The Wasatch Formation (Tw) is an extensive highly fossiliferous geologic formation stretching across several basins in Idaho, Montana, Wyoming, Utah and western Colorado. It preserves fossils dating back to the Early Eocene period. The formation defines the Wasatchian or Lostcabinian (55.8 to 50.3 Ma), a period of time used within the NALMA classification, but the formation ranges in age from the Clarkforkian (56.8 to 55.8 Ma) to Bridgerian (50.3 to 46.2 Ma).

Wasatch fauna consists of many groups of mammals, including numerous genera of primates, artiodactyls, perissodactyls, rodents, carnivora, insectivora, hyaenodonta and others. A number of birds, several reptiles and fish and invertebrates complete the diverse faunal assemblages. Fossil flora and ichnofossils also have been recovered from the formation.

The formation, first named as Wasatch Group in 1873 by Ferdinand Vandeveer Hayden, was deposited in alluvial, fluvial and lacustrine environments and comprises sandstones, siltstones, mudstones and shales with coal or lignite beds representing wet floodplain settings.

The Wasatch Formation is an unconventional tight gas reservoir formation in the Uinta and Piceance Basins of Utah and the coal seams of the formation are mined in Wyoming. At the Fossil Butte National Monument, the formation crops out underlying the Green River Formation. In the Silt Quadrangle of Garfield County, Colorado, the formation overlies the Williams Fork Formation.

Description

Definition

The Wasatch Formation was first named as the Wasatch Group by Ferdinand Vandeveer Hayden in the 1873 edition of his original 1869 publication titled "Preliminary field report of the United States Geological Survey of Colorado and New Mexico: U.S. Geological and Geographical Survey of the Territories", based on sections in the Echo and Weber Canyons, of the Wasatch Mountains. In the language of the native Ute people, Wasatch means "mountain pass" or "low pass over high range." According to William Bright, the mountains were named for a Shoshoni leader who was named with the Shoshoni term wasattsi, meaning "blue heron".

Outcrops

View of Fossil Butte with the Wasatch Formation outcropping in the lower areas

At the base of Fossil Butte are the bright red, purple, yellow and gray beds of the Wasatch Formation. Eroded portions of these horizontal beds slope gradually upward from the valley floor and steepen abruptly. Overlying them and extending to the top of the butte are the much steeper buff-to-white beds of the Green River Formation, which are about 300 feet (91 m) thick. The Wasatch Formation ranges from about 3,000 feet (910 m) in the western part of the Uinta Basin, thinning to 2,000 feet (610 m) in the east. In the Silt Quadrangle of Garfield County, Colorado, the formation overlies the Williams Fork Formation. The formation is exposed in the Desolation and Gray Canyons pertaining to the Colorado Plateau in northeastern Utah, and in Flaming Gorge National Recreation Area at the border of southwestern Wyoming and northeastern Utah.

Extent

Map of the Powder and Wind River and Bighorn Basins
Map of the Green River Basin
Map of the Uinta and Piceance Basins

The Wasatch Formation is found across six states in the northwestern United States, from Montana and Idaho in the north across Utah and Wyoming to Colorado in the southwest. The formation is part of several geologic provinces; the eponymous Wasatch uplift, Uinta uplift, Green River, Piceance, Powder River, Uinta and Paradox Basins and the Colorado Plateau sedimentary province and Yellowstone province.

In Montana, the formation overlies the Fort Union Formation and is overlain by the White River Formation. There is a regional, angular unconformity between the Fort Union and Wasatch Formations in the northern portion of the Powder River Basin.

Subdivision

Generalized stratigraphy of the Wasatch Formation

Many local subdivisions of the formation exist, the following members have been named in the literature:

MemberStatesLithologiesNotes
Alkali Creek TongueWyomingMudstones and sandstones
Atwell GulchColoradoSandstones and mudstones
BullpenWyoming
Cathedral Bluffs TongueColorado, WyomingMudstones and sandstones
ChappoWyoming
Cowley CanyonUtah
Desertion Point TongueWyoming
HiawathaColorado, Utah, Wyoming
Kingsbury ConglomerateWyomingFeldspathic conglomerates
KnightUtah, Wyoming
La BargeWyoming
Lookout Mountain ConglomerateWyomingConglomerates
Luman TongueWyoming
Main BodyWyomingMudstones
MolinaColoradoSandstones
MoncriefWyomingFeldspathic conglomerates
New Fork TongueWyoming
NightingaleWyoming
Niland TongueColorado, Wyoming
Ramsey RanchWyoming
Red Desert TongueWyoming
Renegade TongueColorado, Utah
ShireColoradoSandstones and mudstones
TunpWyoming

