Depositional History of the Viking Formation, Suffield Area, Alberta, Canada

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ABSTRACT A subsurface study of the Viking Formation in southeastern Alberta, between Townships 19 and 26 and Ranges 1 and 16 west of the 4th meridian, was undertaken to determine its depositional environment and depositional history. This area is just north of the transition from the Bow Island Formation of the southern Plains to the Viking Formation of the central Plains, and is in the region of multiple sand development in the Viking Formation. Fourteen Viking cored wells and 250 electric logs distributed throughout the area were studied in detail. The cores examined show vertical successions of structures and textures similar to those of barrier island sands previously described by other authors, and generally allow delineation of lower, middle and upper foreshore zones. There is a lack of recognizable lagoon or eolian facies. Little interference with circulation of normal marine water may be attributable to the distance of the bars from shore, but would also depend on extent and permanence of emergence, which is still speculative. The self-potential curves of the Viking Sandstone are of the typical funnel shape to which Krueger (1968) ascribed barrier bar deposition. Core and electric log examination shows the Viking Formation to consist of two main sands, here called the Upper and Lower Viking Sandstones. A diagnostic 6 to 12 in (15 to 30 cm) bentonite bed within the Viking Formation is correlatable on electric logs as a time datum throughout the study area. This bentonite, in conjunction with several thinner nearby bentonites, gives an average potassium-argon radiometric age of about 100 million years. The thickness of Lloydminster shale between the bentonite datum and the overlying Fish Scales Sandstone increases eastward. Foraminifers studied from samples a few feet above the Viking Formation in the Lloydminster Shale revealed the biostratigraphic position of the Viking Formation to be just below the Miliammina manitobensis Zone. Cross sections utilizing the bentonite as a time datum show the depositional development of the Viking Sandstone. The Lower Viking Sand was deposited as a northwest-trending barrier bar with greatest thickness in the centre of the study area. The Upper Viking sand, deposited above the bentonite time marker, represents an eastward-prograding barrier bar that has its maximum development in the northeast corner of the map area, with a north-northwest trend.