Using fly ash as a tracer overcomes the limitation that the ¹³⁷Cs tracer method has in explaining the processes of soil redistribution prior to a nuclear explosion in the atmosphere.In this study fly ash was used as a time marker to study spatial and temporal characterist ics of the redistribution of soil organic carbon(SOC)in Black soil,Northeast China.Attempts were made to build up a methodology to determine thickness of accumulated layers and the soils underneath using fly ash.Results showed that the method was capable of est imating relative age of the accumulated materials.The surface of the buried soil determined by the fly ash technology was in consistency with that obtained with the method based on variation of SOC concentration with the depth in profiles.The results also indicated that redistribution of soils in the study area occurred prior to the use of steam locomotive.Among the studying geomorphic positions,at the shoulder-slope erosion was the strongest and the content of SOC was the lowest.There was no obvious erosion at the summit because of small slope gradient.Redeposition also took place at backslope,foot-slope and toe slope.The rate of soil deposition ranged between 1.01~5.56 mm a^-1.The study also found that the content of SOC in buried surface layers was higher than that in the plowed layer,which indicated that there was much organic carbon sequestered below the plowed layer.The effects of soil transport and burial need to be considered in assessing agricultural soils as carbon resource or sink of atmospheric CO₂.