The southeast and northwest margins of the Frasnian (Upper Devonian) Cline Channel are preserved in excellent and continuous outcrop exposures at both Cripple Creek and Wapiabi Gap in the Alberta Rocky Mountains. Accretionary and interfingering platform margins allow detailed definition and correlation, from platform to basin, of significant sequence stratigraphic surfaces.
Eight Frasnian third-order composite sequences are defined using stratal and lithofacies stacking patterns, regional correlation of sequence boundaries, and maximum flooding surfaces, constrained by conodont biostratigraphy. They form part of an upper Givetian–Frasnian second-order transgressive–regressive depositional sequence. Most sequence boundaries observed show subaerial exposure. Others are inferred from stratal architecture, e.g., onlap of tidal-flat or reef margin deposits onto foreslope lithofacies.
The Cline Channel was filled asymmetrically from southeast to northwest along the described/studied transect. Progradation of platform margins is on a substrate of platform-derived fine-grained carbonates and extrabasinal clays that form argillaceous carbonates and calcareous shales. Stacking patterns of the composite sequences vary across the Cline Channel. On the southeast side, the second-order Givetian–Frasnian cycle is characterized by initial retrogradation followed by aggradation to retrogradation in the upper mid-Frasnian, and finally, progradation in the upper Frasnian. On the northwest side, the overall stacking pattern is aggradational.
With progressive basin filling, platform edges evolved from rimmed boundstone and/or grainstone to mainly grainstone. Foreslope declivity decreased from a minimum of 10° (WD3) to less than 1.5° (WI1) reflecting more ramp-like foreslopes. Coincident with this change, lowstand geometry evolved from wedge shaped to tabular. Where slope gradients were high, lowstands are wedges, less extensive and abutting antecedent highstands. With development of ramp-like geometries, lowstands became tabular and were detached from their antecedent shelf edges with even minor falls of relative sea level. Gentle slope gradients and larger areas for shallow-water carbonate production facilitated extensive lowstand development. Assignment of strata into systems tracts of ramp-like systems is facilitated by subregional correlation.
Decreasing accommodation within the second-order highstand is indicated by reduction in composite sequences (CSs) thickness and replacement of open marine with platform-interior strata as the basin shallowed and filled. Composite sequences became more asymmetric, developing thin, offlapping falling stage systems tracts in the late Frasnian, accompanied by a higher frequency of lowstands. Continuous outcrop exposures permitted the amount of relative sea-level fall to be estimated for the bounding surfaces of several CSs. Relative sea-level falls ranged from 9 to ~40 m.
