Photoluminescence Chronology Of Second Terrace Terraces In The Upper Han River

The river terraces formed since the Quaternary Period,as an important part of river landforms,are the product of environmental change and one of the ancient environmental information carriers.The upper reaches of the Hanjiang River is uniquely located in the Qinba Mountains and belongs to the north-south climate transition zone.It is sensitive to climate change.At the same time,it is affected by the uplift of the Qinghai-Tibet Plateau and the Qinling orogenic belt,and its tectonic activity is strong.The mountain basins and canyons are distributed alternately in the basin,and the river terraces covering thick loess are mostly developed in the basin,becoming an ideal carrier for recording the paleoenvironmental information of the basin,which has attracted the attention and in-depth research of many scholars.In recent years,research results on the upper reaches of the Han River have mainly focused on first terraces or third terraces and above.Based on chronological research,the climate change process since the last ice age and earlier than the Pleistocene has been reconstructed.The stratigraphic chronological sequence of the Pleistocene period has not yet been established,and the reconstruction of the paleoclimatic evolution history is limited.The study of the secondary terraces in the upper reaches of the Hanjiang River is expected to reveal the climatic evolution law during the Pleistocene period.Based on detailed field investigations of the upper reaches of the Han River,appropriate secondary terraces(BSZC,ZTC,TJZ)were selected for the study in the Hanzhong Basin,Ankang Basin,and Yunxian Basin,respectively.Single Aliquot Regenerative-dose protocol(SAR),Thermally Transferrd Optically stimulated Luminescence(TT-OSL),k-feldspar of Post Infrared Inferred Stimulated Luminescence(pIRIR)method,and Multi-elevated-temperature Post IR IRSL(MET-pIRIR)were used to measure the overburden on the terrace the age of photoluminescence of aeolian loess and river facies sands,combined with climate surrogate indicators,compared with the tectonic activity and climate carrier records of adjacent regions and other regions in the same period,determine the formation age and dynamic mechanism of the secondary terraces in the upper reaches of the Han River To complement and improve the stratigraphic chronology and climate evolution process since the late Pleistocene in the region.The main conclusions are as follows:(1)The Single Aliquot Regenerative-dose protocol(SAR)dating of quartz particles is used to accurately obtain the equivalent dose value of the unsaturated sample of the SAR photoluminescence signal through the selection of preheating conditions and the analysis of the degree of sun degradation Between 145 and 327 Gy;corresponding OSL age,BSZC is in the range of 98.97?54.18ka,ZTC is in the range of 87.49?46.85ka.(2)For some samples whose conventional SAR photoluminescence signal reached saturation,the thermal transfer photoluminescence(TT-OSL),k-feldspar of Post Infrared Inferred Stimulated Luminescence(pIRIR)method and Multi-elevatedtemperature Post IR IRSL(MET-pIRIR)were used for testing.The study found that the Post Infrared Inferred Stimulated Luminescence(pIRIR)method and the Multielevated-temperature Post IR IRSL(MET-pIRIR)measured saturation signal,can not obtain a reliable equivalent dose value.The equivalent dose values(De)obtained by TT-OSL are all less than 2D0,and the luminescence signal is not saturated.The oldest age of the sand layer at the bottom of the secondary terrace is 226.66±22.37ka,and the age error is less than 10%.(3)Combining the measured OSL age data with the climate change and tectonic activity in the same period in the adjacent area,it was determined that the secondary terraces in the upper riches of the Hanjiang River were affected by the tectonic movement and climate change at about 230ka to the present,and the secondary terraces began to appear,and finally around 190ka formed.During the subsequent tectonic stabilization period(190?46ka),thick layers of aeolian loess accumulated on the terrace.(4)Based on the measured OSL age data,the chronological sequence of aeolian loess from the penultimate glacial period to the last glacial period of the secondary terraces in the upper reaches of the Hanjiang River was established.Combining with climate substitution indicators such as magnetic susceptibility,particle size,and chemical element content,it revealed the middle update Climate change law of the upper reaches of the Hanjiang River since the late middle pleistocene:the penultimate glacial period(190?153ka),aeolian loess accumulates in the upper reaches of the Hanjiang River,the climate was cold and dry,and the magnetic susceptibility,clay content,and Rb/Sr of the loess are low;During the glacial period(134?80ka),two layers of loess and three layers of paleosol developed in the ancient soil S1 in the upper reaches of the Hanjiang River,showing the characteristics of climate change of warm-wet-dry-cold-warm-wet-dry-cold-warm-humid;In the last glacial period(70?46ka),the climate in the upper reaches of the Hanjiang River was generally dry and cold,but a warm and humid period appeared at about 54ka.