Only a few studies have been carried out on the relationship between geomorphic surfaces, isotope geochemistry of pedogenic carbonates and paleoecological changes in Iranian arid lands. The aims of this study were to investigate the pedogenic development of geomorphic surfaces in eastern Isfahan and to understand the ecologicological and climatic conditions during evolution of these surfaces. Three pedons on geomorphic surfaces of an alluvial fan were selected and studied. Paleovegetation of the study area was identified using signals from carbon isotopes in pedogenic carbonates. The results indicate that the expansion of C4 plants occurred during periods with low ?18O (Glacial periods). It seems that a decrease in atmospheric carbon dioxide concentration during glacial periods was a primary factor responsible for the expansion of C4 plants, landscape stability and pedogenic development of soils in this region.