Buckle folds are common traps for hydrocarbon in several contractional provinces. Buckle folds form where stratified sequences rest a top salt or some other utterly weak rock as a decollemet zone in units with high competency contrasts by a compressive stress which acted along the length of the rock layers. An important parameter affecting buckle folding of a competent zone above a mobile decollement is existence of a thick lower decollemet. In this paper the effect of detachment zone on folding of rock layers is studied using finite element method. Large deformation formulation is considered. Mohr-Coulomb plasticity model is used to deal with nonlinearity of material during folding. Two cases of folding are considered. In the first case a symmetric fold with equal detachment thickness beneath two flanks is analyzed. In the second case detachment zone is omitted in one flank. Finally, the effect of detachment zone on folding and deformed shape of buckle fold is studied. Manuscript profile