Regional facies trends in the lowermost beds of the Upper Triassic Charlie Lake Formation, in the subsurface of Western Canada

Abstract

Abstract Regionally extensive core coverage in beds of the lowermost Upper Triassic Charlie Lake Formation — between the A marker and underlying Middle Triassic Halfway or Doig beds — in the subsurface of west-central Alberta and adjacent northeast British Columbia facilitate the interpretation of a regional depositional setting. Three broad facies assemblages are identified: 1) red beds; 2) grey beds; and 3) sandstone beds. These three assemblages occur in geographically restricted areas. The red-bed assemblage occurs mostly along the eastern margin of the basin and is interpreted as predominantly intertidal to supratidal, sabkha deposits. The grey-bed assemblage is present between the red-bed and western sandstone assemblages and consists of predominantly intertidal to shallow subtidal beds deposited in a lagoon. Sandstones occur in two locations; in the west they are part of a linear belt, and at the second location they are associated with a local paleogeographic feature, the Beatton High, located within the grey-bed assemblage north of Fort St. John, in northeast British Columbia. The western sandstones are deposits of a barrier-island complex, whereas the sandstones associated with the Beatton High are local tidal channel and fan-delta deposits sourced from the Beatton High. The west-to-east facies changes and north-northwest alignment of the facies define a western, sandy barrier-island complex behind which (to the east) was a lagoon with sabkha deposits at its eastern margin. In the lagoon, a mixture of siliciclastics, carbonates and evaporites were deposited.