Earth Sciences Report 2000-02

Earth Sciences Report 2000-02

ESR 2000-02

Distribution and thickness of salt within the Devonian Elk Point Group, Western Canada Sedimentary Basin

Author(s) Grobe, M. Date 2000-01-01

The Western Canada Sedimentary Basin contains several regionally extensive salt deposits. The major part of these deposits is contained within the Devonian Elk Point Group. Five mappable salt units, reaching a maximum aggregate thickness of 380 m in one area of the basin, have been recognized within this stratigraphic interval. These are (from oldest to youngest) 1) the Lower Lotsberg, 2) the Upper Lotsberg, 3) the Cold Lake, 4) the Prairie Evaporite, and 5) the Hubbard Evaporite salts.

Stratigraphic data for the Elk Point salt units were checked and updated. Data processing and the application of mapping software resulted in the refinement of the some of the salt boundaries and the production of basin-scale depth to, structure, and isopach maps for the Elk Point salt units. The lack of stratigraphic data in the area of Wood Buffalo National Park (northeastern Alberta) and the scarcity of stratigraphic data from the Northwest Territories did not allow confident subsurface mapping of the Cold Lake Salt deposits in these areas. Furthermore, available stratigraphic data for the Hubbard Evaporite Salts (Saskatchewan) were too scarce to warrant an improvement of previous work.

At this stage, only the total thickness of the individual salt units, including intervening non-soluble material (e.g., anhydrite and shale beds) has been considered. As a result of a history of repeated solution and redeposition, the Lower Lotsberg, Upper Lotsberg, and Cold Lake salt units are extraordinarily pure, hence, the reported thicknesses approximate the total brinable thickness. The Prairie Evaporite Salt unit, however, varies considerably in purity within the basin, reflecting ''normal'' marine evaporite deposition, and only approximate ratios of brinable to non-brinable material are available. Detailed mapping of the total brinable thickness of the Prairie Evaporite Salt unit was beyond the scope of this study, but can be achieved using electrophysical log signatures.

The computer-generated isopach map of the Prairie Evaporite salt (where salt > 40%) in some cases closely mimics subsurface features, such as Winnipegosis reef build-ups and areas of local salt collapse. The combination of industry seismic data with stratigraphic data from wells would greatly improve the resolution of the subsurface maps for the Prairie Evaporite Salt.

Grobe, M. (2000): Distribution and thickness of salt within the Devonian Elk Point Group, Western Canada Sedimentary Basin; Alberta Energy and Utilities Board, EUB/AGS Earth Sciences Report 2000-02, 35 p.