The Milk River Formation is a

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

-dominated stratigraphic unit of the Western Canada Sedimentary Basin in southern

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. It was deposited in near-shore to coastal environments during

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

(late

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...

to early

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

) time. Based on uranium-lead dating,

palynology Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...

and stratigraphic relationships, deposition occurred between ~84.1 and 83.6 Ma. 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

petroglyph A petroglyph is an image created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art. Outside North America, scholars often use terms such as "carving", "engraving", or other descriptions ...

s carved into them by

First Nations First nations are indigenous settlers or bands. First Nations, first nations, or first peoples may also refer to: Indigenous groups *List of Indigenous peoples *First Nations in Canada, Indigenous peoples of Canada who are neither Inuit nor Mé ...

people. The formation is fossiliferous and has yielded an extensive

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

fauna (see Tables below), as well as fossil

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

s. In some areas it hosts shallow

natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...

reservoirs.Payenberg, T.D.H., Braman, D.R. and Miall, A.D. 2003. Depositional environments and stratigraphic architecture of the Late Cretaceous and Eagle formations, southern Alberta and north-central Montana: Relationships to shallow gas. Bulletin of Canadian Petroleum Geology, vol. 51, no. 2, p. 155-176.

Stratigraphy and lithology

The Milk River Formation is an eastward-thinning wedge of

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks by ...

sediments that was deposited along the western margin of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...

during

(late

to early

) time. It is age-equivalent to the marine shales of the Lea Park Formation in southeastern Alberta, and to the

Eagle Eagle is the common name for the golden eagle, bald eagle, and other birds of prey in the family of the Accipitridae. Eagles belong to several groups of Genus, genera, some of which are closely related. True eagles comprise the genus ''Aquila ( ...

and Telegraph Creek Formations of north-central

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

.Payenberg, T.D.H., 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 the Eagle Formation in Montana utilising stratigraphy, U-Pb geochronology, and palynology, Canadian Journal of Earth Sciences, vol. 39, p. 1553-1577. In Alberta it is subdivided into the following three members: *Telegraph Creek Member, at the base, consists primarily of mudstones and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

s deposited in offshore marine settings. It has produced the

index fossil Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

''Desmoscaphites bassleri'', which indicates an age of ~84. Ma. *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. *Deadhorse Coulee Member, at the top, consists of predominantly nonmarine

s, siltstones,

s, and

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

beds that were deposited in rivers, floodplains and swamps. Most of the vertebrate fossils have come from this member.

Vertebrates

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

Cartilaginous fishes

Remains of an indeterminate lamnid genus and species are present.

Bony fishes

Remains of Acipenseridae, Amiidae,

Esocidae Esocidae is a family of ray-finned fish in the order Salmoniformes, which contains pike, pickerel, and mudminnows. While the family traditionally only contained the genus ''Esox'', recent genetic and paleontological research have recovered ''Novu ...

, indeterminate genera and species.

Amphibians

Squamates

Indeterminate Anguidae and

Xenosauridae Xenosauridae is a family of anguimorph lizards whose only living representative is the genus '' Xenosaurus'', which is native to Central America. Xenosauridae also includes the extinct genera '' Exostinus'' and '' Restes''. Also known as knob-sca ...

genera and species.

Turtles

Indeterminate Solemydidae and Trionychidae genera and species.

Crocodilians

Dinosaurs

Indeterminate Ankylosauridae, Aves,

Ceratopsidae Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...

Dromaeosauridae Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from ...

Hadrosauridae Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fam ...

, Nodosauridae, Ornithomimidae, Pachycephalosauridae, Protoceratopsidae, Thescelosauridae, and Tyrannosauridae genera and species.

Mammals

Other mammals

Didelphomorphs

Footnotes

References

*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 {{Western Canadian Sedimentary Basin, South AB=yes Geologic formations of Alberta Cretaceous Alberta Upper Cretaceous Series of North America