Study On The Formation And Evolution Of The Megadune-Lake Environment In Badain Jaran Desert Based On Luminecence Chronology

Located in the north of China,Badain Jaran Desert(BJD)is the second largest desert in China.The infrequent megadune group,which is as high as ?500m,concentrates in the southeast of the Badain Jaran Desert.There are more than 100 lakes distributed among the megadunes.Megadunes and lakes are alternative distributed regularly and coexist for a long time in the southeast of BJD,which is a special geomorphology.This huge desert and its special geomorphologic phenomenon is a natural laboratory for research on aeolian geomorphology,aeolian physics,and hydrogeology of arid areas,paleoclimate and paleoenvironment,modern environmental observation and other researches.The BJD is located in the eastern part of the arid central Asia,so the researches about the formation and evolution of the special geomorphology are of scientific significance to reveal the migration mechanism of aeolian material,and interpret the evolution of the paleoclimate and palaeoenvironmental.It is also of scientific significance to predict the environmental effect of aeolian activities and guides the modern aeolian control.Additionally,it also has implications for other astroclastic research.However,there are still disputes about the formation and evolution of the special landform.In particular,more detailed researches of chronology from hinterland of BJD are needed.The OSL dating of various types of sediments(194 samples,collected from 35 sections/sites in BJD)are performed.According to the luminescence chronologies of different type of sediments,the distribution and evolution of these sediments were analyzed to unravel the history influenced by the fluctuation of climate and environment during the cycles of glacial-interglacial stage.Moreover,the formation and evolution of the special landform,alternative distributed by megadunes and lakes,in BJD influenced by climate were also considered.To reveal the formation and evolution of the special landform in BJD systematically,the internal characteristics of the special landforms and geological agent were investigated using Digital Elevation Model(DEM),remote sensing image,field observation and previous studies.The main conclusions are as followed: 1.There are various types of dunes in BJD,the formation and evolution,as well as the ages,of various types of dunes are different.The modern dunes are the most common in the desert and consist of light yellow,dry and loose sands.The OSL chronologies of modern dunes show that they formed during the last few hundred years(<1 ka)The paleodunes are characterized by grayish brown or yellowish brown and with distinct diagonal bedding.The luminescence chronologies of paleodunes concentrate in Holocene,Marine Isotope Stage 3(MIS3)and MIS5 or even earlier periods of relative warmer and wetter.The OSL chronologies of soaked dunes,which is obviously affected by lake water,are complicated due to its complexity of formation process.However,the megadunes are mainly composed of multi-stage dunes superimposed during the fixed-activation process,which is usually appear as the modern dunes at the top covering the paleodunes which were fixed during warm and wet stage.2.The luminescence ages of lacustrine sediments from BJD are mainly concentrated in the early and middle Holocene,MIS3,MIS5 and even earlier stages which are warmer and wetter.This obvious correlation between lake development and climate fluctuation reveals that the water of lakes in BJD is mainly affected by climate,which means that the atmospheric precipitation during the relatively warm and wet period has an important contribution to these lakes.The preliminary luminescence chronologies show that the flood sediments on the southeast edge of BJD were mainly caused by two flood events during middle Holocene.3.Preliminary chronologies show that the formation of eolian and lacustrine sediments in BJD has distinct stages,which are correlated with climatic and environmental fluctuations.This correlation reveals that climatic factors have an important influence on the formation and evolution of special geomorphology in BJD.4.The terrain of BJD is dustpan like.With mountains on three sides and alluvial fan on the other side,the materials from the lower northwest are easy to accumulate at the higher southeast while hard to exit by deflation.Therefore,topographic factors have an important influence on the formation of special geomorphology in BJD.5.The efficient material transport system is another important factor affecting the formation of special geomorphology in BJD.The detrital materials in the BJD were transported by a complete and efficient agents system,which is “Glacier erosion-River transport-Lake deposition-Wind transport-final deposition”.