Epoch of Folding

Epoch of Folding 

a relatively short event characterized by accelerated long-term and, on the whole, continuous tectonic movements, especially folding. Epochs of folding are recorded in rock strata by angular unconformities, owing to a combination of uplifting and erosion. The concept of epochs of folding first appeared in the works of the French geologists A. d’Orbigny and L. Elie de Beaumont. The concept was formulated more completely in 1913 and 1924 by the German geologist H. Stille, who examined the temporal distribution of folding and compiled a catalog of the epochs of folding, which were named after their type localities. According to Stille, epochs of folding are relatively short, global in scale, and separated by epochs of tectonic quiescence.

Stille’s ideas were criticized by, for example, V. I. Popov in 1933, N. S. Shatskii in 1937, J. Gilluly in 1949, and A. L. Ianshin in 1966. The critics argued that folding is a prolonged process, that epochs of tectonic quiescence never occurred, and that the epochs of folding occurred at different times in different regions of the earth. It is now known that although there are discrepancies in the times of onset and termination of the epochs of folding, even within individual folded structures, the main epochs of tectonic deformation—and not just the epochs of folding—generally tend to have occurred at the same times on a global scale. (SeeOROGENIC EPOCH.)