Mapping Formation-Top Offsets in Southwest Alberta, Canada: Methodology and Results

The structural framework of southern Alberta includes three major domains; from west to east these are: 1) the Rocky Mountain fold-and-thrust belt, 2) the Alberta Syncline and 3) the Sweetgrass Arch (Lerand, 1983). In the southern Alberta Plains, deformation structures including faults have also been reported more than 100 km to the east of the triangle zone (Russell and Landes, 1940; Irish, 1968; Skuce et al.,1992; Wright et al., 1994; Hiebert and Spratt, 1996; Lemieux, 1999; Zaitlin et al., 2011). This study presents the results of subsurface bedrock offset mapping in southwestern Alberta, using well log data and geostatistical analysis. A bedrock offset is herein defined as any vertical displacement of a formation top or bedrock horizon; a linear offset represents a potential fault. Three horizons, the Basal Fish Scale Zone (BFSZ), the top of Milk River Formation and the Lower Bearpaw flooding surface, were selected and numerous linear offset structures were recognized and highlighted from these three surfaces. Some of the mapped offsets coincide with previously reported faults in various studies, and suggest basement control.