Lithologies and facies

In the Fossil Basin at the Fossil Butte National Monument, Wyoming, the Wasatch Formation consists primarily of brightly variegated mudstones with subordinate interbedded siltstones, sandstones, and conglomerates and represents deposition on an intermontane alluvial plain. In Mesa County, Colorado, the formation comprises interbedded purple, lavender, red, and gray claystones and shales with local lenses of gray and brown sandstones, conglomeratic sandstones, and volcanic sandstones that are predominantly fluvial and lacustrine in origin. Along the western margin of the Powder River Basin, the Wasatch Formation contains two thick conglomeratic members (in descending order, the Moncrief Member and Kingsbury Conglomerate Member).

The Molina Member of the formation is a zone of distinctly sandier fluvial strata. The over- and underlying members of the Molina are the Atwell Gulch and Shire members, respectively. These members consist of infrequent lenses of fluvial-channel sandstones interbedded within thick units of variegated red, orange, purple and gray overbank and paleosol mudstones.

The Molina Member represents a sudden change in the tectonic and/or climatic regimes, that caused an influx of laterally-continuous, fine, coarse and locally conglomeratic sands into the basin. The type section of the Molina is located near the small town of Molina on the western edge of the basin and is about 90 metres (300 ft) thick. These sandy strata of the Molina Member form continuous, erosion-resistant benches that extend to the north of the type section for approximately 25 kilometres (16 mi). The benches are cut by canyons or "gulches", from which the Atwell Gulch and Shire Gulch members get their names. The Molina forms the principle target within the Wasatch Formation for natural gas exploration, although it is usually called the "G sandstone" in the subsurface.

Provenance

Detrital zircons collected from the middle part of the formation in the Powder River Basin of Wyoming, where the Wasatch Formation reaches a thickness of more than 1,500 metres (4,900 ft) were gathered for U-Pb geochronological analysis. The detrital zircon age spectrum ranged from 1433 to 2957 Ma in age, and consisted of more than 95% Archean age grains, with an age peak of about 2900 Ma. The 2900 Ma age peak is consistent with the age of Archean rocks at the core of the Bighorn Mountains. The sparse Proterozoic grains were likely derived from the recycling of Paleozoic sandstone units. The analysis concluded that the Wasatch sandstone is a first cycle sediment, the Archean core of the Bighorn uplift was exposed and shedding sediment into the Powder River Basin during time of deposition of the Wasatch Formation and the Powder River Basin Wasatch detrital zircon age spectra are distinct from the coeval Willwood Formation in the Bighorn Basin west of the Bighorn Mountains. Cobbles and pebbles in the Wasatch are rich in feldspathic rock fragments, with individual samples containing as much as 40 percent, derived from erosion of the Precambrian core of the Bighorn Mountains. Part of the feldspar has been replaced by calcite cement. Glauconite is present in the Wasatch, although always in volumes of less than 1 percent of the grains. It most probably was derived from the nearby, friable, glauconite-bearing Mesozoic strata of the eastern Bighorn Mountains.

The presence of the Kingsbury Conglomerate at the base of the Wasatch Formation indicates that tectonic activity in the immediate vicinity of the Powder River Basin was intensifying. The conglomerate consists of Mesozoic and Paleozoic rock fragments. The lack of Precambrian fragments indicates that the metamorphic core of the Bighorn Mountains had not been dissected by this early deformation. Deformation in the upper part of the formation has been interpreted as the result of the last phase of uplift during the Laramide orogeny.

Correlations

The basal part of the Wasatch Formation is equivalent to the Flagstaff Formation in the southwest part of the Uinta Basin. The Wasatch Formation is correlated with the Sentinel Butte and Golden Valley Formations of the Williston Basin.

