THE INFLUENCE OF FLEXURAL-SLIP ON THE DEVELOPMENT OF DIFFERENT FOLD SHAPES

Outcrop studies from folds often observe movement between stratigraphic horizons showing that flexural-slip is an active mechanism during folding. Flexural-slip is most efficient between competent units with similar stiffness and weak interface contact (Tanner, 1996) and result in rotation, or kinking of mechanically active foliations during layer parallel buckling. In this study 2D finite element analysis is used to simulate the initiation of frictional sliding during visco-elastic single-layer buckle folding. The competent fold layer in the model is characterized by several competent layers (termed mechanical units) which are separated by a frictional interface enabling slip during the buckling process. Hierarchical initiation of movement between mechanical units is successfully modeled and, along with shape comparisons, show that the center of limb rotation happens at the point of maximum slip. Several sensitivity analyses (including the parameters of layer thickness, number of mechanical units, coefficient of friction, overburden pressure, strain rate, viscosity, Young´s modulus and permeability) give a better understanding of slip initiation, amount of maximum slip and limb rotation as a function of the amount of shortening during the buckling process.