Holocene Environmental Change Of Pedogenensis And Sandstorm Activity In The Midwest Region Of Guanzhong Plain

It is the nearest period from now to Holocene, and it is extremely close to mankind. Holocene environmental change is focal point study in the past; nowadays it has same part too. In recent years, Holocene environmental change becomes one of geographical focus that educational circles study. Understanding Holocene environmental change and sandstorm activity is very important for us to enrich the theory of Holocene environmental change, realize the geographical environment at the present stage, and impel people to develop with natural environment in harmony.After investigating a large number of fields, we chose the imperial Shengli village section of Baoji and Milu village section of Lantian in Guanzhong Plain of the southern loess plateau. These two sections keep excellent records of Holocene environmental change. After investigating exhaustively, we get 81 samples of Baoji section and 95 samples of Lantian section.By studying the ancient environmental information of loess-palaeosol sequence, we could resume and rebuild environmental change of Pedogenensis and sandstorm activity .So we chose grain-size, magnetic susceptibility, Calcium carbonate and pH value of soil four indexes to acquire information about environmental change of Pedogenensis and sandstorm activity since Holocene.The content change of grain-size hit 50~10um and below 5um point out the extent of winter monsoon activity and summer monsoon activity respectively, Calcium carbonate and pH value of soil have reflected the moist degree of the climate at that time. These indexes offered possibility to study environmental change. The peak of grain-size hit 50 ~ 10um and Calcium carbonate value correspond the weak pedological process, in this period the sandstorm activity aggravated. The peak of magnetic susceptibility and grain-size below 5um correspond the strong pedological process, in this period the sandstorm activity subsided.The main results are following:Firstly, the change of climate in this region can be divided into three phrases since Holocene:In early Holocene, climate turned warm gradually, pedological process was becoming strong slowly, sandstorm activity weakened; In middle Holocene,pedological process was very strong, Summer monsoon reached its maximum, sandstorm activity was seldom; In late Holocene, climate deteriorated again, Summer monsoon was weaker and Winter monsoon was stronger, pedological process deteriorated and sandstorm activity increased.Secondly, in this region, during the process of influencing pedological process and sandstorm activity, the natural course is main, the human factor has just aggravated the natural course to a certain extent, the deterioration of this region 's pedological process proved this especially in late Holocene.Thirdly, in reproducing pedological process and sandstorm activity, grain- size, magnetic susceptibility , Calcium carbonate and pH value of soil four indexes have good instructions. Comparatively speaking, the grain-size index changes comparatively fast; especially when the monsoon pattern is changed, so grain-size index is more sensitive than other three indexes in reflecting environmental change of Pedogenensis and sandstorm activity since Holocene.Fourthly, there are obvious differences in pedological process and sandstorm activity of the middle region of Guanzhong Plain and the western region of Guanzhong Plain. That to say, pedological process in the middle region of Guanzhong Plain is superior to the western region and the western region is comparatively sensitive to the effect of the northwest monsoon. In late Holocene, relatively high crude particle content of the middle region section instructs the intensity of sandstorm of this place to be greater than the middle region.Finally, since 3100 a B.P., sandstorm activity have 10 periods that strengthen roughly, and 10 periods that weaken roughly in this region, sandstorm activity is strong at present. During the period of sandstorm activity increased, Winter monsoon is stronger, pedagogical process deteriorated. On the...