Formation-Top Offsets in West Central Alberta, Canada and their Implications for Subsurface Structure

Subsurface bedrock formation-top offsets were mapped in west-central Alberta, Canada. The methodology used well-log data and geostatistical analysis to map the offsets. Five stratigraphic horizons were selected for mapping subsurface bedrock offsets; they are in descending order the flooding surface near the top of the First White Speckled Shale (Wapiabi Formation), the base of the Fish Scales Formation, the top of the Wabamun Group, the top of the Graminia Formation, and the ‘Z marker’ in the Ireton Formation. Across the mapped bedrock offset lineaments, consistent elevation differences were observed at the top of the analyzed formations. The selected surfaces represent, or are close to, the marine flooding surfaces in this area that are considered to have been originally close to horizontal and, therefore, are ideal for mapping formation-top offsets. Numerous local offsets were recognized and highlighted using residual maps of these surfaces, and an isochore map of the interval from the base of the Fish Scales Formation to the flooding surface near the top of the First White Speckled Shale. The lineaments detected in the stratigraphic succession were then compared to interpreted/inferred faults from previous publications; the elevation differences across some of the offset lineaments are interpreted as vertical offset across faults. The maps of offsets generated in this report can be used as a starting point for more detailed analyses of potential faults in west-central Alberta.