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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。
The changes of 210Pb activity in soil can be used to indicate the change of soil erosion rate and calculate the rate of soil erosion. However, the application in other fields, especially the karst environment, is relatively less. During the testing of the young stalagmite dating of caves, it was found that the current assumption of constant initial activity of the CIC (Constant Initial Activity Mode) needs to be verified. Through seasonal sampling and 210Pb radioactivity, soil organic matter and particle size analysis, the radioactive activity of 210Pb in the surface layer of 20-40 cm in the soil profile of Gui Mao Tomb of Guilin in Guangxi Province was significantly affected by seasonality, Environment, changes in soil ecological environment. However, the radioactivity of 210Pb in the soil profile basically remained constant, indicating that the 210 Pb Pb content in the soil layer had little effect on the 210Pb activity of the young sediment layer when the soil layer thickness was more than 20-30 cm. The cave overburden The effect of 210Pb radioactivity mainly lies in the downward migration of soil organic matter and cosmids. Therefore, the key factors affecting the activity of 210Pb in stalagmite cave are the soil thickness, the amount of 210Pb that migrated with organic matter and cosmids in the soil, which is then extended to the 210Pb age of cave young sediments. When the thickness of soil layer is more than 20-30cm Under the relatively closed environment of caves, the CIC model can be used to calculate the age of cave deposits.