Forms of large folds in the Central Appalachians, Pennsylvania

The forms of 1st order and 2nd order folds in the central Appalachians of Pennsylvania were studied. The current prevailing interpretation is that the 1st and 2nd order folds are kink bands or conjugate kink bands. The folds are complicated, but they resemble combinations of chevron like and concentric like forms. The folding theory is applied to complex multilayers, composed of layers of different rheological properties, including the interaction caused by the simultaneous growth of folds with two different wavelengths, in order to study the origin of fold forms in the central Appalachians. An idealized stratigraphic section for rocks in the central Appalachians is divided into structural units with different viscosities and thicknesses based upon study of lithologic descriptions. A detailed field study of the Shikellamy fold, a 3rd order fold near Northumberland, Pennsylvania is presented. The Shikellamy fold is the largest kink line fold known in the central Appalachians. The field evidence suggests that the Shikellamy fold is a monocinal kink fold, but it is unclear how the fold formed.