Cratonic-Margin and Antler-Age Foreland Basin Strata (Middle Devonian to Lower Carboniferous) of the Southern Canadian Rocky Mountains and Adjacent Plains
Lauret E. Savoy, Eric W. Mountjoy, 1995. "Cratonic-Margin and Antler-Age Foreland Basin Strata (Middle Devonian to Lower Carboniferous) of the Southern Canadian Rocky Mountains and Adjacent Plains", Stratigraphic Evolution of Foreland Basins, Steven L. Dorobek, Gerald M. Ross
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Upper Devonian and Lower Carboniferous strata in the Rocky Mountains and adjacent subsurface of southern Canada and adjacent Montana record a series of widely correlated, transgressive-regressive sequences that accumulated along the westward deepening cratonic margin of North America. Several Frasnian to Tournaisian megasequences are recognized: (1) upper Givetian Swan Hills platform and reefs (Beaverhill Lake megacycle); (2) extensive Frasnian Cairn-Peechee and Leduc reefs (Woodbend megacycle); (3) Nisku-Arcs carbonate bank and reefs (Winterburn megacycle); (4) upper Frasnian Ronde-Simla-Winterbum carbonate banks; (5) Famennian Sassenach basin filling; (6) Palliser-Wabamun carbonate ramp; and (7) Famennian-Tournaisian Exshaw and Banff deep-water, partly anoxic deposits. The Famennian and lower Tournaisian strata record a general upward deepening and progressive flooding of the continental margin, and may reflect the development of marginal tectonism related to Antler-age orogenesis. Quartzofeldspathic clastic deposits in the Sassenach(?), Exshaw, and lower Banff Formations reflect the periodic influx of westerly-derived, Antler(?) orogenic-sourced detritus. Depositional patterns, including the westward thickening of most units in the southern Canadian Rocky Mountains, support marked tectonic subsidence in the region from Frasnian to Tournaisian time.
The Givetian to uppermost Frasnian sequence represents a major transgression across Alberta that is divisible into three transgressive cycles, each consisting of a basal carbonate platform overlain by reefs and ending with basin filling (Swan Hills, Leduc, and Nisku reef-building cycles). Dominantly anoxic conditions (overlying Duvernay-Perdrix source beds) occurred immediately adjacent to the reefs when they were of low relief and throughout their development. The reefs kept pace with sea-level changes, resulting in a series of shallowing upward cycles broken by periods of non-deposition. The progressive southwestward thickening of the reefs, reaching three times their thickness in the subsurface, records regional differential subsidence that appears to be related to both tectonic and sedimentary loading of the continental margin and more regional crustal subsidence.
The western part of the Western Canada Sedimentary Basin was filled during the initial Famennian sea-level rise by Sassenach siliciclastic deposits, which may have been derived from a landmass to the southwest. A westward deepening and thickening carbonate ramp (Palliser Formation and Wabamun Group) was bordered to the west by a deep basin (Lussier region) in Famennian time. Carbonate ramp sedimentation ended by late Famennian time with the initial deposition of deep-water Exshaw black shale, roughly coincident with a major sea-level rise and the widespread deposition of similar low-oxygen facies in western North America. The lower Banff Formation consists of starved-basin to deep-ramp lithofacies, which are overlain by shallower-water carbonates of the middle and upper Banff; this sequence records basinward (westward) progradation of the Banff ramp.