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]

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]

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)

Remains of an indeterminate lamnid genus and species are present.

Remains of Acipenseridae, Amiidae, Esocidae, indeterminate genera and species.

Bony fishes reported from the Milk River Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Belonostomus	Indeterminate				Aspidorhynchidae
Lepisosteus	L. occidentalis				Lepisosteidae
Palaeolabrus	Indeterminate				Lepisosteidae

Amphibians reported from the Milk River Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Albanerpeton	A. galaktion				Albanerpetontidae
	A. nexuosus				Albanerpetontidae
Opisthotriton	Indeterminate				Batrachosauroididae

Indeterminate Anguidae and Xenosauridae genera and species.

Indeterminate Solemydidae and Trionychidae genera and species.

Indeterminate Ankylosauridae, Aves, Ceratopsidae, Dromaeosauridae, Hadrosauridae, Nodosauridae, Ornithomimidae, Pachycephalosauridae, Protoceratopsidae, Thescelosauridae, and Tyrannosauridae genera and species.

Dinosaurs reported from the Milk River Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Lithostrotia[6]	Indeterminate			Caudal Centrum	An indeterminate Titanosaurian sauropod, the first from Canada. Cited to be similar to caudals referred to Alamosaurus.[6]
Acrotholus[7]	A. audeti			Skull domes	A pachycephalosaur
Brachyceratops[8]	Indeterminate[8]
Continuoolithus[9]	cf. C. canadensis			One eggshell fragment	Laid by a theropod.
Gryphoceratops[10]	G. morrisoni			Partial right dentary	A leptoceratopsid
Kritosaurus[11]	Indeterminate
Palaeoscincus[12]	Indeterminate
cf. Paronychodon[13]	cf. P. lacustris[13]				Theropoda incertae sedis
Porituberoolithus[9]	cf. P. warnerensis			One eggshell fragment	Laid by a theropod
Prismatoolithus[9]	Indeterminate			6 isolated eggshell fragments	Laid by a theropod.
cf. Richardoestesia[13]	cf. R. gilmorei[13]				Maniraptora incertae sedis
	cf. R. isosceles				Maniraptora incertae sedis
Saurornitholestes[14]	S. langstoni[14]				Dromaeosauridae
Spheroolithus[9]	cf. S. choteauensis			313 isolated eggshell fragments	Laid by an ornithopod.
Triprismatoolithus[9]	Indeterminate			60 isolated eggshell fragments	Laid by a bird or theropod.

Didelphomorphs reported from the Milk River Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Albertatherium	A. primus				Peradectidae
	A. secundus				Peradectidae
Alphadon	A. halleyi				Peradectidae
	Indeterminate				Peradectidae
Aquiladelphis	A. incus				Aquiladelphidae
	A. minor				Aquiladelphidae
Didelphodon	Indeterminate				Stagodontidae
Eodelphis	Indeterminate				Stagodontidae
Iqualadelphis	I. lactea				Pediomyidae
Pediomys	cf. P. clemensi				Pediomyidae
	P. exiguus				Pediomyidae
	P. florencae				Pediomyidae
Protalphadon	P. creber				Peradectidae

• List of dinosaur-bearing rock formations

• Brinkman, D. 2003. A review of nonmarine turtlesfrom the Late Cretaceous of Alberta. Canadian Journal of Earth Sciences 40:557-571.
• Gao, K., Fox, R.C. 1996. Taxonomy and evolution of late Cretaceous lizards (Reptilia: Squamata) from Western Canada. Bulletin of the Carnegie Museum 33: 1-107.
• Hilton, E.J. And Grande, L. 2006. Review of the fossil record of sturgeons, family Acipenseridae (Actinopterygii: Acipenseriformes), from North America. Journal of Paleontology 80: 672-683.
• Larson, D.W. 2008. Diversity and variation of theropod dinosaur teeth from the uppermost Santonian Milk River Formation (Upper Cretaceous), Alberta: a quantitative method supporting identification of the oldest dinosaur tooth assemblage in Canada. Canadian Journal of Earth Sciences 45: 1455-1468.
• Payenberg, T.H.D., Braman, D.R., Davis, D.W., and Miall, A.D. 2002. Litho- and chronostratigraphic relationships of the Santonian–Campanian Milk River Formation in southern Alberta and Eagle Formation in Montana utilising stratigraphy, U–Pb geochronology, and palynology. Canadian Journal of Earth Sciences 39:1553-1577.
• Sullivan, R.M. 2003. Revision of the dinosaur Stegoceras Lambe (Ornithischia, Pachycephalosauridae). Journal of Vertebrate Paleontology 23: 181-207.
• University of Alberta Museum https://web.archive.org/web/20090815182206/http://www.museums.ualberta.ca/dig/search/vpaleo/index.html