Research On The Paleo-Mudflow Deposition Event In The Middle Holocene In The Upper Weihe River

As the core of geography research,the study of human-environment relationship has been widely concerned.Since the beginning of the industrial revolution,a series of environmental problems have erupted,and the relationship between people and environment has become increasingly tense.Scientific understanding of human-environment relationship and the use of objective laws of human-environment relationship to guide human social activities have become the only way to achieve sustainable development of human society.Since the 1980s,global warming has occurred,and extreme climate events have occurred frequently.The Mudflow in the upper reaches of the Weihe River and the vast mountainous areas of China have experienced frequent disasters and heavy losses.The study of Mudflow disasters is imminent.Make the usage of the ancient for today,the climate background and human-environment relationship of the occurrence of the paleo-mudflow disaster were reconstructed through the study of the Holocene paleo-mudflow disaster recorded in the loess-paleosoil profile.This has important theoretical and practical significance for the prevention and control of mudflow disasters and the prediction of future disasters under the current climate instability and human-environment tension.This paper takes the Holocene paleo-soil profile of Zhaojiaya,Tianshui,in the upper reaches of the Weihe River as the research object,and integrates the stratigraphic correlation,photoluminescence dating and regional cultural age data of the Holocene loess paleo-soil profile to establish the stratigraphic framework.At the same time,according to the ancient human cultural relics and the overlapping relationship of the three layers of horizontal sedimentary layers,the age of the 3rd mudslide event was judged;Through the analysis of the particle size and magnetic susceptibility data,it reveals the Holocene climate change in the Tianshui area upstream of the Weihe River;Based on the macroscopic observation and judgment in the field,the material composition and sedimentary characteristics of the three-layer horizontal sediments were further determined by>0.1 mm particle screening and observation,particle size and end-member analysis based on particle size data.Comprehensive analysis to identify three layers of horizontal sediments as paleo-mudflow sediments;Based on the age of the 3rd period of the mudslide and the contents of the ancient human cultural relics,the investigation of the Holocene climate fluctuation events and the evolution of ancient human activities in the Tianshui area,the analysis shows that the three-stage paleo-mudfilw events contained in the ZJY section is a comprehensive product of climate fluctuations and human activities.The above conclusions are as follows:(1)Integrates the stratigraphic correlation,photoluminescence dating and regional cultural age data of the Holocene loess paleo-soil profile to establish the stratigraphic framework.At the same time,according to the ancient human cultural relics and the overlapping relationship of the three layers of Paleo-mudflow,the age of the 3 Paleo-mudflow events were judged:the first phase occurs approximately during the 7000?6000a BP period,the second phase occurs approximately during the 5500?800a BP period,and the third phase occurs approximately during the 4200?4000a BP period.The three period of the mudflow events all occurred in the middle of the Holocene.(2)Through the analysis of ZJY Holocene loess-paleosol sample size and magnetic susceptibility measurement results,the Holocene climatic environment in Tianshui area has experienced three evolution stages:early Holocene(11500?8500a BP),and the temperature is Rapid rise compared with the last glacial period.,the East Asian summer monsoon is enhanced,precipitation is increasing,and the climate is in a period of transition from dry to warm to warm and humid.Generally speaking,the climate is relatively unstable and unstable;The middle of the Holocene(8500?3100a BP),the East Asian summer monsoon is strong and dominates.The climate is warm and humid,the soil is weathered into soil,and the climate table is very unstable.There are many climate deterioration events.In the late Holocene(3100a BP to present),the climate deteriorates again in the middle of the Holocene.Dry and cold transition,biological weathering into soil weakened,combined with human activities leading to surface soil erosion,the climate is more arid.At the same time,the grain size curve and magnetic susceptibility curve of the corresponding period of paleosol have become multiple fluctuations,indicating that there are many climate fluctuations in the mid-Holocene climate in the overall warm background.(3)Based on the macroscopic observation in the field to determine the three horizontal depositions as Paleo-mudflow deposition,the material composition of the three-layer horizontal depositions was further determined by>0.1 mm particle screening and observation,particle size and end-member analysis based on particle size data.And sedimentary characteristics,comprehensive analysis to identify the three horizontal sediments as paleo-mudflow sediments,the profile recorded the Holocene three-stage paleo-mudflow events.Several small mudslide events occurred in the third phase,4 small mudflow events occurred in the first phase;2 minor mudflow events occurred in the second phase;and 1 small mudflow event occurred in the third phase.(4)Research results at home and abroad show that there are significant climate changes during the 7000?6000a BP,5500?4800a BP and 4200?4000a BP in the Loess Plateau.The 3 Paleo?mudflow deposition events discovered in the ZJY profile are the products of these Climate fluctuation.At the same time,the second phase of the cultural relics of Shizhao Village(5800?6800a BP),the cultural relics of Majiayao(4800?5300a BP)and the relics of Qijia culture(3950?4200a BP)were found in the third-stage mudflow sedimentary layer.),which further indicates that the Paleo-mudflow deposition events found in the profile are related to human activities.Under the background of the great development of human civilization,people's transformation and utilization of nature has been step by step.Unreasonable human activities have significantly changed the surface vegetation and surface morphology,which has aggravated the surface vulnerability and the climate with steep rainfall variability.During the abrupt period,short-term intense heavy precipitation washes the fragile surface,and the flowing water and landslide bodies are collected in the upstream channel.Loess particles,gravel and human relics continue to move downward under the flow of water,and finally accumulate in the lower ditch of the downstream ditch,forming a three-stage Paleo-mudflow deposition events recorded in the ZJY profile.