Facies architecture and stratigraphic heterogeneity in glacial deposits and their relation to hydrogeologic function

Glacial deposits are characterized by considerable stratigraphic heterogeneity but existing 'first generation' facies models are based almost exclusively on one-dimensional vertical profile descriptions of widely-spaced boreholes and outcrops. Such models do not adequately predict the three-dimensional geometry and heterogeneity of sedimentary facies for hydrogeologic purposes. This thesis demonstrates alternative approaches to the description of glacial deposits which integrate surface and downhole geophysical methods with architectural element analysis (AEA) of borehole data and outcrops. These methods are applied to better resolve the sedimentary architecture and hydrogeologic function of thick (>200 m) Late Pleistocene strata in southern Ontario.;AEA photomosaics of well exposed Pleistocene outcrops were integrated with an extensive subsurface GIS database consisting of drill core (>2300 m), downhole geophysical logs (natural gamma, EM conductivity) and shallow seismic reflection profiles (>12 line km) collected within a 1380 km 2 area east of Toronto. The basin stratigraphy consists of thick Late Wisconsin tills and intervening interstadial deposits overlying older glaciolacustrine sediments. Three primary aquifer systems were identified and large-scale trends in hydrogeologic parameters (hydraulic heads, transmissivity and hydraulic conductivity) were mapped. Aquifers are confined by finer-grained till deposits, including a thick (up to 60 m) regionally-extensive till member (Northern till) previously described as a homogeneous, highly impermeable aquitard. AEA and seismic reflection profiling in contrast, identify a composite internal till stratigraphy and the presence of heterogeneities over several length scales. Three principal architectural element types are identified: tabular diamict elements (DE), sorted sediment interbeds (I) and deformed zones (DZ) of complexly glaciotectonized strata. Architectural elements are defined by laterally extensive 4 th and 5th order bounding erosion surfaces and their correlative conformities; lower order surfaces define small-scale intra-element heterogeneities, including sorted sediment lenses, minor erosion surfaces and diamict 'increments'.;Accumulation of the Northern till involved aggradation of diamict elements punctuated by periods of non-deposition and subglaciofluvial reworking of till to form sorted interbeds. AEA identifies drumlins as macroforms resulting from aggradation of diamict elements across a pre-existing drumlinized erosion surface.;Interbeds and intra-element heterogeneities provide primary pathways for groundwater and contaminants through the Northern till; the lateral continuity (>103 m2) and interconnectedness of interbeds suggests a stair-case groundwater flow mechanism.