This grid dataset is part of the 3D stratigraphic model of west-central Alberta (WCAB). The grid is a rendering of the thickness and distribution of sediment overlying the WCAB bedrock topography.
The thickness and distribution of sediments overlying the bedrock surface in WCAB is highly varied, ranging from less than 1 m to as much as 125 m. These sediments include Paleogene fluvial deposits, glaciogenic materials deposited during Quaternary glaciation, as well as postglacial sediments.
This dataset supplements Alberta Geological Survey (AGS) Report 93, which includes a full description of the process used to produce the sediment thickness grid.
17997 data points of varying quality and coverage were compiled for the construction of the WCAB bedrock topography. The most significant data source was the extensive collection of well records compiled in the AWWID. The AWWID has abundant, relatively low-quality data records, which include location inaccuracies resulting in numerous wells with duplicate locations. In cases of collocated data, water-well records were evaluated on cross-section to consider surrounding data and the accuracy of lithology information contained within the record. This was a manual process to identify the most correct duplicate well litholog to ensure the bedrock topography was delineated properly in real and synthetic data. Water-well records that were not considered to be correct were maintained in a final database, but not used as input for the modelled surface.
The 17997 data points were used to model the WCAB bedrock topography. The WCAB sediment thickness grid was created by subtracting the WCAB bedrock topography from the Sustainable Resource Development (SRD; 12 m cell size) digital elevation model (DEM) (resampled to a 200 m grid cell size), which represents the present-day land surface.
All borehole, interpreted contours and synthetic data were sampled to the 12 m provincial digital elevation model (DEM) to provide a borehole top elevation (m asl) to correlate lithological descriptions between boreholes to create the WCAB bedrock topography. This process was necessary as the elevation of AWWID water wells, in many cases, was not available/recorded or verified, and if reported was estimated from a topographic map, field investigation or handheld Global Positional System (GPS) device. GPS devices have accuracies reported by the AWWID of ~1-30 m, but are of varying device quality and cannot be assessed for accuracy between devices. Elevation values of moderate- and high-quality data from AGS boreholes and fieldsites, geophysical logs, and previously published geological and hydrogeological maps were also checked with the DEM to verify elevation accuracy and modified to match the DEM, if necessary.
The vertical accuracy of the 12 m DEM is stated as 5 m @ 90% in the WCAB derived from 1:60 000 aerial photographs using photogrammetric methods.
Methodology to create this grid dataset is fully documented in AGS Report 93.
This gridded dataset was derived by subtracting the computer-generated geostatistical model of the WCAB bedrock topography from the DEM (sourced from Sustainable Resource Development; 12 m cell-size and resampled to a 200 m grid cell size), which represents the present-day land surface.
Data used to construct the WCAB bedrock topography were derived from a variety of low- to high-quality borehole data, including lithologs submitted by water well contractors and compiled by the Alberta Water Well Information Database (AWWID), downhole geophysical logs collected from water wells and coal surveys conducted by the Alberta Research Council, AGS borehole logs and field data; stratigraphic picks made from oil and gas geophysical logs by AGS geologists; contour data from the Bedrock Topography of Alberta; and the DEM, where known bedrock outcrop locations were made equal to the elevation value of the DEM.