ABSTRACT

Studies at Fairmont Ridge and Mount Forster (type section of the Mount Forster and Starbird Formations) allow refinement of facies relationships and depositional histories inferred for the Cedared, Burnais, Harrogate (all Eifelian), Mount Forster (probably entirely Eifelian but upper beds possibly Givetian) and Starbird (lower Frasnian) Formations.

In Middle Devonian time, a western landmass postulated near the then site of the Purcell Arch constrained a shallow gulf against the emerged Western Alberta Ridge. Restricted circulation of the warm sea led to deposition of the Burnais evaporites. The evaporites were limited westward by detritus from the western landmass and the detritus similarly formed a barrier to the Harrogate Formation sediments when rising sea level in later Eifelian time allowed development of open-marine carbonates in the gulf. There is no faunal evidence of Givetian time. Givetian rocks may not have been deposited in the region or, if deposited, may have been eroded before the onset of Frasnian sedimentation.

The Rocky Mountain Trench crosses the Windermere High that is charactirezed by very attenuated Lower Paleozoic strata beneath the Sub-Devonian Unconformity. The present location of the High, astride the Trench, indicates that little transverse movement has taken place along the Rocky Mountain Trench in this part of British Columbia.