Till—as a glacial “tectomict”, its internal architecture, and the development of a “typing” method for till differentiation

Till has been studied for over a century, yet still a clear understanding of the mechanics of deposition and/or emplacement of till eludes us. Tills, in the past, have been generally subdivided into sediments formed in various sub-environments of the glacial system. As such it has been generally agreed that tills can be separated in terms of these types based on various attributes, such as clast fabric. Increasingly, such separation into various sub-types of till has become, however, highly debatable and tenuous. Based upon the use of micromorphology and a greater in-depth appreciation of the internal architecture of till, it has become apparent that previously established classifications of till are erroneous. Micromorphology reveals that deposition and/or emplacement of tills is a complex ‘tectonic’ process such that lodgement, melt-out and flow tills, as previously defined, do not appear to exist. Rather a new term better describes tills as glacial ‘tectomicts’. By using micromorphology in establishing the presence of sets of microstructures a statistical method is introduced that permits differentiation of tills from other diamictons. The implications for this new understanding of tills, allied to statistical ‘typing’, is considerable in terms of till formation, glacial stratigraphy and understanding glacial environments in terms of stress histories, porewater transmission, subglacial deformation mechanics, till rheological phase changes, and the timeline of till formation.