Unit Name: Fisher Branch Dolomite
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Early Silurian - middle Silurian (443.7 - 422.9 ma)
Age Justification: Comprises the zone of Virgiana decussata, formerly referred to as the Virgiana zone of Kindle (1914), or unit B of the Interlake Group by Baillie (1951).
Province/Territory: Manitoba
Originator: Stearn, C.W., 1956, p. 16.
Type Locality:
Small scarp 6 km (3.75 mi) northwest of Fisher Branch, Manitoba (SE/4 Sec. 3, Twp. 25, Rge. 2WPM).
Distribution:
Thickness estimated by Stearn is 4.9 m (16 ft), and appears fairly uniform through outcrop belt. The name is applied only in the outcrop belt of southwestern Manitoba. Most outcrops occur in the south Interlake area, in the vicinity of the town of Fisher Branch, as far south as Narcisse (Twp. 19) and as far north as Lake St. Martin. In the northern area outcrops are reported at Grand Rapids, Moose Lake and as far west as Lake Atikameg; occurrences are known at 80.8 km (50.2 mi) north of Grand Rapids on Highway 6, and on the trail west of Baker Lake (Lsd. 15, Sec. 30, Twp 56, Rge. 12WPM).
Lithology:
Greyish yellow to light grey dolomite, medium- to fine-grained and aphanitic, medium- to thick-bedded, fossiliferous. Brachiopods and corals are abundant, and in places Virgiana forms the main constituent of the rock. Somewhat resistant to weathering and occurs as small scarps up to 4 m (13 ft) high in the Fisher Branch area.
Relationship:
The contact with the underlying Stonewall Formation is disconformable and is marked by a widespread red, argillaceous-arenaceous marker bed that is traceable throughout the subsurface of the Williston Basin area of southwestern Manitoba and Saskatchewan. The unit is overlain conformably by the very light grey to white, fine grained, thin bedded fossiliferous dolomite of the Inwood Formation. In the subsurface Fisher Branch strata comprise the basal part of the lower Interlake Group (Porter and Fuller, 1959), or the basal part of the Strathclair Formation of the Interlake Group (King, in: Cowan, 1971).
Other Citations:
Baillie, 1951; Kindle, 1914; King, in: Cowan, 1971; Porter and Fuller, 1959; Stearn, 1956.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: H .R. McCabe
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003