Earth:Duchesne River Formation
| Duchesne River Formation Stratigraphic range: Middle Eocene Template:Period fossil range | |
|---|---|
 Duchesne River Formation outcrop near Roosevelt, Utah | |
| Type | Formation |
| Sub-units | Brennan Basin Member, Dry Gulch Creek Member, Lapoint Member, Starr Flat Member |
| Underlies | Bishop Conglomerate |
| Overlies | Uinta Formation |
| Area | Duchesne and Uinta Counties, northeastern Utah |
| Lithology | |
| Primary | sandstone, mudstone, conglomerate |
| Other | siltstone, tuff |
| Location | |
| Region | Utah |
| Country | United States |
| Type section | |
| Named for | Duchesne River |
The Duchesne River Formation is a Middle Eocene geologic formation in the Uinta Basin of northeastern Utah. It was originally named the Duchesne Formation by Carnegie Museum paleontologist O.A. Peterson,[1] and modified to the Duchesne River Formation by Carnegie Museum paleontologist J.L. Kay,[2] because the term Duschesne Formation was already in use for a Jurassic limestone. Peterson did not provide a type section when naming the formation, only noting that it is named for the Duchesne River, which flows roughly southeast and east to join the Green River.
The formation consists of over 3000 feet (915 m) of fluvial (river-carried) conglomerate, sandstone and fine-grained sedimentary rocks. It is subdivided into four members (below), whose sediments are thought to have eroded from the rising Uinta Mountains to the north and deposited in rivers, floodplains and small lakes.[3][4][5][6][7]
Age
Volcanic ash beds in the formation, sourced derived from volcanoes in the Wasatch Range, East Tintic, and Oquirrh Mountains to the west, have provided radiometric dates for the formation. Dates collected in 1990 range from 38.2 +/-1.8 Ma for the Brennan Basin Member to 28.7 +/-2.0 Ma for the Lapoint Member.[8] These estimate turned out to be too young according to follow-up studies.
A 1992 survey dated an ash bed at the base of the Lapoint Member to 39.74 ± 0.07 Ma,[9][10] and a 2012 study recalibrated this dating to 40.26 ± 0.08 Ma.[11] Another recent (2020) dating of ash beds results in an age of 39.47 ± 0.16 Ma in the upper Dry Gulch member and 39.36 ± 0.15 Ma in the lower Lapoint Member.[12]
Members
The following members were defined by Andersen and Picard (1972):[3] Prior to this more formal usage, Kay (1934) used a three-fold division at his fossil quarry: the Randlett, Halfway, and Lapoint horizons.[2] The Randlett horizon is equivalent to most of the Brennan Basin Member, the Halfway horizon is equivalent to the uppermost Brennan Basin and entire Dry Gulch members, and the Lapoint horizon is equivalent to the Lapoint and Starr Flat member.[11]
Brennan Basin Member
Named for the Brennan Basin in Uintah County. Predominately sandstone that varies from yellow-gray to red brown, very fine, fine, medium, to coarse grained, thin to thick to very thick bedded, generally poorly sorted, and may be nodular, silty, pebbly, and cross stratified. Minor beds of green-gray to red brown, silty to sandy, thin to very thin bedded, poorly sorted claystone, red brown, thin-bedded, nodular, poorly sorted mudstone, yellow brown, very thin bedded, nodular, poorly sorted, horizontally stratified siltstone, and red-purple, sandy, clayey, thin-bedded, medium to coarse crystalline limestone. Contains a diverse late Eocene vertebrate fauna.[3]
Dry Gulch Creek Member
Named for Dry Gulch Creek in Uintah County. Consists of pale red, olive gray to yellow brown, coarse, medium, fine to very fine grained, thin-, thick to very thick bedded, massive, moderately to poorly sorted sandstone that may be horizontally or cross stratified and red, gray to brown, very thin, thin- to thick-bedded, moderately to poorly sorted claystone that may be nodular, micaceous, or laminated. Contains plant remains and a sparse vertebrate fauna.
