a section of the earth’s crust in which rock strata have been compressed into folds. Most folded regions have formed as a regular stage in the development of the mobile sections of the earth’s crust, that is, the geosynclinal belts.
Because of the uneven rate at which tectonic processes developed, folded regions were formed primarily in certain specific epochs, known as epochs of folding. Beginning with the Paleozoic, the following folded regions are identified: the Caledonian folded region (the main folding occurring in the Ordovician, Silurian, and the first half of the Devonian); the Hercynian folded region (late Paleozoic); the Mesozoic, or Cimmerian, folded region (Jurassic and early Cretaceous); and the Alpine folded region (late Cretaceous and Cenozoic). A number of folded regions formed in the Precambrian.
In addition to folds, characteristic features of folded regions include overthrust nappes, regional metamorphism, and an intensified manifestation of magmatic activity. Some folded regions resulted from the bending of the cover of cratons, either on the periphery of geosynclinal regions, as in the Jura Mountains, or in intracratonic folded zones, particularly aulakogenes, as in the Donets Coal Basin.
V. V. BELOUSOV