Evidence for flexural shear folding associated with extensional faults

The maintainance of bed length and bed thickness within the hanging wall of extensional fault systems requires the development of bed-parallel shear. Four field examples of bed-parallel-shear related structures are described from a number of positions within the hanging wall and footwall to extensional faults. Flexural shear folding is a characteristic of both fault bend and fault-propagation folding. The dominant direction of the over-riding shear is directed toward the fault surface in the case of fault-bend folds. The fault surface may be considered to represent the finite neutral surface of the fold. In extensional fault-propagation folds, the direction of the overriding shear is toward the synclinalfold axial surface. The observations suggest that the direction of flexural shear for extensional and contractional folds is opposite for folds of geometrically similar form.