ABSTRACT: Influence of Prevailing Winds and Currents on the Geometry of Some Middle Devonian Winnipegosis Reefs, Williston Basin Area

MINTO, J. W., and DONALD M. KENT,* University of Regina, Regina, Saskatchewan, Canada

The Bluff Reef on the western shore of Dawson Bay on Lake Winnipegosis, western Manitoba, is the site of a detailed outcrop and corehole investigation of a Winnipegosis reef. Outcrops expose about 8 m of a climax community dominated by corals, stromatoporoids, calcareous algae, and microbialites. Coreholes reveal that the climax rocks form a mound about 30 m above the rest of the buildup, occupying about 12 ha (30 ac) at the north end of a total reef area of 36 ha (89 ac). The lower part of the buildup forms the base for the climax community and consists of crinoidal and codiacean algal remains, as well as peloids, all in a matrix of dolomicrite.

The reef appears to have grown in two stages, an elongate southeasterly trending mud-mound followed by a localized climax reef community. Restriction of the climax community to the northern part of the buildup was probably related to better nutrient supply and improved oxygenation of the waters, either due to southerly moving basinal currents or prevailing winds out of the northeast.

Several reefs of the Tableland-Macoun-Hitchcock-Oxbow area of southeastern Saskatchewan have vertical growth phases similar to those of The Bluff Reef, as well as analogous forms. The latter may be related to the same controls as those at The Bluff. However, since other reefs in this region do not have the same geometry, prevailing winds may not have played a part in shaping the reefs. Thus, currents may have been a major influence on reef geometry, at least in southeastern Saskatchewan.

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