Complex structures

Abstract

Following the discussion in Chapter 4 in which overfolds were described, structures in which beds are overturned beyond the vertical, we next consider nappe structures. A nappe arises from a very large overfold in which the strata are nearly horizontal over wide areas. The fold structure is referred to as a recumbent fold and has been ‘pushed over’ so far that both limbs have low angles of dip, and are approximately parallel, although in the case of one limb the beds are actually upside-down; i.e. the succession is inverted. Only at the ‘nose’ of the structure where the strata are folded back on themselves will steep dips be encountered (Fig. 38a).