ABSTRACT: Cratonic-Margin and Antler Foreland-Basin Strata in the Upper Devonian and Lower Carboniferous of the Southern Canadian Rocky Mountains

MOUNTJOY, E. W., McGill University, Montreal, Quebec, Canada, and L. E. SAVOY, Mount Holyoke College, South Hadley, MA

Upper Devonian-Lower Carboniferous strata in the southern Canadian Rocky Mountains record a series of widely correlated transgressive-regressive sequences. A rise of sea level (rapid?) drowned the late Givetian Flume and early Frasnian Cooking Lake platforms. Dominantly anoxic conditions (overlying Duvernay, Perdrix source beds) caused by stratified basin waters occurred immediately adjacent to the "reefs" when they were of low relief.

The reefs kept pace with sea level shifts, resulting in a series of shallowing upward cycles, broken by periods of nondeposition. The reefs were terminated by muddy conditions and other factors brought on by basin filling. The progressive southwestward thickening of the reefs, reaching three times their thickness in the subsurface, suggests that the continental margin was being subjected to tectonic loading.

The western part of the basin was filled during the initial Famennian sea level rise by Sassenach siliciclastics derived from the southwest. A westward-deepening carbonate ramp (Palliser Formation), deposited during several early to late Famennian transgressive-regressive cycles, was bordered to the west by a deep basin (Lussier region). Late Famennian sedimentation patterns record the termination of the carbonate ramp and initial deposition of Exshaw black shale (expansa Zone), roughly coincident with a major sea level rise and the widespread deposition of similar low-oxygen facies in western North America.

Early Carboniferous (Tournaisian) transgressive and highstand systems tracts are indicated by lower Banff starved-basin to deep-ramp facies, and by basinward (westward) progradation of middle and upper Banff, shallower ramp carbonates. Quartzofeldspathic clastics in the Sassenach, Exshaw, and Banff formations reflect the periodic influx of western-derived, Antler(?) orogenic-sourced detritus. Westward thickening of most units in the southern Canadian Rocky Mountains suggests considerable subsidence that appears to be related to Antler tectonic loading along the foreland basin.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)