Lower Viking Research Articles

Paleoenvironments and regional stratigraphic framework of the Middle-Upper Albian Lepine Formation in the Liard Basin, Northern Canada

Abstract The thick Middle to Late Albian Lepine Formation in the Liard Basin of northeastern British Columbia, southern Yukon and Northwest Territories preserves a continuous record of sedimentation during a time of multiple sea-level fluctuations that produced pronounced unconformities elsewhere in the Cretaceous Western Interior Seaway. Although sediment supply was high, the rapidly subsiding sub-basin produced sufficient accommodation to maintain offshore and shelf conditions throughout the interval. Using lithology, micropaleontology, well log correlations and Rock Eval pyrolysis, the 1000 m thick Lepine Formation is divided into five units in upper/lower offshore and shelf facies. The foraminiferal fauna differs substantially from that described from the Peace River Foothills and documents a continuous marine record during flooding of the Joli Fou Sea and the transition to the Mowry Sea. Regional well log correlations show significant thinning of the Lepine Formation southwards to the equivalent upper Buckinghorse and Hasler formations. Markers at transgressive surfaces can be traced for greater than 400 km along the foredeep. The thick, lower to middle part of the Lepine Formation (Units 1-3) contains foraminifera of the Ammobaculites wenonahae Zone and Ammomarginulina Assemblage Zone that record stressed oceanographic conditions related to periods of uplift west and northwest of the Liard Basin during the Joli Fou and lower Viking intervals. The transition between the two major inundations (Joli Fou and Mowry) is represented by a thick continuous interval in the Liard Basin. The Viking marker (lowermost Unit 3), traced in well logs and projected onto the outcrop section, has no obvious biostratigraphic definition. A major increase in foraminiferal diversity occurs near the base of the Bougie member (Unit 4), indicating more normal marine conditions within the Mowry Sea. A major flooding surface above the Bougie member is correlated with the 'Viking grits' (base of Unit 5) transgressive lag in the Peace River region of the Rocky Mountain Foothills.

THE VIKING (ALBIAN) RESERVOIR SANDSTONES OF CENTRAL AND SOUTH-CENTRAL ALBERTA, CANADA Part 1. Geometry and depositional history

Bentonite chronostratigraphy indicates that deposition of the Viking Formation in central and south-central Alberta and SW Saskatchewan occurred within three chrono-intervals, informally designated Basal, Lower and Upper. Sandstone of the Basal and Lower Viking, times were deposited offshore, while most Upper Viking sands formed along the strandline. In general, these Viking sands trend NW-SE, are multiple, parallel, discrete units surrounded by swales, and are of varying thicknesses.

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

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.