ABSTRACT: Upper Devonian (Frasnian) Sequence Stratigraphy, Cairn Formation and Peechee Member of the Canadian Cordillera

MCLEAN, DAVID J., and ERIC W. MOUNTJOY, McGill University, Montreal, Quebec, Canada

The regional correlation of groups of stacked, shallowing-upward cycles within the Cairn Formation reveals an ordered hierarchy of relative sea level changes. Similar vertical stacking patterns appear to occur in the overlying Peechee Member, but poor preservation of meter-scale cyclicity in the sections studied makes regional correlations difficult.

Groups of entirely subtidal cycles and intervals of noncyclic subtidal lithologies punctuate peritidal Cairn and Peechee stratigraphy, suggesting there were periods when buildup growth could not keep pace with sea level rise. These entirely subtidal intervals may correspond to pulses of tectonic subsidence that occurred outboard of the Frasnian epicratonic seas. Tectonic subsidence curves for the southern Canadian Cordillera, corrected for the effects of sediment loading and compaction, suggest that a significant tectonic component of subsidence was superimposed upon Late Devonian eustasy.

Most buildup margins within the Front Ranges of the eastern Cordillera retrograded, although the upper Peechee portion prograded a short distance in two of 13 cases. This geometry is part of a transgressive systems tract followed by a highstand of sea level. Local paleo-caliche horizons and a progressive increase up-section in the abundance of erosional surfaces in the uppermost Peechee reveal the initial stages of sea level fall at the close of Peechee time. Despite rapid syndepositional subsidence, coeval Peechee margins in the eastern Main Ranges commonly aggraded vertically or prograded, partly in response to variable rates of basin sedimentation adjacent to the buildups.

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