Denver Formation
| Denver Formation Stratigraphic range: Late Cretaceous - Paleocene, 68–61 Ma |
|
|---|---|
| Type | Geological formation |
| Unit of | D1 Sequence |
| Underlies | Dawson Arkose |
| Overlies | Arapahoe Formation |
| Thickness | up to 1,580 feet (480 m) |
| Lithology | |
| Primary | Claystone, siltstone, sandstone |
| Other | Conglomerate, tuff, coal, lava |
| Location | |
| Region |
 Colorado
|
| Country |
 USA
|
| Type section | |
| Named for | Denver, Colorado |
| Named by | Emmons, Cross and Eldridge (1896) |
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.
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.
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.
The Denver Formation consists of alluvial fan, fluvial, and paludal deposits that accumulated at the foot of the growing Rocky Mountain Front Ranges. It ranges in thickness from 600 feet (180 m) to 1,580 feet (480 m) in the central part of the Denver Basin. 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 500 feet (150 m) in some areas.
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