- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
Joint or fracture cleavage surfaces in the Paleozoic rocks of the Armorican deformation belt of south Pembrokeshire, Wales, intersect bedding surfaces parallel to adjacent fold axes and form acute angles with stratigraphically higher bedding surfaces, closing toward adjacent anticlinal hinges. They are characteristically interrupted at bedding surfaces and vary in frequency with lithology. Calcareous concretionary rods that are now oriented parallel to the axial trace-fractures, and at right angles to fold axes, are considered to have been originally normal to depositional surfaces. The fractures are interpreted as having formed immediately before or at the beginning of Armorican folding and to have been rotated and sheared during the folding.