Denver Formation

Denver Formation
Stratigraphic range:
TypeGeological formation
Unit ofD1 Sequence[1]
UnderliesDawson Arkose
OverliesArapahoe Formation
Thicknessup to 1,580 ft (480 m)
Lithology
PrimaryClaystone, siltstone, sandstone
OtherConglomerate, tuff, coal, lava
Location
RegionColorado
CountryUnited States
Type section
Named forDenver, Colorado
Named byEmmons, Cross and Eldridge (1896)[2]

The Denver Formation is a geological formation that is present within the central part of the Denver Basin that underlies the Denver, Colorado, area. It ranges in age from latest Cretaceous (Maastrichtian) to early Paleocene (Danian), and includes sediments that were deposited before, during and after the Cretaceous-Paleogene boundary event.[3][4]

The formation is known for its paleontological resources, including dinosaur remains that are found in the Late Cretaceous part of the formation,[5] and it includes aquifers that are important sources of water for the area.[6][7] Some of North America's most iconic end-Cretaceous dinosaurs, such as Triceratops and Tyrannosaurus, were first identified from the Denver Formation before being properly described from better-preserved remains in end-Cretaceous formations further north.[8] The formation also preserves one of the most world's most diverse earliest Paleocene mammalian faunas, providing an important record of the diversification of mammals in the immediate aftermath of the K-Pg extinction.[9]

Stratigraphy

The Denver Formation rests on the Arapahoe Formation, and its base is marked by the first appearance of tuffaceous sediments. It is overlain by the Dawson Arkose.[4][10]

In 2002 the Denver Formation was included as part of a larger unconformity-bounded unit named the D1 sequence, in order to facilitate basin-wide studies and avoid confusion arising from the lateral and vertical facies changes that occur within the Denver Basin. The base of the D1 is marked by the abrupt facies change at the top of the Laramie Formation, and its top is placed at the base of a regional paleosol series. The Arapahoe Formation and the Dawson Arkose are also included in the D1 Sequence.[1]

Thickness and lithology

The Denver Formation consists of alluvial fan, fluvial, and paludal deposits that accumulated at the foot of the growing Rocky Mountain Front Ranges.[1] It ranges in thickness from 600 feet (180 m) to 1,580 feet (480 m) in the central part of the Denver Basin.[11] It is characterized by significant amounts of andesitic volcanic debris,[2] and is composed of primarily of light-grey to brown, lenticular bedded, loosely cemented silty claystone, mudstone, siltstone, tuffaceous sandstone and, in some areas, andesitic conglomerate.[4][10] Beds of low-rank coal and carbonaceous shale occur in the upper 500 feet (150 m) in some areas.[12]

Several early Paleocene lava flows are present in the upper part of the Denver Formation at North and South Table Mountain near Golden, Colorado. The Ralston Dike, a body of intrusive monzonite located several miles to the northwest, probably represents the volcanic vent from which the flows erupted.[10] Generally referred to as basaltic, they are classified either as monzonite (the lowest flow) and latite (the upper two flows),[10] or as shoshonite.[13] They contain the minerals augite, plagioclase, and olivine altered to serpentine, with accessory sanidine and/or orthoclase, apatite, magnetite, and biotite. One of the flows hosts a wide variety of zeolite minerals, including analcime, thomsonite, mesolite, chabazite, and others.[13]

Age and paleontology

The Denver Formation spans the Cretaceous-Paleogene boundary. The lava flows in the upper part of the formation are about 62 to 64 million years old according to radiometric dating,[10] which places them in the early Paleocene Epoch. The Cretaceous-Paleogene boundary occurs in the lower part of the formation, and an exposure of the boundary layer has been identified and documented on South Table Mountain near the city of Golden.[14]

Plant fossils[15] and remains of vertebrates, including turtles[16] and mammals,[17] are found throughout the Denver Formation.[6] Dinosaur remains are restricted to the lower, Late Cretaceous, part.[5][10][18]

Vertebrate paleofauna

Based on the Paleobiology Database except where noted:[19]

Ray-finned fish

Ray-finned fish reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Lepisosteus L. sp. Danian A gar.

Amphibians

Amphibians reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Opisthotriton O. kayi Danian A batrachosauroidid salamander.
Scapherpetonidae indet. A scapherpetonid salamander.

