Selecting four limestone soil profiles as the subject investigated from karst area of central Guizhou Province, and based on careful sampling and analysis, this work discusses geochemical characteristics and behavior of Th enrichment during the formation of limestone soils. The results show that : 1 ) the rock-soil interface is an important geochemical reaction place for significant enrichment of Th, and this mainly stems from residual enrichment of Th through huge changes in volume reduction of weathered residua accompanied by rapid disso- l...