Fort Union Formation

The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane.Wyodak Coal, Tongue River Member of the Fort Union Formation, Powder River Basin, Wyoming: "No-Coal Zones" and Their Effects on Coalbed Methane Production, by Mark Ashley, 2005

Description The Fort Union is mostly of Paleocene age and represents a time of extensive swamps as well as fluvial and lacustrine conditions. The rocks are more sandy in southwestern Wyoming and more coal-bearing in northeast Wyoming and southeast Montana, reflecting a general change from rivers and lakes in the west to swamps in the east, but all three environments were present at various times in most locations.Eocene and Paleocene rocks of the southern and central basins, by Robert E. McDonald, in Geologic Atlas of the Rocky Mountain Region, Rocky Mountain Association of Geologists, Denver, CO, 1972: p. 248

Coal in the Fort Union in the Powder River Basin occurs mainly in the Tongue River Member, where as many as 32 coal seams total more than 300 feet in thickness. One such bed, the Wyodak Coal near Gillette, Wyoming, is as much as thick. Most of the coals in the Fort Union Formation are ranked subbituminous.Cretaceous and Tertiary coals of the Rocky Mountains and Great Plains regions, by R.M. Flores and T.A. Cross, 1991, in Economic Geology, U.S., Geological Society of America, Decade of North American Geology Series, vol. P-2, p. 547-571. One Tongue River locality near Bay Horse has a preservational and depositional environment reminiscent of the famous, younger deposits of the Green River Formation from further south, including dominance by the schooling fish Knightia.

Fossil content

Mammals Cimolestans Cimolestans reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes Images CrustulusC. fontanus Northeastern Montana.Tullock Member.An isolated upper molar. A pantodont.

Leptictids Leptictids reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes Images ProdiacodonP. crustulum Garfield & McCone counties, Montana.Tullock Member.Fragmentary dentary & isolated teeth. A leptictid.

Marsupials Marsupials reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesPeradectesP. sp.Swain Quarry, Wyoming.Upper & lower molars.Reassigned to Swaindelphys.SwaindelphysS. cifelliiSwain Quarry, Wyoming.Upper & lower molars.An opossum.

Primatomorphs Primatomorphs reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesCarpodaptesC. sp.Wind River Basin, Wyoming.Shotgun Member.2 isolated fourth lower premolars.A carpolestid.ChiromyoidesC. caesorHell's Half Acre (UCM locality 78009), Mesa County, Colorado.A single upper incisor (UCM 53515).A plesiadapid.C. gigasPiceance Creek Basin, Colorado.Multiple teeth.A plesiadapid.C. sp.UCM locality 78060, Colorado.A left molar (UCM 41606).A plesiadapid.ElphidotarsiusE. shotgunensisWind River Basin, Wyoming.Shotgun Member.Right ramus of mandible & isolated teeth.A carpolestid.NannodectesN. gaziniFremont County, Colorado.A right maxilla (USGS 16872).A plesiadapid.PalaechthonP., near P. alticuspisWind River Basin, Wyoming.Shotgun Member.3 upper molars & 4 lower molars.A plesiadapiform.P. woodiWind River Basin, Wyoming.Shotgun Member.A lower jaw & 13 isolated teeth.A plesiadapiform.PalenochthaP. cf. minorWind River Basin, Wyoming.Shotgun Member.5 lower teeth.A plesiadapiform.ParomomysP., near P. depressidensWind River Basin, Wyoming.Shotgun Member.Approximately 12 upper teeth, 8 isolated lower teeth & a jaw fragment.A paromomyid.PhenacolemurP. fremontensisWind River Basin, Wyoming.Shotgun Member.A lower jaw & isolated teeth.A paromomyid.P. cf. frugivorusWind River Basin, Wyoming.Shotgun Member.2 upper molars & 8 isolated lower molars.A paromomyid.PlesiadapisP. dubiusPiceance Creek Basin, Colorado.Jaw elements & teeth.A plesiadapid.P. fodinatusPiceance Creek Basin, Colorado.Jaw elements & teeth.A plesiadapid. P. sp.Wind River Basin, Wyoming.Shotgun Member.5 lower molars, 3 anterior upper molars & a premolar.A plesiadapid.PlesiolestesP. cf. problematicusWind River Basin, Wyoming.Shotgun Member.Approximately 45 isolated teeth.A plesiadapiform.PronothodectesP. intermediusWind River Basin, Wyoming.Shotgun Member.Jaw elements & teeth.A plesiadapid.PurgatoriusP. janisae'Harley's Point' UCMP locality V77087, Garfield County, Montana.Tullock Member.UCMP 150018 (right m1), and UCMP 192398 (left m3).A purgatoriid.P. mckeeveriGarfield County, Montana.Tullock Member.Dentary remains & teeth.A purgatoriid.P. cf. P. mckeeveriHarley's Point' UCMP locality V77087, Garfield County, Montana.Tullock Member.UCMP 150019 (right M2), and UCMP 150020 (right M2).A purgatoriid.TorrejoniaCf. T. wilsoniWind River Basin, Wyoming.Shotgun Member.About 14 lower teeth & possibly 3 upper molars.A plesiadapiform. ZanycterisZ. honeyi UMC locality number 92177, Colorado.Atwell Gulch Member.Right maxilla (UCM 87378). A plesiadapiform.

