The Optically Stimulated Luminescence Chronology And Environmental Significance Of Blowouts In The Qaidam Basin

Located in the northeast of Qinghai-Tibet Plateau,Qaidam Basin is widely distributed with various aeolian geomorphology,which is particularly distinctive with its high altitude and the cold and dry natural conditions.The Tiekui Desert in the eastern part is the largest desert in the basin.In the geological history,as the Tiekui River blocked by but passes through the desert,its fluvial action along with the wind action have made great contributions to the desert form.Most ancient dunes developed in the eastern part of the desert are fixed under the action of rivers.Many stationary dunes are eroded by the increasing wind erosion,forming kind of blowouts and activated parabolic dunes based on them.Desert activation mainly occurs in this region.The blowouts on dunes,and their companions parabolic dunes are essential to desert evolution?activation-fixation?,which also enjoy the same significance to the environment.Those blowouts,once regarded as a feedback to climate change and human activities,however,their formation and evolution are rarely known by people,and the research on blowout in Qaidam Basin has not been carried out so far.Chronology is the key method to study the evolution of aeolian geomorphology and its environment.Owing to the authentic results and accessible materials,Optically Stimulated Luminescence Dating has become an important approach to study the late Quaternary aeolian deposits.In this paper,the Single-aliquot Regenerative-dose?SAR?based on OSL dating was used to study the chronology,including blowouts and their companions parabolic dunes in Qaidam Basin.During the experiment,quartz and potassium feldspar were used to test the age,and in order to test the the reliability of potassium feldspar dating in young samples,dating results of feldspar were compared with the quartz of the same section.When investigating in the Tiekui Desert,we found that the upper blowouts are mostly covered with a 3-5 m thick layer of sediments featuring fine particles,and the transition zone of the lower sand layer is a mixture of fine particle and sand material.Horizontal bedding together with cementation,it is logical to conclude that the mixture is a kind of flood sediment under the work of rivers.Therefore,a great number of size samples were collected intensively at the sedimentary layer to figure out its origin in the light of size parameter and Sahu Discriminant Equation.The research conclusions of this study are as follows:?1?The test results of 2⁴ka samples obtained by the pIR₅₀IR₁₈₀ dating method of K-feldspar are quite good,compared with the quartz of the same sample.Furthermore,it is shown that the test signals of young samples are relatively high and stratigraphic sequence is better displayed by pIR₅₀IR₁₈₀ dating.That means the dating method is of great reliability.?2?On the basis of size parameter and Sahu Discriminant Equation,it is concluded that the fine-particle sediments on ancient dunes are kind of flood sediments under the work of rivers.Therefore,the ancient dunes are fixed by floods rather than by loess,which updates the understanding of desert fixation in the Qaidam Basin.The source of flood is mainly from the blockage of rivers by deserts during glacial period,resulting in a continuous interaction from deglaciation to the holocene.?3?By particle size analysis,aeolian sediments in blowouts at different locations in Teikui Desert of the Qaidam Basin are comparatively analyzed.Two conclusions can be drawn from theconsistency of particle size characteristics,between deflation basin and parabolic dunes based on blowouts.The aeolian sediments have moved rapidly from the deflation basin to blowouts.And sediments of ancient dunes are the major source of parabolic dunes.?4?The results show that in the study area,the aeolian sand in the lower part of the blowout section was mainly formed at 8ka.The formation of flood sediments in the upper part of the ancient sand dunes was between 8²ka,and the top of the flood sedimentary layer was about 2ka,followed by aeolian sand in parabolic sand dunes.This shows that the age of the ancient sand dunes began to activate and form a blowout was about 2ka.The Tiekui River cuts through the desert and reduces the flooding effect and the groundwater level,which causes the desert environment to be arid;the late Holocene drought climate background and the gradually increasing human activities also have certain effects.