Architectural element analysis applied to glacial deposits: Internal geometry of a late Pleistocene till sheet, Ontario, Canada

Deposits left by continental ice sheets are characterized by sedimentologic al complexity and stratigraphic heterogeneity, but stratigraphic descriptio ns of such deposits, and resulting "first-generation" facies models, are st ill based primarily on one- or two-dimensional borehole or outcrop data. Re construction of depositional environments, hydrogeological investigations o f Pleistocene glacial deposits, and hydrocarbon exploration in pre-Pleistoc ene glaciated basin fills require a more detailed understanding of the form and heterogeneity of lithofacies sequences in three dimensions. Architectural element analysis is used widely by sedimentologists for categ orizing internal stratigraphic heterogeneity in sandstones, particularly th ose of fluvial origin. This paper demonstrates the first application of arc hitectural element analysis to glacial deposits such as tills. Outcrop, bor ehole, and a broad range of subsurface geophysical data were collected from a thick (60 m) till sheet present across an 80 km(2) study area near Toron to, Canada. The till sheet is not homogeneous, but is composed of three dis tinct architectural elements and associated lithofacies, viz, diamict eleme nts, interbeds of subglaciofluvial sediments, and glaciotectonically deform ed zones. Application of architectural element analysis to these subglacial strata provides insights into the origin of drumlin bedforms and subglacia l processes below the Laurentide Ice Sheet and creates a framework for unde rstanding ground-water and contaminant movement in underlying aquifers.