THE ROLE OF EXPERT KNOWLEDGE IN THE CONSTRUCTION OF A 3-D GEOLOGICAL MODEL OF THE OAK RIDGES MORAINE REGION, CANADA

A study of the 11 000 km2 Oak Ridges Moraine region of southern Ontario was initiated to provide a geological framework for hydrogeological investigations important in land use planning. Sound regional frameworks often require collection of strategic new field data and development of a database to effectively integrate archival data. Terrain analysis and geological mapping, combined with drillcore sedimentology and reflection seismic data can provide new insight for the re-interpretation of stratigraphic events. From this a late glacial regional unconformity was recognized and added to the conceptual stratigraphic model. Significant architectural elements of this unconformity, tunnel channels and drumlinized interfluves, became key datum during 3-D model construction.

Version I of a regional stratigraphic model was revised to incorporate additional expert knowledge to permit improved resolution of tunnel channels. These features are vital to hydrogeological analyses because they may indicate areas in which breaches in the regional Newmarket Till aquitard cause upper and lower aquifer hydraulic connection. A DEM, surficial geology, and subsurface data were used to develop a four-fold channel classification. The largest channels trend NE-SW, are up to 40 km long and < 7 km wide, have up to 50 m of topographic relief, and, extend to depths of 170 m. Between the large channels are two systems of nested channels that are shallower and commonly form an anabranched network. Larger channels completely dissect the regionally-extensive Newmarket Till, whereas smaller channels have a Newmarket Till substrate. The subsurface style and sediment fill of buried channels is well documented by seismic reflection data and drillcore sedimentology.

The regional channel network along with other high-quality geological data and GIS constraints were used to produce a training framework. Based on this expert knowledge, a series of rules and conditions were extracted from the training surface to stratigraphically code water well data. The resulting GIS model of the < 200 m thick sediment stratigraphy has a high degree of geological integrity. Furthermore, the model provides valuable information on the probable dimensions, distribution and character of buried tunnel channel sediment and potential aquifers.