Unit Name: Broken Skull Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Late Cambrian - Early Ordovician (499 - 471.8 ma)
Age Justification: Sparsely fossiliferous with trilobites, brachiopods, gastropods, cephalopods and conodonts. These indicate ages from Late Cambrian (Franconian) to Early Ordovician.
Province/Territory: Northwest Territories; Yukon Territory
Originator: Gabrielse et al., 1973.
Type Locality:
Southern Mackenzie Mountains, Backbone Ranges, 6 km (3.7 mi) southwest of Avalanche Lake, 62°21'N, 127°20'W.
Distribution:
Occurs along a broad belt from Nahanni map area (105I) southeasterly to Flat River map area (95E). Also exposed in cores of anticlines in Root River and Dahadinni map areas (95K and 95N). Maximum thickness of 860 m (2,822 ft) at type locality; thins to 500 m (1,640 ft) near Glacier Lake.
Locality Data:
Thickness(m): Minimum 500, Maximum 860.
Lithology:
In type area, consists of a lower member of buff, orange, yellow, brown, and grey weathering dolostones and limestones and an upper member of grey and yellow-grey weathering dolostones and limestones. Mudcracks and cross-bedding are common and most beds contain variable amounts of well-rounded sand, silt and clay. Sandstone units up to 100 m (328 ft) thick may occur in lower part. Upper member may contain pisolites.
Relationship:
Rests with pronounced unconformity on Middle Cambrian Rockslide and Avalanche formations or Lower Cambrian Sekwi Formation. Contact with overlying Sunblood Formation is sharp, but apparently conformable. Laterally equivalent to Franklin Mountain Formation to the east and Rabbitkettle Formation to the west.
Other Citations:
Fritz, 1979; Jackson, 1978; Ludvigsen, 1975; Tipnis et al., 1978.
References:
Fritz, W.H., 1979. Cambrian stratigraphic sections between southern Nahanni and Broken Skull rivers, southern MacKenzie Mountains: Geological Survey of Canada; Current Research, Paper 79- 1B, pp. 121-126.
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.
Jackson, D.E., 1978. Recent developments in graptolite research; pp. 113-131: in Stelck, C.R. and Chatterton, B.D.E. (eds,), Western and Arctic Canadia Biostratigraphy, Geological Association of Canada Special Paper no. 18, 602 p.
Ludvigsen, R., 1975. Ordovician formations and faunas, southern Mackenzie Mountains; Canadian Journal of Earth Sciences = Journal Canadien des Sciences de la Terre, vol. 12, no. 4, pp. 663-697.
Tipnis, R.S., Chatterton, B.D.E., and Ludvigsen, R., 1978. Ordovician conodont biostratigraphy of the southern District of Mackenzie, Canada; pp. 39-91: in Stelck, C.R. and Chatterton, B.D.E. (eds.), Western and Arctic Canadian Biostratigraphy, Geological Association of Canada, Special Paper no. 18, 602 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: R. Ludvigsen; F.F. Krause
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 20 Jul 2009