TILL - A GLACIAL "TECTOMICT"

Tills, glacial diamictons, have been intensely studied for over a century, yet their origin, classification and differentiation remain centrally problematic to glacial geology. These sediments have been classified based upon visible characteristics and laboratory analyses into several major types: lodgement, meltout and flow tills deemed subglacial, while waterlain tills form within subaqueous environments, and also flow and meltout tills can form within supraglacial and/or proglacial environments. Extensive examination of the many till types using micromorphology, coupled with a greater understanding of subglacial, and submarginal subaqueous environments and deformable, glaciodymanic and rheological, bed conditions has resulted in a new assessment of tills. It is apparent that almost all of these till types have been subjected to intense levels of stress prior to, during and following emplacement. The evidence in the form of micromorphological attributes such as plasmic fabrics, edge to edge crushing, and clay translocation coupled with microstructures suggest that these sediments are not products of glacial depositional processes in the previously understood manner but are rather derivatives of tectonically-induced emplacement. In considering till from the structural point of view, till stratigraphic variation, both in time and space, as well as many textural, structural and geomorphological features of till beds can be more clearly and coherently explained and understood. A model is presented that, correlated with micromorphological features, suggests that till may be best viewed and understood as a “tectomict” rather than a typical depositional sediment.