The Milk River Formation is a sandstone-dominated stratigraphic unit of the Western Canada Sedimentary Basin in southern Alberta, Canada. It was deposited in near-shore to coastal environments during Late Cretaceous (late Santonian to early Campanian) time. Based on uranium-lead dating, palynology and stratigraphic relationships, deposition occurred between ~84.1 and 83.6 Ma.^[3]

Quick Facts Type, Unit of ...

Milk River Formation
Stratigraphic range: Santonian-Campanian ~84.1–83.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Outcrops along the Milk River
Type	Geological formation
Unit of	Montana Group
Sub-units	Deadhorse Coulee Member Virgelle Member Telegraph Creek Member
Underlies	Pakowki Formation
Overlies	Colorado Group
Thickness	up to 113 metres (370 ft)[1]
Lithology
Primary	Sandstone
Other	Siltstone, shale, coal
Location
Region	Alberta
Country	Canada
Type section
Named for	Milk River
Named by	D.B. Dowling, 1916[2]

Close

The sandstones of the Virgelle Member in the centre of the formation are well-exposed at Writing-on-Stone Provincial Park in southwestern Alberta, where they bear petroglyphs carved into them by First Nations people.

The formation is fossiliferous and has yielded an extensive vertebrate fauna (see Tables below), as well as fossil ammonites. In some areas it hosts shallow natural gas reservoirs.^[4]

The Milk River Formation is an eastward-thinning wedge of clastic sediments that was deposited along the western margin of the Western Interior Seaway during Late Cretaceous (late Santonian to early Campanian) time. It is age-equivalent to the marine shales of the Lea Park Formation in southeastern Alberta, and to the Eagle and Telegraph Creek Formations of north-central Montana.^[5][4]

In Alberta it is subdivided into the following three members:^[5]

• Telegraph Creek Member, at the base, consists primarily of mudstones and shales deposited in offshore marine settings. It has produced the ammonite index fossil Desmoscaphites bassleri, which indicates an age of ~84. Ma.^[5][3]
• Virgelle Member, the central member, is a sequence of massive, cliff-forming, yellow to white sandstones that were deposited in shoreface and tidal channel environments. It can be seen at Writing-on-Stone Provincial Park.^[5]
• Deadhorse Coulee Member, at the top, consists of predominantly nonmarine shales, siltstones, sandstones, and coal beds that were deposited in rivers, floodplains and swamps.^[5] Most of the vertebrate fossils have come from this member.^[5]

(references: Brinkman 2003; Gao and Fox 1995; Hilton and Grande 2006; Larson 2008; Sullivan 2003; University of Alberta webpage)

• List of dinosaur-bearing rock formations