郑州邙山马兰黄土的光释光(OSL)测年初步研究

对郑州市西北邙山黄土塬赵下峪(34°58'N,113°22'E)剖面上部马兰黄土(厚约87m)不同层位的24个样品作了细颗粒(4-11μm)组分红外释光(IRSL)测年,其中8个样品同时进行了细颗粒组分绿光释光(GLSL)测年。样品的IRSL和GLSL信号强度都在Daybreak1100TL/OSL检测系统中测量。该系统的本底计数为70-80光子/秒。被检测的IRSL和GLSL波长分别为340-480nm和340±25nm;激发光束波长分别为880±80nm和514±14nm,功率为18mW和15-16mW。所有样品的等效剂量都用再生释光法测定;环境剂量率是通过测定样品的铀、钍和钾含量,按Aitken(1985)的转换系数确定的,考虑了含水量的影响及宇宙射线的贡献。从这批样品的光释光测年结果可得以下初步认识:
(1)8个样品细颗粒组分的IRSL和GLSL测定的等效剂量和年龄值,除1个样品外,都在1-2σ范围内一致。这可能提供了沉积物光释光测年可靠性的一种自检方法。(2)邙山剖面马兰黄土不同层位段的沉积速率变化十分显著,从0.4m/ka到5.6m/ka,并与剖面上质量磁化率测定值的变化大致相吻合。该剖面马兰黄土至少有4个快速堆积层(沉积速率>3m/ka),其磁化率低而变化小;3个缓慢堆积层(沉积速率<0.5m/ka),其磁化率大或变化显著,它们之间有一系列过渡层。(3)邙山马兰黄土大体可三分即上部(L_1-1)埋深2.7-27.5m,中部(L_1-2)埋深27.5-57.9m)和下部(L_1-3)埋深57.9-87.9m。它们的形成年代分别为10.8-36.2ka B P,36.2-70.3ka B P和70.3-80.2ka B P。较详细的黄土-古土壤序列年代表将在文中讨论 

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.