The Environment Information And Magnetic Characteristic Recorded By Loess In Miaodao Islands, China

Loess deposition is a special kind of dust-sediment that came into being under particular environment in quaternary period. Loess deposition in China is widely distributed ,continuously deposited abd sensitively responded to paleo-environment and paleo-climate changes.So it is of great theoretic significance to study loess in Quaternary research . Systemic and overall researches are made on the loess,which is one kind of good carriers of paleo-environmental information of land, It has been an agreement that loess on Plateau is the sediment of aeolian dust. All of the proxies which are used in the research of loess distributed in Northwest China to reflect the variation of paleoclimate have been widely used in the research of Eastern Islands Loess For the reason of thin stratum and the great effects made by contemporary environment, it is an valuable research whether the proxies which are widely used in northwest to reflect paleoclimatal fluctuations could be used in the loess research successfully in those area. Paleo-environmental changes and the sedimentary mode of loess on islands are discussed in this paper and compared with the three profiles of Changdao Island and Islands of East China Sea on the proxies of grain size, magnetism ,CaCO₃ and CBD. Results and acknowledgements of this paper include five aspects as follows:1.The grain size composition of the Aeolian loess on Changdao island is basically consistent with that of other inland loess in China .Through the analysis of experimental outcome of grain size , it's confirmed that the three profiles have the same components carried by wind which consistent with the rule of belt distribution about Loess in China .The sendy grain content of Changdao Loess is higher than that in Islands of East China Sea, The loess in Changdao island belongs to sendy-clayey soil deposition ,while the loess in islands of East China Sea belongs to clay-clayey soil deposition. They all coincide with that sandy-loess zone ,loess zone and clayey-loess zone distribute from west to east in China. Compared with that of other inland loess ,the content of sendy grains of the three loess profiles is relatively higher ,it indicates that the study profiles received not only far Aeolian deposition from northwest by strong winter monsoon as other inland loess but also proximal one from inshore shelf area during the last glacial age. And the content of sendy grains of the loess can be regarded as an index that shows the proportion of Aeolian deposition.2.The content of magnetic minerals of loess on Changdao Island is less comparatively and the ferrous-magnetic minerals play a leading role. The top part of Shengshan about 60cm thickness of the profile contains more anti-ferromagnetic minerals which indicates the violent pedogenesis and weathering. Concentration of stable singe domain magnetic mineralscauses the increase of magnetism in the middle part of the profile And Super-paramagnetic and multidomain minerals dominant the components of loess at the bottom of this profile,different from which it's the multidomain minerals cause the increase of magnetic susceptibility in Langgangshan Islands profile. The content of magnetic minerals of the three profiles are obviously lower than typical loess profile ,it shows that the matter source is different from inland .But the lowest is about30× 10^-8m³kg^-1 ,which is similar to other inland areas, it indicates that the loess source of each area is consistent and it probably relates to land-desertification..3.The magnetic minerals formed during the process of pedogenesis are dissolved by CBD(Citrate-Bicarbonate-Dithionite)which indicates that CBD can be used better to reflect variation of paleoclimate in Changdao loess and loess in Shengshan Island and Langgangshan island even its pedogenesis verlapped with contemporary pedogenesis.Comparing the parameters of loess pre-CBD and post-CBD,it's found out that the magnetic minerals CBD dissolved are not only SP,but SSD and even PSD magnetic minerals. After dissolved by CBD, the main components of magnetic minerals in loess are MD magnetic minerals.4.The change of magnetic susceptibility of loess from Northwest China to East China after dissolved by CBD matches the change made by wind transport.From the conclusion above, it can be concluded that CBD technology may be better used to distinguish the size of magnetic minerals.