Fracture patterns in clasts of diamictites (? tillites)

Abstract

Fracture patterns in some of the clasts of the Gowganda Formation, Ontario, are inconsistent with aqueous deposition and suggest that locally the diamictites are tillites. Similar fracture patterns have been found in the clasts of modern tills in the Cascade Mountains. Rare examples were also seen on the Garvellachs, Scotland. Laboratory experiments indicate that such patterns can be developed by the impaction of one clast against another while surrounded by a compliant matrix. The stresses which induced cracking were of the same order of magnitude as those which can be expected to occur in a sub-glacial environment.