Preliminary Studies On Chronology Of Aggration Red Earth In Jinhua-quzhou Basin

Jinhua-Quzhou Basin is located in central Zhejiang Province,and it's an important distribution area of Quaternary red soil in South China,In-depth study of Quaternary red earth helps reveal information on paleoenvironmental evolution in subtropical regions.There are a large number of research results on the type,genesis,physical and chemical characteristics,and formation environment of laterite,but the chronological study is still blank.In this paper,Optically stimulated luminescence(OSL)dating,geomagnetic dating,grain size,magnetic susceptibility,thermal magnetic and hysteresis loop are used to test the sample of profile LD,PJ and YD from Jinhua-Quzhou Basin,Zhejiang province,Establish a chronology framework and explore the evolution of the environment,We obtained the following conclusions:(1)From the grain size of the components of view,All types of red clay from those profile are homogeneous,Silt(4-63?m)is the first dominant grain size,it's average content is between 53.67%and 64.73%;The content of cosmid(<4?m)is slightly smaller than this,and the average content is between 23.35%and 40.5%;Sand(>63?m)is the least,ranging from 3.39%to 10.95%.It's high for the content of dust particle(10-50?m),which is between 34.19%to 39.19%.those value are similar to the test results from Jiujiang,Jiangxi province,Xuancheng,Tongling Anhui provice and the northern loess,they all have definite wind deposition characteristics,and it's belong to aggration red earth.Even Gravelly textured red clay with the content of dust particle is between 30.88%and 35.27%,which may be the result of the reformation of the aeolian parent materials due to later streamflow.Analysis of particle size sensitive components revealed that among the 1-3 principal components with cumulative contribution rate of more than 85%in three profiles,the dust particle acted as a sensitive grain group.The long-distance carrying process of parent material of aggration red earth,it satisfies the basic principle of optically stimulated luminescence dating,and has the conditions and feasibility of optically stimulated luminescence dating.(2)Beause Gravelly textured red clay are modified by stream water later,In this paper,we only choose 10 samples of and vermiculated red clay and uniform red clay for OSL,which is above Gravelly textured red clay.The age of 60 cm at the lower part of the uniform red clay layer of the profile profile LD is 66.3±5.49 ka,The age of 120 cm at the upper part of the vermiculated red clay layer is 115.32±9.55 ka,The age of 150 cm at the middle of the vermiculated red clay layer is 133.7±10.05 ka;The age of 60 cm at the lower part of the uniform red clay layer of the profile PJ profile is 102.4±14.81 ka,The age of 90 cm at the bottom of the vermiculated red clay layer is 129.39±11.23 ka,The age of 120 cm at the upper part of the vermiculated red clay layer is 13 6.4±12.23 ka;The age of 110 cm and 150 cm at the upper part of the vermiculated red clay layer of the profile profile YD is 103.42±8.41 ka and 106.68±17.46 ka,The age of 175 cm and 250 cm at the middle of the vermiculated red clay layer is 129.66±30.31 ka and 138.92±31.16 ka.The age of three profiles f is comparable,the results of optically stimulated luminescence(OSL)dating of Xuancheng and Langxi in Anhui Province.(3)The samples of three profile are belong to Brunhes normal polarity ehron.We did not find geomagnetic polarity drift in profile LD,But both PJ and YD profiles have 2 negative polarity in samples.We speculate that the two polar inversions may be the Iceland Basin event(188 ka)and the Pringle Falls event(212 ka),respectively according to the data of optically stimulated luminescence and GITS,but we did not find geomagnetic polarity drift in profile LD.That shows the presence of polar events in aggration red earth in Jinhua-Quzhou Basin.(4)Based on optically stimulated luminescence(OSL)dating,geomagnetic dating,we have established an age frame of aggration red earth in Jinhua-Quzhou Basin:The sedimentary age of aggration red earth in the Jinhua-Quzhou Basin spanned the late Middle Pleistocene and Late Pleistocene.Sedimentary age of Gravelly textured layer is between 364.9 ka to 196.9 ka,It's corresponding to the middle and late of Middle Pleistocene;Sedimentary age of the vermiculated layer is between 256.46ka to 95.44ka,It's corresponding to Late Middle Pleistocene;The starting age of the uniform red clay deposits is between 129,4 ka to 95.4 ka,it is a product from late Pleistocene.(5)According to the age frame and comprehensive analysis the data of particle size,thermal magnetic,hysteresis loop,and magnetic susceptibility data,Environmental evolution can divide three periods,what is recorded in aggration red earth of Jinhua-Quzhou Basin:Gravelly textured red clay formation period(about 364.9-196.9 ka):The sediments of this layer are coarser,magnetic susceptibility is the lowest value of each profile,the content of high magnetism mineral are less;Magnetic minerals may be dominated by hematite with a high coercive force,That proved the climate of Middle Pleistocene climate is relatively hot and humid.The vermiculated red clay formation period(about 256.5-95.4 ka):Aeolian parent material generally experience strong chemical weathering,but the tattooing features from strong to weak until stagnation from the bottom to the edge,The time from strong vermiculated red earth to weak vermiculated red earth was 190ka.The content of clay(<4?m)gradually decreases and the content of dust particle(10-50?m)gradually increases from strong vermiculated layer part to weak vermiculated layer.magnetic minerals of this layer was converted from hematite with a high coercive force to maghemite and magnetite with a low coercive force from bottom to top.It shows that the climate changed from hot and humid to cool and dry during the late Middle Pleistocene in Jinhua-Quzhou Basin..The uniform red clay formation period(about started from 129.4 ka):The content of cosmid(<4?m)in uniform red clay is less than vermiculated red clay,decrease in weathering and Magnetic susceptibility values increase significantly.Magnetic minerals may be dominated by Magnetite,the content of magnetic minerals are increased.these evidences indicate that the climate has gradually cool and dry since the late Pleistocene,uniform red clay developed during the last interglacial.