Ungulates Ungulates reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesDissacusD. argenteusPrinceton Quarry, Park County, Wyoming.Upper part of the formation.Jaw elements & teeth.A mesonychid.D. cf. navajoviusPrinceton Quarry, Park County, Wyoming.Upper part of the formation.Jaw elements & teeth.Specimens reassigned to D. argenteus.D. praenuntiusPark County, Wyoming.Upper part of the formation.Mandible (YPM-PU 16159).A mesonychid also known from the Willwood Formation.EctocionE. mediotuberPrinceton Quarry, Wyoming.Dentary.A phenacodontid.PeriptychusP. carinidensMakoshika State Park, Montana.A periptychid also found in the Nacimiento, North Horn, Black Peaks & Animas formations.SigynorumS. magnadivisusGreat Divide Basin, southern Wyoming.China Butte Member.An arctocyonid.

Diapsids Birds A partial ornithurine coracoid bone found in this formation is identical to others found in the older Hell Creek Formation. At present, this unnamed species is the only known individual bird species that have survived the Cretaceous–Paleogene extinction event.Longrich, N.R., Tokaryk, T. and Field, D.J. (2011). "Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary." Proceedings of the National Academy of Sciences, 108(37): 15253-15257. Birds reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesLithornisL. celetiusBangtail Quarry, Sedan Quadrangle, Park County, Montana.A lithornithid.

Crocodilians Crocodilians reported from the Fort Union Formation Genus Species Location Stratigraphic memberMaterial Notes Images AllognathosuchusA. sp. Princeton Quarry, Park County, Wyoming.Anterior end of left dentary (PU 16988).A crocodilian.