Reptiles

Squamates

Squamates reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Anguidae indet. Danian An anguid lizard of uncertain affinities.
aff. Contogenys aff. C. sp. A contogeniid lizard.[20]
cf. Odaxosaurus cf. O. piger An anguid lizard.[21]
Palaeoscincosaurus P. middletoni A contogeniid lizard, formerly considered an early skink. Type locality of genus and species.[21][20]

Turtles

Turtles reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Adocus A. sp. Maastrichtian to Danian An adocid.
Basilemys B. sinuosa Maastrichtian A nanhsiungchelyid.
Denverus D. middletoni Danian A stem-snapping turtle. Type locality of genus and species.[22]
Helopanoplia H. distincta Maastrichtian A plastomenid trionychian.
Hoplochelys H. crassa Danian A kinosternoid.
Macrobaenidae indet. Danian A macrobaenid turtle of uncertain affinities.
Palatobaena P. knellerorum Danian A baenid. Type locality of species.[23]
Plastomenus P. joycei Danian Nearly complete skeleton.[24] A plastomenid. Type locality of species.[24]
Tavachelydra T. stevensoni Danian Nearly complete shells, pelvic material, and cranial material[25] A stem-snapping turtle. Type locality of genus and species.[25]
"Trionyx" "T." singularis Danian A softshell turtle.

Crocodylomorphs

Crocodylomorphs reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Allognathosuchus A. sp. Danian An alligatorine.
Borealosuchus B. sternbergii[26] A eusuchian.

Dinosaurs

The Denver Formation's dinosaur fauna appears to share close similarities with those of other Maastrichtian-aged formations in western North America. However, the dinosaur remains in the Denver Formation are significantly more disarticulated and fragmentary, suggesting that the formation's depositional environment was not conducive to the rapid burial that would have preserved articulated dinosaur skeletons.[8]

This formation represents the first known discoveries to science of Triceratops (a partial cranium with horns) and Tyrannosaurus (a tooth), as well as the type locality for another well-known dinosaur, Ornithomimus.[8]

Ornithischians
Ornithischians reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images

Cionodon[27]

C. arctatus[27]

Maastrichtian

"Fragmentary maxilla, vertebrae, fragmentary postcranial elements."[28]

Later found to be indeterminate hadrosaurid remains.[27]

?Edmontonia ?E. sp. Maastrichtian A nodosaurid ankylosaur.

Edmontosaurus[27]

E. sp.[27]

A hadrosaurid.

Pachycephalosaurus[27]

P. sp.[27][8]

A pachycephalosaur.

Polyonax[27]

P. mortuarius[27]

"Horn fragments, vertebrae."[29] (type specimen)

A dubious ceratopsian

Triceratops[27]

T. galeus[27]

"Nasal horn core."[29]

A dubious ceratopsian

T. horridus (=Bison alticornis)[8]

Type locality of the genus and the first known Triceratops specimen, initially identified as a species of bison.[30]
Saurischians
Saurischians of the Denver Formation
Genus Species Location Stratigraphic position Abundance Notes Images

Aublysodon[27]

A. mirandus[27]

Maastrichtian

Later found to be indeterminate tyrannosauroid remains.[27]

Dromaeosauridae indet. Maastrichtian A dromaeosaur of uncertain affinities. Some remains referred to "Dromaeosaurus".[8]

Ornithomimus[27]

O. velox[27][8]

An ornithomimosaur. Type locality of genus and species.

Tyrannosaurus[27]

T. rex[8]

A tyrannosaur. The very first T. rex fossil known was a tooth collected from this formation.[8]

Mammals

Multituberculates

Multituberculates reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Catopsalis C. alexanderi Danian A taeniolabidid.
Cimexomys C. arapahoensis A "Paracimexomys-group" multituberculate.
C. minor
Kimbetohia K. mziae A ptilodontid.
Mesodma M. ambigua A neoplagiaulacid.
M. hensleighi
Xyronomys X. robinsoni A neoplagiaulacid.

Metatherians

Metatherians reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Thylacodon T. montanensis Danian A herpetotheriid.
T. pusillus

Cimolestans

Cimolestans reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Procerberus P. andesiticus Danian A cimolestid.
P. grandis

Placentals

Former "condylarths".

