| Loess deposited all over the world has been a key Quaternary paleoclimatic archive. Environmental parameters (e.g. magnetic susceptibility) served as paleo-indicators facilitate the reconstructions of paleoenvironment and paleoclimate. However, magnetic characteristics and its spatial discrimination for surficial samples are not so well investigated comparing to magnetic study on loess deposits, which is not systematic enough. For example, distributions of magnetic properties and the pattern for dust component are still not clear enough, as well the correlations to climatic and environmental factors. Thus we plan to investigate the surficial loessic component in field of rock and environmental magnetism, correlate such differentiation to controlling factor like precipitation, wind velocity and so on in East Asian dust sources, with hopes to better understand the origin and transport, to broaden paleoclimate reconstruction based on loess deposition located in drylands, which will certainly provide con theoretical supporting technics in reconstructing paleoenvironment and discovering the global changing pattern.The research regions includes Taklimakan Desert, Gurbantunggut Desert, Qaidam Basin, Gobi Desert, Hexi Corridor. We characterize the composition, concentration and domain state of typical samples by kinds of systematic magnetic measurements, hysteresis loops, low temperature saturation isothermal remanent magnetization variation, low temperature variation of magnetic susceptibility and so on, discuss possible and potential effects to these spatial differentiation by climatic and environmental factors. As well, a typical loess profile located in north of Tianshan Mountains is investigated based on the spatial analysis in dry potential dust sources, in which environmental meanings of magnetic proxies are demonstrated.Preliminary results are summarized as follows:(1) The magnetic investigation is expanded to spatial samples systematically, which is mostly worked in vertical loess depositions in past decades. Combination of vertical and spatial analysis on magnetic changes provide better understanding on loess development as well as the environmental meaning of paleo-proxies like magnetic susceptibility and saturation magnetization. Besides discussion on typical magnetic indicators, new magnetic parameters are suggested to calculate mineral alteration like the surface oxidization of magnetite (maghemitization) post-deposition, for example the Mn (10K), which would be potential paleo-proxy for loess research in arid and semi-arid regions.(2) A grain size dependent model for dust transport is proposed, which shows that the transport way (suspension, creep, saltation) are different for certain mineral because of the separated density. The "heavy" mineral (high density) has a small grain range for suspension travelling, while "light" mineral (low density) has a wide grain size range for suspension travelling. A further deduction is that concentration of heavy mineral will be enriched during travelling downwind wards. This facilitates the difference mineral composition between loess deposited in Chinese Loess Plateau and in drylands in East Asia separately.(3) We analysis the spatial variation and its controlling factor for dust conponent of surface samples in dust sources in East Asia, providing theoratical support for loess reconstruction. Furthermore, Verwey transition models are found to change spatially from source to deposition region, which show a new way to identify the pedogenesis degree for deposited dust.By systematically investigating magnetic properties of surfacial loessic component from East Aisan dust sources, we found that wind "fractional on effect" controls the spatial distribution of magnetite, while the maghematization degree is clear related to annual precipitation, though which is extremely low in arid areas. The magnetci susceptibility in Zhongliang loess profile reflects the concentration variation of input magnetite, which is correlated to the wind velocity. |
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