A Study On The Luminescence Chronology Of The Strata Of Important Human Relics In Ganqing Area

Environmental change is an important driving factor for the development of human prehistoric culture.Studying the relationship between past global changes and human beings is of great significance to the response and adaptation of human society.Holocene is a key period of human prosperity and development in geological history.Human society and civilization developed rapidly in this period.Human sites in Holocene have preserved a variety of scientific information such as geomorphology,climate and environmental changes.As the most frequent prehistoric human activity area in Holocene,Ganqing region has preserved a large number of human sites.In this study,through detailed field investigation in Ganqing area,sections such as Shanglajia(SLJ),Shijiaya(SJY),Zhaojiaya(ZJY),Fanjiacheng(FJC)and others in human relic areas of Guanting Basin and Tianshui Basin were selected respectively.Chronology samples of different sections were systematically collected.The OSL age of the sections in the above-mentioned was obtained by using optically stimulated luminescence dating technology.Combined with archaeological data,a reliable stratigraphic age framework for the study section was finally established and the cultural period of the site was determined.The mudflow disaster events recorded in SLJ and ZJY profiles and the relationship with historical climate are analyzed.Finally,the following conclusions are drawn:(1)Preheating plateau,OSL signal,frequency distribution and dispersion analysis are carried out on 28 loess and 5 pottery OSL samples in this paper.The results show that OSL samples of aeolian sediments and fired pottery samples are suitable for preheating temperature of 260 ?-220?.The equivalent dose dispersion value of OSL samples in Loess Plateau is slightly higher than OSL samples on the front edge of Qinghai-Tibet Plateau.However,after removing the negative samples,the over-dispersion of the samples in the two regions can be calculated by the CAM.(2)Based on OSL dating results,the chronological framework of the loess-soil sequence in Guanting Basin and Tianshui Basin has been established.The specific framework is as follows:1.Malan loess layer(LI-1)in the late Late Pleistocene represents the end of the last glacial period;2.The transitional loess layer(Lt)in the early Holocene;3.Paleosol layer(SO)in mid-Holocene,climate warming first and then cooling gradually in mid-Holocene,and abrupt climate change occurred in 5500-5000a BP and 4200-4000a BP;4.Modern loess layer(LO),represents the end of the middle Holocene;5.Modern soil layer(MS).In Tianshui area,three loess-soil profiles have recorded loess(SO-Lx)deposited in paleosol(SO)in the middle Holocene under the influence of winter wind during the period of weakening East Asian summer monsoon and climate deterioration between 6,000 and 5,000 a BP.(3)Three large-scale flash floods and mudslides recorded in the Shanglajia(SLJ)Proflie of Lajia site in Guanting Basin occurred at about 3850 a BP,3800 a BP and 3600 a BP respectively.The first mudflow was the largest and most destructive destroyed the Qijia cultural settlement at Lajia site,and brought a large amount of red clay sediment out of the ancient remains.(4)The prehistoric mudflow of Zhaojiaya Site in Tianshui Basin occurred in the period of intense Holocene climate change,about 8500?6000 a BP,5500?4900 a BP and 4200?4000 a BP respectively.The first mudflow event occurred in the early Holocene,during the transition from a cold and dry ice age to a warm and humid interglacial period.Heating rain and easy erosion of loess may caused the mudflow event.The second mud flowevent occurred in the mid-Holocene climate transition period.Influenced by the East Asian summer monsoon intensity.The third mudflow event recorded by Zhaojiaya was induced under the multiple factors of this climate change and human activities.At the same time,coupled with the intensification of human surface reconstruction,the last mudflow event.The above-mentioned chronological research on the sections of important human sites in Ganqing region provides a chronological basis for interpreting the causes of prehistoric natural disasters and the climate changes.It also provides important help and scientific significance for further revealing Holocene environmental changes and human migration,the evolution of human-land relationship and the impact of natural disasters on the development of prehistoric culture.