| The Quaternary global climate has experienced many glacial-interglacial cycles,and the law of climate evolution has been paid more and more attention by scholars.Otindag Sandland is one of the typical representatives of desert/sand land in eastern China,is located in the tail region of the eastern monsoon region.The ecological environment is fragile,and is very sensitive to climate change and can respond to global climate change.As one of the dust source areas,it affects the northern and even northern hemisphere climate.In recent years,the research results of the Otindag Sandland have the highest photoluminescence age of 20 ka in sandy sand,and climate change research has mainly focused on the Last Glacial Maximum because of the lack of suitable geological carriers and reliability.Since the Last Glacial Maximum,a reliable chronological framework of the Pleistocene period has not been established,and there is a lack of research on climate change during the Pleistocene.In addition,a large number of volcanoes are distributed in the Otindag sand area,and the basalt age is measured by the K-Ar dating method,and the measurement of volcanic activity within 100,000 years is highly variable.According to the field investigation results,in the interior and marginal areas of the Otindag sand,there is a magma baking layer between the basalt and the underlying sand layer.The magma baking layer is not easily transported and eroded by the wind,and the underlying sand layer age and bake layers can provide both volcanic activity time and sand age data framework.Sandy paleosoil,aeolian sand,lake sand and sand loess and other sediments,the measurement of its chronology not only reflects the period of fixation and expansion of the sand,but also the climatic and environmental conditions of the sand in different periods.Quartz particles and K-feldspar particles were used as dating minerals.The equivalent doses of the samples were determined by quartz conventional SAR method,TT-OSL method,pIRIR(200,290)method and MET-pIRIR method.The results of various experimental methods were compared with each other.Combined with the environmental dose rate of the sample,the photoluminescence chronology of the sand sediment is finally determined.Combining the chronological results of sandland with climate alternative indicators,comparing the climatic carrier records of the same period in the vicinity,analyzing the sequence of light-release chronology,sandstorm activity and climate evolution since the mid-late Pleistocene in Otindag Sandland.Study on the sedimentary profile in the Otindag Sandland,has important scientific value to extend the sandstorm activity history and paleoclimatic evolution time scale since the late Pleistocene in the Otindag Sandland and to improve the paleoclimatic research in the East Asian inland arid area.The following conclusions are drawn:(1)The conventional SAR method and the TT-OSL method were used for the photoluminescence dating using quartz.The maximum ages measured by the two methods were 320.4 ka and 384.2 ka.When the conventional SAR method is selected,the test conditions for the equivalent dose are determined by the preheating plateu,dose recovery and cycle ratio experiments.Finally,the samples of the northern margin of the Otindag Sandland are Pre-heate at 240? and Cut-heat 200?.The samples on the southern margin of the Otindag Sandland were tested under the conditions of Pre-heat 260? and Cut-heat 220?,and then the arithmetic mean of the equivalent dose values of the effective test pieces was taken as the final equivalent.The maximum equivalent dose measured by the conventional SAR method is 383.5 Gy,corresponding to an age of 320.4 ka,and the age error is within 10%.This age breaks the upper limit of the conventional SAR method because the environmental dose rate is low during this period.For samples with OSL signal saturated quartz tested by conventional SAR method and then tested by TT-OSL method,the equivalent dose obtained by TT-OSL method is 985.4 Gy,De<2D0(D0=765.5 Gy),the slope of the OSL growth curve increases with the increase of the regenerative dose,the growth curve does not reach saturation almost passes through the origin,indicating that the equivalent dose value obtained by interpolation is credible,and this method is feasible,the final age is 384.2 ka.(2)For samples with OSL saturated signal by conventional SAR method,the K-feldspar pIRIR(200,290)method and MET-pIRIR method were used to compare the OSL dating.The ages measured by the two methods were 321.2 ka,299.2 ka.Before the test using pIRIR(200,290)method,the first excitation temperature plateu experiment was carried out for reducing the abnormal decay effect of feldspar to a negligible level.Finally,200? is selected as the temperature of first excitation.pIRIR(200,290)method tested sample is aeolian sand under the volcanic baking layer,the equivalent dose value obtained is 945.1 Gy,the corresponding age is 321.2±11.5 ka.In the MET-pIRIR method,based on the dose response curve and the age-temperature plot result,the arithmetic mean(872.2 Gy)of the equivalent dose at 300? was finally determined.The age is 299.2±11.3 ka.Comparing the two feldspar ages of the sample with the quartz age(384.2±68.0 ka),it was found that the three ages were consistent within the error range,but because the quartz age error exceeded 10%.The final decision was 321.2±11.5 ka by the age of deposition as a sand under the volcanic baking layer.(3)Based on the OSL data of the Otindag Sandland profile:the late Middle Pleistocene(321.2 ka,160.3 ka),Late Pleistocene(88.6 ka,21.9?12.2 ka)and Holocene(10.7?1.0 ka)were established.The Otindag Sandland developed aeolian sand layer at 321.2 ka,and develops a lacustrine coarse sand layer at 320.4 ka.The sand activity is strong in the late Middle Pleistocene(321.2 ka),the wind and sand material supply is large,and the sandstorm activity is strong.During the 160.3 ka period,the East Asian summer monsoon weakened,and the sandstorm activity in the Otindag Sandland was strong.The coarse sand of wind transport was deposited in the lake basin,and the sand layer developed in the sand layer;21.9?12.2 ka the sandland was in the last Ice age,and it experienced the YD event.The sand accumulated quickly,and the sandstorm activity was strong.The cold and dry climate accelerated the activation of sand dunes,the dunes expanded,and the sand area expanded.During the Holocene,the Otindag Sandland experienced frequent climate fluctuations and responded to global climate change.The sandland has been in the activation and fixed stages many times.(4)The Otindag Sandland is located in the interior of the Xingmeng orogenic belt,west of the Daxinganling-Taihangshan gravity gradient belt,and in the northward subduction of the Indian plate and the positive subduction of the Pacific plate,the northern nargin of the North China Craton and the Central Asian orogenic belt.The northwest-oriented basement fault activity is enhanced,showing the extensional structural properties.The northern margin of the western North China and the Xingmeng orogenic belt are thinned,and may experience a common upper mantle evolution.The mantle near the fault zone rised and the deep magma invaded,volcanic activity occurred in the late Middle Pleistocene(321.2 ka,155.0 ka)and late Pleistocene(88.6 ka). |
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