The OSL Date Of Sand Wedges In The Southeast Edge Of Badain Jaran Desert And Its Palaeoenvironment Significance

Sand wedge is the product of permafrost under the conditions of cold climate,which has great significance to restore paleoclimate and paleoenvironment.In the southeast edge of Badain Jaran Desert newly discovered several Sand wedge groups,mainly formed in the sillty Sand gravel layer.The OSL dating of the filler in Sand Wedges proves that they were the product of Last Glaciation and Late Glacial Period.It's clear that Badain Jaran Desert belonged to permafrost region during the Last Glaciation and Late Glacial Period,with the mean annual air temperature about-3^-5?,the temperature is 12¹3?lower than present.At that time,the whole Alxa plateau was part of permafrost region,so the desert hinterland and the surrounding Sand dunes should be frozen.The movement and development of the Sand surrounding was suppressed.The Badain Jaran Desert is likely to have entered into the cryosphere during the cold period and the knowledge of Chinese northen desert doesn't belong to the frozen earth region is questionable.In recent years,we have founded four ancient Sand wedge groups and two ice volume of mud in the process of examining the Badain Jaran Desert.The sand wedge samples from Sugui,Jiukeshu and Ba Sing Gault were dated by using Quartz OSL,and the particle size experiment was carried out by selecting sand wedge filler in Sugui and Ba Sing Gault.We collected 3 sand wedges samples in Mandela mountain.For each of3 samples,both Quartz and K-feldspar fractions were extracted for luminescence dating using large aliquot technique?d=6mm?.The results of the two mineral ages were compared.The dose recovery test and luminescence characteristics show that the experiment conditions of K-feldspar pIRIR₁₅₀50 and Quartz SAR protocol are appropriate for these samples.So quartz and feldspar age results are reliable.For three quartz samples,the recycling ratio is basically 0.9¹.1,with a mean of1.023±0.062?n=60?;the heat transfer effects are mostly within 5%;the infrared test indicates that quartz particles are not affected by feldspar pollution.The dose recovery ratio of NL-1618 samples was 0.9¹.1,260°C was selected as the preheating temperature by preheating experiment.For three K-feldspar samples was luminescence dated by using the pIRIR₁₅₀protocol.Their recovery ratio of pIRIR₁₅₀ is between 0.9 and 1.1,and close to 1;the recycling ratio is mostly 0.9¹.1.pIRIR₁₅₀ has a strong signal and the heat transfer effect is less than 5%;The residual doses of the NL-1617,NL-1618 sample are between0.652 and 0.822 Gy,which could be neglected.Anomalous fading test shows that the pIRIR₁₅₀ g-values of the 3 samples are 0.53¹.16?%decade?,and the error caused by the feldspar is not necessary.?1?The OSL dating of sand wedges in the southeast edge of Badain Jaran Desert is?11.13±1.41?^15.7±1.7ka.BP and?44.02±5.85?^74.85±15.75ka.BP,corresponding to the late glacial period and the last glacial period?It's clear that the Badain Jaran Desert has experienced at least two climate cold periods,nearly 75,000years,and the cooling rate may reach 12¹3°C.The sand wedge filler is mainly composed of fine sand,and the sorting is poor,indicating that the sediment has not been transported over a long distance,but is derived from the nearby aeolian sand.?2?The quartz age of two sand wedge samples in Mandela mountain is 15.7±1.7,11.4±1.0 ka BP and K-feldspar ages are 15.45±1.17,12.18±0.89 ka.BP respectively,Both ages from the two methods agree with each other within the error ranges,indicating that the results of the years are reliable.However,there is a big difference in the age of the bottom sample of the sand wedge.The quartz age is 34.0±3.3 ka BP,but the feldspar age is 56.66±4.94 ka.BP.It might be attributed to the surrounding old rock material mixed into the sample.Thus,we refer that the sand wedge of Mandela mountain formed in the late glacier period.?3?According to the Sand wedge groups of the Last Glaciation around in the desert,seasonal frozen soil,can determine the Badain Jaran Desert belongs to the discontinuous island in permafrost regions and the possibility of continuous permafrost is there.At this moment,the desert hinterland and the surrounding crescent dunes should be frozen.So the surface landscape and kinetics process of the Sand landform,subject to the system research in the future.