用210Pb技术判断年轻石笋封闭性研究

通过测试采自桂林地区茅茅头大岩的两个相邻石笋DY-2和DY-3的现代滴水沉积物的²¹⁰Pb放射性活度发现: (1)处于同一洞穴相距约1.5 m, DY-2石笋初始210Pb放射性活度是DY-3石笋的3.0倍, 接取的现代滴水沉积物DY-2是DY-3的1.7倍, 210Pb放射性活度和现代滴水观测均证明DY-3石笋沉积速率大于DY-2石笋, 说明在相同地质背景和地理环境下, ²¹⁰Pb放射性活度可以作为沉积速率的一个判断工具; (2)两石笋²¹⁰Pb放射性活度剖面均呈现一定的波动性, 这与石笋沉积时存在晶间孔隙且与晶间孔隙的分布和大小、密集度有关, DY-3石笋²¹⁰Pb放射性活度剖面的紊乱与石笋晶间孔隙相互联通, 后来²¹⁰Pb与石笋纹层的²¹⁰Pb发生混合和交换有关; (3)处于非封闭系统的石笋氧同位素是否发生同位素的分馏还需进一步研究。

Using 210Pb Technique to Determine the Closure of Young Stalagmites

Based on analyzing the ²¹⁰Pb specific radioactivity of two nearby stalagmites DY-2 and DY-3 in the same cave named Maomaotoudayan cave in Guilin City, the authors obtained the following understanding: (1) although they have grown in the same cave and their distance is about 1.5 meters, the initial ²¹⁰Pb specific radioactivity of DY-2 is 2 times higher than that of DY-3, and the ²¹⁰Pb specific radioactivity of DY-2 is 0.7 times higher than that of DY-3 in modern sediments. And the drip monitoring also certified that the deposition rate of DY-3 is faster than that of DY-2 stalagmite, indicating that the ²¹⁰Pb specific radioactivity could be used as a tool to determine the deposition rate in the same geological background and geographic environment; (2) both of the two stalagmites show fluctuation in the ²¹⁰Pb specific radioactivity profiles, related to the distribution, size and density of intercrystal porosity, the disturbed DY-3 profile might be attributed to the existence of pores in the stalagmite and the mixture of later ²¹⁰Pb with the former ²¹⁰Pb; (3) the problem whether there is an oxygen isotope fractionation in the open system needs further study.