Particle Size Characteristics And Sedimentary Evolution Of Sphagnum Mire At Qizimei Mountains In Western Hubei Province Since 13000 A BP

The sphagnum mire at Qizimei mountains located in subalpine region of central China,which is arounded by mountains and inaccessible,the sedimentary environment is stable,and the surface of the modern peat layer in a better state of natural conservation,it is an ideal area for studying the evolution of climate and environment since the last deglaciation.In this paper,the particle size data since 13000 years of QZMS borehole sediments from the sphagnum mire at Qizimei mountains have been systematically analyzed,based on the lithology of sediments and the framework of AMS¹⁴C,compared with previous research results,this paper explores the evolution of climate in the region over the past 13000 years,and summarizes the evolution of sedimentary environment since 13000 years.In this study,particle size of the sediments was used as a substitute index for reconstructing paleoclimate environment.By analyzing the particle size characteristics of sediments,the material source change,the change of handling mode,the change of hydrodynamic conditions and the evolution of sedimentary environment can be deduced.Particle size features are generally described by particle size component map,basic curves,granularity parameters and particle size C-M diagram,wherein the basic curve comprises a frequency distribution curve and a probability accumulation curve,particle size parameters include median particle size,average particle size,skewness and kurtosis.Based on the comprehensive analysis and comparison of the particle size components,particle size distribution curve,probability accumulation curve,particle size parameter and particle size C-M diagram,the QZMS borehole sediments are divided into four stages,summed up the longitudinal variation of each particle size feature,analyzed the corresponding hydrodynamic conditions,and then deduced the evolution of the sedimentary environment since the study area in 13000 years.The main conclusions of this paper are as follows:?1?The particle size data show that the grain size of QZMS boreholes is mainly composed of fine silt and medium silt,volume percentages were 48.27%,31.05%.The frequency distribution curve is a single peak distribution,from bottom to top,the kurtosis from wide to narrow,skew from nearly symmetrical to positive.Overall,the drilling size is smaller,the power conditions are weak,and the deposition environment is more stable.According to the particle size characteristics,QZMS drilling deposition can be divided into four stages:?1?Stage ? and stage ??93⁴2cm?has little change in particle size and particle size parameters,and the material source is single and uniformly suspended.It should be a creek or a riverbank development environment,the late peat moss wetland began to develop.?2?The fluctuation of the kurtosis and skewness in stage ??42²6cm?is more obvious than that of the previous stage.The kurtosis becomes sharp and the skewness is biased,the source becomes more complicated,sorting worse,reflecting the climate to warm and humid environment,water increases,peat moss wetlands gradually formed.?3?Stage ??26⁶cm?kurtosis and skewness are large on the whole,but the frequency of change is low,particle size components is more stable,indicating that this stage although the climate fluctuations frequently.But the formation of peat moss wetland,the hydrological environment has played a certain regulatory role,so the deposition environment is more stable.?2?The evolution of sedimentary environment in the study area can be divided into four stages:?1?12.9¹1.6 cal.ka BP,climate fluctuation frequency is high,but the magnitude is small,at this time the hydrodynamic conditions are relatively weak.?2?11.6¹0.2 cal.ka BP,the transition stage of late Pleistocene to the Holocene,hydrodynamic conditions continue to be weak,the environment is relatively stable.?3?10.2⁷.7 cal.ka BP,the early Holocene,the climate became warm and wet,and the hydrodynamic conditions were enhanced compared with the previous stage,and the peat wetlands began to form.?4?7.7².0 cal.ka BP,the climate is warm and humid,hydrodynamic conditions achieve to the strongest,kurtosis and skew wave frequency is low,but the magnitude increases,it is swamp wetland environment.?3?The results show that the change of particle size characteristics of the sediments of the sphagnum mire at Qizimei mountains is closely related to the change of hydrological conditions and provenance in the area.With particle size composition and parameter characteristics can invert the evolution of the sedimentary environment in the region,reveal the formation of peat moss wetland development process,and provide scientific reference for the study of the protection of peat moss wetland and the change of climate and environment.