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Arapahoe Formation

The Arapahoe Formation is a geological formation of latest Cretaceous (Maastrichtian) age that is present within the Denver Basin that underlies the Denver, Colorado, area.[3][4] The formation includes fossil leaves[5] and dinosaur remains, although none of the latter have yet been referred to a specific genus.[6] It also includes aquifers that are important sources of water for the area.[7]

Arapahoe Formation
Stratigraphic range: Late Cretaceous
TypeGeological formation
Unit ofD1 Sequence[1]
UnderliesDenver Formation
OverliesLaramie Formation
ThicknessUp to about 300 ft (91 m)
Location
RegionColorado
CountryUnited States
Type section
Named byEmmons, Cross and Eldridge (1896)[2]
Arapahoe Formation - stratigraphy

The Arapahoe Formation consists of alluvial fan and fluvial deposits that prograded eastward from the growing Rocky Mountain Front Ranges. It rests unconformably on the Laramie Formation, and is conformably overlain by the Denver Formation. It reaches a maximum thickness of about 300 ft (91 m).

The base of the Arapahoe Formation is marked by a discontinuous conglomerate, or where the conglomerate is absent, by sandstone beds that commonly contain large ironstone concretions. The conglomerate is composed principally of chert pebbles, but pebbles of granite, gneiss and schist are also present. Medium grey to brown claystone makes up the majority of the formation, with lesser amounts of light grey to light brown quartzose sandstone. The formation top is marked by a change from sandstone and claystone to the tuffaceous sediments of the overlying Denver Formation.[5]

In 2002 the Arapahoe 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 coincides with the base of the Arapahoe Formation and is marked by the abrupt change to conglomerate at the top of the Laramie Formation. The top D1 is placed at the base of a regional paleosol series. The Denver Formation and the Dawson Arkose are also included in the D1 Sequence.[1]

See also edit

Footnotes edit

  1. ^ a b 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. ^ Emmons, S.F., Cross, W. and Eldridge, G.H. 1896. Geology of the Denver Basin in Colorado. U.S. Geological Survey, Monograph 27, p. 153.
  3. ^ Tweto, O. 1979. Geologic map of Colorado. U.S. Geological Survey, Map G77115.
  4. ^ U.S. Geological Survey. "Geologic Unit: Arapahoe". Retrieved 2014-12-27.
  5. ^ a b Van Horn, R. 1957. Bedrock geology of the Golden Quadrangle, Colorado. U.S. Geological Survey, Map GQ 103.
  6. ^ Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.
  7. ^ 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.

References edit

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

arapahoe, formation, geological, formation, latest, cretaceous, maastrichtian, that, present, within, denver, basin, that, underlies, denver, colorado, area, formation, includes, fossil, leaves, dinosaur, remains, although, none, latter, have, been, referred, . The Arapahoe Formation is a geological formation of latest Cretaceous Maastrichtian age that is present within the Denver Basin that underlies the Denver Colorado area 3 4 The formation includes fossil leaves 5 and dinosaur remains although none of the latter have yet been referred to a specific genus 6 It also includes aquifers that are important sources of water for the area 7 Arapahoe FormationStratigraphic range Late CretaceousTypeGeological formationUnit ofD1 Sequence 1 UnderliesDenver FormationOverliesLaramie FormationThicknessUp to about 300 ft 91 m LocationRegionColoradoCountryUnited StatesType sectionNamed byEmmons Cross and Eldridge 1896 2 Arapahoe Formation stratigraphy The Arapahoe Formation consists of alluvial fan and fluvial deposits that prograded eastward from the growing Rocky Mountain Front Ranges It rests unconformably on the Laramie Formation and is conformably overlain by the Denver Formation It reaches a maximum thickness of about 300 ft 91 m The base of the Arapahoe Formation is marked by a discontinuous conglomerate or where the conglomerate is absent by sandstone beds that commonly contain large ironstone concretions The conglomerate is composed principally of chert pebbles but pebbles of granite gneiss and schist are also present Medium grey to brown claystone makes up the majority of the formation with lesser amounts of light grey to light brown quartzose sandstone The formation top is marked by a change from sandstone and claystone to the tuffaceous sediments of the overlying Denver Formation 5 In 2002 the Arapahoe 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 coincides with the base of the Arapahoe Formation and is marked by the abrupt change to conglomerate at the top of the Laramie Formation The top D1 is placed at the base of a regional paleosol series The Denver Formation and the Dawson Arkose are also included in the D1 Sequence 1 See also edit nbsp Earth sciences portal nbsp Paleontology portal nbsp Dinosaurs portal List of dinosaur bearing rock formations List of stratigraphic units with indeterminate dinosaur fossilsFootnotes edit a b Raynolds R G 2002 Upper Cretaceous and Tertiary stratigraphy of the Denver Basin Colorado Rocky Mountain Geology vol 37 no 2 p 111 134 Emmons S F Cross W and Eldridge G H 1896 Geology of the Denver Basin in Colorado U S Geological Survey Monograph 27 p 153 Tweto O 1979 Geologic map of Colorado U S Geological Survey Map G77115 U S Geological Survey Geologic Unit Arapahoe Retrieved 2014 12 27 a b Van Horn R 1957 Bedrock geology of the Golden Quadrangle Colorado U S Geological Survey Map GQ 103 Weishampel et al 2004 Dinosaur distribution Pp 517 607 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 References editWeishampel David B Dodson Peter and Osmolska Halszka eds The Dinosauria 2nd Berkeley University of California Press 861 pp ISBN 0 520 24209 2 Retrieved from https en wikipedia org w index php title Arapahoe Formation amp oldid 998125533, wikipedia, wiki, book, books, library,

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