Unit Name: Pine Point dolostone
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Eifelian - Givetian (397.5 - 385.3 ma)
Age Justification: Biostratigraphy. The Pine Point dolostone is in places fossiliferous, but most fossils are poorly preserved. Norris (1965a) collected fossils from the "Fine-grained Dolomite" member of the Pine Point Formation and reported the presence of Stringocephalus, a brachipod typical of the Givetian Stage. Skall (1975) reported the presence of Middle Givetian ostracodes in facies B. Senior (1977, p. 49) found late Eifelian conodonts in facies A and late Eifelian and mid-Givetian conodonts in facies B (Meijer Drees, 1993).
Province/Territory: Alberta; British Columbia; Northwest Territories
Originator: Meijer Drees, 1993.
The Pine Point dolostone facies is the most widely distributed facies of the Pine Point Assemblage and occupies the inner (southern and eastern) margin and the centre of the Presqu'ile Barrier. The northern limit represents the lateral boundary with the Bituminous shale and limestone beds, the Buffalo River shale and the Sulphur Point limestone. The southern limit represents the change to the Muskeg Formation. In the Pine Point Mines District south of Great Slave Lake, the Pine Point dolostone attains a maximum thickness of about 100 m (328 ft.) (Skall, 1975) and is overlain by the Presqu'ile dolostone. In the region between Great Slave Lake and Trout Lake it overlies the southern flank and the crest of Tathlina Uplift. In several sells, the Pine Point dolostone facies dierctly overlies a silty dolostone or sandstone of the La Loche Formation, and the thickness reaches a minimum value of 12 m (39 ft.) in the Briggs Rabbit Lake No. 1 well. Relatively thick sections occur in the area west of the Cameron Hills, where the dolostone facies reaches a maximum thickness of 213 m (699 ft.). In certain areas over Tathline Uplift, the equivalent of the Lonely Bay limestone member is dolomitized and here, the Pine Point dolostone facies overlies either the Detrital division or Precambrian rocks and includes all the finely crystalline dolostone beds between the top of the Chinchaga and the base of the Watt Mountain Formation. The Pine Point dolostone facies is relatively thin over the crestal part of Tathlina Uplift. The thinning is due partly to the depositional onlap at the base and partly to erosion below the Watt Mountain unconformity (Meijer Drees, 1993).
Thickness(m): Maximum 213.
The informal term Pine Point dolostone is used to describe a greyish brown and light brown, fine crystalline, diagenetic dolostone facies that has partly replaced the platofrm and reefal limestone of the Upper Elk Point subgroup in the area north and northwest of the Mukeg evaporites (Meijer Drees, 1993).
The Pine Point dolostone is a unit of the Pine Point Assemblage. The lower and upper boundaries of this diagnetic facies vary from place to place and do not alway have a stratigraphic significance. In sections where the stratigraphic equivalents of the Lonely Bay and Keg River formations include limestone, the lower boundary of the Pine Point dolostone coincides with the transition from dolostone to limestone. In sections where these two formations are dolomitized, the base of the Pine Point dolostone is selected as the top of the Evaporite or Detrital divisions. In places where the Pine Point dolostone is overlain by the Sulphur Point Formation, the upper boundary coincides with the change in lithology from limestone to fine crystalline dolostone. In places where the white, coarse crystalline Presqu'ile dolostone overlies the Pine Point dolostone, the upper boundary lies at the transition between the white and the greyish brown dolostone facies. In the Tathlina Uplift area, the Pine Point dolostone extends upward to the base of the Watt Mountain Formation. The Pine Point dolostone is virtually equivalent ot the "Fine-grained Dolomite" member of the Pine Point Formation of Belyea and Norris (1962) and Norris (1965a). The Pine Point dolostone includes the dolostone facies A, B, D, E and J of the Pine Point Group of Skall (1975). In the extreme southern part of Great Slave Plain, the lower part of the Pine Point dolostone grades into the Keg River Formation and the upper part interfingers with Muskeg anhydrite. There are lateral facies contacts between the Pine Point dolostone, the Sulphur Point Formation, the Bituminous shale and limestone beds, and the Lonely Bay Formation (Meijer Drees, 1993).
Belyea, H.R. and Norris, A.W., 1962. Middle Devonian and older Palaeozoic formations of southern District of Mackenzie and adjacent areas; Geological Survey of Canada, Paper 62-15, 82 p.
Meijer Drees, N.C., 1993. The Devonian succession in the subsurface of the Great Slave and Great Bear plains, Northwest Territories; Geological Survey of Canada, Bulletin 393, 231 pages.
Norris, A.W., 1965a. Stratigraphy of Middle Devonian and older Paleozoic rocks of the Great Slave Lake region, Northwest Territories; Geological Survey of Canada, Memoir 322, 180 p.
Senior, S.A., 1977. Middle Devonian conodonts from the Presqu'ile Reef, Pine Point, Northwest Territories; B.Sc. thesis, University of Waterloo, Ontario.
Skall, H., 1975. The paleoenvironment of the Pine Point lead-zinc district, pp. 22-47: in An issue devoted to Canadian mineral deposits, Economic Geology, vol. 70, no. 1, pp. 1-253.
Source: GEOLOGICAL SURVEY OF CANADA, CALGARY
Contributor: Michael Pashulka
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 15 Mar 2011