The Folding of General Crumpling

Abstract

General crumpling or true folding (morphologically—complete or holomorphic) is on the whole the result of the bending of strata by the effect of longitudinal compression, i.e., tending parallel to the strata. Unlike block and injection folding, for which individual development of each fold is characteristic, which determines their morphological diversity, general crumpling folding is characterised by the subordination of big groups of folds to a single deformation common to them all. This implies reduction in the size of the whole massif in one direction and an increase in its dimensions in another. The main trend of the contraction is horizontal and of the increase vertical. In a homogeneous medium such deformation would have a regular character; each medium of any size would be deformed in the same way, contracting horizontally and stretching vertically. When, however, the medium is a layered, heterogeneous one and there is a possibility of the layers slipping relative to each other, the compressive deformation parallel to the layers is only partially expressed in their equal thickening. The rest of the deformation takes place through bending of the layers into folds. The ratio of the two depends on the thickness of the layers and their mechanical properties. (See V.V. Beloussov, Structural Geology, 2nd Ed. Mir Publishers, Moscow, 1978; in French.)