Lapoint Member
Named for the town of Lapoint in Uintah County. Composed of olive, green-gray, dark gray, very thin to thin bedded, nodular, poorly sorted, horizontally stratified, laminated claystone; light gray, light brown, gray orange to red brown, thin-bedded, slabby, horizontally stratified, poorly sorted, medium-grained, to thick-bedded, blocky, poorly sorted, coarse-grained sandstone; gray-red to red-brown, thin-bedded, nodular, horizontally stratified, poorly sorted siltstone; and gray-orange, very thick bedded, massive, poorly sorted pebble conglomerate. Abundant late Eocene vertebrates.
Starr Flat
Named for John Starr Flat in Duchesne County. Consists of: 1) red- to yellow-brown, light gray, gray- to yellow-orange, pale red to gray red sandstone that ranges from coarse, medium, fine to very fine grained, thin, thick to very thick bedded, sandy, silty, to clayey, cross-stratified to horizontally stratified, flaggy, blocky, massive, brown-gray, gray-red to olive, sandy to silty; 2) very thin bedded, poorly sorted, platy, laminated, nodular to massive claystone; and 3) gray red, sandy, poorly sorted, thin-bedded, nodular, massive siltstone. Sandstone may also be poorly sorted, pebbly, nodular and massive. No fossils found expect for indeterminate artiodactyl fragments.[11]
Paleobiota
The Randlett fauna (lower Brennan Basin Member) can safely be assigned to the Uintan 3 North American Land Mammal Age (NALMA). On the geomagnetic polarity time scale, it corresponds to the upper part of chron C19r or lower part of chron C19n.[11]
The Halfway and Lapoint faunas (uppermost Brennan Basin, Dry Gulch Creek, and Lapoint members) belong to the Duchesnean NALMA, which is named after the Duchesne River Formation. They both correspond to the upper part of chron C18r.[11]
Mammalia
Artiodactyla
An indeterminate oromerycid is known from the Brennan Basin Member.[13] Reports of Helohyus teeth are probably misidentifications.[14][15]
| Artiodactyls of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Agriochoerus | A. maximus | Lapoint Member[16][13] | An agriochoerid (semi-arboreal oreodont relative) | 
|
| Brachyhyops | B. wyomingensis | Lapoint Member[13] | An entelodont (boar-like hippo relative) | |
| Diplobunops | D. crassus | Brennan Basin Member[13] | An agriochoerid (semi-arboreal oreodont relative) | 
|
| Hypertragulidae | sp. | "Randlett"[17] | An indeterminate hypertragulid | |
| Leptotragulus | L. proavus | Brennan Basin Member[13] | A protoceratid | |
| Pentacemylus | P. progressus | Brennan Basin Member[13] | A homacodontid | |
| Poabromylus | P. kayi | Dry Gulch Creek Member,[11]
Lapoint Member[13] |
A protoceratid | |
| Protoreodon | P. primus | Brennan Basin Member[13] | An agriochoerid (semi-arboreal oreodont relative) | .jpg)
|
| P. pumilus | Brennan Basin Member[13] | |||
| P. sp. cf. P. pumilus | Lapoint Member[13] | |||
| Simimeryx | S. minutus | Lapoint Member[13] | An early ruminant, possibly a hypertragulid | |
Carnivoramorphs
A large indeterminate carnivoran, possibly a miacid or amphicyonid, is known from the Lapoint Member.[16][13]
| Carnivoramorphs of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Eosictis[14] | E. avinoffi | Dry Gulch Creek Member or Lapoint Member[11] | An indeterminate carnivoran | |
| Hyaenodon | H. sp. cf. H. vetus | Lapoint Member[13] | A hyaenodontine hyaenodont | 
|
| Pleurocyon? or Uintacyon? | sp. | "Randlett"[14][17] | An indeterminate carnivoran | |
| Simidectes | S. sp. cf. S. magnus | Brennan Basin Member[13] | An early carnivoramorph | |
Eulipotyphla
Another indeterminate eulipotyphlan species is known from the Dry Gulch Creek Member.[11]
