The Variation Of Vegetation And Climate And Its Impact On Human Activities From Late Deglacial Period In Western Sichuan, China

As the largest alpine wetland and peat deposition area in China which is influenced by the Asian monsoon,the Zoige wetland is climatically and environmentally sensitive.As a natural archive in global change research,peat stores copious environmental information.Here,this thesis reports new data on the pollenspore,geochemical elements,magnetic susceptibility,humification and carbon isotopic composition of organic matter(813Corg)in a 450 cm peat profile HY2014 from the southern Zoige wetland.Based on closely spaced accelerator mass spectrometry(AMS)14C dating,this paper established a high-resolution geochronological framework beginning at 14057 cal.a BP.Moreover,this paper reconstructed the evolution history of the palaeovegetation and palaeoenvironment and their controlling mechanism,and environmental effect.Holocene is most related to human evolution and human civilization,and this paper is also aim to explain the rise and fall of the ancient cultures and the migration of human,and the relation between the human activities and climatically change in the western Sichuan,China.(1)Pollen percentage and results from multivariate statistical analysis of 40 surface sediments and moss samples indicate that sporopollen correspond to the vegetation zone very well.The variation of vegetation in the past 14052 a including alpine shrub meadow,forest and bog,and shrubby meadow.(2)Based on pollen percentage of surface samples from this study and from the East Asia Pollen Database,this thesis quantitatively reconstructs the mean annual temperature(MAT)and mean annual precipitation(MAP)over the past 14052 a by 3 methods,which including weighted averaging partial least squares regression method(WAPLS),Multiple Linear Regression(MLR)and R-Q Correspondence Analysis(CA).Ultimately,the results from the WAPLS is used for the coming discussion.The quantified climatic reconstruction shows that MAT and MAP increased quickly from the Early Holocene,and then decreased gradually.However,the reconstructed MAT and MAP were higher and lower than those in nowadays,respectively.Furthermore,stepwise acidification and climate cooling began to increase markedly at 6000 cal.a BP and were strongest beginning at 3050 cal.a BP,also could be found in environmental proxies in this thesis or other publications.(3)Before 10916 cal.a BP,the lake shrunk and peat began to develop under cold and dry conditions.More 813Corg originated from hydrophyte and marsh plants.From 10916 to 3050 cal.a BP,peat was widely and well developed,and the climate was warm and humid,despite a cooling and drying trend.The HY2014 profile experienced an optimum climate during 10916-6000 cal.a BP,when Trees and Shrubs,Trans(%)had the highest values and Ti content,and Rb/Sr ratio that benefited from high productivity and weathering intensity were lower,and 813Corg mainly originated from terrestrial C3 plants.During this phase,the plant and forest extended and peat developed well and mature.After 3050 cal.a BP,the climate was the coldest and driest.The environment change was mainly controlled by summer solar insolation,and the Zoige wetland was significantly influenced by the Indian summer monsoon.(4)During the Guiyuanqiao Culture period(5100?4600 cal.a BP),the MAT and MAP were higher,then less human had moved to the CDP.Thereafter,the climate was colder and drier,which attracted human migration to the CDP,similar to the conditions that attracted people from the upper reaches of the Yellow River to the northwest of Sichuan Plateau from 6000 cal.a BP.The climate parameters in the Sanxingdui Culture period were lowest.And MAT and MAP in the Late Shu Period were lower than those in the former Jinsha-Shierqiao Culture period.The elevation,number and scale,superposed state and accumulation characteristic of the archaeological sites,and the distance between them of rivers and so on were varied accordingly.(5)After 6000 cal.a BP,the climate in the CDP was colder and drier,while was more and land were provided for human living in the Chengdu Plain.The rise farming is especially an excellent mean of adapting to living in plain.Furthermore,the spatial distribution,slope and aspect of the archaeological site,and living and production tools have also changed accordingly.The characteristic and the possible value of this these is the quantitative study,providing the specific values of MAT and MAP between 10900 and 6000 cal.a BP,which seted as the optimum period in the Holocene.Furthermore,the quantitatively reconstructed results were used to discuss human migration and cultural evolution and how ancient people responded to the climate change in western Sichuan,which would enrich the research of environmental archaeology in the upper reaches of the Yangtze River and paleoclimate in the Zoige wetland.