Study On Optically Stimulated Luminescence Dating And Developmental Model Of Alpine Meadow Soil In Three River Headwater Region

The alpine meadow is widely distributed in the Qinghai-Tibet Plateau,and the alpine grassland ecosystem is an important barrier to maintain the ecological security of the surrounding area and the country.Alpine meadow soil is widely distributed in the Three River Headwater region and is representative in the whole Qinghai-Tibet Plateau.However,the lack of geochronological research on alpine meadow soil in this area limits the understanding of the occurrence process of alpine meadow soil.Especially in the Three River Headwater region,the topographic fluctuations are great and the parent materials are developed under the action of various geomorphic forces.The pattern is not clear.In this paper,58 OSL samples from 21 alpine meadow soil profiles in the Yangtze river,Yellow River and Lancang River basins were dated by OSL dating method.At the same time,the physical and chemical characteristics of soil were obtained,and the formation time and soil-forming process of meadow soil in this area were analyzed and discussed.The study concluded:1.The alpine meadow soils in the Three River Headwater region were mainly developed in early Holocene 13-8 Ka and late Holocene 3-0 Ka.The matte formation time was less than 1 k A in the Late Holocene,the parent material developed in the Early Holocene～10 Ka,and the parent material of a few profiles was in the last glacial～30 Ka.2.The grain size distribution curve of alpine meadow soil showed that the alpine meadow soil in slope and piedmont,alluvial fan and river terrace profiles were distributed in three peak-mode,with the peak values of～8μm,～60μm and～500μm,indicating three material sources of different transportation modes,and the content of silt at 60μm was the highest.The grain size distribution of alpine meadow soil in valley and flood plain shows single peak,and the coarse-grained aeolian sand is dominant,and the distribution is uniform.3.According to the ratios of K₂O/Al₂o₃-Zr/Nb,K₂O/Al₂O3-Tio₂/Al₂O₃,TiO₂/Al₂O₃-Zr/Nb and K₂O/Al₂O₃-Zr/Tiof provenance indication,the materials of alpine soils in the Three River Headwater region have homology characteristics.There is no obvious relationship between parent material of meadow soil and weathering products of in-situ bedrock.4.According to the comparison of the formation age,grain size and element ratio of alpine meadow soil,the alpine meadow soil in Three River Headwater region is developed by mixed parent material,which is provided by aeolian deposition and various topographic conditions.The parent material types of different topographic conditions are slope accumulation parent material,alluvial parent material and river sand-sand parent material.5.Three River Headwater meadow soil was mainly formed in holocene or developed on holocene parent material.Holocene or the last interglacial climate is warm and wet,conducive to the development of soil.In the late Holocene,relatively dry and cold aeolian dust release provided important parent material for meadow soil.Aeolian deposition has a strong anti-erosion effect and promotes the development of meadow soil.