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

• Published in: Bulletin of Canadian Petroleum Geology
• Main Authors: Jowett, D.M.S., Schroder-Adams, C. (Claudia)
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2005
• Subjects: British Columbia; Canada; Joli; Liard; Northwest Territories; Rocky Mountain Foothills; Yukon; Peace River
• Online Access: https://ir.library.carleton.ca/pub/2423; https://doi.org/10.2113/53.1.25

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.