THREE-DIMENSIONAL GEOLOGICAL MAPPING OF QUATERNARY SEDIMENTS IN GLACIATED NORTH AMERICA: ITS IMPORTANCE AND CHALLENGES

Quaternary sediments cover a large portion of the North American near-surface (0-200 m) landmass which largely supports human infrastructures, hosts major granular aquifers and controls recharge to underlying fractured rock aquifers. Quaternary sediments also contain landfills, aggregate resources, cover mineral deposits, and play a role in seismic ground-shaking and other geohazards. Surficial maps and three-dimensional models of Quaternary sediments can thus help address a wide range of societal issues. Advances in remote sensing and mapping techniques are changing the way surficial sediments are being mapped, but only a small proportion of the critical areas of the North American near-surface landmass have been mapped in three dimensions; and not all models are readily available to researchers and the public.

Selected 3d mapping case studies in glaciated North America are examined to assess how geological knowledge and data of various types are integrated at different scales. The analysis shows that limited coverage by high quality subsurface data coupled with the use of large water well data of uneven quality remains a major problem and a limitation of three-dimensional mapping of watersheds and populated areas. At broader scales, compilation maps coupled with regional stratigraphic knowledge and conceptual models might be one approach to develop first-order 3D maps that can be useful for certain applications. Models constrained by well distributed high quality data of various types and dimensions are generally those that are developed at a more local scale for specific applications such as contaminated sites, aggregate resources, or for mineral exploration of buried targets. These models are constrained by the highest level of sedimentologic descriptions and may also include geophysical properties and geochemical composition data.