A note on the mullion structures from the Ardennes and north Eifel

Abstract

The structures first described as boudinage by Lohest at the type locality near Bastogne in the Ardennes are the results of layer parallel compression of the competent beds. Since at present the term boudinage is almost invariably associated with stretching of the bedding, inspite of the usual priority rules, the author has used the term mullions for these structures, because their descriptions fit the accepted definition of mullions. These mullions are regarded to be produced by further modification of gentle sinusoidal buckles initiated at the boundary of a competent layer by compression. Examples of progressive deformation are cited, where the mullions, which originated at an earlier stage of deformation, are "refolded" by folds developed at a later stage. A quantitative determination of strain has been made from the mullion structures at the well known exposure near Dedenborn.