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.

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