南海全新世珊瑚礁ESR和铀系年龄的研究

ESR AND URANIUM SERIES AGES OF HOLOCENE CORAL REEFS IN THE SOUTH CHINA SEA

用ESR和铀系方法对几个南海珊瑚礁浅钻的样品进行了年龄测定,实验结果表明这两种方法测定的年龄基本一致,这些珊瑚礁形成千全新世早期。在用附加剂量法求取总剂量值时,不论样品饱和的磁效应如何,采用指数方程拟合均可取得较好的效果。研究中发现样品的天然ESR信号强度I_0和样品磁饱和剂量时的ESR信号强度I_(max)之比可以很好的反映α辐射效率——k值的大小,用文中提出的方程确定k值可以提高海洋碳酸盐ESR测年的精度。

The ages of 14 samples of coral reefs from several shallow drilling holes in the South China Sea were determined by both ESR and uranium series (^(230)Th/^(234)U) methods, and the experimental results show ideal agreement between ESR and uranium series data. These coral reefs formed in the early part of the Holocene.It was found that the effects of magnetic saturation of the samples were different from each other in this research. In the determination of the natural total dose of the coral reef by use of the additive dose method satisfactory resultswere obtained using the exponential fitting.Different α radiant efficiencies——k values——should be selected for different samples because of the different effects of the magnetic saturation of various samples. There is an obvious positive correlation between the k value and the ratio of the natural ESR signal intensity (I_0) to the ESR signal intensity of magnetic saturation (I_(max)) of the samples. Based on some ESR ages of samples in chemical closure systems and the ratios of I_0/I_(max), a linear equation for determining the k value can be obtained; k=4.386×I_0/I_(max)+0.095. Employing the formula the k value of the samples can be given readily. The use of the formula is advantageous to improve the precision of ESR dating of marine carbonates.