Unit Name: Foremost Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Santonian (85.8 - 83.5 ma)
Age Justification: The Foremost contains a rich fauna of fresh water pelecypods of Santonian age, including Fusconia, Quadrula and Elliptio. Brackish water forms are represented by Corbula, Ostrea, Anomia, Corbicula and Volsella, and a sparse marine fauna is represented by Nucula, Yoldia and Pteria. The gastropods Hydrobia, Viviparus, Campeloma, Veratella, Malania and the marine form Polinices are also present.
Originator: Dowling, D.B., 1915.
Chin Coulee, near Foremost, Alberta.
The Foremost Formation crops out between Lethbridge, Medicine Hat and Milk River in southeastern Alberta, and along the valleys of the South Saskatchewan, Oldman and Bow rivers as far north as Eyremore. Its thickness ranges from 168 m (550 ft) near Lethbridge to 107 m (350 ft) in the vicinity of Medicine Hat and to 73 m (240 ft) in the Milk River Gorge.
"At the top there is generally a zone composed of coal seams and carbonaceous shales. This zone ranges from 80 to 220 ft (24.4 to 67 m) in thickness, and is given such local names as Taber coal horizon, Grassy Lake lignite Member and Redcliff coal zone. Below this a zone composed of sandstone, shales, Ostrea and Corbula beds, with a few beds of carbonaceous shale. This zone is 33 to 76.3 m (100 to 250 ft) thick. On the west flank of the Sweetgrass Arch this is underlain by another coal zone approximately 9.2 m (30 ft) thick. This lowest zone is called the McKay coal horizon and loses its identity eastward as it passes into marine equivalents of the Pakowki Formation. The McKay coal horizon is underlain by the basal Foremost sandstone locally called the Verdigris Sandstone, from its occurrence in Verdigris coulee, near Milk River town" (Crockford, 1949).
The unit is overlain by the Oldman Formation and underlain by marine Pakowki shales.
Dawson (1882) included the Milk River beds, Pakowki shales and what is now known as the Foremost and Oldman formations in his Belly River series, that is, all the beds between the Alberta and Bearpaw formations. Williams and Dyer (1930) restricted the term Belly River to the Foremost and what is now known as the Oldman formations. Russell and Landes (1940) raised the Foremost and Oldman to formation status.
Crockford, 1949; Dawson, 1882; Dowling, 1915; Russell and Landes, 1940; Thompson and Oxford, 1953; Williams and Dyer, 1930.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: ASPG Lexicon 1960
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003