Paleontological significance

The Wasatch Formation is the defining formation for the Wasatchian, ranging from 55.8 to 50.3 Ma, within the NALMA classification. The Wasatchian followed the Clarkforkian stage (56.8-55.8 Ma) and is defined by the simultaneous first appearance of adapid and omomyid euprimates, hyaenodontid creodonts, perissodactyls and artiodactyls. The deposits of the formation were laid down during a period of globally high temperatures during the Paleocene-Eocene Thermal Maximum (PETM). Mean annual temperatures were around 25 °C (77 °F) and temperature variations were minimal during this time.

At the Fossil Butte National Monument, the Wasatch Formation preserved ichnofossils attributed to arthropods and described as Lunulichnus tuberosus. Trace fossils are common within the upper part of the Main Body Member. These traces occur in three distinct alluvial depositional settings: flood basin/alluvial plain, crevasse splay, and fluvial channel. Flood basin deposits (dominated by alluvial paleosols with pronounced color variegation) are characterized by common Planolites, rare Skolithos and small, meniscate plug-shaped burrows, possibly Celliforma.

Crevasse splay deposits (current-rippled to planar laminated, fine-grained sandstone to siltstone) are characterized by a mixed assemblage of vertical (Arenicolites, Skolithos, unwalled sinuous shafts, shafts with discoidal lenses of sediment), sub-vertical (Camborygma and Thalassinoides) and horizontal (Scoyenia, Rusophycus, Taenidium, Planolites and Palaeophycus) burrows. Large, vertically oriented burrows (Camborygma, cf. Ophiomorpha, Spongeliomorpha and Thalassinoides) are the dominant forms within fluvial channel deposits.

Fossil content

Among the following fossils have been found in the formation:

Mammals

Primates

Artiodactyls

Perissodactyls

Hyaenodonta

Acreodi

Carnivora

Cimolesta

Dinocerata

Erinaceomorpha

  • Adunator meizon

Eutheria

Ferae

Glires

Insectivora

Leptictida

  • Palaeictops cf. bicuspis
  • Prodiacodon cf. concordiarcensis
  • Prodiacodon cf. furor
  • Prodiacodon cf. tauricinerei

Lipotyphla

  • Cedrocherus aceratus
  • Eoictops novaceki
  • Entomolestes sp.
  • Adapisoricinae indet.

Macroscelidea

  • Aletodon cf. quadravus
  • Apheliscus nitidus
  • Apheliscus cf. insidiosus
  • Dorraletes diminutivus
  • Haplomylus speirianus
  • Haplomylus cf. scottianus
  • Litocherus lacunatus
  • Scenopagus priscus
  • Scenopagus sp.

Multituberculata

Pantodonta

Pholidota

  • Palaeanodon sp.

Placentalia

Soricomorpha

  • Leptacodon cf. munusculum
  • Nyctitherium serotinum
  • Leptacodon sp.
  • Wyonycteris sp.

Taeniodonta

Theriiformes

Birds

Reptiles

Amphibians

Bony fish

Cartilaginous fish

  • Washakiebatis kirklandi

Invertebrates

Bivalves

  • Asimina vesperalis
  • Davidia antiqua
  • Unio wasatchensis

Gastropods

Mollusks

Flora

Ichnofossils

Herbivore expansion

The mammal fauna of the formation is part of the fourth phase of herbivore expansion spanning about 115 Ma from the Aptian to Holocene, and correlated with the Wind River and Wilcox Formations of the United States and the Laguna del Hunco Formation of Argentina.

Economic geology

Petroleum geology

The Wasatch Formation is a tight gas reservoir rock in the Greater Natural Buttes Field in the Uinta Basin of Utah and Colorado. The formation is characterized by porosity ranging from 6 to 20% and permeability of up to 1 mD. Based on 409 samples from the Wasatch Formation, average porosity is 8.75 percent and average permeability is 0.095 mD. The production rates after 2 years are 100–1,000 mscf/day for gas, 0.35–3.4 barrel per day for oil, and less than 1 barrel per day for water. The water:gas ratio ranges from 0.1 to 10 barrels per million standard cubic feet, indicating that free water is produced along with water dissolved in gas in the reservoir. Oil in the Bluebell-Altamont Field in the Uinta Basin and gas in the Piceance Creek Field in the Piceance Basin are produced from the Wasatch Formation.

As of May 2019, tight gas from the Wasatch Formation and underlying Mesaverde Group has been produced more than 1.76 trillion cubic feet (TCF) of gas from over 3,000 wells in the Uinta Basin, mostly from the Natural Buttes gas field in the eastern part of the basin. In the Piceance Basin, the Mesaverde Group and Wasatch Formation produced more than 7.7 TCF from over 12,000 wells, mostly from the central part of the basin.

