ABSTRACT: Sequence Stratigraphy of the Uppermost Frasnian Winterburn Group (Devonian), Central Alberta, Canada

GILHOOLY, MURRAY, K. POTMA, J. WEISSENBERGER, and P. WONG, Esso Resources Canada Ltd., Calgary, Alberta, Canada

The Winterburn Group of central Alberta is composed of two depositional sequences, up to 100 m thick, informally termed a lower Nisku sequence and an upper Graminia sequence. Each sequence consists of a lower transgressive and an upper regressive phase of sedimentation. These sequences occur in the upper part of the second-order Givetian-Frasnian transgressive-regressive sequence (Gilwood to Graminia sequence). As a result, these third-order sequences are dominated by a more regressive style of sedimentation than is seen in those which occur earlier in the second-order sequence.

Transgressive portions of each sequence are represented in deeper water environments by organic-rich basin-fill shales and carbonate muds and locally by coral-stromatoporoid pinnacle reefs. In shallow water platform areas stromatoporoid-coral shoal deposits and restricted platform interior carbonate sedimentation occurred.

Regressive portions of sequences are characterized in deeper water environments by deposition of platform-derived carbonate mud, extrabasinal-derived fine siliciclastics, and evaporites. Platform sedimentation was dominated by thin-bedded restricted platform interior carbonates, evaporites, and siliciclastics.

The nature of boundaries between these sequences is dependent upon geographic position within the basin. In areas of low subsidence or high sedimentation rates, such as those underlain by Leduc Formation reef complexes, a basinward shift in facies belts is seen at sequence boundaries. In basinal areas, and in platform settings with high subsidence rates, sequence boundaries occur within conformable facies successions in shoaling-upward cycles.

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