PRELIMINARY STUDY OF OSL DATING OF THE MALAN LOESS AT MANGSHAN PLATEAU, ZHENGZHOU,HENAN PROVINCE

Twenty-four loess samples collected from the Malan loess of a thickness of 87m,at Zhaoxiayu section (34° 58'N and 113° 22'E) in Mangshan hill,Henan province,have been dated for the fine grains using IRSL,with a wavelength of 340-480nm,and GLSL,with a wavelength of 340±25nm,in an automated Daybreak 1100 TL/OSL system with background counting rate of 70-80 photons per second,and stimulated by an infrared beam (880±80nm,18mW) and a green beam (514±14nm,15-16mW) respectively.The regenerated luminescence method was employed for equivalent dose (De) determination of each sample.Environmental dose rate of the sample was calulated from the uranium,thorium and potassium analysis by using the compilation of Aitken (1985),taking into account the water content and cosmic ray contribution.On the basis of the OSL dating results of these samples,the following preliminary conclusions can be drawn.1.Comparison of De values and dates obtained from IRSL analysis with those from GLSL measurement for eight samples shows that they are in agreement within 1-2σ,except one sample.So it may provide a possible cross checking technique for reliability of sediment OSL dating.2.The deposition rate varies significantly from 0.4 m/ka to 5.6 m/ka with different horizons of the sediments and is approximately coincident with the variations of the magnetic susceptbility of the section.There are at least four rapidly depositing layers (deposition rate>3m/ka) with lower susceptibility and three slowly depositing layers (deposition rate <0.5 m/ka) with a higher or remarkably different susceptibility.There are a series of transition layers between.3.The Malan loess can be divided into three units at Zhaoxiayu section,the Upper unit at a depth of 2.7m to 27.5m,the Middle unit composed of paleosol and loess alternations at a depth from 27.5m to 57.9m and the Lower unit at a depth of 57.9m to 87.9m their age heing estimated as 10 8-36.2ka B P,36.2-70.3 ka B P and 70.3-80.2 ka B P respectively.A detalled time-scale of loess-paleosol sequence of the Malan loess is discussed.