Characteristics And Controlling Factors Of Lacustrine In Xinfa Reservoir On The Northeastern Slope Of Greater Khingan Mountains

The dammed lake system is very sensitive to climatic events,geological disasters and river erosion.The dammed lake sediment research is a hot research spot for the study of paleoclimate and palaeo-environment.In addition,the dammed lake sediment process and dam-breaking has a great impact on the national economy,which is of great practical significance to study its sediment characteristics and protect such lakes.Xinfa Reservoir is a typical artificial dammed lake,built in 1959,but broken in2021.Combining with the local meteorological facilities,the sediment study of Xinfa Reservoir can accurately describe the sedimentary sequence,reveal its evolution process and control factors.This results revealed the response of the sedimentation process of dammed lake to climatic events,which is helpful for the national economic construction.In this paper,the sediment characteristics and grain size end-menmber analysis are used as the main method to reveal the characteristics of the sedimentary sequence of Xinfa Reservoir from 1965 to 2021,combined with the borehole coring,grain size analysis,elemental analysis and dating.The controlling factors of its evolution process were also revealed with the help of the climate data from the local weather station.The following are the results;There are four sediment facies in Xinfa Reservoir;river,delta,lake and inertia flow,6 sub-sediment facies,including river channel,delta plain,delta front,shore shallow lake,(semi)deep lake and flood deposit.The main sediment environment from bottom to top changed from fluvial facies to semi-deep lake + flood environment,and then to shallow lake + delta environment,and then rapidly to semi-deep lake +flood environment,and then rapidly to semi-deep lake and strong progradational delta sedimentary environment.The main sediment of this reservoir are the lake and flood sediment in a dammed lake sedimentary system.The sediment grainsize can be divided into three main end-members;end-member 1(5.19-5.741φ),end-member 2(2.997-4.271φ),end-member 3(1.139-3.171φ).There are obvious differences in the control factors of the three end-members,the content of end-member 1 is proportional to the annual average wind speed,the content of end-member 3 is proportional to the annual precipitation,the control factor of end-member 2 is other than the wind speed and rainfall,and it is inferred that the runoff carries debris to the normal sediment in the lake.The time-series analysis of the three end-element components divides the sedimentary sequence during 1965-2021 into four stages(1:1965-1974,2:1974-1976,3:1976-2019,4:2019-2021).These four stages correspond strongly to sedimentary facies and climate evolution,among which;1 and 3 correspond to semi-deep lake +flood deposit under normal climate conditions,2 correspond to shoreline shallow lake+ delta deposit under drought and low rainfall conditions,and 4 correspond to heavy rainfall climatic conditions lower semi-deep lake + strong progradational delta deposits.Through the summary of these four stages,it is determined that there are three sedimentary models in the study area,the sediment model driven by normal climate,the sediment model driven by high temperature and drought,and the sediment model driven by heavy rainfall.