DEFORMATION IN QUATERNARY GLACIAL DEPOSITS OF THE WATERLOO REGION, CANADA

The Waterloo moraine is a complex interlobate or kame moraine formed during the Late Wisconsin. The moraine has recently been the subject of renewed interest due to rising pressures on groundwater resources. The Ontario Geological Survey's Groundwater Resources Mapping Program has, in part, focused on delineating the nature and distribution of subsurface Quaternary deposits in the Waterloo region. The region is underlain by 1) regionally extensive tills (including the Catfish Creek Till) and associated deposits, 2) stratified deposits and discontinuous lenses of Maryhill Till within the moraine, and 3) upper tills and associated deposits that onlap the outer margins of the moraine.

Various types of deformation structures have been reported from this area, but none of these have been systematically studied. Deformation structures can be useful indicators of local depositional processes, which in turn can be used to better understand the overall development of the moraine and the hydrostratigraphy of the region. Detailed sedimentological analyses are thus being carried out to characterize and assess the significance of deformation structures in these deposits.

Results from two sites are presented here. At site 1 on the Waterloo moraine, high-angle normal faults occur with offsets up to 175 cm and dipping from 45 to 86° towards the SW and NE. This site is located in close proximity to a SE trending topographic high, which is thought to represent an ice contact slope. Similar faulting in glaciofluvial deposits has been interpreted as recording melting of buried ice.

At site 2 on the eastern edge of the Waterloo moraine, complex deformation structures in sand occur beneath a diamict previously mapped as a fine-grained facies of the Catfish Creek Till. This sand unit also contains randomly-oriented sedimentary dikes of mud and sand, < 5 cm thick and up to several metres long, that laterally can be traced into the overlying diamict unit. The deformation structures likely record fluidization and water escape under high pore water pressure. The dikes suggest the overlying diamict was also under significant pressure. The origin of the fine-grained facies of the Catfish Creek Till is as yet poorly understood, but the deformation recorded at this site suggests that it may have been deposited in a subglacial setting.