ABSTRACT

Stratigraphic nomenclature is revised for Middle Ordovician, Upper Ordovician, and Silurian rocks of the southern Rocky Mountains of Canada. Lower Ordovician stratigraphy is briefly reviewed. The names Glenogle Shales, Mount Wilson Quartzite, and Skoki Formation are retained. Coverage of the Beaverfoot Formation is restricted to carbonate rocks and includes both Upper Ordovician and Lower Silurian strata. The terms Wonah Quartzite and Brisco Formation are considered obsolete. Four new rock units are proposed.

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The common lithotopes suggest platform carbonate fringing the Canadian Shield in Late Ordovician and Early Silurian time and covering the whole of the southern Rocky Mountains. The eastern part of the mountains was the site of similar deposits in Middle Ordovician time, but miogeosynclinal shales and limestones accumulated farther southwest. The locus of facies change trends northwest and lies just west of the British Columbia-Alberta boundary.

Middle and Upper Silurian rocks are absent from the southern Rockies, and the basal Devonian rocks rest unconformably on Precambrian to Lower Silurian strata.

Faunal studies allow recognition of four brachiopod-coral-trilobite zones within the Beaverfoot Formation and a conodont zone in the basal Beaverfoot and the uppermost Mount Wilson. Three brachiopod zones are present within the Skoki Formation. Of these, the Anomalorthis and Orthidiella zones correlate with Whiterock zones in the Antelope Valley Limestone of Nevada. A new brachiopod zone can be recognized near the base of the Skoki and is considered uppermost Canadian and may be in part equivalent to the Pseudocybele trilobite zone of Utah and Nevada.

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