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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 969

Last Page: 969

Title: Reef Facies of Winnipegosis Formation (Middle Devonian), Williston Basin, North Dakota: ABSTRACT

Author(s): Nancy A. Perrin

Article Type: Meeting abstract


The Winnipegosis Formation is a carbonate unit deposited in the Elk Point basin during the Middle Devonian. The Elk Point, a narrow, elongate basin extending southeastward from northern Alberta-Northwest Territories through central Saskatchewan and southwestern Manitoba to northeastern Montana and most of North Dakota, was flooded during the Kaskaskia transgression. The Winnipegosis Formation in the North Dakota part of this basin represents a transgressive-regressive stratigraphic sequence. The Winnipegosis has been studied on the basis of well cores from the Williston basin area of North Dakota. The following depositional environments are recognized: a carbonate platform in west and southwest, a platform-restricted basin in north-central, and a reef in east-central Nort Dakota.

The reef environment, where highly productive, has been studied in south-central Saskatchewan (Winnipegosis Formation) and northern Alberta (Keg River, an equivalent formation). To date there has been no production from the reef facies in North Dakota and only limited production from the platform environment. The reef facies is a porous and permeable dolomitized limestone; dolomitization is so extensive that the original fabric can seldom be discerned. Organisms that were present are now recognized as ghosts, as distinctive porosity patterns, and rarely as recognizable skeletons. In many parts of the reef facies, it is difficult to reconstruct the original fabric. Interpretation of the reef environment in the Winnipegosis Formation is based on comparisons of highly dolomitized fossils in the reef facies with fossils found in other facies, with fossils better preserved in less altered parts of the reef facies, with previously described reefs in Canada, and with fossils present in the reefs that crop out in Manitoba.

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