Squamates Squamates reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesAnguidaeGenus & species indeterminateSwain Quarry, Carbon County, Wyoming.Fragmentary jaw elements.An anguid lizard.cf. AnguidaeSwain Quarry, Carbon County, Wyoming.6 partial dentaries.Provisionally referred to anguid lizards based on size & shape.Contogenyscf. C. sloaniSwain Quarry, Carbon County, Wyoming.Posterior part of a right maxilla (AMNH 12069).A skink.ExostinusE. cf. E. lancensisSwain Quarry, Carbon County, Wyoming.4 partial dentaries.A xenosaurid lizard.E. rugosusPrinceton & Schaff quarries, Park County, Wyoming.Multiple specimens.A xenosaurid lizard.GlyptosaurinaeGenus & species indeterminateSwain Quarry, Carbon County, Wyoming.Several jaw remains.A glyptosaurine lizard.Glyptosaurinae or OdaxosaurinaeGenus & species indeterminateSwain Quarry, Carbon County, Wyoming.Fragmentary jaw elements & osteoderms.Indeterminate lizard remains.MachaerosaurusM. torrejonensisSwain Quarry, Carbon County, Wyoming.Numerous jaw elements.An anguid lizard also known from the Nacimiento Formation.OdaxosaurusO. pigerSwain Quarry, Carbon County, Wyoming.Many fragmentary jaw remains.An anguid lizard.OligodontosaurusO. wyomingensisPark County, Wyoming.A left mandible (PU 14246).An amphisbaenian.Palaeosaniwacf. P. canadensisSwain Quarry, Carbon County, Wyoming.Medial part of left dentary (AMNH 15957).A large anguimorph lizard.PalaeoxantusiaP. feraSwain Quarry, Carbon County, Wyoming.Numerous jaw elements.A night lizard.PancelosaurusP. pigerPrinceton, Fritz & Schaff quarries, Park County, Wyoming.Multiple skull elements.An anguid lizard.ProvaranosaurusP. acutusPrinceton Quarry, Park County, Wyoming.PU 14243 (left maxilla), 14561 (anterior portion of left dentary) & 17145 ( fragment of left maxilla).A palaeovaranid lizard.cf. P. sp.Swain Quarry, Carbon County, Wyoming.3 partial dentaries (AMNH 14306, 14307 & 14309).A palaeovaranid lizard.RhineuridaeUnidentified genus & speciesFritz Quarry, Park County, Wyoming.An almost complete right dentary & a broken vertebra (PU 18627).An amphisbaenian.Saniwacf. S. sp.Swain Quarry, Carbon County, Wyoming.2 trunk vertebrae (AMNH 15960 & 16003).A varanid.SwainiguanoidesS. milleriSwain Quarry, Carbon County, Wyoming.Jaw elements.An iguanid.

Testudines Testudines reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesAtoposemysA. entopterosMontana.Tullock Member.A softshell turtle.AxestemysA. montinsanaPTRM Site V02017, Slope County, North Dakota.Numerous skull, limb & shell fragments.A softshell turtle also found in the Melville & Denver formations.CardiochelyonC. rogerwoodiReis Quarry, Park County, Wyoming.Partial skeleton (YPM PU14671).A kinosternoid formerly thought to be a platysternid.CedrobaenaC. putoriusCedar Point Quarry, Wyoming.Shell & skull elements.A baenid turtle also found in the Hell Creek Formation.HutchemysH. arctochelysBurns Mine, Washoe Area, Carbon County, Montana.Tongue River Member.Multiple shell elements.A softshell turtle.H. rememdiumFallon County, Montana.Ekalaka Member.A near complete postcranial skeleton (YPM PU 16795) & shell elements.A softshell turtle.H. sp.Duffy's Ranch, Sweet Grass County, Montana.YPM PU 11566.A softshell turtle. PtychogasterP. sp. Princeton Quarry & Reiss Locality, Park County, Wyoming.PU 17794 (fragments of the skull & shell), 14671 & 16443 (shells). A turtle. TullochelysT. montanusMontana.Tullock Member.A chelydrid turtle also known from the Hell Creek Formation.

Amphibians Amphibians reported from the Fort Union Formation Genus Species Locality Stratigraphic memberMaterial Notes ImagesAmphiumaA. jepseniPark County, Wyoming.PU 14666 (partial vertebral column), 14668 (partial skull) & 16788 (dislocated vertebrae).An aquatic salamander.AnuraIncertae sedisPark County, Wyoming.PU 14662 (distal end of right radioulna), 14663 (proximal end of left radioulna), 14669 (phalanx), 13372 (right maxilla).A frog.DiscoglossidaeUndescribed genus & speciesPark County, Wyoming.Distal end of right humerus (PU 14670).A frog similar to undescribed discoglossid remains from the Hell Creek Formation.EorhinophrynusE. sp.Princeton & Fritz quarries, Park County, Wyoming.Humeri & vertebrae.A burrowing toad.OpisthotritonO. kayiPrinceton Quarry, Park County, Wyoming.Multiple specimens.A salamander. ScapherpetonS. tectum Princeton & Schaff quarries, Park County, Wyoming.PU 20583 (3 broken vertebrae, an atlas, an ilium & a rib) & PU 19500 (a humerus). A salamander.

Fish