Milk River Formation

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.

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.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.

The area was probably a dense forest during the Late Cretaceous with conifers from the Yew family being common alongside flowering plants like magnolias and figs. The ground was covered in horsetails and sensitive ferns.

Stratigraphy and lithology

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.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 shales deposited in offshore marine settings. It has produced the ammonite index fossil 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 shales, siltstones, sandstones, and coal 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.

Cartilaginous fishes reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesLonchidionIndeterminateHybodontoideaMyledaphusM. bipartitusRhinobatoidei

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

Bony fishes reported from the Milk River Formation Genus Species Location Stratigraphic position Material Notes ImagesBelonostomusIndeterminateAspidorhynchidaeLepisosteusL. occidentalisLepisosteidaePalaeolabrusIndeterminateLepisosteidae

Amphibians

Amphibians reported from the Milk River Formation Genus Species Location Stratigraphic position Material Notes ImagesAlbanerpetonA. galaktionAlbanerpetontidaeA. nexuosusAlbanerpetontidaeOpisthotritonIndeterminateBatrachosauroididae

Squamates Indeterminate Anguidae and Xenosauridae genera and species.

Squamates reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesAocnodromeusA. corrugatusScincidaeChamopsIndeterminateTeiidaeConiophiscf. C. precedensAniliidaeCnephasaurusC. locustivorusIguanidaeGlyptogenysG. ornataTeiidaeParasaniwa?IndeterminateNecrosauridaePenemabuyaP. antecessorScincidaeSphenosiagonS. simplexTeiidae

Turtles Indeterminate Solemydidae and Trionychidae genera and species.

Turtles reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesAdocusIndeterminateAdocidaeBasilemysIndeterminateNanhsiungchelyidae?BoremysIndeterminateBaenidae?CompsemysIndeterminateFamily indeterminantNeurankylusN. lithographicusBaenidaePlesiobaenaIndeterminateBaenidae

Crocodilians

Crocodilians reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesGilchristosuchusG. palatinus

Dinosaurs 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 ImagesLithostrotiaIndeterminateCaudal centrumAn indeterminate Titanosaurian sauropod, the first from Canada. Cited to be similar to caudals referred to Alamosaurus.AcrotholusA. audetiSkull domesA pachycephalosaurBrachyceratopsListed as "cf. Brachyceratops sp." in "1.4 Alberta, Canada; 5. Milk River Formation," in Weishampel, et al. (2004). Page 576.IndeterminateContinuoolithuscf. C. canadensisOne eggshell fragmentLaid by a theropodGryphoceratopsG. morrisoniPartial right dentaryA leptoceratopsidKritosaurusListed as "cf. Kritosaurus sp." in "1.4 Alberta, Canada; 5. Milk River Formation," in Weishampel, et al. (2004). Page 576.IndeterminatePalaeoscincusListed as "cf. Kritosaurus" in "1.4 Alberta, Canada; 5. Milk River Formation," in Weishampel, et al. (2004). Page 576.Indeterminatecf. Paronychodoncf. P. lacustrisTheropoda incertae sedisPorituberoolithuscf. P. warnerensisOne eggshell fragmentLaid by a theropodPrismatoolithusIndeterminate6 isolated eggshell fragmentsLaid by a theropodcf. Richardoestesiacf. R. gilmorei"1.4 Alberta, Canada; 5. Milk River Formation," in Weishampel, et al. (2004). Page 576.Maniraptora incertae sediscf. R. isoscelesManiraptora incertae sedisSaurornitholestesListed as "cf. Saurornitholestes langstoni" in "1.4 Alberta, Canada; 5. Milk River Formation," in Weishampel, et al. (2004). Page 576.S. langstoniDromaeosauridaeSpheroolithuscf. S. choteauensis313 isolated eggshell fragmentsLaid by an ornithopodTriprismatoolithusIndeterminate60 isolated eggshell fragmentsLaid by a bird or theropod

Mammals

Other mammals

Other mammals reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesAlticonodonA. lindoeiTriconodontidaeCimexomysC. antiquusNeoplagiaulacidae?C. magisterNeoplagiaulacidae?CimolodonC. electusCimolodontidaeC. similisCimolodontidaeCimolomysIndeterminateCimolomyidaeEctypoduscf. E. powelliMeniscoessus M. ferox CimolomyidaeMesodmaMesodma senectaIndeterminateMictodonMictodon simpsoniTinodontidaeParacimexomysP. magisterFamily indeterminentParanyctoidesParanyctoides maleficusNyctitheriidaePicopsis P. pattersoni PicopsidaeIndeterminatePicopsidaePotamotelsesP. aquilensisPotamotelsidaeSymmetrodontoidesS. canadensisSpalacotheriidaeViridomysV. orbatusNeoplagiaulacidae?

Didelphomorphs

Didelphomorphs reported from the Milk River Formation Genus Species Location Stratigraphic position Material Notes ImagesAlbertatheriumA. primusPeradectidaeA. secundusPeradectidaeAlphadonA. halleyiPeradectidaeIndeterminatePeradectidaeAquiladelphisA. incusAquiladelphidaeA. minorAquiladelphidaeDidelphodonIndeterminateStagodontidaeEodelphisIndeterminateStagodontidaeIqualadelphisI. lacteaPediomyidaePediomyscf. P. clemensi PediomyidaeP. exiguus PediomyidaeP. florencae PediomyidaeProtalphadonP. creberPeradectidae

Flora Most of the flora noted here come from the paper cited here.

Ferns

Ferns reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesCladophlebisC. simplicima EquisetumE. sp.OnocleaO. hebridicaTapeinidium T. undulatum

Gymnosperms Conifers reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesBrachyphyllum B. douglasiElatocladusE. albertaensisGeinitziaG. formosaCephalotaxopsis C. heterophyllaSequoiaS. majorProtophyllocladusP. polymorpha

Angiosperms Flowering plants reported from the Milk River Formation Genus Species Location Stratigraphic position Material NotesTrochodendroidesT. arcticaA Katsura relativeIlex I. mammillataLaurophyllum L. sp.A laurelAlnus A. perantiquaPopulitesP. wickendeniFicus F. trinervisA figMagnoliaM. coalvillensisA magnoliaMenispermites M. spCassiaC. sp.A legume

Milk River Formation

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