Laramie Formation
| Laramie Formation Stratigraphic range: Upper Cretaceous |
|
|---|---|
| Type | Geological formation |
| Underlies | Arapahoe conglomerate |
| Overlies | Fox Hills Formation |
| Thickness | 200-400 ft (60-120 m) |
| Lithology | |
| Primary | Sandstone, mudstone, clay, coal |
| Location | |
| Named by | Clarence King |
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.[1]
The formation is exposed around the edges of the Denver Basin and ranges from 400–500 feet (120-150 m) on the western side of the basin and 200–300 feet (60-90 m) 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 coal and an upper unnamed member composed predominately of 90 to 190 m of drab-colored mudstone, some sandstone, and thin coal beds.[2][3] Nodular ironstone concretions occur in the mudstones that contain plant remains. The coal and clay were once economically important.[3] The Laramie Formation was deposited on a coastal plain containing coastal swamp. Some of the material in the sandstones originated from silicic volcanoes far to the west.[4]
Contents |
[edit] Paleofauna
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)[5].
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) [6].
List of Fossil Vertebrates (data from Carpenter 1979;[7]; Hutchinson and Holroyd 2003)
[edit] Cartilaginous fishes
| Cartilaginous fishes of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
|
cf. I. avonicola |
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|
L. selachos |
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|
M. bipartitus |
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|
S. americana |
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[edit] Bony fishes
| Bony fishes of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
|
Indeterminate |
|
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|
A. occidentalis |
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[edit] Amphibians
| Amphibians of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
|
Indeterminate |
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|
L. bairdi |
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|
O. kayi |
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S. tectum |
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[edit] Turtles
| Turtles of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
|
Indeterminate |
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|
cf. B. sinuosa |
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|
C. victa |
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|
cf. H. distincta |
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|
cf. P. antique |
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[edit] Squamates
| Squamates of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
|
O. piger |
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[edit] Crocodilians
| Crocodilians of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
|
Indeterminate |
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[edit] Dinosaurs
Color key
|
Notes Uncertain or tentative data are in small text; |
| Dinosaurs reported from the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
|
C. goldenensis |
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|
Indeterminate |
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|
Indeterminate[8] |
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E. annectens[9] |
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E. regalis[9] |
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O. minutus[9] |
"Partial metatarsals II-IV."[10] |
The specimens are now lost.[10] |
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|
Indeterminate[9] |
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|
T. neglectus[9] |
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T. latus[9] |
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T. horridus[9] |
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T. operatus[9] |
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|
T. rex |
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[edit] Mammals
| Mammals of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
|
Indeterminate |
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|
Indeterminate |
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|
cf. Mesodma |
Indeterminate |
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[edit] 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.[11] The palynomorphs indicate an early Maastrichtian age (68-69 mya), which is supported by magnetostratigraphy.[12] 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.[13] 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.
Color key
|
Notes Uncertain or tentative data are in small text; |
| Flora of the Laramie Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
|
Aquilapollenites striatus |
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|
“Ficus” |
“Ficus” planicostata |
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|
Ilexpollenites compactus |
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|
Interpollis cf. I. supplingensis |
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|
Marmarthia pearsonii |
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|
“Myrica” |
“Myrica” torreyi |
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|
Platanites marginata |
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|
Sabalites sp. |
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|
Tricolpites interangulus |
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[edit] Uranium
Uranium deposits occur in sandstones of the Laramie Formation in Weld County, Colorado. (See Uranium mining in Colorado)
[edit] See also
[edit] Footnotes
- ^ King, C. 1876. Report of the Geological Exploration of the Fortieth Parallel. U.S.Geographical and Geological Survey.
- ^ Eldridge, G.H., 1888, On some stratigraphical and structural features of the country about Denver, Colorado: Colorado. Scientific Society Proceedings, v. 3, pt. 1, p. 86 118.
- ^ a b Shroba, R.R., and Carrara, P.E., 1996, Surficial geologic map of the Rocky Flats environmental technology site and vicinity, Jefferson and Boulder Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map, I 2526.
- ^ Wilson, M. 2002. Petrographic provenance analysis of Kiowa Core sandstone samples, 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: 173-187.
- ^ Report on the vertebrate paleontology of northern Colorado. Geological Exploration of the Fortieth Parallel. U.S. Geological and Geographical Survey.
- ^ Vertebrate fauna of the Laramie Formation (Maastrichtian), Weld County, Colorado. Contributions to Geology, University of Wyoming 17: 37-49.
- ^ 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.
- ^ a b Listed as "cf. Emontonia sp." in "3.4 Colorado, United States; 4. Lower Kirtland Formation," in Weishampel, et al. (2004). Page 581.
- ^ a b c d e f g h i j k l m n o "3.4 Colorado, United States; 4. Lower Kirtland Formation," in Weishampel, et al. (2004). Page 581.
- ^ a b "Table 11.1," in Weishampel, et al. (2004). Page 216.
- ^ 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.
- ^ *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.
- ^ 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.
[edit] References
- Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.
