This dataset has stratigraphic and lithological picks of the upper bedrock and Quaternary geological units in the Athabasca Oil Sands Area extending north from Cold Lake to the Fort McMurray region. The picks were compiled from the mid-1970s to 2006 to construct maps of the subsurface distribution, structure, topography and thickness of near-surface bedrock and Quaternary stratigraphic units.
Alberta Geological Survey staff, as well as staff from industry and other government departments, interpreted the data.
Every record in the dataset is complete regarding geospatial information pertaining to its x, y and z attributes. Spatial locations are not unique in this dataset, although attempts were made to reduce duplications of borehole locations. Because different sources supplied the data over 30 years, with location information provided in different formats, including different projections, some data appear to be unique, when in fact they are simply offsets of the same log due to conversions from one co-ordinate system to another (e.g., NAD27 converted to NAD83).
Data are missing for some of the tops of the stratigraphic units, but in those cases, a bottom-of-unit elevation exists. Blank entries in the attribute field indicate absent data. Supplementary or non-critical data may also be absent.
In some cases, multiple entries of a formation with different elevations in a given borehole reflect sample description intervals within the stratigraphic unit. In this respect, the data were entered more as a litholog than a stratigraphic log. We assumed the uppermost elevation to be the elevation of the top of the stratigraphic unit in this case.
We grouped geological data into two classes: data pertaining to stratigraphy with no supplementary lithological data and data related to lithological properties, independent of stratigraphic classification. Generally, for a given borehole, stratigraphy information or lithology information will exist, but seldom both. Furthermore, for a given location, not all geological information may be complete. That is, only some units within the sequence may have been interpreted and captured in the dataset.
We did not interpret all borehole data from the region. We gave preference to data from boreholes drilled by Alberta Geological Survey, as these had the most abundant and diverse amounts of information, including sample analyses, and served as references or type wells in the local areas of interest. These borehole names are identified with the "AGS-" prefix.
We accepted information from external sources as is, with little to no validation of quality or accuracy.
Horizontal accuracy can differ by as much as 200 metres, depending on the source of the information (e.g., paper map), the precision of the co-ordinates provided (e.g., corner of LSD, centre of LSD or centre of section) or the projection (NAD27 vs. NAD83).
For some geographic areas, such as the Cold Lake region, we attempted to determine precise well locations by comparing locations recorded on the water-well logs to dwellings depicted on 1:50 000 topography maps.
Some borehole data, particularly those provided by industry, were surveyed and have a higher degree of accuracy.
We derived the elevation values from at least three sources:
- 1:50 000 scale topographic maps;
- interpolations from digital elevation models; and
- surveys (especially for oil and gas and geotechnical boreholes).
Vertical accuracy ranged from tens of centimetres in surveyed well bores to more than 10 metres in estimates from paper topographic maps.
Alberta Geological Survey (AGS) staff interpreted the stratigraphic picks from various undocumented sources of data, including water-well records (both lithologs and electric logs), oil and gas petrophysical logs (mainly gamma and resistivity), and lithologs and petrophysical logs from geotechnical and environmental boreholes. We derived the lithological information from newly drilled AGS boreholes or from boreholes drilled by the water-well, environmental and geotechnical industries.
Original units of geospatial measurement included co-ordinates from numerous formats, such as Dominion Land Survey, latitude and longitude, Universal Transverse Mercator or other Mercator projections. We converted all records with different units of geospatial measurement to latitude-longitude decimal degrees NAD83 co-ordinates.