The vertical positional error in the Precambrian surface grid is a function of the quality of the formation top pick set, including data density and the surface complexity (i.e., topographic variability), and the removal of points from the pick set that are identified as outliers.

Error in the pick elevation has two sources, error in the kelly bushing (KB) elevation, from which the pick elevation is derived, and actual errors in the making of the stratigraphic pick. Combined, these two sources of error are likely to have the largest impact on the grid’s vertical accuracy. The occurrence and magnitude of these errors are difficult to quantify. However, they were mitigated in the creation of this grid through comparison with existing published pick data sets and by geostatistical evaluation to identify and remove outliers.

Step 1: (Create the 2.5D grid) The Precambrian top surface was modelled in Petrel using convergent interpolation based on picks of the top. The data were quality weighted during surface interpolation, giving greater weight to the higher quality data from the AGS geologists (1.0), over the lower quality data from the previously unpublished Precambrian modelling dataset (0.8).

Step 2: (Clip the 2.5D grid) The Precambrian top surface was then clipped using the geo-edge for the extent of the Precambrian exclusive of the area of near the deformation belt.

Step 3: (Merge grid to create continuous surface) The Precambrian top surface was merged with the bedrock topography and DEM surface in the northeast part of the province.