In places where there were no data, or where data were absent, we assigned the value -999 to the grid cell to denote null values in the modelled surface. In the case of the digital elevation model (DEM), which was imported from other sources, the edges of the input grid were all null data (-999) to constrain the geometry of the grid to reflect the NTS map boundary geometry. This geometry was propagated throughout the grid surfaces by the assignment of -999 to ensure their edges conformed to the DEM geometry.
Stratigraphic pick data used to generate the surfaces were derived from a number of sources, including new picks made during the course of the study. Because of varied degrees of certainty regarding the quality of those data, all data were ranked in terms of quality, with the author's picks ranked highest. This ranking was applied to screen data only in areas where more than one stratigraphic pick was made at a given location. In those cases, the highest-ranked value was incorporated into the calculations. It is important to note that all data were used in the process, and that in the absence of any other data, lower quality data were used along with data of higher quality.
Digital datasets in the model had a varied degree of precision depending on the nature of the surface modelled. For example, the surface DEM had the greatest precision as it was modelled from a 76-metre-grid-resolution source file, and it was exposed and easily validated. Precision of the other surfaces varied according to data density and knowledge regarding the processes of formation or deposition. Therefore, the modelled surfaces reflect not only data density and quality, but also knowledge regarding the processes, which is depicted through the addition of synthetic data, such as digital, hand-drawn contours. Consequently, grids of surfaces with the least amount of knowledge or data were validated and constrained by surfaces that carried a higher degree of confidence. Surfaces of geological units were tested against the two major unconformities in the study area - the topography of the bedrock surface, which itself was tested against the topography of the present-day land surface. This internal validation and testing was done more rigorously for the bedrock topography and lower-drift stratigraphic units. This process produced surface grids with geospatial integrity (that is, lower surfaces do not cross surfaces of higher units), and enabled the construction of a bedrock subcrop map that was entirely constrained by the geometry of the bedrock surface. Testing of geospatial integrity of the bedrock geology surfaces that lie beneath the bedrock surface was not as rigorous, and in some cases, surfaces of lower bedrock units may cross higher units. These occurrences, while present, are rare.
Horizontal_Coordinate_System_Definition:
Planar:
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: row and column
Coordinate_Representation:
Abscissa_Resolution: 250
Ordinate_Resolution: 250
Planar_Distance_Units: meters
Grid_Coordinate_System:
Grid_Coordinate_System_Name: Universal Transverse Mercator
Universal_Transverse_Mercator_(UTM):
UTM_Zone_Number: 12
Transverse_Mercator:
Scale_Factor_at_Central_Meridian: 0.999600
Longitude_of_Central_Meridian: -111.000000
Latitude_of_Projection_Origin: 0.000000
False_Easting: 500000.000000
False_Northing: 0.000000
Geodetic_Model:
Horizontal_Datum_Name: North American Datum of 1983
Ellipsoid_Name: Geodetic Reference System 80
Semi-Major_Axis: 6378137.000000
Denominator_of_Flattening_Ratio: 298.257222
A series of digital grids were generated for surfaces of geological units ranging from the top of the McMurray Formation to the present-day land surfaces. The grids were generated from hard data consisting of stratigraphic picks made from geophysical logs and lithologs, as well as from synthetic data consisting of digital hand-drawn contour lines, particularly for the bedrock topography and the drift aquifer units resting on the bedrock surface. Initial digital modelling was done using MCadContour software on an Apple Macintosh computer, which was later exported to PC-supported software platforms, such as Viewlog (see Alberta Geological Survey Earth Sciences Report 2002-03). All modelled surfaces were done on a 250 m grid-cell size, using Inverse Distance Weighted interpolation method.
The bedrock geology units were modelled from stratigraphic picks derived from Alberta Energy and Utilities Board databases. The bedrock topography and drift aquifer units were modelled from stratigraphic picks made on resistivity and gamma logs derived mainly from oil and gas exploration. Hand-digitized contours of the bedrock surface were used as synthetic data to enhance the resolution of the modelled surface. All bedrock geology surfaces were tested against the bedrock topography (an unconformable surface) to create a bedrock subcrop map. Gridded surfaces were then stacked in proper stratigraphic order to generate a 2.5-D model of the geological setting.