Multibend fault-bend folding

Abstract

This paper shows how slightly complex but angular fault shapes with only a few bends lead to broadly curved and/or highly complex folds. A common perception exists that simple, angular fold geometries are a necessary consequence of the normal assumptions of fault-bend fold theory — namely angular fault-bends, straight faults and flexural slip. To the contrary, it is shown here that exact application of these low-level assumptions produces great complexity from simple fault shapes. This complexity is caused by the combination of (1) generation of new axial surfaces by displacement of hangingwall cut-offs past successive fault bends and (2) fragmentation of axial surfaces by mutual interference. The result is entwined arrays of fold axial surfaces that produce quasi-curved and/or complex folds from discrete angular fault bends. Fold complexity grows in a highly non-linear way. In the most extreme case the number of fold axial-surface segments grows as the fourth power of the number of fault bends. This paper presents examples of the immense variety of complex fold geometries that are thus generated.