Mining

Coal

Coal is mined from the Wasatch Formation in Wyoming. Together with the Fort Union Formation, the Wasatch Formation represents the thickest coal bed deposits in the state.

Uranium

The fluvial sandstones contain uranium roll front deposits. The formation is the main producer of uranium in the state. Ore zones contain uraninite and pyrite. Oxidized ores include uranophane, meta-autunite, and phosphuranylite.

Wasatchian correlations

Wasatchian correlations in North America
FormationWasatchDeBequeClaronIndian MeadowsPass PeakTatmanWillwoodGolden ValleyColdwaterAllenbyKamloopsOotsa LakeMargaretNanjemoyHatchetigbeeTetas de CabraHannold HillCoalmontCucharaGalisteoSan JoseYpresian (IUCS) • Itaboraian (SALMA) Bumbanian (ALMA) • Mangaorapan (NZ)
BasinPowder River Uinta Piceance Colorado Plateau Wind River Green River BighornPiceanceColorado PlateauWind RiverGreen RiverBighornWillistonOkanaganPrincetonBuck CreekNechakoSverdrupPotomacGoMLaguna SaladaRio GrandeNorth ParkRatonGalisteoSan JuanColdwater BedsMargaret FormationKamloops GroupGalisteo FormationTatman FormationWillwood FormationGolden Valley FormationNanjemoy FormationLas Tetas de Cabra FormationCoalmont FormationAllenby FormationDeBeque FormationClaron FormationIndian Meadows FormationPass Peak FormationHatchetigbee Bluff FormationHannold Hill FormationCuchara FormationSan Jose FormationOotsa Lake GroupWasatch FormationWasatch Formation (North America)
CountryUnited StatesCanadaUnited StatesMexicoUnited States
Copelemur
Coryphodon
Diacodexis
Homogalax
Oxyaena
Paramys
Primates
Birds
Reptiles
Fish
Insects
Flora
EnvironmentsAlluvial-fluvio-lacustrineFluvialFluvialFluvio-lacustrineFluvialLacustrineFluvio-lacustrineDeltaic-paludalShallow marineFluvialShallow marineFluvialFluvialWasatchian volcanoclastics Wasatchian fauna Wasatchian flora
VolcanicYesNoYesNoYesNoYesNoYesNo

See also

Bibliography

Wasatch publications

Geology publications

  • Drake II, Ronald M.; Schenk, Christopher J.; Mercier, Tracey J.; Le, Phuong A.; Finn, Thomas M.; Johnson, Ronald C.; Woodall, Cheryl A.; Gaswirth, Stephanie B.; Marra, Janet K. Pitman, Heidi M. Leathers-Miller, Seth S. Haines, and Marilyn E. Tennyson, Kristen R. (2019), , USGS Fact Sheet, 3027: 1–2{{citation}}: CS1 maint: multiple names: authors list (link)
  • Anderson, Ian; Malone, David; Craddock, John (2017), , Geological Society of America Annual Meeting, p. 1
  • Nelson, Philip H.; Hoffman, Eric L. (2009), "Gas, Water, and Oil Production from the Wasatch Formation, Greater Natural Buttes Field, Uinta Basin, Utah", USGS Open File Report, 1049: 1–19
  • Shroba, Ralph R.; Scott, Robert B. (2001), , USGS Miscellaneous Field Studies Map, MF-2331: 1–31
  • Carrara, Paul E (2000), , USGS Miscellaneous Field Studies Map, MF-2326: 1–14
  • Constenius, Kurt (1996), , Geological Society of America Bulletin, 108 (1): 20–39, Bibcode:, doi:
  • Lorenz, John; Nadon, Greg; LaFreniere, Lorraine (1996), "Geology of the Molina Member of the Wasatch Formation, Piceance Basin, Colorado", Sandia Report, UC-132: 1–30
  • Roehler, H. W (1991), , United States Geological Survey Professional Paper, 1506-B: B1–B38
  • Whipkey, C.H.; Cavaroc, V.V.; Flores, R.M. (1991), "Uplift of the Bighorn Mountains, Wyoming and Montana A Sandstone Provenance Study", United States Geological Survey Bulletin, 1917-D: D1–D21
  • Pocknall, David T (1987), , PALAIOS, 2 (4): 368–376, Bibcode:, doi:, JSTOR
  • Sanborn, Albert F (1981), Potential petroleum resources of northeastern Utah and northwestern Colorado, Western Slope (Western Colorado), Epis, R. C.; Callender, J. F.; (eds.), New Mexico Geological Society 32nd Annual Fall Field Conference Guidebook, pp. 255–266
  • Langden, Raymond E (1973), "Geology and geochemistry of the Highland uranium deposit", Wyoming Geological Association Earth Science Bulletin, December: 41–48
  • Heinrich, E. Wm (1958), Mineralogy and Geology of Radioactive Raw Materials, McGraw-Hill Book Company, Inc., pp. 420–426
  • Darton, N.H (1921), Geologic structure of parts of New Mexico, USGS, pp. 173–275

