THE GLACIO-STRATIGRAPHIC ORGANIZATION OF QUATERNARY SEDIMENTS IN THE OILSANDS (IN SITU) AREA, ALBERTA: IMPLICATIONS FOR HYDROGEOLOGICAL MODELLING
A glacio-stratigraphic architecture is presented to interpret the hydrostratigraphic sequences resulting from multiple glaciations. It demonstrates an increasing confidence of interpretation as new methods of till differentiation are applied, from recognition of cyclic till sedimentary sequences in petrophysical logs, to characterization by mineralogy and geochemistry, and lastly to mapping of nonglacial events from weathered profiles on buried till surfaces. The resulting three-dimensional geological model provides predictive capabilities for assessing impacts on the hydrogeological system. Key elements of the model are the recognition that: nonstratified diamict (till) units and stratified fluvial complexes are associated with advance and retreat phases of each glaciation; till sheets form the foundation of the framework, with major aquifers nested between; distinct mineralogy of tills can assist in regional correlations and determine relative stratigraphic age; there is a cyclicity in the vertical facies associations; and, bedrock topography is a first-order control on the distribution of fluvial sediments. The implications of this complex architecture include: there is an increased probability of encountering regional aquifers at interfaces of regional tills; and, glaciofluvial downcutting and superposition of sediments produces a stair-stepped hydraulic connection resulting in an increased likelihood of hydraulic communication between surface water bodies and deep aquifers.