Surface Features Of Quartz Grains Of Aeolian Deposit In South China And Its Environmental Significance

Based on different types of quaternary aeolian sediments in south China such as aggradation Quaternary red earth(reticulate red clay, homogeneous red soil, yellow brown soil), the Xiashu loess, aeolian sand and aeolian sand, the research of grain size analysis and observation on surface features of quartz grains is done, we found that different types of eolian deposition of materials are closely linked, the main conclusions are as follows:(1) Different types of quaternary aeolian sediments in southern China has the similarity on grain size content and surface features of quartz grains. From the grain size composition analysis, silt is the dominant grain size in reticulate red clay, homogeneous red soil, yellow brown soil, and the Xiashu loess, but there is a difference on silt and clay content, silt (4～63μm)mean content shows:Xiashu loess (77.81%)> yellow brown soil (66.65%)> homogeneous clay (65.36%)> reticulate red clay (62.90%), and the average content of clay shows:reticulate red clay (35.52%)> homogeneous clay (31.36%)> yellow brown soil (28.75%)> Xiashu loess (19.76%). From the quartz grain shape analysis, aggradation Quaternary red earth and the Xiashu loess are in poor psephicity, but in comparison, the Xiashu loess is less accretion clay grinding roundness, there is a difference on roundness in different aggradation Quaternary red earth layers,showing that the reticulate red clay roundness is better than the homogeneous clay, homogeneous clay roundness slightly better than the yellow brown soil, aggradation Quaternary red earth and the Xiashu loess have characteristics of eolian features such as dish-shaped pits, crescent shaped pits, pockmarked pits, at the same time also shows the underwater environment characteristics such as conchoidal breakage fractures, Ⅴ-shaped pits, hit the ditch, and so on, generally speaking,eolian characteristics are superimposed on underwater environment characteristics, there are chemistry traces such as SiO2dissolution and precipitation. The chances of mechanical characteristics occurred show Xiashu loess> yellow brown soil> homogeneous clay> reticulate red clay, SiO2dissolution and precipitation chemical traces show reticulate red clay> homogeneous clay> yellow brown soil> Xiashu loess.(2)In different areas of south China, quaternary aeolian sand has evident difference on grain size and surface features of quartz grains. Although The profile of Gufodong, Qingfeng and Henggang are all aeolian sands, but they show great differences on silt and clay content. sand content of Gufodong profile is70.08%～100%, mean content is89.07%;sand content of Qingfeng profile is45.99%～90.77%, mean content is73.23%; Henggang profile26.79%～88.40%, mean content is45.29%. Obviously, Henggang profile, located in the inland,coming from riverbed sediment, contains more silt and clay particles, but the Gufodong and Qingfeng profile, located in the coastal areas, coming from sand of the beach,contains less silt and clay particles. From the point of quartz grain surface morphology, the sand of Gufodong、Qingfeng and Henggang profile, all inherit typical characteristics of underwater environment (Conchoidal fractures, Ⅴ-shaped pits, triangle pits, etc.), at the same time, aeolian characteristics (dish-shaped pits, crescent shaped pits, pockmarked pits, etc.)inherited. In addition, SiO2dissolution and precipitation chemical traces on sand surface is well developed, implying these sands experienced both aeolian and underwater environment, and accepted weathering of soil reconstruction. On the other hand, coastal aeolian sand, shows better psephicity than inland riverbed aeolian sand. By comparing we also found that the chances of underwater environment characteristics such as Conchoidal fracture, Ⅴ-shaped pits occurred show Henggang profile>Gufodong profile>Qingfeng profile; and dish-shaped pits, crescent-shaped pits,pockmarked pits show Qingfeng profile>Gufodong profile>Henggang profile; From the aspect of SiO2dissolution and precipitation chemical traces,show Qingfeng profile>Gufodong profile>Henggang profile; Siliceous ball, siliceous scales, siliceous films SiO2precipitation and crystal growth, such show Henggang profile>Gufodong profile>Gufodong profile, the three profiles, the difference in the respect of psephicity, and the chances of aeolian marks, underwater environment characteristics occurred reflects the difference between the land and sea and latitude on the influence of quartz sand.(3)In south China aeolian deposit grain size and quartz grain morphology revealed that different types of eolian deposition are closely linked. In terms of grain size, on the respect of aeolian sand composition of<63μm component silt is the dominant grain size, its content is more or less with yellow brown soil and the Xiashu loess, aeolian deposit coming from coastal and inland riverbed areas in wind season can be a source of Quaternary red earth. The inference is confirmed by the quartz grain surface morphology, quartz grain surface morphology in different layers of Quaternary red earth show several marks of dynamic role, and underwater environment characteristics are often inherited by aeolian features and chemical traces. Thus proves that the aggradation Quaternary red earth in southern China have several source materials, combining previous research achievements of inference,we infer that in the ice age, sea level is reduced, the continental shelf area was exposed, the loose deposit was moved by wind in the coastal zone, became coastal dunes, silt was carried by wind and accumulated in appropriate places, at the same time, strong ancient winter wind can carry faraway source of dust in the. north to the south, and also can carry the loose deposit in the middle and lower reaches of the Yangtze river to the south, coarse grains accumulated,and formed inland sand dunes, dust transported to distant place became aggradation Quaternary red earth and Xiashu loess, in southern China formed aggradation Quaternary red earth and Xiashu loess. Dust deposition in southern China, therefore, not only materials with multiple source, but also carried by multiple strengths, the winter wind, summer wind, and typhoon,all could carry sand and dust. After dust, sediment accumulation is affected by regional climate, in the aspect of the reformation of weathering of soil, Xiashu loess,which is located in the north subtropical region of China is weaker than aggradation Quaternary red earth in central and south China and south subtropical region, this phenomenon reflects the effects of sediment accumulation after latitude zonality.