| Eulipotyphlans of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Centetodon | C. sp. | Lapoint Member[13] | A geolabidid. Previously identified as Protictops alticuspidens.[16] | |
Lagomorpha
| Lagomorphs of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Mytonolagus | M. sp. | Brennan Basin Member,[13]
Dry Gulch Creek Member[11] |
An early leporid (rabbit) | |
Mesonychia
| Mesonychians of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Hessolestes | H. ultimus | Lapoint Member[13] | A mesonychid | |
Metatheria
| Metatherians of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Copedelphys | C. sp. | Dry Gulch Creek Member[11] | A herpetotheriid | |
Perissodactyla
| Perissodactyls of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Colodon | C. sp. | Lapoint Member[13] | A helaletid (tapir relative) | 
|
| Dilophodon | D. leotanus | Brennan Basin Member[13] | A helaletid (tapir relative). Sometimes considered a species of Heteraletes.[14] | |
| cf. Diplacodon | cf. D. elatus | Brennan Basin Member[18] | A brontothere | 
|
| Duchesneodus | D. uintensis | Brennan Basin Member,[11] | A brontothere, previously identified as "Teleodus" or Protitanotherium.[14][11] | 
|
| Epihippus (Duchesnehippus) | E. (D.) intermedius | Dry Gulch Creek Member,[11]
Lapoint Member[13] |
An early equid (horse) | |
| Epitriplopus | E. medius | Brennan Basin Member[13] | A hyracodontid ("running rhino") | |
| Hyracodon | H. medius | Lapoint Member[13] | A hyracodontid ("running rhino") | 
|
| H. primus | Lapoint Member[16] | |||
| Megalamynodon | M. regalis | Brennan Basin Member[13] | An amynodontid (hippo-like rhino) | |
| "Mesamynodon" | "M." medius | Brennan Basin Member | A hyracodontid ("running rhino"), possibly synonymous with Epitriplopus medius.[19] | |
| Uintaceras | U. sp. | Brennan Basin Member[13] | A rhinocerotoid (rhino relative) | 
|
Rodentia
An indeterminate sciuravid or myomorph is known from the Brennan Basin Member, and an indeterminate myomorph is known from the Dry Gulch Creek Member.[11]
| Rodents of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| Adjidaumo | A. sp. cf. A. craigi | Dry Gulch Creek Member[11] | An eomyid | |
| Eutypomys | E. sp. | Dry Gulch Creek Member[11] | A eutypomyid | |
| Griphomys | G. sp. | Dry Gulch Creek Member[11] | An indeterminate rodent. | |
| Heliscomys | H. sp. | Dry Gulch Creek Member[11] | A heliscomyid | |
| Metanoiamys | M. lacus | Dry Gulch Creek Member[11] | An eomyid | |
| M. sp. cf. M. korthi | Dry Gulch Creek Member[11] | |||
| Microeutypomys | M. sp. | Dry Gulch Creek Member[11] | A eutypomyid | |
| Mytonomys | M. robustus | Brennan Basin Member[13] | An ailuravine ischyromyid. Leptotomus kayi is a synonym of this species. | |
| Pareumys | P. guensbergi | Dry Gulch Creek Member,[11]
Lapoint Member[13] |
A cylindrodontid | |
| P. sp. aff. P. milleri | Brennan Basin Member[13] | |||
| Paradjidaumo | P. sp. | Dry Gulch Creek Member[11] | An eomyid | |
| Passaliscomys | P. sp. | Dry Gulch Creek Member[11] | A heliscomyid | |
| Protadjidaumo | P. sp. cf. P. typus | Dry Gulch Creek Member[11] | An eomyid | |
| P. typus | Dry Gulch Creek Member,[11]
Lapoint Member[13] |
|||
| Simiacritomys | S. sp. | Dry Gulch Creek Member[11] | An eomyid | |
Reptilia
| Reptiles of the Duchesne River Formation | ||||
|---|---|---|---|---|
| Genus / Taxon | Species | Member | Notes | Images |
| "Crocodylus" | "C." acer | Brennan Basin Member | A crocodyloid | 
|
| Cymatholcus | C. longus | "Halfway"[17] | A tortoise | |
See also
- List of fossiliferous stratigraphic units in Utah
- Paleontology in Utah
References
- ↑ Peterson, O.A., 1932, New species from the Oligocene of the Uinta [Utah]: Carnegie Museum Annals, v. 21, no. 2, p. 61-78.
