Denver Formation

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.Tweto, O. 1979. Geologic map of Colorado. U.S. Geological Survey, Map G77115.

The formation is known for its paleontological resources, including dinosaur remains that are found in the Late Cretaceous part of the formation, and it includes aquifers that are important sources of water for the area.USGS Aquifer Basics 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. 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.

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.

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.

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.Raynolds, R.G. 2002. Upper Cretaceous and Tertiary stratigraphy of the Denver Basin, Colorado. Rocky Mountain Geology, vol. 37, no. 2, p. 111-134. It ranges in thickness from to in the central part of the Denver Basin.U.S. Geological Survey Professional Paper 1698, Chapter F It is characterized by significant amounts of andesitic volcanic debris, 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. Beds of low-rank coal and carbonaceous shale occur in the upper in some areas.

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.Van Horn, R. 1957. Bedrock geology of the Golden Quadrangle, Colorado. U.S. Geological Survey, Map GQ-103. Generally referred to as basaltic, they are classified either as monzonite (the lowest flow) and latite (the upper two flows), or as shoshonite. 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.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.

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, 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.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.

Plant fossilsJohnson, 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. and remains of vertebrates, including turtlesHutchison, 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. and mammals,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. are found throughout the Denver Formation.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. Dinosaur remains are restricted to the lower, Late Cretaceous, part.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. .Carpenter, K. and Young, D.B. 2002. Late Cretaceous dinosaurs from the Denver Basin, Colorado. Rocky Mountain Geology, vol. 37, p. 237-254.

Vertebrate paleofauna Based on the Paleobiology Database except where noted:

Ray-finned fish Ray-finned fish reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesLepisosteusL. sp.DanianA gar.

Amphibians Amphibians reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesOpisthotritonO. kayiDanianA batrachosauroidid salamander.Scapherpetonidae indet.A scapherpetonid salamander.

Reptiles

Squamates Squamates reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesAnguidae indet.DanianAn anguid lizard of uncertain affinities.aff. Contogenysaff. C. sp.A contogeniid lizard.cf. Odaxosauruscf. O. pigerAn anguid lizard.PalaeoscincosaurusP. middletoniA contogeniid lizard, formerly considered an early skink. Type locality of genus and species.

Turtles Turtles reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesAdocusA. sp.Maastrichtian to DanianAn adocid.BasilemysB. sinuosaMaastrichtianA nanhsiungchelyid.DenverusD. middletoniDanianA stem-snapping turtle. Type locality of genus and species.HelopanopliaH. distinctaMaastrichtianA plastomenid trionychian.HoplochelysH. crassaDanianA kinosternoid.Macrobaenidae indet.DanianA macrobaenid turtle of uncertain affinities.PalatobaenaP. knellerorumDanianA baenid. Type locality of species.PlastomenusP. joyceiDanianNearly complete skeleton.A plastomenid. Type locality of species.TavachelydraT. stevensoniDanianNearly complete shells, pelvic material, and cranial materialA stem-snapping turtle. Type locality of genus and species."Trionyx""T." singularisDanianA softshell turtle.

Crocodylomorphs Crocodylomorphs reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesMandrasuchusM. milleriCorral BluffsDanianAn alligatorine, type locality of genus and species.BorealosuchusB. sternbergiiA 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.

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.

Ornithischians Ornithischians reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesCionodonC. arctatusMaastrichtian"Fragmentary maxilla, vertebrae, fragmentary postcranial elements.""Table 20.1," in Weishampel, et al. (2004). Page 442.Later found to be indeterminate hadrosaurid remains."3.4 Colorado, United States; 6. Denver Formation," in Weishampel, et al. (2004). Page 581.?Edmontonia?E. sp.MaastrichtianA nodosaurid ankylosaur.EdmontosaurusE. sp.A hadrosaurid.PachycephalosaurusP. sp.A pachycephalosaur.PolyonaxP. mortuarius"Horn fragments, vertebrae.""Table 23.1," in Weishampel, et al. (2004). Page 496. (type specimen)A dubious ceratopsianTriceratopsT. galeus"Nasal horn core."A dubious ceratopsianT. horridus (=Bison alticornis)Type locality of the genus and the first known Triceratops specimen, initially identified as a species of bison.

Saurischians Saurischians of the Denver Formation Genus Species Location Stratigraphic position Abundance NotesImagesAublysodonA. mirandusMaastrichtianLater found to be indeterminate tyrannosauroid remains.Dromaeosauridae indet.MaastrichtianA dromaeosaur of uncertain affinities. Some remains referred to "Dromaeosaurus".OrnithomimusO. veloxAn ornithomimosaur. Type locality of genus and species.TyrannosaurusT. rexA tyrannosaur. The very first T. rex fossil known was a tooth collected from this formation.

Mammals

Multituberculates Multituberculates reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesCatopsalisC. alexanderiDanianA taeniolabidid.CimexomysC. arapahoensisA "Paracimexomys-group" multituberculate.C. minorKimbetohiaK. mziaeA ptilodontid.MesodmaM. ambiguaA neoplagiaulacid.M. hensleighiXyronomysX. robinsoniA neoplagiaulacid.

Metatherians Metatherians reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesThylacodonT. montanensisDanianA herpetotheriid.T. pusillus

Cimolestans Cimolestans reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesProcerberusP. andesiticusDanianA cimolestid.P. grandis

Placentals Former "condylarths". Placentals reported from the Denver Formation Genus Species Location Stratigraphic position Material NotesImagesAlticonusA. gaziniDanianA periptychid paraxonian. Type locality of genus and species.AurariaA. urbanaA periptychid paraxonian. Type locality of genus and species.AmpliconusA. browniA periptychid paraxonian. Type locality of genus and species.BaioconodonB. denverensisAn arctocyonid paraxonian.B. nordicusConacodonC. delphaeA periptychid paraxonian.C. harbouraeC. matthewiDesmatoclaenusD. protogonioidesAn arctocyonid paraxonian.EctoconusE. ditrigonusA periptychid paraxonian.HaploconusH. entoconusA periptychid paraxonian.LoxolophusL. hyattianusAn arctocyonid paraxonian.MaioranaM. sp.An arctocyonid paraxonian.MilitocodonM. lydaeA periptychid paraxonian. Type locality of genus and species.Miniconus M. archibaldiA periptychid paraxonian.Mioclaenidae indet.A mioclaenid.OxyclaenusO. cuspidatusAn arctocyonid paraxonian.O. subbituminusOxyprimusO. galadrielaeAn arctocyonid paraxonian.PeriptychusP. coarctatusA periptychid paraxonian.ProtungulatumP. donnaeA protungulatid euungulate.

Denver Formation

Bron en licentie