TANG Wei1, YIN Jianjun1*, WANG Hua1, YANG Hui1, MA Zhibang2, TU Linling1
(1. Institute of Karst Geology, Chinese Academy of Geological Sciences, The International Research Center on karst under the Auspices of UNESCO, Key Laboratory of Karst Dynamics of Ministry of Land and Resources & Guangxi, Guilin 541004, China;
2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)
Abstract:The variation of soil 210Pb radioactive activity can be used as an index of soil erosion and to calculate the rate of soil erosion, but besides these, 210Pb method was rarely be used, especially in karst environment. While the author applied that method in young stalagmites dating, some problems appeared. Constant initial concentration (CIC) model were used in most of the young speleothems dating using 210Pb method, but which supposedconstant initial 210Pb radioactive activity needsto be proved. Though the CIC model was proved in lacustrine environment, the 210Pb in speleothems was not acquired from the outside atmosphere directly. So the variation of 210Pb should be more complex than the lacustrine environment. So we chose MaomaotouCave, Guilin, Southern China as an example, studied the seasonal variation soil 210Pb above cave and the soil 210Pb variation in soil profile. After the sample treatment and measurement in the lab, we found obvious variation of 210Pb radioactive activity in top 20-30 cm of the soil, which may link to the monsoonal climate and soil organic matter content. But the bottom soil 210Pb keeps constant in the whole year.We found that the soil 210Pb influences cave speleothems little where the soil depth is above 20-30 cm, and the speleothems210Pb mainly affect by the downward 210Pb adsorb on organic matters and soil clays. So the key factors influencing the speleothems 210Pb from the soil layers above cave should be the soil depth, the amount of 210Pb downward which adsorb on organic matters and soil clays.And if the soil depth is above 20-30 cm, and the cave is in a close system, CIC model can be used in young speleothems dating.
Key Words: 210Pb; radioactive activity; soil layer; CIC model; dating; young speleothem; Guilin
EARTH AND ENVIRONMENT Vol. 43, No.5 Tot No.307, 2015, Page 498-504
