The Relationship Between The Loess Deposition In Liaodong Peninsula And The Desertification On Yellow Sea And Bohai Sea

Loess is a special earthy deposits which is formed in dry and cold climatic conditions in Quaternary Ice Age, characterized by widespread deposition of continuity,and paleoclimate evolution can be revealed through the study of loess,and global environmental change can be indicated too.The cause of loess research has experienced a tortuous development process which has undergone through Upheaval Dominant period into Aeolian theory Dominant period,and into Weathered Residual Theory Dominant period,in which the history of Aeolian theory lasted the longest time,and when we research the cause of the loess sediment,we essentially discuss the material source of the loess.The typical loess of Loess Plateau is a strong evidence of Aeolian theory ,but the loess of eastern coastal in China,investigated by many scholars,was found that coastal loess grain size and magnetic susceptibility are very different from the loess of Loess Plateau.In this paper,the loess material source is determined through the loess grain size,and the relationship between the loess of coastal shelf and desertification is researched.The author came to Anzi mountain Zhoujiagou near a brick factory twice to investigate the loess,including the Geological and Geomorphological features,profile measurement,sample collection and so on.In this paper,the grain size experiment was done in Peking university,and the analysis of grain size indoor is shown that the loess diameter of all samples in this district basically focus between 4φand 6φ,according to the above data,we find that the loess grain size composition is thick.On this basis,we have done the comparative analysis of grain size between the loess in Zhoujiagou and Qiding mountain,Temple Islands,Luochuan,and modern aeolian and beach sand of Temperate coast in the Yallow Sea and the Bohai Sea,there is more content of the fine sand in the volume fraction of the Malan loess,but there is more silt in the Lishi loess,and both of their grain size concentrated in the 4—6φ,so the loess grain size is a little coarse in Liaodong Peninsula compared with Loess Plateau.According to eolian principle,there is smaller grain size in Liaodong Peninsula than in Loess Plateau,so it shows that loess sediments consisits either dust deposition from inland northwest or fine-grained components in diluvial gravel from western Liaoning Province and Bohai Bay.According to the experimental data,the grain size of Malan loessis more coarse than it of Lishi loess,so it indicates that East Asian winter monsoon prevails in late Pleistocene in which the temperature is very low and it is less precipitation and there is weak Secondary soil-forming ,accordingly in this period,there is a global regression phenomenon—the Yellow Sea and Bohai Sea shelf completely exposed,then,because of wind erosion,it has experienced wind erosion depression after the wind erosion platform,eventualy shelf desertification has been formed which also provided coarser material source for Malan loess.The summer monsoon was stronger than the winter monsoon in the Middle Pleistocene,in which the temperature rose and the precipitation increased and pedogenesis increased too, therefore,the grain size of Lishi loess is smaller,and it is found that the magnetic susceptibility of Malan loess is lower than lishi loess.From this we can see the deposition of loess in Liaodong Peninsula closely linked shelf desertification of Yellow Sea and Bohai Sea.Through the study of loess distribution and properties and sequence ancient environment characteristics can be revived,and the evolution law of the ancient environment can be a important basis for predicting the climate change in Dalian and the surrounding area,the results of the research can become the the important data of the environment and can also provide new teaching materials.