A general classification of subglacially-deformed materials is propose
d, based on sed iment properties and their relationship to styles of s
ubglacial strain. Deformation till is defined as homogenized, usually
diamictic material formed by glacially-induced shear of subsole materi
als. Three types are recognized: Type A, formed by pervasive, ductile
deformation; type B, formed by brittle shear; and comminution till, pr
oduced by the reduction of void space by in situ crushing and abrasion
. The term glacitectonite is adopted for materials that have undergone
subglacial shear but retain some of the structural characteristics of
the parent material. Original structures may be truncated by glacitec
tonic fabric elements (Type A) or distorted but not truncated (Type B)
. The principles of strain and material response, particle orientation
mechanisms, fabric development and drainage conditions are reviewed.
Examples of deformation tills and glacitectonites from Breidamerkurjok
ull, Iceland; Slettmarkbreen, Norway; Loch Lomond, Scotland; and East
Yorkshire, England, are used to illustrate the nature of subglacially-
deformed materials and their relationship to former subglacial strain
and drainage conditions. The geologic evidence suggests a continuum of
bed strengths can be recognized in deforming substrata, ranging from
high strength, low-strain Type B deformation till and comminution till
to low strength, high strain Type A deformation (C) 1996 Elsevier Sci
ence Ltd