THREE-DIMENSIONAL GLACIAL GEOLOGY OF THE INTERLOBATE ORANGEVILLE MORAINE, SOUTHWESTERN ONTARIO, CANADA

The Ontario Geological Survey is undertaking regional scale 3-D hydrostratigraphic mapping of glacial sediments in select areas of Southern Ontario. This is part of a broader initiative designed to provide geoscience information for the identification, protection and sustainable use of the provincial groundwater resource. The full workflow comprises the assembly and standardization of existing subsurface data; acquisition of new geological and geophysical information; the development of a conceptual geological model; the interpretation of the subsurface data; and the generation of products for scientific, technical and non-technical clients.

The Orangeville-Fergus project area encompasses 1550 km² centred on the Late Wisconsinan interlobate Orangeville moraine. Bedrock dips to the southwest and deep buried bedrock valleys extending back from the Niagara Escarpment host important sediment aquifers. Eight key regional-scale sediment packages comprise: 1) older tills and localized coarse-textured stratified sediments; 2) a pre-Late Wisconsinan aquifer that sporadically contains organic material; 3) the main Late Wisconsinan Nissouri Phase Catfish Creek Till that forms a key stratigraphic marker across the region; 4) Erie Phase aquifers and aquitards deposited during and following the break-up of Catfish Creek ice consisting of coarse-textured glaciofluvial and subaquatic fan sediments, fine-textured glaciolacustrine sediments and diamicton. This package includes the Orangeville moraine and Rockwood buried-bedrock valley fill; 5) Port Bruce Phase Tavistock, Port Stanley and upper sandy tills and upper Maryhill drift, deposited during lobate advances from the northwest, northeast and southeast, and forming the upper aquitard across much of the study area; 6) outwash gravels deposited in incised channels; 7) Mackinaw Phase Wentworth Till and debris flows forming the Paris moraine and recording the maximum extent of the Erie–Ontario ice lobe during this ice advance; and 8) glaciofluvial and coarse-textured glaciolacustrine sediments overlying Wentworth Till in the far southeast of the study area. Closed depressions within the granular deposits of the Orangeville and Paris moraines facilitate recharge and ensure a healthy groundwater flow system at the head of three watersheds.