Denver Formation

{{Infobox rockunit

| name = Denver Formation

| image =

| caption =

| type = Geological formation

| age = Late Cretaceous-Paleocene

| period = Danian

| prilithology = Claystone, siltstone, sandstone

| otherlithology = Conglomerate, tuff, coal, lava

| namedfor = Denver, Colorado

| namedby = Emmons, Cross and Eldridge (1896)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.

| region = Colorado

| country = United States

| coordinates =

| unitof = D1 Sequence

| subunits =

| underlies = Dawson Arkose

| overlies = Arapahoe Formation

| thickness = up to {{convert|1580|ft|m|-1|abbr=on}}

| extent =

| area =

| map =

| map_caption =

}}

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, and includes sediments that were deposited before, during and after the Cretaceous-Paleogene boundary event.{{Cite web|url=http://ngmdb.usgs.gov/Geolex/UnitRefs/DenverRefs_7901.html|title=Geologic Unit: Denver Formation|author=U.S. Geological Survey| access-date=2014-12-27}}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.[http://capp.water.usgs.gov/aquiferBasics/ext_denver.html USGS Aquifer Basics][http://capp.water.usgs.gov/gwa/ch_c/C-text6.html]

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

File:North Table Mountain.jpg.]]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 {{convert|600|ft|m|-1}} to {{convert|1580|ft|m|-1}} in the central part of the Denver Basin.[http://pubs.usgs.gov/pp/2005/1698/508/chapF.html 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 {{convert|500|ft|m|-1}} in some areas.{{Cite web |url=http://geology.cr.usgs.gov/energy/coal/PP1625A/Chapters/SD.pdf |title=U.S. Geological Survey Professional Paper 1625-A, Chapter SD |access-date=2014-08-30 |archive-url=https://web.archive.org/web/20030505085132/http://geology.cr.usgs.gov/energy/coal/PP1625A/Chapters/SD.pdf |archive-date=2003-05-05 |url-status=dead }}

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. {{ISBN|0-520-24209-2}}.Carpenter, K. and Young, D.B. 2002. Late Cretaceous dinosaurs from the Denver Basin, Colorado. Rocky Mountain Geology, vol. 37, p. 237-254.

Cretaceous vertebrate paleofauna

= Ornithischian dinosaurs =

colspan="7" align="center" \|Ornithischians reported from the Denver Formation
class="wikitable" align="center" width="100%"
Genus ! Species ! Location ! Stratigraphic position ! Material ! Notes ! Images
style="background:#E6E6E6;" \| Cionodon \|style="background:#E6E6E6;" \| C. arctatus \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| "Fragmentary maxilla, vertebrae, fragmentary postcranial elements.""Table 20.1," in Weishampel, et al. (2004). Page 442. \|style="background:#E6E6E6;" \| Later found to be indeterminate hadrosaurid remains."3.4 Colorado, United States; 6. Denver Formation," in Weishampel, et al. (2004). Page 581. \| rowspan="99" \| File:Anatotitan BW.jpg]] File:Pachycephalosaurus_Reconstruction.jpg]] File:Triceratops by Tom Patker.png]]
Edmontosaurus \| Indeterminate \| \| \| \|
Pachycephalosaurus \| Indeterminate \| \| \| \|
style="background:#E6E6E6;" \| Polyonax \|style="background:#E6E6E6;" \| P. mortuarius \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| "Horn fragments, vertebrae.""Table 23.1," in Weishampel, et al. (2004). Page 496. (type specimen) \|style="background:#E6E6E6;" \| A dubious ceratopsian
rowspan="2" \| Triceratops \|style="background:#E6E6E6;" \| T. galeus \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| "Nasal horn core." \|style="background:#E6E6E6;" \| A dubious ceratopsian
Indeterminate \| \| \| \|

= Saurischian dinosaurs =

colspan="7" align="center" \|Saurischians of the Denver Formation
class="wikitable" align="center" width="100%"
Genus ! Species ! Location ! Stratigraphic position ! Abundance ! Notes ! Images
style="background:#E6E6E6;" \| Aublysodon \|style="background:#E6E6E6;" \| A. mirandus \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| \|style="background:#E6E6E6;" \| Later found to be indeterminate tyrannosauroid remains. \| rowspan="99" \| File:"Ornithomimus" sp. by Tom Parker.png]] File:Tyrannosaurus-rex-Profile-steveoc86.png]]
Ornithomimus \| O. velox \| \| \| \|
Tyrannosaurus \| Indeterminate \| \| \| \|

References

= 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}}