Stratal relationships of the Upper Triassic Baldonnel Formation, Williston Lake, northeastern British Columbia

Abstract

The Upper Triassic (Upper Carnian to lowermost Norian, from conodonts) Baldonnel Forma-tion outcrops extensively along the shores of Williston Lake, northeastern British Columbia. This mixed siliciclastic-carbonate unit consists primarily of calcareous to dolomitic siltstone, sandstone, and bioclastic grainstone beds. It thickens westward (basinward), as marginal marine and continental strata of the underly-ing Charlie Lake Formation grade laterally and vertically into shallow marine strata typical of the Baldonnel Formation. The basal contact of the Baldonnel with the Charlie Lake Formation is characterized by an erosional unconformity at Brown Hill, but is conformable both landward (east) and basinward (west) of this locality. A dark, organic-rich, calcareous siltstone unit (Ducette Member) occurs within the medial Baldonnel Formation in western localities, but thins and pinches out eastward. The upper contact with the Pardonet Formation is conformable in the east, but characterized by an erosional unconformity in the west (basinward).