Maps

State maps

  • Tweto, Ogden (1979), , USGS, p. 1
  • Love, J.D.; Christiansen, A.C. (1985), , USGS, p. 1

Quadrangle maps

  • Carrara, Paul E (2000), , USGS Miscellaneous Field Studies Map, MF-2326: 1
  • Shroba, Ralph R.; Scott, Robert B. (2001), , USGS Miscellaneous Field Studies Map, MF-2331: 1
  • Dover, J.H (1995), , USGS Miscellaneous Investigations Series Map, I-2210: 1
  • Bryant, Bruce; Nichols, D.J. (1990), , USGS Miscellaneous Investigations Series Map, I-1944: 1

Other maps

  • Molnia, Carol L (2013), , USGS Scientific Investigations Map, 3240: 1
  • Heffern, Edward L.; Coates, D.A.; Whiteman, Jason; Ellis, M.S. (1993), , USGS Coal Map, 142: 1

Paleontology publications

  • Divay, J. D.; Murray, A. M. (2016), "An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A", Journal of Vertebrate Paleontology, 36 (5) e1196211, Bibcode:, doi:, S2CID
  • Gunnell, G. F.; Zonneveld, J.-P.; Bartels, W. S. (2016), , Journal of Paleontology, 90 (5): 981–1011, Bibcode:, doi:, S2CID
  • Strait, S. G.; Holroyd, P. A.; Denvir, C. A.; Rankin, B. D. (2016), "Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming", PaleoBios, 33: 1–28, doi:
  • Holroyd, P. A.; Rankin, B. D. (2014), "Additions to the latest Paleocene Buckman Hollow local fauna, Chappo Member of the Wasatch Formation, Lincoln County, southwestern Wyoming", Palaeontologia Electronica, 16: 26
  • Rankin, Brian D.; Holroyd, Patricia A. (2014), "Aceroryctes dulcis, a new palaeoryctid (Mammalia, Eutheria) from the early Eocene of the Wasatch Formation of southwestern Wyoming, USA", Canadian Journal of Earth Sciences, 51 (10): 919–926, Bibcode:, doi:
  • Stidham, Thomas A (2014), "A new species of Limnofregata (Pelecaniformes: Fregatidae) from the Early Eocene Wasatch Formation of Wyoming: implications for palaeoecology and palaeobiology", Palaeontology, 58 (2): 1–11, doi:
  • Stucky, Richard K.; Covert, Herbert H. (2014), "A new genus and species of early Eocene (Ypresian) Artiodactyla (Mammalia), Gagadon minimonstrum, from Bitter Creek, Wyoming, U.S.A.", Journal of Vertebrate Paleontology, 34 (3): 731–736, Bibcode:, doi:, S2CID
  • Hutchison, J. H (2013), New turtles from the Paleogene of North America. In D. B. Brinkman, P. A. Holroyd, J. D. Gardner (eds.), Morphology and Evolution of Turtles, pp. 477–497
  • Smith, K. T.; Gauthier, J. A. (2013), "Early Eocene lizards of the Wasatch Formation near Bitter Creek, Wyoming: diversity and paleoenvironment during an interval of global warming", Bulletin of the Peabody Museum of Natural History, 54 (2): 135–230, Bibcode:, doi:, S2CID
  • Anemone, Robert L.; Dawson, M. R.; Beard, K. C. (2012), "The early Eocene rodent Tuscahomys (Cylindrodontidae) from the Great Divide Basin, Wyoming: Phylogeny, biogeography, and paleoecology", Annals of Carnegie Museum, 80: 187–205
  • Anemone, Robert L.; Dirks, Wendy (2009), , Geologica Acta, 7: 113–124
  • Holroyd, P. A.; Strait, S. G. (2008), New data onLoveina(Primates: Omomyidae) from the early Eocene Wasatch Formation and implications for washakiin relationships, J. G. Fleagle, C. C. Gilbert (eds.), Elwyn Simons: A Search for Origins, pp. 243–257
  • Secord, R (2008), "The Tiffanian Land-Mammal Age (middle and late Paleocene) in the northern Bighorn Basin, Wyoming", University of Michigan Papers on Paleontology, 35: 1–192
