【摘要】 土壤210Pb放射性活度变化可以用来指示土壤侵蚀速率变化、计算水土流失速率,但是在其他方面的应用,特别是岩溶环境的应用相对较少。在进行洞穴年轻沉积石笋年代测试过程中,发现目前应用的CIC(恒定初始放射性活度模式)初始活度恒定的假设需要进行验证。通过对广西桂林茅茅头大岩上覆土壤层进行季节采样和210Pb放射性活度、土壤有机质、粒径等分析,发现土壤剖面表层20~30cm内的210Pb放射性活度季节变化明显,可能响应了大气环境、土壤生态环境的变化。但是土壤剖面基底210Pb放射性活度基本保持恒定,说明土壤层厚度大于20~30cm时,土壤层中210 Pb变化对洞穴年轻沉积物表层210Pb活度变化影响不大,洞穴上覆层对洞穴沉积物210Pb放射性活度的影响主要在于土壤有机质和粘粒向下迁移。因此,影响洞穴石笋210Pb放射性活度的关键因素在土壤厚度、土壤中随有机质和粘粒迁移的210 Pb量的变化,进而推广到洞穴年轻沉积物210Pb定年,在土壤层厚度大于20~30cm时,洞穴相对封闭环境下,可以应用CIC模式对洞穴沉积物进行年龄计算。更多还原

【Abstract】 The variation of soil 210 Pb radioactive activity can be used as an index of soil erosion and to calculate the rate of soil erosion,but besides these,210 Pb 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 210 Pb method,but which supposed constant initial 210 Pb radioactive activity needs to be proved.Though the CIC model was proved in lacustrine environment,the 210 Pb in speleothems was not acquired from the outside atmosphere directly.So the variation of 210 Pb should be more complex than the lacustrine environment.So we chose Maomaotou Cave,Guilin,Southern China as an example,studied the seasonal variation soil 210 Pb above cave and the soil 210 Pb variation in soil profile.After the sample treatment and measurement in the lab,we found obvious variation of 210 Pb 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 210 Pb keeps constant in the whole year.We found that the soil 210 Pb influences cave speleothems little where the soil depth is above 20-30 cm,and the speleothems 210 Pb mainly affect by the downward 210 Pb adsorb on organic matters and soil clays.So the key factors influencing the speleothems 210 Pb from the soil layers above cave should be the soil depth,the amount of210 Pb 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.更多还原