Unit Name: Little Dal Formation
Unit Type: Lithostratigraphic
Age Interval: Helikian (1750 - 1000 ma)
Age Justification: Stromatolites and algal oncolites
Province/Territory: Northwest Territories
Originator: Gabrielse et al., 1973
On generally east-trending ridge about 9.6 km (6 mi) southeast of Little Dal (now Coates) Lake, Mackenzie Mountains, N.W.T. Type section was measured in two legs, the lower extending eastward from 62 deg 38'N, 126 deg 37'W, the upper extending westward from 62 deg 35'N, 126 deg 26'W.
The Little Dal Formation is up to 2,200 m (6,700 ft) thick. So far as presently known, all subunits thin northeastward. The formation occurs at the base of the Plateau Thrust Sheet and the region in front of it, around the Mackenzie Arch from North Nahanni River to Snake River. The formation is partly to completely missing over the crest of the Mackenzie Arch because of erosion at the sub-Upper Cambrian and older unconformities.
Thickness(m): Maximum 2200.
The Little Dal Formation is readily divisible into a least six mappable units of formational rank, as follows: 1) 'Upper carbonate subunit' (highest), largely cyclical, peritidal dolomites with minor shales, and near the top, minor sandstone and locally gypsum, algal stromatolites are common, oolite is prominent near the base; 2) 'Rusty shale subunit', rusty-weathering, mud-cracked varicoloured shale with minor orthoquartzite and peritidal, partly stromatolitic carbonate; 3) 'Gypsum subunit', almost entirely white, red, and locally dark grey gypsum; 4) 'Grainstone subunit', peritidal dolomite, in part platy, sandy, mud-cracked, in part dolomitized, massive ooid grainstone; 5) 'Basinal sequence', (not developed at type section), mainly limestone (dolomite)/ shale/siltstone rhythmite, a basal member is red (locally grey) nodular limestone, west of Mountain River, giant stromatolitic reefs are embedded in reef talus and rhythmite; and 6) 'Mud-cracked subunit' (lowest), coarsening-upward cycles involving mudrocks and sandstone, large and widespread mud-cracks and a few beds of dolomitized oolite.
The Little Dal conformably overlies the Katherine Gp. Its contact with, the overlying Redstone River Fm is conformable at basinward localities and unconformable on the flanks of (Redstone River) basins. Over much of the region, it is overlain by post-Redstone River formations. The Little Dal corresponds to much of the Shaler Gp of Victoria Island and includes the Dead End Fm of older literature.
The formation was erected from strata mapped in Glacier Lake (95L) and Wrigley Lake (95M) map-area. Subsequent mapping and stratigraphic studies in areas farther north (Aitken, 1977a; Aitken and Cook, 1974a; Aitken et al., 1973b) mistakenly applied the name Little Dal ("Little Dal s.s.") only to the uppermost major mappable unit of the Little Dal equivalent in those areas, and treated the underlying Little Dal equivalents as parts of an informal 'Map-unit H5'. This error, partly due to earlier mis-mapping of 'upper' and 'lower' divisions of the Little Dal, was eventually recognized (Aitken et al., 1978a) Thus, 'Map-unit H5' became obsolete, and the desirability of treating the Little Dal as a group became obvious.
See Little Dal Group.
Aitken, J.D. and Cook, D.G., 1974a. Carcajou Canyon map-area, District of Mackenzie Northwest Territories; Geological Survey of Canada, Paper 74-13, 28 p.
Aitken, J.D., 1977a. New data on correlation of the Little Dal Formation and a revision of Proterozoic map unit 'H5', in, Report of Activities, Part A, Blackadar, R.G., Griffin, P.J., Dumych, H., and Irish, E.J.W. (Eds. and Compilers); Geological Survey of Canada, Paper 77-1A, pp. 131-135.
Aitken, J.D., Long, D.G.F., and Semikhatov, M.A., 1978b. Correlation of Helikian Strata, Mackenzie Mountains - Brock Inlier - Victoria Island, in, Current Research, Part A, II: Scientific and Technical Notes, Blackadar, R.G., Griffin, P.J., Dumych, H., and Irish, E.J.W. (Eds. and compilers); Geological Survey of Canada, Paper 78-1A, pp. 485-486.
Aitken, J.D., Macqueen, R.W., and Usher, J.L., 1973b. Reconnaissance studies of Proterozoic and Cambrian stratigraphy, lower Mackenzie River area (Operation Norman), District of Mackenzie; Geological Survey of Canada, Paper 73-9, 178 p.
Gabrielse, H., Blusson, S.L., and Roddick, J.A., 1973. Geology of the Flat River, Glacier Lake and Wrigley Lake map-areas, District of Mackenzie and Yukon Territory; Geological Survey of Canada, Memoir 366 (Parts I and II), 421 p.
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: J.D. Aitken; D.W. Morrow
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 24 Feb 2011