Placentals reported from the Denver Formation
Genus Species Location Stratigraphic position Material Notes Images
Alticonus A. gazini Danian A periptychid paraxonian. Type locality of genus and species.
Auraria A. urbana A periptychid paraxonian. Type locality of genus and species.
Ampliconus A. browni A periptychid paraxonian. Type locality of genus and species.
Baioconodon B. denverensis An arctocyonid paraxonian.
B. nordicus
Conacodon C. delphae A periptychid paraxonian.
C. harbourae
C. matthewi
Desmatoclaenus D. protogonioides An arctocyonid paraxonian.
Ectoconus E. ditrigonus A periptychid paraxonian.
Haploconus H. entoconus A periptychid paraxonian.
Loxolophus L. hyattianus An arctocyonid paraxonian.
Maiorana M. sp. An arctocyonid paraxonian.
Militocodon M. lydae A periptychid paraxonian. Type locality of genus and species.[31]
Miniconus M. archibaldi A periptychid paraxonian.
Mioclaenidae indet. A mioclaenid.
Oxyclaenus O. cuspidatus An arctocyonid paraxonian.
O. subbituminus
Oxyprimus O. galadrielae An arctocyonid paraxonian.
Periptychus P. coarctatus A periptychid paraxonian.
Protungulatum P. donnae A protungulatid euungulate.

