Unit Name: Shaunavon Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Bathonian (167.7 - 164.7 ma)
Originator: Milner, R.L. and Thomas, G.E., 1954.
Type well in the Tidewater A.O. Eastend Crown No. 1, in Lsd. 15, Sec. 11, Twp. 6, Rge. 20W3M, southwestern Saskatchewan, between 1,427 and 1,470 m (4,680 and 4,820 ft).
The buff color, purity and consistency of lithology of the lower member are characteristics traceable across the Williston basin as far east as 104 deg W. There the limestone grades into green grey calcareous sandstones and, with similar facies of the upper member grade into the lower Melita Formation of Manitoba. The Shaunavon Formation is 42 to 48 m (138 to 157 ft) thick and is distributed across Montana and North Dakota as the upper part of the Sawtooth and Piper formations.
There are two members: The lower is a buff to tan, lithographic, i.e., earthy, microcrystalline limestone, generally massive, with a thickness of up to 32 m (105 ft). Fossil diversity is restricted, but features abundant corals, pelecypods, gastropods, echinoids, Foraminifera and algae. An oolitic bed 6 to 7 m (20 to 23 ft) thick, as well as dolomitization are widely distributed at the top of the member in the region west of Rge. 1 5W3M. The upper member is constituted of grey, very fine- to fine-grained, calcite-cemented quartzose sandstone, blue-grey and green-grey quartz sand and nucleated, oolitic limestone, shell calcarenite and calcirudite, coquina and argillaceous limestone; as well as tan dolomite, and marlstone and shales ranging from tan to green to darker grey and grey black in color. Stratigraphically the member comprises tabular and lenticular beds separated by sedimentation breaks ranging from diastems to true hiatuses, featuring dolomitization horizons and channel forms dissecting underlying beds to depths of 21 m (69 ft). The member is up to 30 m (98 ft) thick.
The Shaunavon Formation is gradational to the upper member of the Gravelbourg Formation. The contact zone is marked by alternation or calcilutite and dark green calcareous shales over the basal 1 m (3 ft). However, the presence of solution pitted surfaces on calcilutite layers indicate at least diastematic breaks. The formation is taken as the equivalent of the Sawtooth of Alberta; and its upper and lower members are direct equivalents of the Bowes and Firemoon members of the Piper Formation.
Christopher, 1974, 1984a; Francis, 1956; Milner and Thomas, 1954; Nordquist, 1955; Poulton, 1984.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: J.E. Christopher
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003