Geochemical Characteristics Of River Terrace Sediments And Climate Change In Tongbai Section Of The Upper Huaihe River Since The Last Glacial Maximum

As an important climate proxy,geochemical elements have been widely used in marine,lake,loess and other sediments.However,the enrichment of geochemical elements in river sediments is strongly disturbed by factors such as hydrodynamic conditions.Therefore,how to effectively mine the paleoclimate information of geochemical elements in river sediments is of great significance.The Huaihe River Basin is located in the north-south transition zone of eastern China.The natural geographical elements in the basin have significant complexity and climate sensitivity.In addition,the frequent occurrence of meteorological disasters in the Huaihe River Basin has had a significant impact on the national economic construction in the basin.In this paper,the Tongbai section of the upper reaches of the Huaihe River is taken as the research area,and the geochemical element characteristics of the river terrace sediments and the paleoclimate changes indicated by them are discussed.This study can not only deepen the application of geochemical elements in river sediments,but also provide some reference for the prevention and control of meteorological disasters in the Huaihe River Basin.Through detailed field investigation,it is found that there are good river terrace sedimentary profiles on both sides of the modern river channel in the upper reaches of the Huaihe River.In this paper,the sediments of T2 and T1 terraces of Huaihe River were taken as the research objects.Based on the optically stimulated luminescence（OSL）and ¹⁴C chronology methods,combined with the elements and grain size indexes,the geochemical elements characteristics of river sediments in the upper reaches of Huaihe River were discussed,and the element indexes with weak hydrodynamic disturbance were analyzed and screened.On this basis,the climatic evolution characteristics of the upper reaches of Huaihe River since the last ice age were preliminarily reconstructed.The main conclusions of this study are as follows:（1）The content of silt in T2 and T1 terrace sediments is higher,and the content of sand and clay is lower.From bottom to top,the clay and silt content of the two sections showed a fluctuating upward trend.The change of median particle size also indicates the bottom-up refinement trend of sediments in the profile.The geochemical elements in the profile are characterized by high content of Si O₂and Al₂O₃,and the relative content is Si O₂>Al₂O₃>Mn>P>Ce.The Al₂O₃in the profile shows a fluctuating upward trend,while Si O₂is the opposite.（2）The correlation analysis of element abundance and particle size shows that P,Mn,Ce,Si O₂and Al₂O₃are weakly correlated or not correlated with median particle size and silt content.That is to say,the enrichment of these elements is almost not affected by hydrodynamic conditions,so it can be used as a climate proxy index in this area.Among them,SiO₂and Al₂O₃indicate the dry and wet changes of the climate,Ce element indicates the cold and warm changes of the climate,and P and Mn are typical humid elements.（3）Since the last glacial maximum,the climate change in the Tongbai section of the upper reaches of the Huaihe River has gone through five stages,roughly showing the characteristics of cold dry-cold wet-warm wet-warm wet-warm wet.The general trend is developing in the direction of warm wet,and there are several small climate fluctuations in the middle.