Physico-chemical Studies Of The Holocene Palaeoflood Slackwater Deposits In The Qishuihe River Valley

It is the nearest period from now to Holocene, and it is extremely close to mankind. Human's culture had developed fleetly in Holocene. The west of Guangzhong Basion is located in Loess Plain. The Holocene loess profiles provide detailed information about environment change. Meanwhile, Guanzhong Basin is one of the headstream of human culture and the center of china's civilization. The ancestors created LaoGanTai culture,YangShao culture, LongShan culture and XiaShangZhou culture.The ancient human had to migrate other place to find new possessions and food when environment change so very strong or abrupt that climate is too aridity. So it is very important to study the of palaeoflood and physical chemistry character of Holocene palaeoflood deposit in Qishuihe River.The author selects one typical Holocene LC loess-palaeosoil sequence and flood deposit HXZ-E. The result revealed the rule of Holocene climatic change. On the basis of outdoor observation and indoor experimental analysis, selects the proxy substitute indexes, such as magnetic susceptibility, grain-size (>0.1mm),CaCO₃ and loess-on-ignition which have an important indicative significance to paleocilmatic evolution. Through the comparison study of these climatic substitute indexes, the thesis reveals the process of the evolution of climatic environment and human culture in the eastern area of Guangzhong Basion. Finally ,the thesis investigates the relationship between the evolution of environment and that of human culture.The results are as follows:Compared with loess layer and soil layer, palaeoflood deposit can be identified through chemical elements grain-size, magnetic susceptibility, CaCO₃ and loss-on-ignition, clay/silt ratio.The relationship of the magnetic susceptibility loss-on-ignition and clay/silt ratio is better. The magnetic susceptibility is the highest in SWD2,SWD4. In the SWD1,SWD3,SWD5 palaeoflood deposits the magnetic susceptibility are lower than the palaeosol but higher than that in Malan loess. The magnetic susceptibility is lower in the coarse palaeoflood deposits and higher in the fine palaeoflood deposits. The clay/silt ratio is higher in the SWD2,SWD4. It is lower in the SWD1,SWD3,SWD5 palaeoflood deposits. The clay/silt ratio is also lower in the bottom of palaeoflood deposits, and it is higher in the upper of palaeoflood. The loss-on-ignition is the highest in the fine palaeoflood. It is lower in the coarse palaeoflood than that in palaeosol. The CaCO₃ is irregular in the palaeoflood because of the happening flood times and the time of the deposition. The CaCO₃ is lower than that in Malan loess and higher than that in palaeoflood deposits.Compared the NGZ profile and LC profile we revealed the climate of the west of Guangzhong Basin. (1) During the stage of late Pleinstocene Loess (L₁)accumulation (>11500 a B.P.), climate was clod and dry. Sand blown by wind and dust storms were intense and soil humidity was very low . (2) the end of the last ice age～8500 a B.P., through comprehensive analysis of these proxy climate substitute indexes reveals: this was a period in which the temperature risen and the precipitation increased, but it was mainly still dry and cold; there were flood deposits in the dust sediments of late stage. (3) 8500～6000 a B.P. according comprehensive analysis of these proxy climate substitute indexes shows: this was a period in which the temperature was the highest and the precipitation was the greatest. (4) 6000～5000 a B.P., though comprehensive analysis of these proxy climatic substitute indexes indicates: this was a dry and cold period in which the temperature was the lowest and the precipitation was the least. (5)5000～3000 a B.P., through comprehensive analysis of these proxy climate substitute indexes indicates: this was another warmth and humidity period in which the temperature risen and the precipitation decreased, but the warmth and humidity were not as proper an those in the best period mentioned above. (6)Since 3100 a B.P., though comprehensive analysis of these proxy climate substitute indexes indicates: this was a dry and period in which the temperature fell the precipitation decreased.In HXZ-E profile shows that 5 palaeoflood events in it. In the palaeoflood contains Keshengzhuang culture, Miaodigou culture and Xiazhong culture. Compared with the cultural remains and loess-paleosol we reveal occurrence time of the palaeoflood. We reveal the palaeoflood occurrence cause and the impacting human Being. The palaeoflood were caused by climatic environment and human activity.