A regressive-transgressive cycle is recognized within the Mistaya Formation (uppermost Cambrian) and the basal silty member of the Survey Peak Formation (Ordovician) in western Alberta. The regressive cycle consists of shallow-water peritidal carbonates which reflect a gradual shallowing of the carbonate-shoal complex, culminating in a subtidal to supratidal sequence. Lithofacies recognized within this basal sequence A are: (1) interbedded biosparite and millimeter-laminated biomicrite (open platform-subtidal shelf); and (2) interfingering oosparite, intraclastic biosparite, and biosparite (oolitic shoal complex). These lithofacies grade vertically into sequence B of: (1) laminated biosparite and biomicrite (open platform-subtidal shelf); (2) algal

Figure

biolithite composed of algal thrombolites, and columnar and polygonal stromatolites (bioherm complex); (3) cross-stratified biosparite and intrasparite (tidal channels); and (4) dolomitic intramicrite, laminated mat algae, and laminated and fenestral dolomite (supratidal flat). The distribution of lithofacies reflects a shallowing of the carbonate complex, culminating in the intertidal stromatolites and supratidal mat algae developing on top of the thrombolitic bioherm.

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The transgressive cycle marks the drowning of the thrombolitic bioherm by a rise in sea level. Lithofacies recognized within the transgressive sequence C are: (1) millimeter-laminated micrite and biomicrite (subtidal shelf); and (2) tabular-bedded biosparite (open platform). The lateral expansion of the platform biosparite sands over the thrombolitic bioherm, intertidal, and supratidal environments coincides with the mass trilobite extinction between the deposition of the Mistaya and Survey Peak Formations.

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