Study On The Physical Chemistry Character Of Holocene Palaeoflood Deposit In LuoYang Basin

Human's culture had developed fleetly in Holocene. Ancient human created resplendent culture, such as LaoGuanTai culture, YangShao culture, LongShan culture and XiaShangZhou culture. The Neolithic culture development clearly responded to the environment changes. Zhou tribe had to migrate other place to find new possession and food when environmental changes so very strong or abrupt that climate is too aridity. LuoYang basin became the center of China in 770 BC, when Zhou King takes the LuoYi as his new national capital. So, it is very important to study the background of palaeoflood and physical chemistry character of Holocene palaeoflood deposit in LuoYang basin.Based on the detailed field investigation in LuoYang basin, one typical Holocene GDZ loess-palaeosoil sequence and four flood deposit profiles were studied by the proxy climatic data of magnetic susceptibility, loss-on-ignition, CaCO₃ and geochemical elements. The result revealed the climatic change, which brought about by monsoon change and discrimination between dust accumulation and palaeoflood deposit. The main result can be identified as follow.1. The background of Holocene palaeoflood deposit in Luoyang basin. The Malan Loess indicate that Aeolian dust and drought in the Last Glacial before 11, 500 a B. P.. Late Last Glacial between 14, 700 a B. P. and 11, 500 a B. P. shows changefully climate. The data of magnetic susceptibility and loss-on-ignition can be clearly identified the Younger Dryas in the Late Last Glacial loess. The early Holocene between 11, 500 a B. P. and 8, 500 a B. P. is the interim before Holocene Climatic Optimum. It is also drought and cold in Luoyang basin. The palaeosoil SO developed during Holocene Climatic Optimum that was dated to 8, 500a B. P.～3, 100a B. P. in Luoyang basin. It indicated that Climate optimum, faintish Aeolian dust and soil formation. The analytical data indicated that increased climatic aridity in 3, 100 a B. P.. It was caused by a shift from the dominance of the maritime monsoon to the continental monsoon in the East Asia. The marked aridity induced a considerable deterioration of environment and degradation of land resources. It reveals intensified aeolian dust storms and dust accumulation, associated with a reduction in soil moisture and biopedogenesis at 3100 aB. P. The Aeolian dust rate is higher than early Holocene. It can be proved by that the contents of elements in new loess are more than Malan loess. High-resolution data can indicated that wind power is enhanced. The coarse sand can be sediment in Luoyang basin. At the operation of same enhanced wind, the sand on the floodplain can be blow toward river terrace and cover palaeoflood deposit. The climate change and human activity after 3100 a B. P. is the background of palaeoflood. Although the climate is drought and cold, the climate is fluctuant and human activity is enhanced. So palaeoflood is frequent in Luoyang basin.2. Compared With loess layer and soil layer, palaeoflood deposit can be identified through chemical elements grain-size, magnetic susceptibility, CaCO₃ and loss-on-ignition. The average content of Si, Na in palaeoflood deposit was small than it in loess layer or soil layer. The average content of Al₂O₃,Fe₂O₃,CaO,MgO,K₂O,Ti in the flood deposit was more than it in loess layer or soil layer. The main elements which migration in palaeosoil was small in flood deposit except Ca and Mg. However the main elements that were enriched in palaeosoil was more in flood deposit. The trace elements Ba,Mn,P,Sr were enriched in the flood deposit. And trace elements Cu,Ni,Rb,Zn,Rb were enriched in clay deposit. The content of them in thick flood deposit was small than them in palaeosoil layer and more than them in loess layer.3. The palaeoflood deposits have higher magnetic susceptibility, CaCO₃ content and loss-on-ignition. Compared with flood deposits, the loess and soil layer have lower magnetic susceptibility, CaCO₃ content and loss-on-ignition. Among the palaeoflood deposits, magnetic susceptibility enriched in sand or sility sand deposit. On the other hand, loss-on-ignition enriched in clay deposit.