  • Labandeira, C (2006), , Geologica Acta, 4: 409–438
  • Wilf, P.; Labandeira, C. C.; Johnson, K. R.; Ellis, B. (2006), "Decoupled plant and insect diversity after the end-Cretaceous extinction", Science, 313 (5790): 1112–1115, Bibcode:, doi:, PMID , S2CID
  • Zonneveld, John-Paul; Lavigne, Jason M.; Bartels, William S.; Gunnell, Gregg F. (2006), , Ichnos, 13 (2): 87–94, Bibcode:, doi:, S2CID
  • Scott, C. S.; Fox, R. C. (2005), "Windows on the evolution of Picrodus (Plesiadapiformes: Primates): morphology and relationships of a species complex from the Paleocene of Alberta", Journal of Paleontology, 79 (4): 635–657, doi:
  • Morlo, M.; Gunnell, G. F. (2003), "Small Limnocyonines (Hyaenodontidae, Mammalia) From the Bridgerian Middle Eocene of Wyoming: Thinocyon, Prolimnocyon, And Iridodon, New Genus", Contributions from the Museum of Paleontology, University of Michigan, 31: 43–78
  • Smith, K. T.; Holroyd, P. A. (2003), "Rare taxa, biostratigraphy, and the Wasatchian-Bridgerian boundary in North America", Geological Society of America Special Paper, 369: 501–511
  • Alroy, J (2002), Synonymies and reidentifications of North American fossil mammals
  • Froehlich, D. J (2002), "Quo vadis Eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla)", Zoological Journal of the Linnean Society, 134 (2): 141–256, doi:
  • Gunnell, G. F (2002), "Notharctine primates (Adapiformes) from the early to middle Eocene (Wasatchian-Bridgerian) of Wyoming: transitional species and the origins of Notharctus and Smilodectes", Journal of Human Evolution, 43 (3): 353–380, Bibcode:, doi:, PMID
  • Manchester, S. R (2002), "Leaves and fruits of Davidia (Cornales) from the Paleocene of North America", Systematic Botany, 27: 368–382
  • Muldoon, K. M.; Gunnell, G. F. (2002), "Omomyid primates (Tarsiiformes) from the Early Middle Eocene at South Pass, Greater Green River Basin, Wyoming", Journal of Human Evolution, 43 (4): 479–511, doi:, PMID
  • Scott, C. S.; Fox, R. C.; Youzwyshyn, G. P. (2002), "New earliest Tiffanian (late Paleocene) mammals from Cochrane 2, southwestern Alberta, Canada", Acta Palaeontologica Polonica, 47: 691–704
  • Foster, J. R (2001), "Salamander tracks (Ambystomichnus?) from the Cathedral Bluffs Tongue of the Wasatch Formation (Eocene), northeastern Green River Basin, Wyoming", Journal of Paleontology, 75 (4): 901–904, Bibcode:, doi:, S2CID
  • Gunnell, G. F.; Bartels, W. S. (2001), Basin margins, biodiversity, evolutionary innovation, and the origin of new taxa, Eocene biodiversity: unusual occurrences and rarely sampled habitats (G. F. Gunnell, ed.), pp. 403–432
  • Wilf, P (2000), "Late Paleocene-early Eocene climate changes in southwestern Wyoming: Paleobotanical analysis", Geological Society of America Bulletin, 112 (2): 292–307, Bibcode:, doi:
  • Zonneveld, J.-P.; Gunnell, G. F.; Bartels, W. S. (2000), "Early Eocene fossil vertebrates from the southwestern Green River Basin, Lincoln and Uinta counties, Wyoming", Journal of Vertebrate Paleontology, 20 (2): 369–386, doi:
  • Manchester, S. R.; Crane, P. R.; Golovneva, L. B. (1999), "An extinct genus with affinities to the extant Davida and Camptotheca (Cornales) from the Paleoecene of North America and Eastern Asia", International Journal of Plant Sciences, 160: 188–207, doi:, S2CID
