TOWARDS A SEAMLESS MODEL OF QUATERNARY SEDIMENTS FOR CONTINENTAL-SCALE HYDROGEOLOGY IN NORTH AMERICA

Regional and continental-scale surficial geological information in the form of map compilations have been available for some time in North America. As hydrogeological models are being developed at such broad scales, there is an increasing need for a new generation of compilation maps that better integrate surface and subsurface information in a common digital format. In Canada, the development of such a product has been hampered by both the scarcity of subsurface data in some remote areas where thick stratigraphic sequences occur (e.g. Hudson Bay Lowlands) and the fact that large subsurface datasets have yet to be compiled in file formats, and at scales that would allow seamless coverage across provincial boundaries. Furthermore, thickness maps, where available, are generally not subdivided according to a stratigraphic framework.

Here we present a preliminary digital map of Quaternary sediment types and their estimated thickness for Canada and parts of the United States. Based on existing compilations, this map brings the data together and is designed for continental-scale groundwater flow modelling. The map consists of merged triangulated surfaces whose internal mesh structures match sediment unit contacts from pre-existing polygon-based map compilations. Thickness data, mainly derived from available thickness maps, are stored as values (i.e. min, average, max) for each node. The map represents the first layer of a generalized three layer model consisting of: 1) a surface layer; 2) a subsurface layer representing the characteristics of the dominant subsurface unit (based on stratigraphic information); and, 3) locally, a deeper layer to account for important known buried valley aquifers. Thickness data is thus broken down according to this simplified 3-layer framework. The full 3-layer model has been completed for Saskatchewan and the same approach is currently being applied to the rest of the model domain. Upon completion, the model will store hydraulic parameter values which will significantly improve transfer of data to numerical models compared to previous map compilations. This represents moving one step further towards a full three-dimensional Quaternary geological framework model for North America.