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Platform-to-Basin Transition in the Middle Devonian Winnipegosis Formation, Southwestern Manitoba, Canada

David M. McDonald and Previous HitNancyTop Chow
University of Manitoba, Winnipeg, MB

The Middle Devonian Winnipegosis Formation, known for its isolated reef plays in Saskatchewan and North Dakota, is a member of the Elk Point Group, which is a cyclical succession of carbonate and evaporite rocks. Little work has been done on the Winnipegosis Formation in the subsurface and outcrop belt of southwestern Manitoba at the eastern erosional margin of the Elk Point Basin. Based on detailed core examination, the Winnipegosis Formation in this region has been divided into lithofacies associations which represent the Lower Winnipegosis ramp deposits and the Upper Winnipegosis platform, isolated reef, and inter-reef deposits. The eastern platform margin is approximately coincident with the Birdtail-Waskada Axis, which represents the Precambrian Churchill-Superior crustal boundary zone and raises the issue of tectonically controlled basin differentiation.

Bituminous laminites occur in ramp, inter-reef, and platform margin successions in the Winnipegosis Formation and are source rocks for reef reservoirs in deeper basinal settings. The organic petrology of bituminous laminites in southwestern Manitoba provides an opportunity to evaluate the controls on the accumulation of sedimentary organic matter (productivity vs. preservation) and the inception of reef growth. As the strata found in outcrop were never substantially buried, the organic-rich facies did not mature to the extent of their deep-basin counterparts enabling detailed maceral examination, thereby providing insight into their origin and petroleum genesis in the Winnipegosis Formation.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005