THE ORANGEVILLE MORAINE PROJECT: FROM A SOUTHWESTERN ONTARIO QUATERNARY STRATIGRAPHIC FRAMEWORK TO A 3-D MODEL AND BEYOND

The Ontario Geological Survey is undertaking regional scale 3-D mapping of glacial sediments to provide geoscience information for the identification, protection and sustainable use of the provincial groundwater resource. A stratigraphic framework, developed for previous southwestern Ontario 3-D mapping projects, has been adapted to the Quaternary sediments in the 1550 km² interlobate Orangeville Moraine area. A series of 43 continuously cored boreholes, ground gravity surveys and legacy datasets have been used to map the bedrock surface and overlying Quaternary sediments.

The southwest-dipping Paleozoic bedrock surface is characterized by deep re-entrant valleys that extend from the Niagara Escarpment and a series of shallower generally north east trending buried-bedrock valleys. Older tills, silt- and clay-rich glaciolacustrine and localized coarse-textured stratified sediments, likely deposited during ice retreat, are concentrated in the western and central portions of the area. Catfish Creek Till, deposited by the main (regional) Late Wisconsinan ice sheet, forms a key aquitard and an important stratigraphic marker across the region. A series of aquifers, including Orangeville Moraine glaciofluvial and subaquatic fan sediments, and fine-textured glaciolacustrine and diamicton aquitards were deposited during and following the break-up of the ice. Late glacial tills form the upper aquitard across much of the region and define the maximum extent of Huron-Georgian Bay and Erie-Ontario lobate ice advances.

Mapping the distribution and characteristics of regional-scale Quaternary sediment packages in the subsurface means it is now possible to model groundwater flow with increased accuracy. Buried-bedrock valleys, long viewed as potentially important sources of water, have been mapped in detail revealing knick points, plunge pools, disappearing streams and scarps that subdivide the valley systems. Derivative maps show areas with greatest groundwater recharge potential and vulnerability to surface contamination. Using a common stratigraphic framework allows the distribution, thickness and structural contours of units in contiguous 3-D project areas to be mapped quickly and easily as well as facilitating the generation of ‘super models’.