  • Gunnell, G. F (1998), "Mammalian Fauna From the Lower Bridger Formation (Bridger A, Early Middle Eocene) of the Southern Green River Basin, Wyoming", Contributions from the Museum of Paleontology, University of Michigan, 30: 83–130
  • Lucas, S. G (1998), Fossil mammals and the Paleocene/Eocene series boundary in Europe, North America, and Asia, M.-P. Aubry, S. G. Lucas and W. A. Berggren (eds.), Late Paleocene–Early Eocene Biotic and Climatic Events in the Marine and Terrestrial Records, pp. 451–500
  • Clyde, W. C.; Zonneveld, J.-P.; Stamatakos, J.; Gunnell, G. F.; Bartels, W. S. (1997), "Magnetostratigraphy across the Wasatchian-Bridgerian boundary (early to middle Eocene) in the western Green River Basin, Wyoming", Journal of Geology, 105: 657–669, doi:, S2CID
  • Polly, P. D (1996), "The skeleton of Gazinocyon vulpeculus gen. et. comb nov. and the cladistic relationships of Hyaenodontidae (Eutheria, Mammalia)", Journal of Vertebrate Paleontology, 16 (2): 303–319, Bibcode:, doi:
  • Rose, K. D.; Bown, T. M. (1996), "A new plesiadapiform (Mammalia: Plesiadapiformes) from the early Eocene of the Bighorn Basin, Wyoming", Annals of Carnegie Museum, 65 (3): 305–321, Bibcode:, doi:
  • Gunnell, G. F (1994), "Paleocene mammals and faunal analysis of the Chappo Type Locality (Tiffanian), Green River Basin, Wyoming", Journal of Vertebrate Paleontology, 14 (1): 81–104, Bibcode:, doi:
  • Covert, H. H.; Hamrick, M. W. (1993), "Description of new skeletal remains of the early Eocene anaptomorphine primate Absarokius (Omomyidae) and a discussion about its adaptive profile", Journal of Human Evolution, 25 (5): 351–362, Bibcode:, doi:
  • Williamson, T. E.; Lucas, S. G. (1992), "Meniscotherium (Mammalia, Condylarthra) from the Paleocene-Eocene of Western North America)", New Mexico Museum of Natural History & Science Bulletin, 1: 1–75
  • Hamrick, M. W.; Covert, H. H. (1991), "A late Wasatchian mammalian fauna from the Washakie Basin, Wyoming", Journal of Vertebrate Paleontology, 11: 33A
  • Hutchison, J. H (1991), "Early Kinosterninae (Reptilia: Testudines) and their phylogenetic significance", Journal of Vertebrate Paleontology, 11 (2): 145–167, Bibcode:, doi:
  • Stucky, R. K.; Krishtalka, L. (1990), "Revision of the Wind River Faunas, Early Eocene of Central Wyoming. Part 10. Bunophorus (Mammalia, Artiodactyla)", Annals of Carnegie Museum, 59 (2): 149–171, Bibcode:, doi:
  • Thewissen, J. G. M. (1990), "Evolution of Paleocene and Eocene Phenacodontidae (Mammalia, Condylarthra)", University of Michigan Papers on Paleontology, 29: 1–107
  • Gunnell, G. F (1989), "Evolutionary History of Microsyopoidea (Mammalia, ?Primates) and the Relationship Between Plesiadapiformes and Primates", University of Michigan Papers on Paleontology, 27: 1–157
  • Beard, K. C (1988), "New notharctine primate fossils from the early Eocene of New Mexico and southern Wyoming and the phylogeny of Notharctinae", American Journal of Physical Anthropology, 75 (4): 439–469, Bibcode:, doi:
  • Honey, J. G (1988), "Geology and paleoecology of the Cottonwood Creek delta in the Eocene Tipton Tongue of the Green River Formation and a mammalian fauna from the Eocene Cathedral Bluffs Tongue of the Wasatch Formation, Southeast Washakie Basin, Wyoming", United States Geological Survey Bulletin, 1669-C
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