Fountain Formation

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Fountain Formation
Stratigraphic range: Late Pennsylvanian
Roxborough.jpg
Red rocks typical of The Fountain Formation seen at Roxborough State Park near Littleton, Colorado
Type sedimentary
Underlies Lyons Formation
Overlies Gleneyrie Formation
Thickness 0-4500 ft[1]
Lithology
Primary sandstone, conglomerate
Other limestone, shale
Location
Region Denver Basin
Extent Colorado, Wyoming
Type section
Named for Fountain Creek
Named by C. W. Cross, 1894

The Fountain Formation is a Pennsylvanian bedrock unit consisting primarily of conglomerate, sandstone, or arkose, in the states of Colorado and Wyoming in the USA, along the east side of the Front Range of the Rocky Mountains, and along the west edge of the Denver Basin.

Origin of name[edit]

The Fountain Formation was named by geologist W. C. Cross in 1894 for exposures along Fountain Creek in El Paso County.[2]

Stratigraphy[edit]

Fountain Formation unconformably overlying Precambrian rocks at the parking lot of Red Rocks Park

The Fountain unconformably overlies Precambrian granite and gneiss. Outcrops of the formation typically dip steeply to the east.

Depositional environment[edit]

The formation was formed by the erosion of the Ancestral Rocky Mountains, and deposition by fluvial processes as alluvial fans.

The characteristic predominant red color and the composition of the Fountain reflect that of the granites and gneisses from which it was eroded.

Notable Exposures[edit]

Outcrop of the Fountain Formation at Garden of the Gods

Fossils[edit]

Marine invertebrates have been discovered in a limestone and shale member of the Fountain Formation, outcropping on a low hogback in Perry Park. Invertebrates include bryozoans, brachiopods, crinoids, echinoids, and gastropods.[3]

Plant fossils have been discovered in Garden Park north of Cañon City, including Lepidophloios laricinus, Sigillaria, Syringodendron sp., Lepidophyloides sp., Lepidostrobus sp., Lepidostrobophyllum sp., Calamites, Neuropterus sp., Cyclopteris sp., and Stigmaria ficoides.[4]

Age[edit]

Rocks of the Fountain Formation are considered to be of Late Pennsylvanian age, and are between 290 and 296 million years old.

References[edit]

  1. ^ Frederickson, E.A., De Lay, M., and Saylor, W.W., 1956, Ralston formation of Canon City embayment, Colorado: American Association of Petroleum Geologists Bulletin, v. 40, no. 9, p. 2120-2148.
  2. ^ Cross, C.W., 1894, Description of the Pikes Peak sheet [Colorado]: U.S. Geological Survey Geologic Atlas of the United States, Pikes Peak folio, no. 7, 5 p.
  3. ^ Ellis, C.H., 1966, Paleontologic age of the Fountain Formation south of Denver, Colorado: The Mountain Geologist, v. 3, no. 4, p. 155-160.
  4. ^ Jennings, J.R., 1980, Fossil plants from the Fountain Formation (Pennsylvanian) of Colorado: Journal of Paleontology, v. 54, no. 1, p. 149-158.