See also

References

  1. ^ a b c Raynolds, R.G. 2002. Upper Cretaceous and Tertiary stratigraphy of the Denver Basin, Colorado. Rocky Mountain Geology, vol. 37, no. 2, p. 111-134.
  2. ^ a b Emmons, S.F., Cross, W. and Eldridge, G.H. 1896. Geology of the Denver Basin in Colorado. U.S. Geological Survey, Monograph 27, p. 160.
  3. ^ U.S. Geological Survey. "Geologic Unit: Denver Formation". Retrieved 2014-12-27.
  4. ^ a b c Tweto, O. 1979. Geologic map of Colorado. U.S. Geological Survey, Map G77115.
  5. ^ a b Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 574-588. ISBN 0-520-24209-2.
  6. ^ a b Raynolds, R.G. and Johnson, K.R. 2003. Synopsis of the stratigraphy and paleontology of the uppermost Cretaceous and lower Tertiary strata in the Denver Basin, Colorado. Rocky Mountain Geology, vol. 38, no. 1, p. 171-181.
  7. ^ USGS Aquifer Basics[1]
  8. ^ a b c d e f g h i Carpenter, K. (2002-11-01). "Late Cretaceous dinosaurs from the Denver Basin, Colorado". Rocky Mountain Geology. 37 (2): 237–254. doi:10.2113/gsrocky.37.2.237. ISSN 1555-7332.
  9. ^ Dahlberg, Elisa L.; Eberle, Jaelyn J.; Sertich, Joseph J. W.; Miller, Ian M. (2016). "A new earliest Paleocene (Puercan) mammalian fauna from Colorado's Denver Basin, U.S.A." Rocky Mountain Geology. 51 (1): 1–22. doi:10.2113/gsrocky.51.1.1. ISSN 1555-7332.
  10. ^ a b c d e f Van Horn, R. 1957. Bedrock geology of the Golden Quadrangle, Colorado. U.S. Geological Survey, Map GQ-103.
  11. ^ U.S. Geological Survey Professional Paper 1698, Chapter F
  12. ^ "U.S. Geological Survey Professional Paper 1625-A, Chapter SD" (PDF). Archived from the original (PDF) on 2003-05-05. Retrieved 2014-08-30.
  13. ^ a b Kile D.E., 2004. Zeolites and associated minerals from the Table Mountains near Golden, Jefferson County, Colorado. Rocks and Minerals, vol. 79, no. 4, p. 218-238.
  14. ^ Kauffman, E.G., Upchurch, G.R. Jr., and Nichols, D.J., 2005. The Cretaceous-Tertiary boundary at South Table Mountain near Golden, Colorado. In: Extinction Events in Earth History, Lecture Notes in Earth Sciences, vol. 30, p. 365-392.
  15. ^ Johnson, K.R., Reynolds, M.L., Werth, K.W., and Thomasson, J.R. 2003. Overview of the Late Cretaceous, early Paleocene, and early Eocene megafloras of the Denver Basin, Colorado. Rocky Mountain Geology, vol. 38, no. 1, p. 101-120.
  16. ^ Hutchison, J.H. and Holroyd, P.A. 2003. Late Cretaceous and early Paleocene turtles of the Denver Basin, Colorado. Rocky Mountain Geology, vol. 38, no. 1, p. 121-142.
  17. ^ Eberle, J.J. 2003. Puercan mammalian systematics and biostratigraphy in the Denver Formation, Denver Basin, Colorado. Rocky Mountain Geology, vol. 38, no. 1. p. 143-169.
  18. ^ Carpenter, K. and Young, D.B. 2002. Late Cretaceous dinosaurs from the Denver Basin, Colorado. Rocky Mountain Geology, vol. 37, p. 237-254.
  19. ^ "PBDB". paleobiodb.org. Retrieved 2026-03-19.
  20. ^ a b Nydam, Randall L.; Fitzpatrick, Brandon M. (2009-09-12). "The occurrence ofContogenys-like lizards in the Late Cretaceous and Early Tertiary of the western interior of the U.S.A." Journal of Vertebrate Paleontology. 29 (3): 677–701. doi:10.1671/039.029.0331. ISSN 0272-4634. Archived from the original on 2024-07-16.
  21. ^ a b Sullivan, Robert M.; Lucas, Spencer G. (1996-12-31). "Palaeoscincosaurus middletoni , new genus and species (Squamata: ?Scincidae) from the early Paleocene (Puercan) Denver Formation, Colorado". Journal of Vertebrate Paleontology. 16 (4): 666–672. doi:10.1080/02724634.1996.10011356. ISSN 0272-4634.
  22. ^ Hutchison, J. H. (2003-05-01). "Late Cretaceous and early Paleocene turtles of the Denver Basin, Colorado". Rocky Mountain Geology. 38 (1): 121–142. doi:10.2113/gsrocky.38.1.121. ISSN 1555-7332.
  23. ^ Lyson, Tyler R.; Petermann, Holger; Toth, Natalie; Bastien, Salvador; Miller, Ian M. (2021-03-04). "A new baenid turtle, Palatobaena knellerorum sp. nov., from the lower Paleocene (Danian) Denver Formation of south-central Colorado, U.S.A." Journal of Vertebrate Paleontology. 41 (2). doi:10.1080/02724634.2021.1925558. ISSN 0272-4634.
  24. ^ a b Lyson, Tyler R.; Petermann, Holger; Miller, Ian M. (2021-01-02). "A new plastomenid trionychid turtle, Plastomenus joycei , sp. nov., from the earliest Paleocene (Danian) Denver Formation of south-central Colorado, U.S.A." Journal of Vertebrate Paleontology. 41 (1). doi:10.1080/02724634.2021.1913600. ISSN 0272-4634.
  25. ^ a b Lyson, Tyler R.; Petermann, Holger; Bastien, Salvador; Toth, Natalie; Tamez-Galvan, Evan; Sherman, Sadie M.; Joyce, Walter G. (2025-08-05). "A new pan-chelydrid turtle, Tavachelydra stevensoni gen. et sp. nov., from the lower Paleocene (early Danian, Puercan) Corral Bluffs Study Area in the Denver Basin, Colorado". Swiss Journal of Palaeontology. 144 (1): 46. doi:10.1186/s13358-025-00375-4. ISSN 1664-2384. PMC 12325531. PMID 40778004.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  26. ^ Lessner, Emily J.; Petermann, Holger; Lyson, Tyler R. (2024-05-03). "First record of Borealosuchus sternbergii from the lower Paleocene Denver Formation (lower Danian), Colorado (Denver Basin)". Journal of Vertebrate Paleontology. 44 (3). doi:10.1080/02724634.2024.2434214. ISSN 0272-4634.
  27. ^ a b c d e f g h i j k l m n o p q "3.4 Colorado, United States; 6. Denver Formation," in Weishampel, et al. (2004). Page 581.
  28. ^ "Table 20.1," in Weishampel, et al. (2004). Page 442.
  29. ^ a b "Table 23.1," in Weishampel, et al. (2004). Page 496.
  30. ^ Carpenter, K. (2006). "Bison" alticornis and O.C. Marsh's early views on ceratopsians". In Carpenter, K. (ed.). Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Bloomington and Indianapolis: Indiana University Press. pp. 349–364. ISBN 978-0-253-34817-3.
  31. ^ Weaver, Lucas N.; Crowell, Jordan W.; Chester, Stephen G. B.; Lyson, Tyler R. (2024-04-30). "Skull of a new periptychid mammal from the lower Paleocene Denver Formation of Colorado (Corral Bluffs, El Paso County)". Journal of Mammalian Evolution. 31 (2): 16. doi:10.1007/s10914-024-09716-5. ISSN 1573-7055.

Bibliography

  • Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2


39°44′N 104°59′W / 39.74°N 104.98°W / 39.74; -104.98 (Denver Formation)

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