Name extended into ND from MB, CN for gray, blue, and reddish-brown shale, sandy shale, and sandstone encountered in subsurface in western ND in Williston basin. Found in four wells. Underlain by Deadwood? formation; overlain by the Red River formation. Ordovician in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Previous evidence for age. Assigns formation to Middle Ordovician, but suggests that it may eventually prove to be Late Ordovician age. Underlain by Deadwood formation; overlain by Red River formation of Bighorn group in Williston basin, eastern MT and nearby areas.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 9 (fig. 2), 44+; C.G. Carlson, 1958 (1959), Stratigraphy of Deadwood-Winnipeg interval in North Dakota and northwestern South Dakota, 2nd Intl. Williston Basin Symp., p. 20-26. Winnipeg formation. Sandstone, shale, and siltstone, thickness up to 357 feet. Divided into (descending) Roughlock member, Icebox member (= Roughlock and Icebox formations of McCoy, 1952, units D and C of Whitewood formation of Butler and others, 1955, respectively), and Black Island member. Underlies Red River or Whitewood formation; unconformably overlies Deadwood formation. Fossils. Age is Middle Ordovician (Chazyan to Trentonian).
[Discussion is chiefly subsurface of North Dakota, northwestern South Dakota, eastern Montana, and Saskatchewan and Manitoba, Canada.]

Source: Publication.

Designated a group [rather than formation as in earlier reports] in Williston basin and adjacent parts of Powder River basin. Includes (ascending): Icebox shale and Roughlock silt[stone] (raised to formation rank) in outcrops in the Black Hills in Williston and Powder River basins. Includes (ascending): Burgen sandstone and an upper unnamed unit (the Winnipeg shale of basin terminology) in the subsurface of Williston basin. Underlain unconformably by Deadwood formation [including SCOLITHUS sandstone at top in the Black Hills, SD]; overlain conformably by Whitewood dolomite in the Black Hills, SD, and by Red River formation of Bighorn group in Williston basin, northwestern SD, western ND, and eastern MT. Middle Ordovician in age based on correlation with the pre-Bromide part of the Simpson group of OK.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 1835 (fig. 3), 1836-1837. Winnipeg Group. Rank is raised to group in subsurface of North Dakota. Divided into (descending) Roughlock Formation, calcareous shale and siltstone; Icebox Formation, noncalcareous shale; and Black Island Formation, sandstone. Thickness up to 320+ feet (Nesson anticline, North Dakota). Underlies Red River Formation; unconformably overlies Deadwood Formation or, where absent, Precambrian rocks. Age is Middle Ordovician.

Source: Publication.

Winnipeg Formation used in the Black Hills, SD and WY, in Williston and Powder River basins, to include (ascending): Icebox Shale and Roughlock Formation. Winnipeg Group used in Williston basin [north of the Black Hills] to include (ascending): Black Island Formation, Icebox Shale, and Roughlock Formation. Middle Ordovician (Black River and Trenton) in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).