标准生长曲线法在华南沿海老红砂石英光释光测年中的适用性

摘要

如何快速准确地建立老红砂剖面年代学标尺或区域年代学框架,是在实践中有待解决的问题.而标准生长曲线法(SGC)在减少样品测试时间、提高测年仪器的测试效率方面具有独特的优势,因此在内陆黄土及沙漠沉积年代测定中得到了广泛应用.在福建和海南海岸带老红砂分布区采集了4个剖面的测年样品共计20个,应用单片再生剂量法(SAR)及SGC法进行定年研究.结果表明:(1)福建和海南海岸带老红砂样品释光(OSL)信号均以快组分为主,在信号积分通道前0.64 s快组分的信号占据总体信号的80％以上,适合使用SAR及SGC方法测年;其快、中组分光电离截面分别为:福建老红砂2.62×10-17 cm2和3.24× 10-18cm2,海南老红砂2.66× 10-17cm2和3.51×10-18 cm2;2个区域样品的IRSL(红外激发释光信号)/OSL信号比值表明,较老样品的红外释光信号明显高于较年轻的样品,这可能是受到长石包裹体的影响,但其比值均小于10％,符合SAR与SGC测试要求.(2) SGC法在华南海岸地区老红砂OSL年代学研究中具有较好的适用性,不同样品之间的剂量生长曲线存在着相似的增长模式,可以建立标准生长曲线;但福建与海南老红砂样品之间的标准生长曲线具有较大的差异,因此在较大区域范围内运用标准生曲线法应当谨慎小心.%Development of an accurate chronological and stratigraphic framework in Old Red Sands remains a challenge in practice.Compared to the traditional single aliquot regeneration (SAR) method,standardised growth curve (SGC) has unique advantages in reducing the testing time and improving the testing efficiency of luminescence dating.Therefore,it has been widely applied in the dating of loess and desert sediments in inland China.In this paper,we will attempt to apply the SGC method to the chronological analysis of the Old Red Sands deposited along the coast of South China.From the Old Red Sands along the coastal belts of Fujian and Hainan,a total of 20 samples were collected from four sections for dating using both the SAR and SGC methods.Two meaningful conclusions can be drawn from this study.Firstly,the luminescence signals in the Old Red Sands from both Fujian and Hainan are dominated by fast components.With more than 80％ of fast components in the signal integration channel before O.64s,it is suitable to use both SAR and SGC for dating.The photoionization cross section of the Fujian Old Red Sands is 2.62 ×10-17 cm2 and 3.24×10-18 cm2 and is 2.66×10-17 cm2 and 3.51×10-18 cm2 for the Hainan Old Red Sands.The IR depletion ratio (IRSL/OSL) of samples from these two areas shows that the IR luminescence signals in older samples are significantly higher than those in the younger ones,which may be affected by the feldspar inclusions.Nevertheless,all the IRSL/OSL values are less than 10％,complying with the SAR and SGC test requirements.Secondly,the SGC method is more effective in OSL chronological studies of the Old Red Sands at coastal areas in South China.The dose growth curves among different samples show similar growth model.Therefore,a standard growth curve can be established.However,the standard growth curves between Fujian and Hainan Old Red Sands show significant differences.Therefore,extra cautions need to be exercised when applying the standard curve method to larger areas.