- ↑ 2.0 2.1 Kay, J.L., 1934, The Tertiary formations of the Uinta basin, Utah: Carnegie Museum Annals, v. 23, p. 357-372.
- ↑ 3.0 3.1 3.2 Andersen, D.W., and Picard, M.D., 1972, Stratigraphy of the Duchesne River Formation (Eocene-Oligocene?), northern Uinta basin, northeastern Utah: Utah Geological and Mineral Survey Bulletin, no. 97, 29 p.
- ↑ Sato, Takashi; Chan, Marjorie A. (2015-12-01). "Fluvial Facies Architecture and Sequence Stratigraphy of the Tertiary Duchesne River Formation, Uinta Basin, Utah, U.S.A.". Journal of Sedimentary Research 85 (12): 1438–1454. doi:10.2110/jsr.2015.90. ISSN 1527-1404. https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/85/12/1438/145445/Fluvial-Facies-Architecture-and-Sequence.
- ↑ Murphey, Paul; Townsend, K.E.; Friscia, Anthony; Westgate, James; Evanoff, Emmett; Gunnell, Gregg (2017-02-17). "Paleontology and stratigraphy of Middle Eocene rock units in the southern Green River and Uinta Basins, Wyoming and Utah". Geology of the Intermountain West 4: 1–53. doi:10.31711/giw.v4.pp1-53. ISSN 2380-7601. https://giw.utahgeology.org/giw/index.php/GIW/article/view/14.
- ↑ Sato, Takashi; Chan, Marjorie; Ekdale, Allan (2018-09-18). "Trace fossils and fluvial-lacustrine ichnofacies of the Eocene Uinta and Duchesne River Formations, northern Uinta Basin, Utah". Geology of the Intermountain West 5: 209–226. doi:10.31711/giw.v5.pp209-226. ISSN 2380-7601. https://giw.utahgeology.org/giw/index.php/GIW/article/view/31.
- ↑ Webb, Casey; Jensen, Michael; Kowallis, Bart; Christiansen, Eric; Sprinkel, Douglas; Hudson, Sam (2022-09-14). "Stratigraphic relationships of the Eocene Duchesne River Formation and Oligocene Bishop Conglomerate, northeastern Utah—pulsed sedimentary response to rollback of the subducted Farallon slab". Geology of the Intermountain West 9: 153–179. doi:10.31711/giw.v9.pp153-179. ISSN 2380-7601. https://giw.utahgeology.org/giw/index.php/GIW/article/view/119.
- ↑ Bryant, Bruce, Naeser, C.W., Marvin, R.F., and Mehnert, H.H., 1990, Upper Cretaceous and Paleogene sedimentary rocks and isotopic ages of Paleogene tuffs, Uinta basin, Utah, IN Evolution of sedimentary basins; Uinta and Piceance basins: U.S. Geological Survey Bulletin, 1787-J, p. J1-J22.
