Laramie Formation

Laramie Formation

The Laramie Formation is a geologic formation of Cretaceous age, named by Clarence King in 1876 for exposures in northeastern Colorado, in the United States.King, C. 1876. Report of the Geological Exploration of the Fortieth Parallel. U.S.Geographical and Geological Survey. ]

The formation is exposed around the edges of the Denver Basin and ranges from 400-500 feet on the western side of the basin and 200-300 feet thick on the eastern side. The Laramie conformably overlies the Fox Hills Sandstone and unconformably underlies the Arapahoe Conglomerate. The formation can be divided into a lower unnamed member containing bedded sandstone, clay, and

Fauna

Fossil vertebrates from the Laramie Formation were among the first dinosaurs to be discovered in the American West (Carpenter and Young 2003). In 1873, Edward D. Cope accompanied Ferdinand V. Hayden, who was leader of the U.S. Geological and Geographical Survey of the Territories. The route of the expedition included eastern Colorado where Cope collected specimens in what is now the Laramie Formation along Bijou Creek on the east side of the Denver Basin (Cope, 1874) Report on the vertebrate paleontology of northern Colorado. Geological Exploration of the Fortieth Parallel. U.S.Geographical and Geological Survey. ] .

Cope named three species of dinosaurs without description: "Cinodon arctatus" (later changed to "Cionodon arctatus"), "Polyonax mortuarius" and "Agathaumas milo" (later renamed "Hadrosaurus occidentalis"). These specimens are currently in the American Museum of Natural History. These specimens are very scrappy and the names no longer considered valid. Subsequent discoveries of dinosaurs occur through the formation, and include a nearly complete skull of "Triceratops". Non-dinosaur vertebrates also occur (Carpenter 1979) Vertebrate fauna of the Laramie Formation (Maastrichtian), Weld County, Colorado. Contributions to Geology, University of Wyoming 17: 37-49. ] .

List of Fossil Vertebrates (data from Carpenter 1979; Carpenter, K. and Young, B. 2002. Late Cretaceous dinosaurs from the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. I., Rocky Mountain Geology 37:237-254.] ; Hutchinson and Holroyd 2003)

Chondrichthyes

Reptilia

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Mammalia

Flora

Fossil pollen (palynomorphs) include bryophyte and pteridophyte spores, gymnosperm pollen, and abundant angiosperm pollen, including "Aquilapollenites striatus", "Ilexpollenites compactus", "Interpollis" cf. "I. supplingensis", and "Tricolpites interangulus".Nichols, D.J., and Fleming, R. F. 2002. Palynology and palynostratigraphy of Maastrichtian, Paleocene, and Eocene strata in the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. I., Rocky Mountain Geology 37: 135-163.] The palynomorphs indicate an early Maastrichtian age (68-69 mya), which is supported by magnetostratigraphy.*Hicks, J.F., Johnson, K.R., Obradovich, J. D., Miggins, D.P., and Tauxe, L. 2003. Magnetostratigraphyof Upper Cretaceous (Maastrichtian) to lower Eocene strata of the Denver Basin,Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. II., Rocky Mountain Geology 38: 1-27.] Magnetostratigraphy also shows that the Laramie Formation becomes progressively younger eastward as deposition followed the regression of the Western Interior Seaway.

Fossil leaves are abundant, especially in the shales and sandstones associated with coal.Johnson, K. R., Reynolds, M.L., Werth, K.W., and Thomasson, J.R. 2003. Overview of theLate Cretaceous, early Paleocene, and early Eocene megafloras of the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. II., Rocky Mountain Geology 38: 101-120.] Dicot angiosperms dominate, with lesser amounts of ferns, palms, and herbaceous lycopods. Interestingly, conifers are rare. Common plants include “"Ficus"” "planicostata", “"Myrica"” "torreyi", "Sabalites" sp., "Platanites marginata", and "Marmarthia pearsonii".

Uranium

"Uranium" deposits occur in sandstones of the Laramie Formation in Weld County, Colorado. (See "Uranium mining in Colorado")

ee also

* List of dinosaur-bearing rock formations

References


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