Two pedogenic models for paleoclimatic records of magnetic susceptibility from Chinese and Siberian loess |
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| Authors: | Liu XiuMing Liu TungSheng Paul Hesse Xia DunSheng Jiri Chlachula Wang Guan |
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| Institution: | (1) Key Laboratory of Western China’s Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou, 730000, China;(2) Department of Physical Geography, Macquarie University, NSW, 2109, Australia;(3) Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;(4) Key Laboratory of Desert and Desertification, Institute of Cold and Arid Regions Environmental and Engineering, Chinese Academy of Sciences, Lanzhou, 730000, China;(5) Laboratory for palaeoecology, Technical University Brno, FT VUT Zlin, 762 72 Zlin, Czech Republic |
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| Abstract: | 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. |
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| Keywords: | Siberian loess Chinese loess paleoclimate magnetic susceptibility magnetic mineralogy environmental magnetism |
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