ABSTRACT: Sequence Stratigraphy of Lower to Middle Devonian Strata in the Northern Canadian Cordillera: Eustasy versus Tectonism

MORROW, DAVID W., and TOM T. UYENO, Geological Survey of Canada, Calgary, Alberta, Canada

The Mackenzie Fold Belt and the Northern Yukon Fold Complex of Northern Canada contain one of the thickest and most complete Lower and Middle Devonian successions (i.e., lower part of Kaskaskia Sequence) exposed anywhere in the world. Conodonts and graptolites indicate that sedimentation was continuous throughout Early and Middle Devonian times. Major shifts in the areas and patterns of deposition and the presence of regional unconformities indicate that several long-term changes in relative sea level occurred across these areas of mixed shelf and basinal deposition.

The regional unconformity at the base of the Devonian across Mackenzie Shelf is part of the basal Kaskaskia unconformity of Western Canada and the United States. Reconstruction of depositional dip cross sections across Mackenzie Shelf of northern Canada suggests that the entire Lower to Middle Devonian forms a single large transgressive-regressive (T-R) sequence that was itself onlapped by basinal sediments of the succeeding Middle Devonian Taghanic Onlap sequence. Brightly colored marginal marine siliciclastics of the Lochkovian-aged Delorme Group form the initial onlap phase of this T-R sequence. Transgression continued during deposition of the Arnica, Landry, and Bear Rock formations followed by regression during Hume and Nahanni deposition. The nearly isochronous upper contact of he Nahanni and Hume formations of earliest Givetian age with overlying basinal shales marks the top of this sequence.

Deposition of this T-R sequence spanned about 30 million years during a second order cycle of sea level fluctuation indicated on some published sea level curves. One important interregional unconformity at the base of the Headless Formation (i.e., the mid-Chinchaga break) punctuates this sequence. Shales of the Funeral and Mount Baird formations are shelf edge sediment wedges deposited during the time of exposure associated with this unconformity.

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