Unit Name: Brent Island Limestone
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Early Ordovician (485.4 - 470 ma)
Age Justification: Conodonts, including Macerodus dianae, have been described by Fåhraeus and Nowlan (1978). These indicate a Tremadoc-Early Arenig age. Cooper (1937) suggested the Brent Island Limestone could include Cambrian strata (see also Stouge, 1983). Gastropods and trilobites also occur (Cooper, 1937).
Province/Territory: Newfoundland & Labrador

Originator: Cooper, 1937.

Type Locality:
North and South Brent islands, Hare Bay, Great Northern Peninsula, northern Newfoundland (NTS 2 M/4, 5).

Distribution:
Cooper (1937) suggested a minimum thickness of 105 m. Stouge (1983) considered 140 m to be a more realistic thickness. The formation is exposed on the Brent islands Direction Island, the northern end of Long Island, inland areas of the St. Julien's map sheet (NTS 2 M/4), and the southwest part of the Salmon River map sheet (NTS 2 P/1). It is also found in the White Arm Pond window beneath the Hare Bay Allochthon (Stouge, 1983).

Lithology:
Well bedded dark grey limestone and dolostone; chert is common and boundstone (stromatolite and thrombolite) mounds occur. The carbonates are dominantly fossiliferous and bioturbated. Interbedded wackestones and packstones are overlain in shoaling-upward sequences by laminated and flaser-bedded, frequently mudcracked, lime mudstones and/or dolostones. Mottled dolomitic burrows occur locally.

Relationship:
The Brent Island Limestone conformably overlies dolostones of the Petit Jardin Formation, within parautochthonous Lower Paleozoic platformal strata, west of the Hare Bay Allochthon. It is equivalent to the Ordovician Watt's Bight and Boat Harbour formations (both informal), which are part of the autochthonous Lower Paleozoic sequence on the western side of the Great Northern Peninsula. In the Port au Port area (NTS 12 B/10, 11), equivalent rocks are called the Upper Cambrian-Lower Ordovician Isthmus Bay formation. In the Humber Arm (NTS 12 G/1) and Goose Arm (NTS 12 H/4) areas, equivalent strata are included in the Upper Cambrian-Lower Ordovician Hughes Brook Formation. The St. George Group, as defined by Knight (1983a), includes in ascending order the Watts Bight (informal), Boat Harbour (informal), Catoche, Brent Island, and Aguathuna (informal) formations.

History:
The name Brent Island Limestone was first used by Cooper (1937) who assigned it to the St. George Series (now St. George Group). Stouge (1983) used the term Brent Island formation parautochthonous rocks beneath and immediately west of the Hare Bay Allochthon. Knight (pers. comm. to editor) has proposed that the Brent Island Limestone be replaced by the Boat Harbour Formation.

References:
Cooper, J.R., 1937. Geology and mineral deposits of the Hare Bay area; Newfoundland Department of Natural Resources, Geological Section, Bulletin 9, 36 p.
Fåhraeus, L.E. and Nowlan, G.S., 1978. Franconian (Late Cambrian) to early Champlainian (Middle Ordovician) conodonts from the Cow Head Group, western Newfoundland: Journal of Paleontol-ogy, vol. 52, pp. 444-471.
Knight, I., 1983a. Geology of the Carboniferous Bay St. George Subbasin. Map 82-001. In Geology of the Carboniferous Bay St. George Subbasin, Western Newfoundland. Government of Newfoundland and Labrador, Department of Mines and Energy, Mineral Development Division, Memoir 1, 382 pages. GS# NFLD/1314.
Stouge, S., 1983. Notes on the geology of the St. Julien's map-area (2 M/4), Great Northern Peninsula Newfoundland: Newfoundland Department of Mines and Energy, Mineral Development Division.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 6, Atlantic Canada; G.L. Williams, L.R. Fyffe, R.J. Wardle, S.P. Colman-Sadd, Boehner, R.C. (editor)
Contributor: I. Knight
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 25 Jun 2009