- ↑ Prothero, Donald R.; Swisher III, Carl C. (1992), "2. Magnetostratigraphy and Geochronology of the Terrestrial Eocene-Oligocene Transition in North America", Eocene-Oligocene Climatic and Biotic Evolution (Princeton University Press): pp. 46–73, doi:10.1515/9781400862924.46, ISBN 978-1-4008-6292-4, https://doi.org/10.1515/9781400862924.46, retrieved 2026-08-29
- ↑ Robinson, Peter; Gunnell, Gregg F.; Walsh, Stephen L.; Clyde, William C.; Storer, John E.; Stucky, Richard K.; Froehlich, David J.; Ferrusquia-Villafranca, Ismael et al. (2004), Woodburne, Michael O., ed., "4. Wasatchian Through Duchesnean Biochronology", Late Cretaceous and Cenozoic Mammals of North America (Columbia University Press): pp. 106–155, doi:10.7312/wood13040-006, ISBN 978-0-231-13040-0, https://www.degruyter.com/document/doi/10.7312/wood13040-006/html, retrieved 2026-08-29
- ↑ 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19 11.20 11.21 11.22 11.23 11.24 11.25 11.26 11.27 Kelly, T.S.; Murphey, P.C.; Walsh, S.L. (2012). "New records of small mammals from the middle Eocene Duchesne River Formation, Utah, and their implications for the Uintan–Duchesnean North American Land Mammal Age transition." Paludicola 8: 208–251.
- ↑ Jensen, Michael; Kowallis, Bart; Christiansen, Eric; Webb, Casey; Dorais, Michael; Sprinkel, Douglas; Jicha, Brian (2020-03-18). "Fallout tuffs in the Eocene Duchesne River Formation, northeastern Utah—ages, compositions, and likely source". Geology of the Intermountain West 7: 1–27. doi:10.31711/giw.v7.pp1-27. ISSN 2380-7601. https://giw.utahgeology.org/giw/index.php/GIW/article/view/68.
- ↑ 13.00 13.01 13.02 13.03 13.04 13.05 13.06 13.07 13.08 13.09 13.10 13.11 13.12 13.13 13.14 13.15 13.16 13.17 13.18 13.19 13.20 13.21 13.22 13.23 13.24 13.25 13.26 13.27 13.28 Rasmussen, D. Tab; Hamblin, Alden H.; Tabrum, Alan R. (1999). "The Mammals of the Eocene Duchesne River Formation". Vertebrate Paleontology in Utah: Utah Geological Survey Miscellaneous Publications 99-1: 421-427. https://archive.org/details/vertebratepaleon0000unse_y3q5.
- ↑ 14.0 14.1 14.2 14.3 14.4 Scott, William B. (1945). "The Mammalia of the Duchesne River Oligocene". Transactions of the American Philosophical Society (American Philosophical Society) 34 (3): 209–253. doi:10.2307/1005542. ISSN 0065-9746.
- ↑ Gazin, Charles Lewis (1955). "A review of the Upper Eocene Artiodactyla of North America". Smithsonian Miscellaneous Collections 128 (8): 1–96. https://repository.si.edu/bitstream/handle/10088/22913/SMC_128_Gazin_1955_8_1-96.pdf.
- ↑ 16.0 16.1 16.2 16.3 Emry, Robert J. (1981). "Additions to the Mammalian Fauna of the Type Duchesnean, with Comments on the Status of the Duchesnean "Age"". Journal of Paleontology (Paleontological Society) 55 (3): 563–570. ISSN 0022-3360.
- ↑ 17.0 17.1 17.2 Warner, Mont Marcellus (1963). "SEDIMENTATION OF THE DUCHESNE RIVER FORMATION, UINTA BASIN, UTAH". University of Iowa dissertation. https://www.proquest.com/docview/302119010.
- ↑ Burger, B. J.; Tackett II, L. (2014-08-27). "The stratigraphic importance of the brontothere (cf. Diplacodon elatus) in the Brennan Basin Member of the Duchesne River Formation of Utah" (in en). Fossil Record 17 (2): 69–74. doi:10.5194/fr-17-69-2014. ISSN 2193-0074. https://fr.copernicus.org/articles/17/69/2014/.
- ↑ Radinsky, Leonard B. (1967). "A review of the Rhinocerotoid family Hyracodontidae (Perissodactyla)". Bulletin of the American Museum of Natural History 136 (1): 1-45. https://rhinoresourcecenter.com/wp-content/uploads/2011/02/1487346232.pdf.
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