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Milk River Formation

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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]

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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]

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Stratigraphy and lithology

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Sandstones of the Milk River Formation at Writing-on-Stone Provincial Park

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]
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Vertebrates

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(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.

More information Cartilaginous fishes reported from the Milk River Formation, Genus ...

Bony fishes

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

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Amphibians

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Squamates

Indeterminate Anguidae and Xenosauridae genera and species.

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Turtles

Indeterminate Solemydidae and Trionychidae genera and species.

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Crocodilians

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Dinosaurs

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

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
More information Dinosaurs reported from the Milk River Formation, Genus ...

Mammals

Other mammals

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Didelphomorphs

More information Didelphomorphs reported from the Milk River Formation, Genus ...
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See also

Footnotes

References

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