Top of the Belly River Group in the Alberta Plains: Subsurface Stratigraphic Picks and Modelled Surface

This report presents subsurface stratigraphic picks of the top of the Belly River Group in the Alberta Plains (Townships 1 to 50, Ranges 1W4 to 2W5) made from wireline geophysical well logs. Representative geophysical logs demonstrate the criteria used to make picks and to highlight regional geological variability. Well data were screened to detect errors resulting from deviated wells, as well as incorrect ground and kelly-bushing elevation data. Statistical methods identified local and regional statistical outliers, which were examined individually and either confirmed or removed.

A structural contour map of the top of the Belly River Group is included to illustrate the regional structure. Areas of anomalous local structure were identified in several areas. Deviations from regional strike on the structure map, consistent with transverse faults, exist near Lethbridge, where the Monarch Fault Zone has been mapped. A bowl-shaped structural anomaly with a central uplift was identified near Bow City. The Bow City anomaly, which affects the Bearpaw Formation but has little surface expression, is broadly similar in shape and size to the Eagle Butte Impact Structure, located on the eastern flank of the Cypress Hills.