Study On The Age Of The Soil Parent Material In The Qinghai Lake Basin

Soil is the core of ecosystem structure and function,and the most active life layer in the natural environment.Soil formation is influenced by the soil parent material,climate,topography,time and biotic factors.As the preliminary condition of soil formation and development,the soil parent material has an important impact on the physical,chemical and biological properties of soil.The types of soil parent material in the Qinghai Lake basin are diverse.Alluvial stream deposits,lacustrine deposits,aeolian deposits(loess and aeolian sand),moraines,glaciofluvial deposits are widely distributed and a few of residual parent material.However,there are scarcely reported the formed age of different types of soil parent material,resulting in its development process and environmental background are still unclear on Tibetan plateau.A total of 27 profiles of alluvial alluvial parent material,aeolian sediment parent material and residual sediment parent material were selected in the Qinghai Lake Basin.Use the optical stimulated luminescence dating of different soil generation layers in the profile,and establish a corresponding chronological framework to obtain the age when different types of soil-forming parent materials begin to form and develop.In addition,the grain size,organic matter content and geochemical element content of the soil bulk samples were carried out.Combined with the records of paleoenvironmental and paleoclimate background,the development patterns and the climatic background of three types of soil parent material overlying soils were analyzed in the Qinghai Lake basin.The results shows that: 1.The aeolian deposits parent material in Qinghai lake basin has developed since the last Deglaciation period(~ 12.9ka);The alluvial stream deposits parent material begins to develop at 15.8 ka,and ~12.9-8.2 ka is the concentrated stage of development.The residual parent material begins to develop at ~14-10.2 ka.2.Combining the flour viscosity ratio,Chemical Index of Alteration(CIA)values and Rb/Sr value of each section,it is concluded that the weathering degree of soil overlying the profile of aeolian sedimentary type was the highest,followed by alluvial parent material soil profile,and the weathering degree of residual parent material soil profile is the weakest.According to the relationship between soil thickness and age,the net accumulation rate of overlying soil of each type was calculated.The accumulation rate of overlying soil of aeolian parent material type was the highest,followed by the accumulation rate of overlying soil of alluvial and diluvial parent material type,and the accumulation rate of overlying soil of residual parent material type was the lowest.3.The development mode of soil formed by the aeolian dust parent materials is aeolian dust aggradation.While the alluvial stream deposits and residual parent material soil is mainly developed by aeolian dust aggradation with mixed-parent material.4.The climate of the last deglaciation period and the early Holocene has strong sandstorm activity,and the soil probability density show increasing trend.During the middle Holocene,the climate was warm and wet,and the wind-sand activity was weak,which was the main soil development period.In the late Holocene,the climate tended to be dry and cold,and the wind and sand activities increased again,the soil's probability density reached its highest since the deglaciation.