关键词: 古土壤, ¹⁴C测年, 胡敏酸, 胡敏素

Abstract: Based on 44 ¹⁴C dates of humic acids and humins under different weather conditions,a statistics analysis was made to estimate their performance in paleosols.The following suggestions are reached:(1)A normal distribution analysis for HA/HM values deduced from 44 ¹⁴C dates results in average value of 0.98 with standard deviation of 0.20.This seems that the humin may be the oldest fraction of soil and its ¹⁴C age can represent the age of the paleosol.(2)The relationship between HA/HM value and the age of paleosol samples shows that the ages of humic acid and humin are indistinguishable for samples deposited in late Quaternary,but are obviously different from paleosol samples in Holocene.Their different behaviors in late Quaternary and Holocene may be related to the pollutant due to Holocene soil exposed to the surface and easily influenced by pollutant.Therefore it is suggested to use the different fractions for Holocene soil to obtain reliable radiocarbon ages for soil samples.(3)Assuming that the modern carbon pollutant entered into soil one-off,the amount of modern carbon into original carbon is estimated to be about 1.49% for late Quaternary soil sample,but this value increases to 21.37% in Holocene soil.Therefore,the amount of pollutant for Holocene soil is over 15 times than that for late Quaternary soil.If such pollutant continues to enter into soil with similar quantity during deposition,the impact percentages are 5.71% and 30.46% for late Quaternary and Holocene soil samples,respectively.The amount of modern carbon by continuously entering into soil is 2.6 times that of the one-off entering into soil for one sample in the same condition.It is further needed to state that which fractions could obtain more reliable ages for soil samples still depends on other factors such as geomorphic location,climatic zone,and soil type.

Key words: paleosol, radiocarbon dating, humic acid, humin