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Stratigraphic Architecture of the Frasnian Cline Channel, Central Alberta Front Ranges


A sequence stratigraphic interpretation for the Frasnian strata of the central Alberta Rocky Mountains is presented. Six third-order depositional sequences are recognized and correlated across the study area, comprising the middle of a second-order depositional sequence, spanning the latest Givetian to end Frasnian of the Alberta basin. The base of the succession unconformably overlies Middle Cambrian strata, representing transgressive onlap of the West Alberta Ridge, an antecedent landmass. This transgression initiated two large carbonate complexes, from south to north, the Fairholme and the Southesk Cairn. In the Woodbend Sequence One (WD1), these complexes became separated by the marine Cline Channel, which connected the Alberta Basin with the Paleo-Pacific. The WD1 platform south of the channel was characterized by open marine circulation and poorly developed margins. The basal Woodbend Sequence Two (WD2) displays well-developed in situ carbonate lowstands on both sides of the Channel (Kiska Creek, Wapiabi Gap). The WD2 margin at Cripple Creek formed following a significant southward retreat of the platform, while the Wapiabi Gap margin was aggradational. Time equivalent basinal sediment consisted of the organic-rich Duvernay Formation. Differing margin styles continued in the basal Woodbend Three, a widespread, ramp-style lowstand developed south of the channel – with an aggradational reefal margin in the north. Significant transgressive and highstand shrinking of the carbonate platforms and Ireton Formation illitic shale bank progradation occurred. Ramp-style deposition dominated the Winterburn Sequences One and Two. The former developed a notable lowstand with subsequent progradation over older shale banks south of the Channel, with limited progradation in the north. Significant erosional downcutting occurred at the base of the Winterburn Sequence Two (Wapiabi Gap). The basal Winterburn Sequence Three (WI3) was a restricted platform carbonate and fine-grained siliciclastic coastal plain, filling and onlapping erosional surfaces (Wapiabi Gap). Salt casts and collapse breccia in WI 3 siltstone (Cripple Creek), indicates significant basinal restriction. Margin styles and third-order sequence stacking were controlled by shale bank distribution and relative sea level. Sequence and bounding surface correlations are well constrained and supported by biostratigraphy (conodonts).