Brecciation of clasts in diamictites of the Gowganda Formation, Ontario, Canada

Igneous boulders in the Gowganda Formation were brecciated prior to the induration of the diamictites in which they occur. The breccias evidently represent the results of the maximum stresses imposed on a lodgment till in the final stages of emplacement. The stresses necessary to fracture granitoid clasts are likely to occur at the base of glaciers of unremarkable size, and could easily be imposed by small glaciers if the pore pressure in the underlying till dropped as a result of sudden leakage of pore fluid.