SUPERPOSED BUCKLING IN MULTILAYERS

Experiments with soft models indicate that, just as in the case of a single-layer, the mode of superposed buckling in multilayers is essentially controlled by the shape of the early folds. A thin multilayer embedded in an incompetent host may undergo superposed buckling in any one of the four standard modes observed in single-layers. In general, however, the geometry of superposed folds is more varied in multilayers. A fifth mode appears only in multilayers, whereas the other four standard modes may be modified during refolding in multilayers. When different orders of buckling folds develop, the interference pattern of the smaller folds is distorted by that of larger disharmonic folds. There are several consequences of this distortion: (i) the degree of complexity of outcrop may vary in layers of different lithology; (ii) a morphology similar to that produced by three or more generations of superposed folds may develop even when there are only two distinct events of deformation; and (iii) there may be a significant lowering of the axial direction stability of the new folds. The experiments also indicate that the type 1 interference pattern may be produced in mode 1, mode 2, modified mode 2 and mode 5 folding. In addition, the experiments show that there are some special features associated with superposed buckling of parallel flexural-slip folds in thick multilayers.