediun size moves toward coarse side. The kurtosis of loess is medium, while peak of reworked loess is steep. In summary, the loess and the reworked loess were transported and sorted by different dynamics before the dust deposited. In addition, the depositing environments were also different. The evidences from the grain size show the loess in Yili area is a typical eolian deposit.Cite
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The malan loess in the zhaitang basin is one late pleistocene marker stratum in China.In order to reveal the origin and palaeoenvironment of the loess in Zhaitang basin the texture and structure and grain size of the loess and its carbonate and ferromanganese aggregate in this area are studied.The result shows that the texture and structure and grain size of the loess in Zhaitang basin are similar to those of loess on the middle reach of the Huanghe River.They are of eolian deposition.But the lishi loess in Zhaitang basin is different from the loess on the middle reach of Huanghe River in that it was subject to multiple proluvial deluvial processes in its deposition process.The Malan loess were also subject to several congeliturbations,indicating that the temperature in some stages of the loess formation process in Zhaitang basin was comparatably low.
Texture (cosmology)
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Silt
Paleosol
Loess plateau
Deposition
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Previous studies have indicated that a genetically meaningful decomposition (unmixing) of loess grain‐size distributions can be accomplished with the end‐member modeling algorithm EMMA. The independent decomposition of two series of loess grain‐size records from the NE Tibetan Plateau and Loess Plateau spanning the last glacial‐interglacial cycle indicates that the two data sets are described by very similar mixing models. The average mixing model presented here is regarded as representative for the vast loess region in northern China and allows quantification of the contribution of three loess components to the loess grain‐size distributions. A genetic interpretation and the paleoclimatic significance of the average mixing model have been provided by comparison of the modeled loess components with modern dust samples in terms of their grain‐size distribution and flux rates, and by the distribution patterns of the loess components across the Loess Plateau reconstructed for the last two glacial‐interglacial cycles. The sandy and silty loess components represent the coarse dust fraction supplied by saltation and short‐term suspension processes over the proximal part of the Loess Plateau during major dust outbreaks in spring and early summer. The low‐level winter monsoon (northwesterly wind system) is the likely transporting agent for these dust events. A clayey loess component represents the fine dust component supplied over the entire Loess Plateau by long‐term suspension processes during major dust outbreaks and as part of a background supply system. The clayey loess component in the glacial loess deposits is dominantly supplied during major dust outbreaks by the northwesterly winter monsoon, whereas the clayey loess component in the interglacial paleosols is mainly supplied by non‐dust‐storm processes, possibly with a significant contribution by the high‐level subtropical jet stream (westerly winds).
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Atterberg limits
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Silt
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Outwash plain
Peninsula
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Loess deposits with varying thicknesses are widely distributed on intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous region.A systematic grain-size analysis was performed along the Fujiazhuang loess section of the Qingzhou area.The analytic results of the samples were correlated with those of the samples taken from Quaternary loess-paleosol of the Loess Plateau,modern dust fallouts in Beijing and fluvial deposits.The results show that the grain-size distribution of the Qingzhou loess is very similar to that of modern dust fallouts in Beijing and loess of the Loess Plateau but notably different from that of the fluvial samples.In the whole loess-paleosol sequence,the grain-size variation of the Qingzhou loess is consistent with the typical eolian loess and paleosol of the Loess Plateau.The loess is coarse in size,while the paleosol is fine in size.The above-mentioned results provide evidence for the eolian origin of the Qingzhou loess in the sedimentological context.The grain-size distribution of the Qingzhou loess combined with the previous studies indicates that the main provenances of the Qingzhou loess are the marine strata exposed in the flood plain of the Yellow River and Laizhou Bay north of the sedimentary region and less commonly distal silt and dust carried by highlayer circulation from northwest inland.
Paleosol
Silt
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Loess layers with different thicknesses are piled up widely on terraces of the Dasha River and piedmont zones. According to a study of the Zhangxia loess section, the author thinks that the materials of the loess have complex sources, comprising not only materials transported by west wind drifts and northwest and Laizhou Bay air currents but also local materials. During their accumulation, they were subjected to the action of water. The accumulation and development of the Zhangxia loess and paleosol accorded with the late Pleistocene climatic change and were also influenced by local microrelief, with black loam and Holocene deposits being absent. Zhangxia and Zibo are located in the central part of Shandong, where loess is finer in grain size, so loess in Shandong has no regularity to follow on the whole, which more evidently shows that the loess is complex and variable.
Paleosol
River terraces
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