Late Mesozoic Reactivation of Precambrian Basement Structures and their Resulting Effects on the Sequence Stratigraphic Architecture of the Viking Formation of East-Central Alberta, Canada

The Lower Cretaceous Viking Formation is a siliciclastic unit that occurs in the subsurface of Alberta in the Western Canadian sedimentary basin. This study focuses on a lowstand paleoshoreline trend extending along strike between two hydrocarbon-producing fields, Joarcam and Judy Creek (250 km NW). The Viking Formation in these fields records depositional thicknesses ranging from 20 to 30 m. Between these two fields, however, the formation is anomalously thick (45–60 m), complicating the recognition and correlation of key stratigraphic surfaces. Marine flooding surfaces above and below the Viking Formation are routinely employed as stratigraphic datums in order to remove postdepositional deformation and facilitate the development of a sequence stratigraphic framework. However, as each successive surface is employed as the datum, the other flooding surfaces within the formation become distorted, resulting in unrealistic depositional geometries. These geometries are best explained to be the result of structural readjustments during Viking deposition.The Precambrian lithosphere of the Canadian Shield forms the Western Canadian sedimentary basin basement, with major structures previously mapped using gravity and magnetic anomaly studies. Locally, the increased accommodation observed within the Viking Formation of central Alberta is attributed to differential reactivation of the Paleoproterozoic Snowbird tectonic zone basement structures, which flank the areas of anomalously thick deposits and trend approximately normal to the regional strike of the Western Canadian sedimentary basin. The Snowbird tectonic zone faults are interpreted to have been reactivated during renewed tectonic loading in the southern Canadian Cordillera during Aptian–Albian time, causing subtle readjustments along basement faults that caused variable syndepositional subsidence. By selecting successive datums, the gross Viking interval can be recognized to have accumulated prior to, during, and following structural reactivation.