Chromaticity Characteristics Of Soil In The Fura Profile Of The Republican Basin And Its Recorded Environmental Evolution

At present,various climatic and environmental problems on a global and regional scale are becoming increasingly prominent,the frequency and intensity of extreme weather are increasing,and the study of environmental change has become a research hotspot in recent years.The Gonghe Basin,located in the northeastern margin of the Qinghai Tibet Plateau,is in the transitional zone of westerly circulation,monsoon circulation and plateau monsoon.It is sensitive to climate change and is an ideal place to study the evolution of climate and environment.In the sediments,the color change is the most intuitive,which can well reflect the changes of the ancient climate and environment.In this paper,the typical aeolian sedimentary latsed profile（ML）of the Republic Basin was selected as the research object,and the luminance（L^*）,redness（a^*）,yellowness（b^*）,saturation（C^*）and hue angle（h^*）values of soil chromaticity parameters were measured by CM-5 spectrophotometer,and the red-yellow ratio（a^*/b^*）was calculated,the change characteristics of chromaticity parameters in the profile were analyzed,combined with¹⁴C and OSL dating data,and compared with the relevant climate auxiliary indicators of particle size and geochemical elements.The environmental evolution since the last glacial period in the Republic Basin region is reconstructed.The study came to the following conclusions:（1）The chromaticity parameters L^*,a^*,b^*,C^*,h^*of ML profile have similar variation characteristics.The high value appears in the paleosol layer,and the low value appears in the loess and eolian sand layer;The trend of changes in a^*/b^*values is opposite to that of L^*,a^*,b^*,C^*,and h^*.（2）The significant correlation between chromaticity parameters and particle size and element indicators indicates that chromaticity parameters are good substitute indicators for climate change and have clear climate significance.Among them,the chromaticity parameters L^*,a^*,b^*,C^*,and h^*indicate high values of climate temperature and humidity,while low values indicate cold and dry climate;The climate significance of a^*/b^*values is opposite,with high values indicating cold and dry climate,while low values indicating warm and humid climate.（3）By utilizing the functional relationship between chromaticity parameters and temperature and precipitation,the reconstructed profile paleotemperature and paleoprecipitation curves exhibit synchronous and co directional changes.During the formation of paleosol,the regional temperature was higher and precipitation was more.During the formation of eolian sand and loess,the regional temperature and precipitation decreased.（4）According to the characteristics of chromaticity changes,the environment in the Gonghe Basin region has undergone a process of cold dry,warm wet,and cold dry evolution.It can be further divided into three main stages:the relatively cold and dry last glacial maximum（before 16.87 ka BP）,the relatively warm and wet last deglaciation（16.87～10.74 ka BP）,and the Holocene（since 10.74 ka BP）,when the overall environment tends to become cold and dry.The environmental evolution process reflected by chromaticity indicators is not only highly consistent with existing research results within the region,but also highly consistent with global environmental changes.