Unit Name: Blackstone Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Cenomanian - Turonian (99.6 - 89.3 ma)
Age Justification: Contains ammonites and pelecypods from the Zones of Dunveganoceras to Prionocyclus woollgari of Cenomanian and Turonian age. Foraminifera were described by Wall and Germundson (1963), who identified Albian Miliammina manitobensis from basal beds in the type region, and Cenomanian and Turonian assemblages, including a lower pelagic microfauna of Hedbergella and Heterohelix.
Originator: Malloch, 1911.
Bighorn River, central foothills Sec. 30, Twp. 39, Rge. 17W5M, Alberta (Stott, 1963).
The formation is recognized along the foothills from the International Boundary to Athabasca River. It increases in thickness from 79.9 m (262 ft) at Lynx Creek in the Carbondale map-area to 426.7 m (1,400 ft) at Thistle Creek, a tributary of Brazeau River. It decreases in thickness from west to east across the foothills.
Thickness(m): Maximum 426.7.
Consists mainly of dark grey to black marine mudstone and siltstone with minor beds of argillaceous limestone, sandstone, bentonite, and some sideritic concretions. The formation contains more silt in westernmost exposures along the foothills. It is divided into four members: the Sunkay consists of shale, siltstone and thin coarse sandstone; Vimy consists of calcareous shale and siltstone; Haven of rusty weathering shale; and the Opabin of concretionary mudstone.
The Blackstone Formation belongs to the Alberta Group (Stott, 1963). Regional relationships, distinct boundaries lack of interbedding with the underlying Blairmore and Luscar Groups basal pebble beds, and local unconformities indicate that the basal Blackstone contact is disconformable. It is equivalent to the lower part of the Colorado Shale to the east, and to the north the pre-Cardium part of the Kaskapau, Dunvegan and Shaftsbury formations. To the south it grades into the lower part of the Marias River Shale and upper Blackleaf Member. A layer of coarse gritty sandstone in the Sunkay Member probably represents the Fish Scale Marker Horizon.
Malloch, G.S., 1911. Bighorn Coal Basin, Alberta; Geological Survey of Canada, Memoir 9, 78 p.
Stott, D.F., 1963. The Cretaceous Alberta Group and equivalent rocks, Rocky Mountain Foothills, Alberta. Geol. Surv. Can., Memoir 317.
Wall, J.H. and Germundson, R.K., 1963. Microfaunas, megafaunas, and rock-stratigraphic units in the Alberta Group (Cretaceous) of the Rocky Mountain Foothills; Bull. Can. Petrol. Geol., vol. 11, no. 4.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: D.F. Stott
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 13 Feb 2009