Abstract

The carbonate-dominant Upper Triassic Baldonnel and Pardonet formations were deposited in the west-facing extensional Peace River Basin, in a midlatitudinal setting on the northwestern margin of the supercontinent Pangea. Subsurface distribution of the Pardonet is restricted to northeastern British Columbia, but the Baldonnel extends into west-central Alberta. This paper describes the stratigraphic framework, internal subdivisions, composition, facies and depositional setting of the two units and discusses the relationship between the overlying uppermost Triassic Bocock Formation and the Pardonet. A number of unconformities and flooding surfaces in the underlying upper Charlie Lake Formation, and in the Baldonnel and Pardonet, are documented, including two newly defined unconformities. Facies maps for the Baldonnel and Pardonet north and south of the Peace River-Williston Lake area in northeastern British Columbia demonstrate the westward-deepening ramp setting of these units and the influence of paleostructure on facies. Facies changes and increase in thickness of both the Baldonnel and the Pardonet in the Foothills of northeastern British Columbia south of Williston Lake reflect the influence of the southwestern extension of the Fort St. John Graben. The structural low defined by this extension is designated the Hudson Hope Embayment in this paper. The Embayment lies north of the northern termination of the upper Paleozoic Sukunka Uplift, which is roughly parallel to and en echelon with the Permian Beatton High to the northeast. Although the influence of these two highs on Triassic sedimentation, if any, remains unclear, the Baldonnel is thinned and the Pardonet missing over a smaller structural high on trend with the western end of the Beatton High. The boundary between the underlying Upper Triassic Charlie Lake Formation and the Baldonnel Formation in northeastern British Columbia is diachronous. The trace of the Siphon unconformity demonstrates this diachroneity most clearly: in the type section well of the Charlie Lake and Baldonnel formations near Fort St. John in British Columbia, the Siphon unconformity lies about 50 m below the "type" boundary between the two units but farther westward, in the Foothills of British Columbia (Cypress-Sikanni area), the formation boundary lies at or a few metres above the Siphon unconformity. Sequence-stratigraphic interpretations of the uppermost Charlie Lake-Baldonnel transition suggest that it represents a retrogradational transgressive systems tract that extends through northeastern British Columbia into west-central Alberta, where it includes the Worsley Member of the upper Charlie Lake Formation. The Baldonnel and Pardonet formations are the youngest major carbonate reservoir facies (outside the Williston Basin) in western Canada. Initial in-place reserves for crude oil for the combined units are 6 X 10 6 m 3 (38 million barrels), and 132X10 9 m 3 (4.7 Tcf) of raw gas, with the latter exceeding 9 Tcf if projected reserves in the Monkman trend in the Foothills of northeastern British Columbia are included.

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