Unit Name: Ramparts Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: ? Frasnian - Givetian
Age Justification: Terebratuloid, spiriferoid, rhynchonelloid, and rare productoid brachiopods, tabulate and rare solitary rugose corals, abundant stromatoporoids, odd molluscs, a richly diversified assemblage of ostracodes, and conodonts of the varcus Zone (lower part) and hermanni-cristatus Zone (upper part) have been reported from the Ramparts Fm. The terebratuloids Rensselandia laevis Meek and Stringocephalus spp. are guides to the lower part; a large species of the smooth spiriferoid Warrenella, and the rhynchonelloids Leiorhynchus hippocastanea (Crickmay) and Hadrorhynchia sandersoni (Warren) are found high in the upper part.
Province/Territory: Northwest Territories
Originator: Kindle and Bosworth, 1921
Type Locality:
The Ramparts of the Mackenzie River, a narrow, cliff-faced constriction of the lower Mackenzie River, 1 to 2 km (0.6 to 1.2 mi) southwest of Fort Good Hope, District of Mackenzie, Northwest Territories.
Distribution:
Known mainly from the segment of the Mackenzie River valley, the flanking Franklin and Mackenzie mountains, and the Mackenzie Plain surrounding Norman Wells, from about Fort Norman in the south to beyond Fort Good Hope in the north. Outliers have been reported from the western flank of the upper Mackenzie River valley (Hume, 1954; Law, 1971). Thicknesses are highly variable, dependent on accepted stratigraphic limits (in dispute), development of upper part (reef, and effects of Early Frasnian and later erosion, but taken at its greatest stratigraphic extent, thicknesses between 45 and 245 m (148-804 ft) are most commonly reported. Few, if any, would dispute that the lowest 45 m (148 ft) of the section at the type locality belong to the Ramparts Fm.
Lithology:
Lower beds of the type and other sections are composed mainly of well-bedded medium-to fine-grained, grey, bioclastic limestones with some thinner-bedded, fine-grained darker-grey, argillaceous limestone, thin beds of dark-grey, calcareous shale, and a prominent 0.3 to 1.2 m (1-4 ft) thick marker of black, calcareous shale about 38 m (125 ft) above the base. Upper beds, partly exposed in the type section, but more completely exposed in other sections, are composed mainly of thick-bedded to massive, light-grey, reef limestone, variable in grain size, with abundant rock-forming, laminar to bulbous stromatoporoids. The upper beds may be introduced by irregularly bedded limestones, between 27 and 37 m (89-121 ft) thick, locally cherty, with numerous tabulate corals and digitate stromatoporoids, and terminated by at least 16.5 m (54 ft) of thin- to medium-bedded, platy dark-grey, bituminous limestones with even darker shale partings.
Relationship:
Conformably overlying the Middle Devonian (Givetian) Hare Indian Fm, the Ramparts Fm is succeeded disconformably by the Upper Devonian (Frasnian) "unnamed beds" of Braun (1966), or "allochthonous beds" of MacKenzie (1970), Canol Fm, and Imperial Fm.
History:
As a stratigraphic unit, Ramparts Fm has had a checkered history (Caldwell, 1964). A broad interpretation of it is taken herein, and so conceived, its internal stratigraphy has been, and remains, in dispute, subject to widely disparate interpretation. Among more recent examples, Crickmay (1970) believed the upper to be the Beavertail Fm, of Late Devonian (Frasnian) age, lying disconformably on the lower part of "true" Ramparts Fm, whereas Braun (1977) distinguished the upper part as the conformable Kee Scarp Member and claimed a Middle Devonian (Givetian) age for the entire formation. For additional comment, see Beavertail Fm and Kee Scarp Member.
References:
Kindle, E.M. and Bosworth, T.O., 1921. Oil-bearing Rocks of Lower Mackenzie River Valley, Northwest Territories; Geological Survey of Canada, Summary Report 1920, Part B, pp. 37-63.
MacKenzie, W.S., 1970. Allochthonous reef-debris limestone turbidites Powell Creek Northwest Territories: Bulletin of Canadian Petroleum Geology, vol. 18, no. 4, pp. 474-492.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 2, Yukon Territory and District of Mackenzie; L.V. Hills, E.V. Sangster and L.B. Suneby (editor)
Contributor: W.G.E. Caldwell; L.V. Hills
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 31 Mar 2010